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NBS SPECIAL PUBLICATION

U.S. DEPARTMENT OF COMMERCE / National Bureau of Standards

Proceedings of a Meeting on

Traceability for Ionizing

Radiation Measurements

-QO

' 100

.U57

No, 609

1982

c. 2
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards' was established by an act of Congress on March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology

and facilitate their effective application for public benefit. To this end, the Bureau conducts

research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau's technical work is per- formed by the National Measurement Laboratory, the National Engineering Laboratory, and

the Institute for Computer Sciences and Technology.

THE NATIONAL MEASUREMENT LABORATORY provides the national system of physical and chemical and materials measurement; coordinates the system with measurement

systems of other nations and furnishes essential services leading to accurate and uniform

physical and chemical measurement throughout the Nation's scientific community, industry,

and commerce; conducts materials research leading to improved methods of measurement,

standards, and data on the properties of materials needed by industry, commerce, educational

institutions, and Government; provides advisory and research services to other Government

agencies; develops, produces, and distributes Standard Reference Materials; and provides

calibration services. The Laboratory consists of the following centers:

Absolute Physical Quantities2 — Radiation Research — Thermodynamics and

Molecular Science — Analytical Chemistry — Materials Science. THE NATIONAL ENGINEERING LABORATORY provides technology and technical ser- vices to the public and private sectors to address national needs and to solve national problems; conducts research in engineering and applied science in support of these efforts; builds and maintains competence in the necessary disciplines required to carry out this research and technical service; develops engineering data and measurement capabilities;

provides engineering measurement traceability services; develops test methods and proposes

engineering standards and code changes; develops and proposes new engineering practices;

and develops and improves mechanisms to transfer results of its research to the ultimate user. The Laboratory consists of the following centers:

Applied Mathematics — Electronics and Electrical Engineering2 — Mechanical

Engineering and Process Technology2 — Building Technology — Fire Research —

Consumer Product Technology — Field Methods.

THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts

research and provides scientific and technical services to aid Federal agencies in the selection, acquisition, application, and use of computer technology to improve effectiveness and

economy in Government operations in accordance with Public Law 89-306 (40 U.S.C. 759), relevant Executive Orders, and other directives; carries out this mission by managing the Federal Information Processing Standards Program, developing Federal ADP standards

guidelines, and managing Federal participation in ADP voluntary standardization activities; provides scientific and technological advisory services and assistance to Federal agencies; and

provides the technical foundation for computer-related policies of the Federal Government.

The Institute consists of the following centers:

Programming Science and Technology — Computer Systems Engineering.

'Headquarters and Laboratories at Gaithersburg, MD, unless otherwise noted; mailing address Washington, DC 20234.

2 Some divisions within the center are located at Boulder, CO 80303.
Proceedings of a Meeting on Traceabiiity

for Ionizing Radiation Measurements

/J 6

Proceedings of a meeting held at the National Bureau of Standards,

Gaithersburg, MD, on May 8-9, 1980

Edited by:

H. Thompson Heaton, II

Center for Radiation Research

National Measurement Laboratory

National Bureau of Standards

Gaithersburg, MD 20234

National Bureau of Standards

Library, E-Ot Admin. Bide.

MAR 1 W82

ftoi aa- - Culls,

Ocioo

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued February 1982
Library of Congress Catalog Card Number: 81-600197

National Bureau of Standards Special Publication 609

Nat. Bur. Stand. (U.S.), Spec. Publ. 609, 175 pages (Feb. 1982)

CODEN: XNBSAV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1982
PREFACE

The phrases "traceable to NBS" or "traceable

to the national standards" are increasingly being

used in Federal and State regulations, voluntary

standards, technical articles, and advertisements,

often without any indications of what is meant by the phrase or how it is achieved. To provide some guidance on how traceability can be achieved in the area of ionizing radiation measurements, a two-day seminar was organized and held at the National Bureau of Standards, Gaithersburg,

Maryland, on May 8-9, 1980. These proceedings

include the 21 papers presented at that seminar on Traceability for Ionizing Radiation Measurements.

The first six speakers in this meeting covered

the basic concepts of traceability from different

perspectives and described the national standards

for radiation dosimetry, radioactivity measurements, and neutron measurements. The remainder of

the speakers dealt with specific programs for achieving traceability for applications in gov- ernmental laboratories, and for medical, occupational, and environmental radiation measurements.

An important point made by many of the speakers is that the development and use of secondary (intermediate level) standards laboratories offers an effective mechanism for responding to the rapidly

increasing number of requests for instrument calibrations, radioactive sources, measurements, etc. which are traceable to national standards.

In order to achieve broad and even coverage

of the field, papers were presented by invitation

only, although the meeting was open to anyone. Eight of the speakers were from NBS and 13 from

other organizations. A total of 79 people repre- senting 45 different organizations registered for

the meeting.

The papers are printed in the proceedings as they were received from the authors and in the order they were presented in the sessions.

However, two of the sessions, Traceability in Governmental Laboratories and Traceability in Medical Applications, were actually presented in the reverse order. For convenience, the seminar

notation for the sessions has been preserved. To speed publication of the proceedings, all papers were submitted by the authors in camera-ready form.

The editor is greatly indebted to the authors and

all those who assisted in the preparation of the manuscript. Their efforts have made it possible to get the proceedings in print much more rapidly than would otherwise have been the case.

When commercial equipment, instruments, and materials are mentioned or identified in these

proceedings it is intended only to adequately

specify experimental procedure. In no case does

such identification imply recommendation or endorsement by the National Bureau of Standards,

nor does it imply that the material or equipment

identified is necessarily the best available for

the purpose.

The editor gratefully acknowledges the as- sistance of the National Bureau of Standards

Technical Information and Publications Division

in the preparation of these proceedings; of Mrs. Kathy Stang of the National Measurement Laboratory and Miss Jo Ann Lorden of the Public Infor- mation Division for help in the arrangements for

the seminar, and of Mrs. E. Kramer for the excellent secretarial assistance.

H. Thompson Heaton, II Center for Radiation Research

in
ABSTRACT

These proceedings are the compilation of 21 papers presented at a seminar on Traceabil ity for Ionizing Radiation Measurements held at the National Bureau of

Standards, Gaithersburg, MD, on May 8-9, 1980. General concepts for trace- ability were presented from several perspectives. The national standards for radiation dosimetry, radioactivity measurements, and neutron measurements were

described. Specific programs for achieving traceabil ity to the national stan- dards for radiation measurements in medical , occupational , and environmental

applications were summarized.

Key words: Calibrations, ionizing radiation, measurements, national standards,

quality assurance, secondary standard laboratory, traceabil ity.
TABLE OF CONTENTS

Preface iii

Abstract iv

INTRODUCTORY SESSION

Chairperson: R.S. Caswell

Welcoming Remarks

C.E. Kuyatt.... 1

Traceability - A View From the NBS Center for Radiation

Research

E.H. Eisenhower 3

Traceability of Radiation Measurements: Musings of a User

R.L. Kathren 11

Radiation Measurement Traceability in the United Kingdom

W.A. Jennings 19

National Standards for Radiaton Dosimetry

R. Loevinger 29

National Standards for Radioactivity Measurements

L.M. Cavallo... 31

National Standards for Neutron Measurements

J. A. Grundl 39

NBS Services for Ionizing Radiation Measurements

H.T. Heaton, II 45

TRACEABILITY IN GOVERNMENTAL LABORATORIES

Chairperson: E.H. Eisenhower

The Calibration Program of the Bureau of Radiological Health

T.R. Ohlhaber 59

The EPA National Quality Assurance Program

A.N. Jarvis 65

The LLL Calibration and Standards Facility

G.W. Campbell 67

State of Illinois Regional Calibration Laboratory

M. Neuweg 77

TRACEABILITY IN MEDICAL APPLICATIONS

Chairperson: R. Loevinger

The American Association of Physicists in Medicine's Regional

Calibration Laboratory System

R.J. Shalek, L.J. Humphries, and W.F. Hanson 81

NBS Traceability Programs for Radiation Therapy

C. G. Soares and M. Ehrlich 89

Traceability Programs for Nuclear Medicine

D. B. Golas 99

v
TRACEABILITY IN ENVIRONMENTAL APPLICATIONS

Chairperson: J.M.R. Hutchinson

The Role of Calibration Standards in Environmental

Thermoluminescence Dosimetry

T.F. Gesell, M.F. Jones and G. de Planque mi

The National Bureau of Standards Low-Level Radioactivity- Measurements Program

K.G.W. Inn and J.R. Noyce 117

Nuclear Regulatory Commission Traceability Concerns in Inspection and Enforcement Program

L.K. Cohen... 129

Radon and Radon Daughter Field Measurements

A.C. George 135

TRACEABILITY IN OCCUPATIONAL AND INDUSTRIAL APPLICATIONS

Chairperson: M. Ehrlich

Performance Testing of Personnel Dosimetry Services

P. A. Plato and C.G. Hudson 145

Occupational Exposure Measurements in NRC Regulatory Guides

A. Brodsky 149

Dosimetry for Industrial Radiation Processing

W.L. McLaughlin, J.C. Humpreys and A. Miller 171

List of Attendees. 179

vi
WELCOMING REMARKS

Chris E. Kuyatt, Director

Center for Radiation Research

National Bureau of Standards

Washington, DC 20234

I am happy to have this opportunity to welcome you to NBS to attend the seminar on "Trace- ability for Ionizing Radiation Measurements".

This meeting is sponsored by the Center for Radiation Research and is part of the 1980 series of

"NBS Measurement Seminars". For those of you

familiar with previous seminars the Center has organized as part of the NBS series, there are

several new features of the present meeting. The biggest difference is that for the first time we

have invited outside speakers. This will allow a broader view to be presented. Previous meetings

have covered several major topics with detailed

talks on how NBS performed its measurements.

Since the specific laboratory techniques that NBS uses are not necessarily appropriate for others,

this seminar will concentrate on a single broad

topic, namely traceabi 1 ity. Speakers have been requested to submit written versions of their

presentations and these will be published as an NBS Special Publication. You will be receiving a copy of this publication.

The term "traceabi 1 ity to NBS" or "trace- ability to the national standards" is being used more frequently. Several examples include:

Federal and state regulations, voluntary standards

such as those published by the American National

Standards Institute, contracts (particularly

military contracts including MIL specs), international sales of technical products, advertising

(especially involving radioactive sources) internal

quality control, and litigation. If the measure- ment process itself becomes challenged in court

cases, this will probably have the greatest im- petus in encouraging stronger ties to the national

standards. Currently, the major pressure for

traceabi! ity comes from regulatory action.

One of the major problems with the use of the word traceabi! ity is that it usually is not de- fined in the document in which it is used. In fact, traceabi 1 ity can be defined in several ways.

If one uses a simple definition such as an un- broken path, one can almost always find some path,

no matter how tenuous, which will lead back to the national standards. I am reminded of an incident

a few years ago in which our storeroom was selling meter sticks which not only had a significant bow

to them but the printing of the scale was very

inaccurate. Since it came from the NBS storeroom,

it would fulfill some definition of traceabi 1 ity

to NBS yet it was valueless in its intended function of measuring distance. Clearly, we must

first consider what we want to achieve through

traceabi 1 ity , and then define traceabi 1 ity so that

it will achieve the desired objective.

If one goes to the other extreme and gives a very technical definition for a commonly used

word there can still be problems in that many

people may not realize that the word is being used

in a restricted manner. An example of assigning a technical meaning to a common word is "the quantity for measuring the amount of radiation re- sulting from the exposure of an individual to x rays is exposure". In this case the word exposure

is used in two quite different contexts. Even though the technical definition of exposure has existed since 1928, one can look at both the popu- lar press and many scientific articles and observe

that the technical application of the word is being misused. One possibility to avoid similar

problems with the word traceabi 1 ity is to always

use the word with an adjective. Hopefully this

will flag the reader that the word is not being

used in its common sense.

These examples point to the need for everyone

to understand what is meant in a particular situation when using the word "traceabi 1 i ty" . One fact which should be kept clearly in mind is that

NBS does not have the legal authority to define

what is meant by "traceabil ity to NBS", and can only comment as to whether or not mechanisms exist

which would allow the traceabil ity required by someone else to be demonstrated. It is necessary

that whoever uses the phrase "traceable to NBS" defines it in such a way that the objective of re- quiring it in the first place can be met.

One problem with having NBS define the meaning of "traceabil ity to NBS" is that like all organizations NBS is a collection of individuals,

each with his own concept of the meaning of traceability. These concepts are modified by the needs

in each individual's specific measurement area.

If one tries to give a general definition it may

be so vague or complicated that it is not of much

use in specific cases. The problem is somewhat

easier if one goes to a specific measurement area

such as ionizing radiation measurements; but, even

in the past, various members of CRR have used different definitions of traceabil ity, not all of

which were completely compatible. One of the main

objectives of this meeting is to examine how the various definitions could be made compatible when

the objective of requiring traceabil ity is to ensure that accurate measurements are being made.

Several on-going programs will be described as examples of how traceabil ity is achieved for particular types of radiation measurements. This

seminar is intended to stimulate discussion,

and hence, the meeting is designed to be somewhat

flexible in its schedule to encourage an active

interaction between the speakers and the audience.

I hope all of you will take advantage of this op- portunity and engage in a lively two days of discussion.

1

Traceability - A View From the NBS Center for Radiation Research

Elmer H. Eisenhower

Office of Radiation Measurement

Center for Radiation Research

National Bureau of Standards

Washington, DC 20234

This paper presents general information about the traceabi lity of ionizing

radiation measurements to the appropriate national physical measurement standards.

It describes fundamental concepts that should serve as the basis of more specific

considerations of traceability, some common problems encountered in making statements about traceability, and the means and methods used to achieve traceability.

Distinctions between the two principal types of traceability (instrument and

measurement) are identified and the differences in the ways they are achieved are summarized. Some of the ambiguities that may occur in statements about trace- ability are recognized, and preferred ways of making unambiguous statements are

given. The importance of means and methods for achieving traceability is emphasized,

since statements about traceability have limited usefulness unless the specific

means and methods can be identified for a particular measurement under consideration.

The technical and institutional elements that provide these means and methods

constitute the national measurement support system. Present weaknesses in this

system are identified, and two measurement quality assurance programs are described

as examples of how the system can be improved.

(Calibrations; instruments; ionizing radiation; measurements; measurement support

system; quality assurance; standards; traceability)

Introduction

In recent years, it has become apparent that traceability is desirable but not particularly

understandable. The desire arises from a growing

national awareness of the value of quality assurance in products and procedures. The limited

understanding results partly from the mistaken

belief that the meaning of traceability is self- evident and therefore needs no discussion. This

lack of discussion has resulted in a multitude of misinterpretations, ambiguous statements, and considerable confusion. Understanding is further

limited by the fact that traceability is an evolving concept and lacks a universally accepted

definition [1].

This paper will present some general information that should be useful in more specific

considerations of traceability. It will describe

the fundamental concepts that should be the foundation for such considerations, some problems

encountered in making statements about traceability,

and the means and methods used to achieve traceability. To avoid details that may only apply to

a limited situation, the subject will be treated in

a simplified manner and fundamentals will be emphasized. The views expressed in this paper are solely those of the author, and do not necessarily

represent a consensus of the NBS staff or management. The subject matter will be limited to measurement of ionizing radiation.

Although any discussion of traceability could

reasonably start at the international level and

proceed from there, this paper will consider only

the national structure. Thus the national physical

measurement standards will be regarded as the common point to which measurements should be re- ferred.

Fundamental Concepts

The desirability of measurements that are nationally consistent (in agreement) was expressed

in 1778 by the Articles of Confederation. A more

recent expression of this desire is contained in a 1950 statement of the primary function of the National Bureau of Standards, which is:

"The custody, maintenance, and development of

the national standards of measurement, and the provision of means and methods for making mea- surement consistent with those standards..."

[2]

Although this statement clearly assigns to NBS

the responsibility for providing "means and methods" that enable measurement to be consistent with

national standards, the Bureau has not been given

any authority to require such consistency. Other

organizations and agencies have, however, instituted requirements of this type. Any such re- quirements for consistency should be developed in consultation with NBS because the existing "means and methods" may not be adequate, and the requirements may therefore be impractical.

Consistency of measurements with the national

standards may be either demonstrated or implied.

Those who require that measurements be consistent

with standards must decide whether implied con- sistency is adequate, or whether it must be dem- onstrated. In either case, some action or actions

3
must be taken if consistency is to be achieved.

These actions are the "means and methods" employed

in the process of achieving consistency. If it can be shown that such actions have been taken and

that they were appropriate, the measurement is considered to be consistent with the standard.

Regardless of what actions are taken to achieve

this consistency, it is essential that they be documented. Such documentation is the only evidence that the process occurred and was appropriate. Thus, in a general sense, traceability

can be defined as the ability to show that appropriate documented actions have been taken to demonstrate or imply that a measurement is con- sistent with a standard.

Instrument (Artifact) Traceability

If implied consistency of a measurement with

a standard is sufficient, it can be achieved

through a calibration process. In this case, the instrument used to make the measurement is calibrated by comparison with the appropriate national

standard, either directly or indirectly through

intermediate calibrations. This is the traditional type of traceability and, in some cases,

the only type that presently can be achieved.

Although a radiation source is not an in- strument, it is frequently utilized in the in- strument calibration process, and should therefore

also be calibrated in a manner that provides

traceability to the appropriate national standard.

The term "instrument traceability" may therefore

be used generically to include both instruments

and sources. (The term "artifact traceability" may

also be used to include instruments and sources generically.) It may be defined as the ability to show that a particular instrument or radiation

source either has been calibrated against the appropriate national standard or against another

standard in a chain or echelon of calibrations

ultimately leading to a calibration against the national standard.

A major disadvantage of instrument trace- ability is the inability to demonstrate that the measurement made with a traceable instrument is indeed consistent with the national standard.

Since the traceability chain ends with the in- strument, as shown in Figure 1, the consistency of

the measurement must be implied. If the instru- ment is used properly, and if the conditions under

which the measurement is made are favorable, this

implication may be valid. However, since the quality of the measurement itself has not been demonstrated, there remains some degree of un- certainty about the validity of the result.

Since no calibration of an instrument or

source is valid indefinitely, it should be re- peated at suitable time intervals. The acceptable

time between subsequent calibrations is dependent

upon the circumstances of the particular situation.

INSTRUMENT TRACEABILITY MEASUREMENT TRACEABILITY

NATIONAL

LEVEL

NATIONAL

STANDARD

CALIBRATION

INTERMEDIATE

LEVEL

TRANSFER

STANDARD

FIELD

LEVEL

CALIBRATION

FIELD INSTRUMENT

NATIONAL

STANDARDS

LABORATORY

PERFORMANCE

TEST

INTERMEDIATE

STANDARDS

LABORATORY

PERFORMANCE

TEST

MEASUREMENT

MAKER

Figure 1. Schematic indication of the difference between the traceability chains for instrument trace- ability and measurement traceability.

4
Measurement Traceability

If demonstrated consistency of a measurement

with a standard is desired or required, the trace- ability chain must be extended beyond the instru- ment to the measurement, as indicated in Figure 1. In this case, traceability is a characteristic of

the measurement itself, and there is documented

evidence that the measurement is consistent with

the appropriate standard. Thus measurement

traceability may be defined as the ability to show

that a measurement process produces results for which the total measurement uncertainty relative

to a national or other designated standard is quantified. This is the most desirable type of

traceability, since it is based on a demonstration

that the complete measurement process is under

control, including the instrument, its user, and

the procedures.

Measurement traceability is usually achieved

through utilization of a transport standard*,

which may be in the form of a radiation source or

a dosimetry device that originates from NBS or an intermediate standards laboratory directly trace- able to NBS for the particular measurement under

consideration. When a radiation source is used,

its output is measured by the participant who

receives it, and the result is reported to the originating laboratory. If the reported value compares favorably with the value determined by

the originating laboratory, a statement of sat- isfactory performance is provided to the par- ticipant.

When the transport standard takes the form of

a dosimetry device, it is sent to the participant

who administers a nominal measured dose (or ex- posure). The device is then returned to the originating laboratory, where the administered

dose (or exposure) is evaluated. If the par- ticipant's nominal measured value is within the acceptable range of uncertainty, a statement of

satisfactory performance is provided.

An obvious advantage of measurement trace- ability is that it can be achieved without utilization of a transfer standard (instrument or

source) that has been calibrated by NBS. Measurement traceability is possible without instrument

traceability, and the latter can be optional for anyone who demonstrates measurement traceability.

Thus periodic demonstration of adequate measurement performance through the use of a transport

standard may eliminate, or substantially reduce,

the need for (and cost of) periodic instrument or

source calibrations.

Since a demonstration of satisfactory per- formance can not reasonably guarantee similar

performance for an indefinite period of time, the demonstration process should be repeated periodically.

In summary, the relationship between the desired type of consistency of the measurement and

standard, the process by which that consistency is achieved, and the resultant type of traceability

is shown in the following table:

Type of consistency

desired

Implied

Demonstrated

Process by

which it is achieved

Calibration

Performance

Test

Type of trace- ability which

results

Instrument

(Artifact)

Measurement

*A transport standard is intended for use in the determination of measurement traceability through

a performance test. In distinction, a transfer

standard has been compared directly or indirectly

with the national standard and is intended to serve as a reference for calibrations.

Measurement Uncertainty

The objective of a measurement is to de- termine how many units of a particular radiation

quantity are present, within an acceptable range of uncertainty. The uncertainty of the measure- ment is meant to be a credible estimate of the likely limits to its actual error (i.e., the difference between the measured value and the "true" value), and is usually expressed as a percentage of the measured value. This uncertainty consists of both random and systematic

components, and may be estimated in terms of the difference between the measured value and the value that would be obtained if the national

standards themselves were used to make the measurement. In effect, the "true" value is defined

by the national standards (at least in the legal

sense). The uncertainty of the measurement is therefore an indicator of how consistent it is with the national standard. In practice, an upper

limit of uncertainty (e.g., 5%, 10%, etc.) is usually established as that which is deemed to be acceptable for the particular measurement of

interest.

For implied consistency of a measurement with

the national standard, the uncertainty of the measurement is also implied. In this case, the traceability chain ends with the instrument used

to make the measurement, and the only definitive statement of uncertainty that can be made is that

which applies to calibration of the instrument.

It is somewhat presumptuous to assume that the measurement uncertainty is the same as the calibration uncertainty, unless the conditions en- countered during the measurement are identical to those that existed at the time of calibration.

Since this rarely (if ever) happens in practice,

the measurement uncertainty is nearly always

greater than the calibration uncertainty.

For demonstrated consistency of a measurement

with a standard, the traceability chain ends with

the measurement itself, and the uncertainty is determined without implication.

5
Statements About Traceability

The National Bureau of Standards encourages

and supports the concept of traceability, and its application by other organizations and agencies,

because it leads to more accurate and uniform measurements on a national basis. However, since

NBS must provide "means and methods" for achieve- ment of traceability, it is an interested (and

sometimes concerned) party when others make statements about traceability. Such statements

are increasingly made in Federal regulations and regulatory guides, state regulations, contracts,

voluntary standards, and in advertising.

Sometimes the statements about traceability

are good, but many times they are vague, am- biguous, and lead to confusion. As a result, NBS

is getting increasing numbers of requests for definition of traceability, for clarification of traceability statements made by others, and for

recommended procedures to be used to achieve

satisfactory traceability. In an attempt to study this general problem, and to possibly

identify better ways to make statements about

traceability, a cooperative effort was initiated

with the Nuclear Regulatory Commission. The objective is to jointly develop more workable,

understandable, and meaningful statements. This

effort has resulted in significant improvements

of traceability statements in several regulatory

guides, with additional specific projects cur- rently underway.

An early conclusion resulting from this

cooperative effort was that general definitions

of traceability, such as the one given earlier in this paper, are relatively easy to state, but are also of little value. To be more useful, a definition must be specific to the particular measurement and radiation quantity of interest.

In effect, traceability must be defined for each

type of measurement included in the variety of possible types of radiation measurements. A meaningful definition of traceability for a particular type of measurement must include an indication of the "means and methods" used to achieve consistency with the appropriate standard. These means and methods will be quite

different, for example, for the measurement of

low-energy x rays as compared with the measure- ment of radon concentration.

Statements About "Traceable To"

Some ambiguous statements that appeared in various documents over the past few years name

the following entities as the objectives to which

traceability is desired:

NBS radiation measurement system

NBS radioactivity measurement system

national measurement system

national radioactivity measurement system

NBS standard reference materials

national system of measurements and standards

nationally accepted measurement system

A basic problem arises from the fact that nearly all of these objectives are undefined and

therefore are subject to a variety of interpretations. The readers must decide for themselves

what is meant by ambiguous terms such as "system", "measurement system", "national system",

"national measurement system", or "nationally

accepted measurement system", and their interpretations will differ significantly.

When such statements are attempted, it is essential to keep in mind the relevant fundamental concept, i.e., the ability to show that actions have been taken to make a measurement

consistent with a standard. If this basic

concept is adhered to, an unambiguous statement

is possible, namely "traceable to the national

standard". Since national standards and NBS are synonymous, an alternative statement could be "traceable to NBS". If an appropriate national

standard is not maintained by NBS for the quantity of interest and an alternative standard

serves as the point of reference, it should be identified specifically in any statement about

traceability to it.

Statements About "Traceability Of "

Most statements about traceability take the general form of "X is traceable to Y" (or should

be). This is equivalent to saying that X has the characteristic of traceability, and one can therefore recognize the traceability of X. In recent statements, the characteristic of trace- ability has been assigned to a range of things,

including

a measurement

an instrument

a radiation source

a standard

a laboratory

a calibration

a measurement system

a technique

In descending order, statements about "trace- ability of" these items range from highly de- sirable to highly ambiguous. As indicated

earlier in this paper, traceability of a mea- surement is the best indicator of consistency

with a standard because it is based on demonstrated performance. Traceability of an instru- ment or source results in only implied consistency. If "a standard" is actually an instrument

or a source, it can have the characteristic of

(generic) instrument traceability.

When considering "traceability of a labo- ratory" the possibility of ambiguity increases

substantially. This statement has little meaning

unless additional information is provided for

clarification, such as the particular type of measurement for which traceability is claimed.

Since calibration is a process that provides to

an instrument or radiation source the characteristic of traceability, that characteristic is

a property of the instrument or source, and not

of the process. The term "traceability of a measurement system" is subject to a variety of

interpretations and can lead to confusion unless

the "system" is carefully defined. Finally, the

6
concept of traceability of a technique is invalid

because there is no national standard technique

to which one could be traceable. As mentioned

earlier, traceability is a characteristic of

either a measurement, instrument, or source, and

a technique is none of these.

To avoid unnecessary confusion and misunderstandings, statements should be limited to traceability of either a measurement, an instrument, or a radiation source. It is reasonable to make statements about traceability of a standard

as long as that standard consists of an instru- ment or source. This set of items which can have

the characteristic of traceability (measurement,

instrument, source, and standard) should be sufficient for the purpose of making unambiguous

statements.

Direct and Indirect Traceability

To the extent possible, terms used in statements about traceability should be in agreement

with common interpretation and usage. If un- usual, uncommon meanings are assigned to common

words, the potential for misinterpretation in- creases substantially. Thus the definition of direct traceability that would be most consistent

with common expectation is "that traceability

which results from direct comparison with a standard". If the standard under consideration

is maintained by NBS, the result is direct trace- ability to the national standard. (One step

removed from the national standard).

In contrast to direct traceability, indirect

traceability results from indirect comparison

with a standard, through one or more intermediates. (More than one step removed from the national standard).

For the majority of field measurements, it is sufficient to achieve traceability to NBS through

an intermediate level of laboratories which

provide calibrations and measurement - related

services. Ideally, the laboratories at this

level will have measurement traceability to NBS. At a minimum, they should have instruments or radiation sources which are either directly or indirectly traceable to the national standards.

Utilization of an intermediate level (or

levels) results in the type of measurement sup- port system (MSS) illustrated in Figure 2. In concept, this MSS can be an effective mechanism

for providing consistency of measurements with

the national standards. The problem is that the links between the various levels are presently

undefined and undeveloped for many types of

radiation measurements. These links consist of

two basic types of interactions between lev- els — technical and institutional.

The technical elements of the measurement

support system are:

" measurement standards, including the national

standards and the transfer standards used at the intermediate level

°ca! ibrations of transfer standards by NBS, and of field instruments by intermediate

laboratories

" measurement quality assurance programs , including performance testing services

provided by NBS or by an intermediate laboratory

" field instruments used to make measurements

at the field (user) level

Means and Methods

It is relatively easy to make the general

observations that measurements should be con- sistent with standards, that measurement trace- ability is more desirable than instrument trace- ability, and that statements about traceability

should be unambiguous. The achievement of these

objectives is, however, more difficult. Even correct statements about traceability have little or no value unless they are supported by technical programs that provide the means and methods

needed to enable measurements to be consistent

with standards. An evaluation of existing

national programs leads to the realization that there is a key problem, which is that the means

and methods for achieving measurement consistency

with the national standards (i.e., the trace- ability mechanisms) are unspecified and inadequate in many cases. As a result, many state- ments about traceability will have limited

meaning and value until the means and methods

become adequate.

National Measurement Support System

It is impractical and unnecessary for the thousands of radiation measurements made each day

to be directly traceable to the national standards..

'procedures used for measurements, calibrations, and measurement quality assurance

(MQA)

'training of personnel who perform measurements, calibrations, and MQA

'records that document specific actions that

have been taken

PRIMARY LEVEL

INTERMEDIATE LEVEL

FIELD USE LEVEL

PRIVATE SECTOR FEDERAL

SECTOR

STATE SECTOR

INDUSTRY

MEDICINE

PRIME CONTRACTORS OTHER AGENCIES

STATE AND LOCAL GOVERNMENTS

Figure 2. Schematic showing the national mea- surement support system three-level

concept.
The institutional elements of the measurement support system are the:

" national standards laboratory that maintains

the national reference standards and pro- vides related services

" intermediate standards laboratories that use transfer standards as the basis of calibrations and other services provided by them

" field level entities , such as laboratories,

companies, or individuals that measure

radiation as a user or a concerned party

" voluntary standards-writing organizations

and professional societies that define,

develop, and document various traceability

interactions.

Each element, whether of the technical or

institutional type, is essential for an effective measurement support system. To the extent necessary, the actions of the various institutional

elements should be coordinated and planned.

Measurement Quality Assurance (MQA)

The purpose of a measurement quality as- surance program is to provide a satisfactory

degree of assurance that the measurer's process

is under control at all times. Such a program

includes a variety of periodic actions, depending

upon the specific nature of the measurement. In

a general sense, an MQA program consists of

procedures that enable a measurer to assure on a continuing basis that the total measurement

uncertainty relative to the national standard is quantified and sufficiently small to meet re- quirements.

A performance test can be an important part

of an overall MQA program. As mentioned earlier

in this paper, such a test provides an effective

method for achieving measurement traceability

(demonstrated consistency with national standards). Each test is specific to a particular

type of measurement, and usually employs a transport standard. If it is administered by NBS, it results in direct measurement traceability. When

an MQA performance test is administered by some other laboratory that has traceability to the national standard for the measurement under

consideration, it results in indirect measurement

traceability.

Since MQA performance tests demonstrate

proficiency only at the time a test is taken, it

is desirable to take additional actions that assure adequate performance between tests. These

can include internal consistency checks, such as the frequent use of stable radiation sources to check instrument response, and control charts

that would warn of unusual response or instability in the measurement process.

It is important to recognize the desirability of measurement quality assurance, and the value of MQA performance tests, at all levels of

8

the measurement support sytem -- national,

intermediate, and field.

An Ideal Measurement Support System

For many reasons which will not be treated

in this paper, the support system illustrated in Figure 2 is felt to be highly desirable [3]. It represents the best conceivable long-term system

for both technical and political reasons and,

fortunately, comes very close to the present

situation. The three primary sectors are Fed- eral, state, and private, and each has a direct

interaction with NBS. This arrangement avoids

potential conflicts of interest, and is con- sistent with the present policies of most

regulatory agencies.

In the interest of accuracy and uniformity

for all measurements made in the United States,

the technical nature of interactions between any

two levels of the MSS should depend only on the radiation quantity of interest, and not on whether the Federal, state, or private sector is involved. For example, the interactions with

NBS should be identical for intermediate laboratories in all sectors for a particular type of

radiation measurement.

Intermediate standards laboratories can provide a number of services for the field

level. Using transfer standards that were

calibrated by NBS, they can calibrate instru- ments or sources for field use. They can also

provide MQA performance tests and advice on MQA

procedures for use at the field level. Inter- mediate standards laboratories can be convenient

sources of education and training for fieldlevel measurers, for example by providing short

courses or observation of calibration procedures.

These laboratories can also test new instruments

to determine whether stated performance specifications are actually achieved.

A number of intermediate laboratories

already exist in the Federal sector, and their

interactions with NBS are being improved. A recent survey conducted by the Conference of

Radiation Control Program Directors identified

laboratories presently existing in the private sector that can serve as intermediate standards

laboratories [4]. At this time, NBS is co- operating with several states to develop pilot

intermediate laboratories in their sector. Thus

the ideal measurement support system appears to

be feasible, at least in terms of a sufficient

number of suitable intermediate standards

laboratories.

As it presently exists, the national mea- surement support system has both strengths and weaknesses. To more nearly approach the ideal system, the following weaknesses should be corrected [3]:

"Additional national standards should be developed, specifically for high-energy

photons, electrons, and neutrons.

"Transfer standards are needed for some radiation quantities.
°More intermediate standards laboratories are needed in the state sector.

"Many documented procedures (criteria) should

be developed for operation of intermediate

laboratories, and for their interactions

with NBS and the field level.

"Suitable measurement quality assurance

programs should be designed and implemented,

including MQA performance tests, for intermediate laboratories and the field level.

"Training is needed for operators of intermediate laboratories and for those who make

field-level measurements.

Coordination of the MSS is needed to achieve

national uniformity and consistency of measurement results.

It is encouraging to note that the present measurement support system is gradually being

improved in response to various incentives. This progress is, however, quite slow and results

primarily from the occasional need to solve

specific, limited problems.

Examples of Specific Traceability Programs

As indicated earlier in this paper, general

definitions of traceability have limited value. The most valuable statements about traceability

are those that identify the specific means and methods by which it is achieved for a particular

type of measurement. If the means and methods are well-documented, and consistency with national

standards is demonstrated, unambiguous trace- ability statements can be made and defended. Two examples of national programs that enable such statements follow.

The American Association of Physicists in Medicine (AAPM) has an ongoing program for ac- creditation of laboratories that calibrate ra- diation-measuring instruments used primarily in radiation therapy. Three laboratories have been accredited so far: M.D. Anderson Hospital

(Houston, Texas), Sloan-Kettering Memorial Hospital (New York, N.Y.), and Victoreen Instrument

Company (Cleveland, Ohio). Accreditation by the AAPM is based on documented criteria that must be satisfied by candidate laboratories. Interactions

between NBS and the accredited laboratories are specified, including calibration of transfer

standards by NBS and periodic MQA performance

tests. All the technical requirements for un- ambiguous traceability are satisfied in this

program: standards, calibrations, MQA, procedures

and records. The institutional requirements are also satisfied, including three good examples of intermediate standards laboratories.

The second example consists of a national program that is still under development. Since

1973 NBS has cooperated with the states, various

Federal agencies, and the Health Physics Society

in an attempt to establish a performance testing program for the organizations that provide per- sonnel monitoring services. Criteria have been developed that will form the basis of a future

routine performance testing program [5]. As the future national program is envisioned,

there will be a testing laboratory at the intermediate level which will periodically test the performance of personnel monitoring services. The

NBS role will be to ensure that the testing laboratory uses procedures that maintain consistency with

national measurement standards. In this quality assurance role, NBS will periodically calibrate the radiation sources and instruments used by the testing laboratory, and will monitor overall

technical performance.

In these two examples, specific, documented

criteria and intermediate standards laboratories

serve as the principal ingredients of programs that

result in unambiguous, easily-recognized traceability.

Conclusion

This paper was addressed to general considerations of traceability for measurements of ionizing

radiation. Some of the fundamental concepts which

are relevant to traceability for all types of mea- surements were identified, and the problem of

ambiguity in statements about traceability was treated. The "means and methods" by which ra- diation measurements can be made consistent with

national standards were recognized, and two examples were given of programs that employ appro- priate means and methods to achieve unambiguous

traceability.

The most effective national measurement sup- port system would provide those technical and institutional elements required to ensure the continuing adequacy of radiation measurements for whatever purpose those measurements are made. Some

of the required elements are in place and func- tioning for some types of measurements, but many

have not yet been developed. These weaknesses must

be corrected with additional technical programs and institutional improvements (particularly intermediate standards laboratories) before some present

ambiguities about traceability can be eliminated.

References

Belanger, Brian C, "Traceability: An Evo- lving Concept", ASTM Standardization News, p. 22, January 1980.

Act of 22 July 1950, 64 Stat. 371 (Public

Law 619, 81 Congress), to amend a 1901 Act

to provide basic authority for the per- formance of certain functions and activities

of the Department of Commerce.

"Requirements for an Effective National

Ionizing Radiation Measurements Program", a report to the Congress by the National Bureau of Standards. NBS Special Publication 603, March 1981

"Directory of Commercial Calibration Services for Ionizing Radiation Survey Instru- ments", prepared by the Conference of
Radiation Control Program Directors, NBS GCR

80-296, April 1981.

Draft American National Standard N13.ll,

"Criteria for Testing Personnel Dosimetry

Performance", prepared by the Health Physics

Society Standards Committee, Working Group

1.4, April 1981.
TRACEABILITY OF RADIATION MEASUREMENTS: MUSINGS OF A USER

Ronald L. Kathren

Battelle, Pacific Northwest Laboratories

Richland, Washington 99352

Although users of radiation desire measurement traceability for a number of reasons, including legal, regulatory, contractual, and quality assurance requirements, there exists no real definition of the term in the technical literature.

Definitions are proposed for both traceability and traceability to the National Bureau of Standards. The hierarchy of radiation standards is discussed and allowable uncertainties are given for each level. Areas of need with respect to radiation standards are identified, and a system of secondary radiation calibration

laboratories is proposed as a means of providing quality calibrations and trace- ability on a routine basis.

(calibration, definitions, hierarchy of standards, National Bureau of Standards,

radiation, standards, traceability)

By Way of Introduction: Traceability and the User

Traceability--specif ically traceability to the National Bureau of Standards— is a much desired

and sought after commodity among users of sources

of ionizing radiations. Indeed, a 1976 study by the National Bureau of Standards revealed that

the provision of transfer standards to "...establish and maintain traceability to NBS primary

standards" was considered to be the most impor- tant possible NBS service by the Conference of Radiation Control Program Directors. [1]

While perhaps not all user groups would rank traceability of prime import within the possible

range of NBS services, most users do consider NBS traceability important for a variety of reasons, including:

1. Legal and regulatory requirements,

including license conditions imposed by

regulatory agencies.

2. Contractual requirements.

3. Quality assurance/quality control.

4. Compliance with voluntary standards,

both national and international.

5. Health and safety considerations, including protection against lawsuits stemming

from improperly measured personnel expo- sures to radiation.

6. Legal protection.

7. Achieving a competitive edge.

8. Peace of mind and security in the knowledge that the "best" practicable mea- surements have been made.

9. Scientific satisfaction.

Some of the above overlap and the relative value

given to each may vary among users, but in the main, the above reasons are explicit and do not require explanation or amplification.

There has, in recent years, been increasing

effort within the broad area of ionizing radiation measurement traceability. Cavallo, Ehrlich,

and Hutchinson recently described traceability

programs and their resultsL2 ]; virtually all of

the programs currently underway are for radioactivity or are applicable to medical (usually

therapeutic) uses of radiation. U>2] Most nota- ble among the latter is the American Association

of Physicists in the Medicine Regional Calibration

Laboratory program, which provides radiological

calibrations primarily for reference class instru- ments used in radiation therapy.

It might be a useful digression at this point

to briefly touch on radioactivity, as opposed to radiological, standardization. Radioactivity

standardization refers to measurement of the abso- lute or "true" disintegration of emission rate of

a radioactive source; radiological standardization

refers to dose or exposure rates associated with a particular source. Radioactivity measurements are usually made on fairly small (i.e. low activity) sources by direct measurement--i .e. counting—of

the emitted particle or radiation; radiological measurements or standardizations are usually

accomplished by measuring secondary effects of the emitted radiation(s) , e.g. energy deposition

in the form of heat produced in a specific medium

or current flow or capacitance changes produced by

ionization in a gaseous medium. Hence, radioactivity standardization is usually achieved by

direct means (i.e. counting of emitted particles)

and reported in units of activity (becquerels,

curies). Radiological standardization is usually

accomplished by indirect means, and may be reported in units of exposure (C/kg or R), doses,

fluence rate, or yield (e.g. particles per sec- ond) instead of activity. The distinction is important, because while traceability is impor- tant for both (particularly in health physics),

there appear to be greater needs, probably because

of the greater difficulties of measurement, con- version, and source characterization in the radiological area, and especially the greater uncer- tainty generally associated with radiological measurements.
While on the subject of terminology, it might

also be instructive to examine just what is meant

by traceability. The dictionary, as expected, is of little use for a technical term, merely defining traceability as 'capable of being traced.' However, review of the dictionary also points to some interesting if unexpected relationshipssimilarities, that is, between traceability and a certain type of nonscientif ic endeavor.

On the Similarities Between Traceability and Pornography

Interestingly and perhaps surprisingly, por- nography and traceability have certain similarities. Pornography, for example, has no true definition. According to the dictionary, pornography

is simply "obscene literature or arf'Pj; and since there exists no uniform legal definition of what is obscene,* by logical extension pornography

is also not defined. However, the same jurists

and legal scholars who fail at exact definition

can readily recognize and identify pornography as such. Thus, they rest their case.

A similar situation exists with regard to traceability. We all know what it is, and can readily recognize and identify it, even though no definition apparently exists. While preparing

this presentation, more than 150 works dealing

with measurement of radiation were checked,

including such standard texts as JohnsTM]; all four volumes of Attix, Roesch, and Tochil inPJ;

such classics as Hine and BrownelU^J; and some older but still excellent works, such as Glasser's

Medical Physicsl^]; Glasser, Quimby, Taylor and WeatherwaxlPJ ; that yade mecum of the health

physicist, the Radiological Health Handbook ^],

with its excellent and extensive glossary; numerous reports of the National Council on Radiation Protection and Measurements and International

Commission on Radiological Units; various handbooks, encyclopedias, and dictionaries of physics

and chemistry; ANSI and other standards; and, of course, various reports of the National Bureau of Standards. Nowhere was there a definition of traceability--not even in the ANSI glossaries of quality assurance of nuclear science and tech- nology terms, l10>11] although the paper by

Cavallo, Ehrlich and Hutchinson, previously mentioned, did describe traceability as referring to the agreement between the measurement of a physical quantity with results of NBS within an accep- table limit of uncertainty. [2] This would seem

to be more of a description of intercomparison,

for among users, traceability, as used in the vernacular, goes somewhat beyond this description.

There is, however, a most interesting and germane discussion of traceability in a recent publication of the National Bureau of Standards

which bears repetition here:

* The definition of obscenity depends on the pre- vailing community standards, which, of course, means that what is obscene in one place may be quite proper elsewhere.

"Traceability is a term which a number

of contracting and regulatory agencies have invoked to specify the standards used in the calibration of instruments.

Perhaps the first and most far-reaching

traceability requirement has been that of the Dept. of Defense (MIL-C-45662A) , "Calibration

Systems Requirements," which states (sec.

3.2.5.1):

'Measuring and test equipment shall be calibrated by the contractor or a commercial

facility utilizing reference standards (or

interim standards) whose calibration is cer- tified as being traceable to the National Bureau of Standards, has been derived from

accepted values of natural physical constants,

or has been derived by the ratio type of self- calibration techniques.'

This specification does not define the term 'traceable' (nor do those of any other

government agency)." [12]

The first and last sentences of the above quotation, taken from NBS Special Publication 250, tell the whole story, viz. a requirement for trace- ability without a definition of the term. Indeed,

NBS points out further along in Publication 250

that it gives no special meaning to traceability

and indeed legally cannot do so, at least in the context of procurement contracts or related

activities.

Despite the fact that there is apparently no definition for traceability or traceable to the National Bureau of Standards, these terms Ire coming into greater and more widespread use in science, engineering, industry, and commerce. The increased emphasis on quality assurance has

led to the imposition of traceability requirements throughout the nuclear power industry and elsewhere, but the recipient of such requirements

has little to go on other than word of mouth or vague guidelines.

An exception is the Institute of Electrical

and Electronic Engineers standard on calibration,

which provides the following statement regarding

traceability:

M&TE (measurement and test equipment)

shall be calibrated utilizing reference stan- dards whose calibration has a known valid

relationship to nationally recognized stan- dards or accepted values of natural physical constants. If no national standard exists,

the basis for calibration shall be documented.

Reference standards used in the calibration program shall be identified on calibration data records and supported by certificates, reports, or data sheets attesting to the calibration date, calibration facility,

environmental conditions, and data which

shows conformance to accuracy requirements. E13.

This statement provides reasonable guidance as to how traceabil ity might be achieved, but it falls

short of being a definition.

12
The concept of traceability has been discussed

in a recent paper by Brian Belanger of NBS.LHJ

In his presentation before the ASTM, Belanger

traced the historical development of traceability,

noting its purposes and uses, as well as the legal and contractual requirements that may be imposed

on the user. In threading his way through the

legal and contractual requirements maze he clearly

underscores, at least by implication, the need for a consistent and meaningful definition and application of traceability among them. Although

his discussion is articulate, where definitions

are concerned and with regard to how traceability

might be achieved, he neither offers nor suggests

the adoption of a specific 'universal' definition.

The legal vulnerability and intense frustration of attempting to fulfill traceability re- quirements is intensified by the lack of a practical and simple accepted definition. The

apparent purpose of traceability is simply to assure that measurements are reasonably correct;

as for a definition for traceability in the sense

in which the word is commonly used (among those

concerned with radiological measurements at least) the following is proposed:

traceabil ity— the means or series of steps

and associated documentation by which a measurement or measuring instrument is relatable to a recognized standard.

Similarly, by extension, traceability to NBS can

be defined as

...the means or series of steps and asso- ciated documentation by which a measurement

or measuring instrument is relatable to one

or more standards or measurements of the U.S. National Bureau of Standards.

It would seem that acceptance or at least agree- ment with the above definitions would provide

some modicum of relief from the present state of affairs, and at the same time remove an interesting parallel between radiological science and pornography.

Of Standards and Their Hierarchy

Nearly a quarter century ago, A. G. McNish of the National Bureau of Standards put forth a classification scheme for standards of ionizing

radiation that expanded the previously accepted

two-tier level of primary and secondary standards. [15,16] T n i S classification scheme, rec- ognized by the National Committee (now Council)

on Radiation Protection and Measurements (NCRP)

and described in simplified form in NBS Handbook 80, L17J showed the relationships among five

categories (prototype, derived, calibration, in- struments, and materials) and several orders or levels of standards. The levels or orders were,

in effect, a hierarchy of standards.

At the top of the hierarchy, McNish proposed

an international standard of a single (or group

of) preparation(s) or radioactivity to be selected by an international committee. National stan - dards , such as those held by NBS or its equivalent

in other countries, would be a select group calibrated against the international one(s). To pro- tect the national standards from wear and tear and

to provide backup capability, another set of stan- dards, national reference standards would be created, these of course being cross-calibrated

against the national standards. Ordinary calibration work would be carried out with national working standards, cross-calibrated with the reference

level. Also cross-calibrated with the national

reference standards would be laboratory reference

standards, maintained by an individual organization for its own purposes. Day-to-day work would

involve the use of laboratory reference standards , these being analogous to the national working

standards.

Implicit in the McNish scheme is a direct line

of traceability to the NBS, with NBS providing

laboratories with their basic calibrations or standardization. Recommended in somewhat modified form at least for radioactivity by the NCRP

in 1978, [18] the McNish scheme has regretably

never been fully adopted. Although it called for direct traceability to the NBS, it also hinted,

albeit vaguely, at the possibilities of laboratories calibrating standards for other labora-

. tories, but made no provision for a situation

where direct traceability to NBS was not possible, as might be the case if a user desired a different energy, intensity, or geometry than

could be conveniently supplied by the Bureau.

A few years later, a simple hierarchial stan- dards scheme was proposed for radiological mea- surements by Kathren and Larson, [19] and by

Kathren.[20] This scheme, applicable to radioactivity as well, is reproduced in Figure 1. It features a six-level hierarchy of standards and makes allowance for the situation in which direct

line traceability to NBS is impossible or other

wise not feasible. In this scheme, international

standards lie at the top of the hierarchy and are those fundamental physical standards which serve

as the basis for our system of units and measurements. These are ordinarily established by

treaty or agreement of international scientific

bodies.

National standards are the exclusive province

of the National Bureau of Standards and represent

the highest achievable state-of-the-art. Thus,

these would have the minimum of uncertainty and would represent the fruits of the most sophisticated instrumentation and measurement techniques.

These would, wherever possible, be related to in- ternational standards. However, this need not be the case, for a specific national standard might

be developed for a need more or less unique to one country although this situation would be con- sidered exceptional.

Secondary or derived standards would be sources and instruments directly calibrated by

13
INTERNATIONAL

STANDARDS

~~r~

NATIONAL

STANDARDS

SECONDARY (DERIVED)

STANDARDS - —H- -

LABORATORY

STANDARDS

it

OPERATIONAL

STANDARDS

1

I NONSTANDARD

< » IMPLIES I NTERCOMPARABILITY IMPLIES NO I NTERCOMPARABILITY

FIGURE 1 . A Hierarchy of Standards

[

2°]

the National Bureau of Standards or intercompared

with NBS sources or instruments with no intervening steps. As such, these would have somewhat

greater uncertainty than national standards but would serve satisfactorily as the basic standards

of industrial and other users.

Instruments and sources calibrated against

secondary standards, or well recognized instru- ments such as extrapolation chambers utilized for standardization would have larger allowable error

and would qualify as laboratory standards . In- cluded in this group are instruments and sources which are not routinely calibrated by NBS but which are utilized for standardization. For all practical purposes, use of these instruments and sources would be restricted to a well -control led laboratory with known, if not controlled geometry,

scattering and other conditions. Free air chambers, extrapolation chambers, and long counters

can serve as laboratory standards, as can practically any detector if its response characteristics

are known and the measurement conditions rigidly

controlled.

Operational standards assume even greater but

still acceptable and known error limits, and pre- sume an instrument or source used under relatively

uncontrolled conditions. As an example, the mea- surement of ionizing electromagnetic radiation

levels inside a reactor containment might be accomplished with uncontrolled and unknown

scattering conditions, a wide mixture of energies,

and perhaps even a mixed radiation field. A wide

variety of instruments might be used for operational purposes. Generally, these would have wide response characteristics, be simple and easy to use, and permit accumulation of several measurements, economically.

Table I sets down what appears to be the achievable uncertainty for various types of mea- surements at each level in the standards hierarchy, based on the present state-of-the-art.

TABLE I . Uncertainty of Measurements with the Radiation Standards Hierarchy

Level Radiation Quantity Allowable Comments Uncertainty

National All Any State of NBS Only

Secondary Alpha, Activity i 1" Must specify

Beta nuclide

IER* Exposure or 2* All directly

Dose traceable to Neutron Fluence Rate

or Yield

+ 5* NBS; may be only certain

Beta Dose + 5% specific energies or sources

Laboratory Alpha, Activity ± 2 * All measureBeta ments under

IER Exposure or + 5% controlled,

Dose specific

IER Dose +10* 1 aboratory

Neutron Fluence Rate +HW conditions;wider

or Yield range of energies Neutron Dose or Dose +20% and sources than Equivalent available above Beta Dose +10*

Beta Fluence rate + 10*

Operational Alpha, Activity + 5* Al lowable error Beta considered to IER Exposure or +20* be currently

Dose attainable by Neutron Dose or Dose +50* measurement in Equivalent the field under Beta Dose +35* semi-controlled

conditions

*IER = ionizing electromagnetic radiation.

For dose measurements, medium must be specified.

Some Areas of Need

Although NBS has, in general, done a fine job

of providing radiological calibrations, the mag- nitude of the task is growing at an enormous rate. The expansion of the nuclear industry, especially

nuclear power, has created a breadth and quantity

of calibrations that could not have been foreseen

a generation ago. Moreover, new and increased

quality assurance requirements and personnel do- simetry demands have put the user in an awkward situation, for what the user needs and demands,

NBS may be unable to supply. Supply may be outside the scope of the NBS mission, or may be nighly specialized and out of limited application, or may be restricted by budgetary or man- power or equipment considerations, or may be simply not reasonable with the given state-of-theart.

14
Moreover, the NBS emphasis has been primarily

research, and in the case of calibration services,

oriented to the medical profession. Those in industry, and in particular the nuclear industry,

have urgent need for certain types of calibration

and standardization services which NBS does not now offer. For example, there is a need for high

level [on the order of 10^ rads (air) per hour]

photon calibrations for emergency radiological

monitoring instrumentation and for area monitoring

instrumentation as may be installed in power re- actor containments. In the wake of the accident

at the Three Mile Island Nuclear Generating

Station, this need may assume critical (pun not intended) dimensions, and capabilities in this area urgently need to be developed.

Another important area of need relates to the standardization and development of dose measurements. Radiological traceabil ity, if it is to be truly meaningful, must provide the wherewithal of dose measurement traceabil ity for not only

photons— i.e. ionizing electromagnetic radiation

(IER)--but also for betas, neutrons, and mixed

fields. Dose traceabil ity might also be neces- sary for high energy IER — i.e. photons with energies above a few MeV.

One area, ripe for development, relates to provision of different energies of IER. For many

years, the NBS has provided a standard series of filtered x-ray beams, but these are now inadequate

to the needs of greatly expanded user body. Specifically, K-f luorescence x-rays, essentially

monoeneKjetic, are highly useful and perhaps

mandatory for energy dependence and dosimetry

studies, radiological evaluation of monitoring

instruments, calibrating dosimeters, and for a whole host of activities related to health and radiological physics. Regretably, this capability, so easily developed, does not exist within

NBS, although it has been adopted elsewhere. [21] Hence, there can be no real traceabil ity to NBS

in this area, however great the need.

On the other hand, NBS has done an outstanding job developing monoenergetic or nearly monoenergetic neutron sources. [22] This valuable

work should be extended, and the service advertised, so to speak, so that it can be taken ad- vantage of by a larger segment of the industrial

and research community. Greater neutron capability needs development; additional sources, with a wider range of neutron exposure rates would be welcomed by the users in the field. Indeed, calibration in units of dose as well as fluence rate would serve the users well.

Certainly there are many other areas in which

traceability does not truly exist because of lack of capability within NBS; some of these include

characterization of beta energy spectra along with

the establishment of standard beta spectra and sources, standardized pulsed radiation fields, and the establishment of standards and traceability

for instrumentation used for sampling environmental media for radioactivity. The task, taken in toto is clearly a herculean one, and not neces- sarily in keeping with the charter or existing

capabilities of NBS. Certainly the NBS charter

15

and funding level can be expanded, but there is perhaps another solution which may be more

practicable.

Towards a Meaningful and Pragmatic Solution

Many of the above needs could be met by the establishment of secondary calibration and stan- dards laboratories with appropriate capability.

Such laboratories would be chartered by NBS and thus periodically be required to demonstrate their

capabilities and quality in the manner prescribed

by, and to the satisfaction of the Bureau. The

secondary laboratories would be selffunding, and would not be operated by NBS. Rather they would

be operated by appropriate organizations—national

laboratories or universities, for example, with

already existing specialized capabilities and with

no commercial ax to grind. Secondary laboratories

might be selected on the basis of location (i.e.

regional) as well as on the basis of specialized

calibrations or measurements (e.g. pulsed

radiations) they could perform.

Alternatively, NBS could develop a number of regional secondary laboratories for the performance of routine calibrations and certain specialized radiation measurements. However, the cost

of such a program (not to mention the time neces- sary for their development) would work against

them. Also, some may question whether or not this is an appropriate course for NBS. In any

event, the system of secondary laboratories has precedent, namely the Regional Calibration Laboratories of the American Association of Physicists in Medicine and the Regional Radiologic

Physics Centers of the National Cancer Institute. [23,24] j n either case, the Bureau itself

would be freed from the need to provide more or

less routine calibration services and could better

fullfill its role as the national ionizing radiation standards laboratory, providing pioneering,

fundamental research in radiological standardization, as well as specific reference sources and measurements.

One might use the word 'esoteric' to describe

the NBS role, with the more applied and routine

calibrations performed by a satellite or secondary laboratory. Although traceability would be sought wherever possible, in some cases the sources and/or instruments or techniques used by

this laboratory might not be directly traceable

to national standards held by NBS. One reason

for this lack of traceability might be that no direct pathway exists. However, to serve the existing needs of the industry and research com- munity, a secondary reference laboratory, providing standardized and precise radiological field

and pragmatic, often ad hoc calibrations, could

serve. As noted, this secondary laboratory may

or may not be run by the Bureau, but in any case

it must have close ties to the Bureau.

While users in general and in particular the nuclear power industry need a service facility of secondary standards level, they must be made to realize that Bureau "traceability" is not a man- datory or always available goal. Indeed, the quest to achieve such traceability is often
counterproductive. For example, in nuclear power plants, a common quality assurance requirement is "traceabil ity to the National Bureau of Standards." What may well be acceptable is trace- ability through a large number—perhaps as many

as a dozen or even more-- intervening steps, some

of which may not even be continuous or relevant

to each other. Similarly, "traceabil ity to the National Bureau of Standards" for gamma spectroscopy may involve only a single source giving a single energy point, far removed from the energies

the system is actually used for. These examples,

in my view, are a distortion of the meaning of the phrase "traceable to the National Bureau of Standards", and may introduce sufficient uncer- tainty as to render the ultimate measurement meaningless. In general, the fewer number of steps

the better, and a system of service oriented

secondary laboratories attuned to the needs of

its users could go a long way towards ensuring

that radiation measurements in the field are within reasonable bounds of uncertainty, and that

traceabil ity remains a meaningful and useful con- cept and activity.

References

1 Eisenhower, E. H., "Report of the National Bureau of Standards' Survey of State Mea- surement Needs" in Proc. Ninth Annual

National Conference on Radiation Control , Meeting Today's Challenges , June 19-23,

1977, HEW Pub li cat ion "(FDA) 78-8054

(April 1978).

2 Cavallo, L. , M. Ehrlich, and

J. M. Hutchinson, "Traceabil ity in Ionizing Measurements Systems" in National and Inter- national Standardization of Radiation Dosime- try , Proc. Symp., Atlanta, 5-7 December

1977, Vol. 1, International Atomic Energy

Agency, Vienna (1978), pp. 65-88.

3 Barnhai c, C. L., Ed., American College Dic- tionary , Random House, New York (1960),

p. 944.

4 Johns, H. E., and J. R. Cunningham, The

Physics of Radiology , Charles C. Thomas,

Springfield, Illinois, Third Edition

(1974).

5 Attix, F. H., W. C. Roesch, and E. Tochilin,

Radiation Dosimetry , Academic Press, New

York (Vol. 1, 1968; Vol. 2, 1966; Vol. 3, 1969). Also, Topics in Radiation Dosimetry , Academic Press, New York (1972).

6 Hine, G. J., and G. F. Brownell, Radiation

Dosimetry , Academic Press, New York (1956).

7 Glasser, 0., Ed., Medical Physics , YearBook

Publishers, Chicago, 3 vols (1944, 1950,

1960).

8 Glasser, 0., E. H. Quimby, L. S. Taylor, and

J. L. Weatherwax, Physical Foundations of Radiology, Paul B. Hoeber, New York, 2nd Edition (1952).

9 Radiological Health Handbook , U.S. Department of Health, Education and Welfare,

Revised Edition (January 1970).

10 American National Standard "Glossary of Terms in Nuclear Science and Technology",

ANS-9/ANSI Nl.l - 1976, American National

Standards Institute, New York.

11 American National Standard "Quality Assurance Terms and Definitions", ANSI

N45. 2. 10-1973, American Society of Mechanical Engineers, New York.

12 National Bureau of Standards, "Calibration

and Related Measurement Services", NBS Special Publication 250 (1978), pp. 7-8.

13 Institute of Electrical and Electronic Engineers, "Control of Measuring and Test Equipment", IEEE Standard 498-1975, New York

(1975), p. 9.

14 Belanger, B.C., "Traceability - An Evolving

Concept", Standardization News 8:22 (1980).

15 McNish, A. G. "Classification and Nomen- clature for Standards of Measurement", IRE Trans. Instr . 1-7:371 (1958).

16 McNish, A. G., "Nomenclature for Standards

of Radioactivity", Int. J. Appl. Radiation

Radioisot . 8:145 (1960).

17 National Committee on Radiation Protection

and Measurements, "A Manual of Radioactivity

Procedures", U.S. National Bureau of Standards Handbook 80, Washington, D.C. (November 20, 1961).

18 National Council on Radiation Protection and Measurements, "A Handbook of Radioactivity

Measurements Procedures", NCRP Report No. 58,

Washington, D.C. (November 1, 1978).

19 Kathren, R. L. and H. V. Larson, "Radiological Calibration and Standardization for Health Physics", Health Phys . 16:177

(1969).

20 Kathren, R. L., "Standard Sources for Health

Physics Instrument Calibration", Health

Phys . 29:143 (1975).

21 Thompson, I. M. G., "International Standard

Reference Radiations and their Application

to the Type Testing of Dosimetric Apparatus", in National and International

Standardization of Radiation Dosimetry , Proc. Symp., Atlanta, 5-9 December 19/7,

Vol. 1, International Atomic Energy Agency,

Vienna (1978), pp. 343-365.

22 Schwartz, R. B., and J. A. Grundl, "NBS Standard Reference Neutron Fields for Personnel Dosimetry Calibration", op_. cit ., pp. 367-376.

16
23 "AAPM Radiological Physics Center: A Status

Report", Medical Phys . 1:41 (1974).

24 ''Regional Radiological Physics Center Coor- dinating Committee: Cancer Control Program", Medical Phys . 1:287 (1974).

Acknowledgement . The helpful discussions with

Dale Fleming and Craig Yoder, Battelle, Pacific

Northwest Laboratories, and Daniel Garland,

Westinghouse Hanford Corporation, are appreciated

and hereby acknowledged.

17

RADIATION MEASUREMENT TRACEABILITY IN THE UNITED KINGDOM

W. A. Jennings

National Physical Laboratory

Teddington, Middlesex, OT11 OLW, UK

The concept of traceability in the UK, along with the role of the National Physical Laboratory, is presented. In respect of the measurement

of ionizing radiations, the legal position in the UK is summarised and a three-tier system of Regulations, Codes of Practice and Guidance Notes is

described, with particular reference to the field of radiological protection.

The impact of the relevant European Directive in this field, and the preparation of the consequential Ionizing Radiation Regulations in the UK, are

discussed, including the need for type—testing, etc. The role of the British Calibration Service, including the operation of personal dosimetry

services is introduced. Radiotherapy calibrations, radioactivity measurements, and industrial radiation processing are then considered, and finally,

the role of the various international links is mentioned.

(Calibrations, codes of practice, ionizing radiation, regulations, standards,

traceability, type testing.)

Introduction

delighted to receive, last November, (a) Prom the British Standards

n to participate in this seminar on Institution, we find (4):

I was an invitatii

traceability in radiation measurement. At that

time, there was reason to believe that some uncertain features in the UK traceability chain

would be clarified by the Spring, but in the

event, the uncertainties in question have yet to be resolved?' Adding to these the uncertainties

in the parallel international scene, I can only

present the position as I understand it at this

moment in time, partly operational, partly

propositional and partly aspirational, — to coin

a word or two!'

Traceability

What is meant by 'traceability* in this context? Looking at the programme, I note that

this talk will have been preceded by two major

contributions providing two views on •traceability', one from the Centre for Radiation

Research, and the other from the standpoint of

the user. Moreover, I am aware of several discussions on this topic in the US literature, such

as those by Belanger (1), Daneman (2), Landvater (3), and others. Indeed Belanger discusses the merits of some four possible definitions of traceability. Since I am here to report

on the UK scene, I propose to confine myself to presenting the definitions currently put forward

by two of the interested organisations in my

country, the British Standards Institution, BSI, and the British Calibration Service, BCS.

Traceability, "the concept of

establishing a valid calibration of a measuring instrument or measurement

standard, by a step-by-step comparison

with better standards up to an accepted or specified standard. In

general, the concept of traceability

implies eventual reference to an

appropriate national or international

standard"

.

In a recent BSI document entitled

•Specification for Measurement and Calibration

Systems 1 (5), under 'traceability', further

provisos are made; for example, it states that all measurement standards in use in the calibration

system shall be supported by certificates, reports, or data sheets attesting to the data, accuracy and

conditions under which the results were obtained

and are valid. All documents must be signed by a responsible person".

(b) My second definition is taken

from the British Calibration

Service, (6)

"Traceability to national standards means :

(i) That each standard used for

calibration purposes has itself

been calibrated against a standard of higher quality up

to the level at which the higher quality instrument is the accepted national standard".

19
(ii) "That the frequency of such

calibration, which is dependent on the type, quality,

stability, use and environment of the lower quality

standard, is such as to establish reasonable confidence that its value will

not move outside the limits

of its specification between

successive calibrations".

(iii) "That the calibration of any

instrument against a standard

is valid in exact terms only

at the time of calibration,

and its performance thereafter must be inferred from

a knowledge of the factors

mentioned in (ii) above".

The BCS operates through 'Approved

Laboratories'', and approval entails much more than the validity of the calibration standards

in use. In addition to the equipment, approval

relates to the quality of the staff, organisation

and procedures employed. Supervision subsequent to approval includes the operation of an audit measurement scheme. Such features are con- sidered necessary to ensure that the concept of

traceability has any real meaning. On the other

hand, traceability does not necessarily imply

high accuracy as such, as sometimes assumed. Clearly the number of steps, or echelons, in the calibration chain must be limited, and the procedure adopted at each step must be consistent

with whatever accuracy is deemed appropriate,

and the accuracy claimed must be specified. It is perfectly reasonable, for example in radiation protection measurements in the field, to insist on traceable readings, even at a low

accuracy.

The National Physical Laboratory

In the UK, the National Physical

Laboratory, NFL, develops the techniques for the realisation of the units of measurement of the principal physical quantities, and is the custodian of the resulting national primary

standards. It is responsible both for the com- parison of these with those of other countries,

and for providing essential calibration services

based upon them, with a view to disseminating

measurement units throughout the UK. Generally,

the NPL endeavours to develop and promote good measurement practice; and provides advisory ser- vices to government, industry and others. The standards which are in service, or under development, include the principal ones for the quantities of interest in the measurement of

ionizing radiations, - namely the quantity

exposure for X and y-rays; absorbed dose for X, y and 3-rays, and electrons; fluence for neutrons; and activity for radionuclides.

In addition, in order to disseminate the units for these quantities, secondary standards

have been developed at NPL as transfer devices

where this was considered necessary. Such

transfer devices may take various forms, such as an instrument with an appropriate probe, as in

the case of X-ray measurements, or calibrated

radioactive sources used in a jig to produce

standardised fields, as in the case of P-ray

measurements. These different approaches were described in a talk which I gave at a Symposium on •National and International Standardisation in

Radiation Dosimetry' held in Atlanta in 1977 (Jennings (7)).

Before summarising dissemination procedures, we must first examine the legal requirements, as these differ in the different fields of

application. Thus, the position in the medical

field, in radiation processing, and in respect of

radiation hazards, will require separate consideration.

Legal requirements

Although the national measurements

standards are located at NFL, and the NFL comes under the Department of Industry, the NFL is not responsible for legal metrology as such, - apart

from the provision of the relevant primary

standards. Responsibility for the Weights and Measures Act (1963), which lays down legal requirements for regular comparisons of secondary

and local standards, and thus effectively

provides for a traceability chain, is now vested

in the Department of Trade. However, this does

not relate to radiation measurement. Indeed, the evolution of radiation control in the UK from Common Law to Legislation and Codes of Practice, over the years since 1 94&, would call for a talk

on that topic alone, I can only summarise the salient points.

'Statute Law', embodying Acts of

Parliament, differs from 'Common Law', which is

built up from precedents resulting from previous

judgments. Common Law included, for example, the doctrine of 'strict liability', which imposed a duty on manufacturers, and other persons who are in possession of goods which they know to be unusually dangerous, to exercise reasonable care

to make the goods as safe as possible, and to explain their hidden dangers before parting with

them. More recently, the Health and Safety at Work etc Act, 1974, introduced wider statutory

duties where the goods are for the use of persons

at work.

Radiological Protection

Let us consider the position in respect of radiological protection. The Radioactive

Substances Act, 1948, gave powers which later resulted in regulations regarding the carriage of

radioactive materials. The Factories Act, 1 961

,

resulted in regulations concerning the use of ionizing radiations for both unsealed ( 1 968) and

sealed (1969) radioactive sources. In addition, a series of non-statutory Codes of Practice have

been issued by a number of government departments,

official bodies and associations, having a bearing

on the radiological protection of persons. For

example, the Radioactive Substances Advisory

20
Committee, set up under the Radioactive Substances Act, 1948, sponsored, and the Department

of Health published, a 'Code of Practice for the

Protection of Persons against Ionizing Radiations

arising from Medical and Dental Use* (revised

version, 1972). A similar Code in respect of

teaching establishments was published by the Department of Employment, in preference to Regulations (revised version, 1 968)

.

This approach may be difficult at first

to appreciate, but it is demonstrably more flexible than legislation alone. Indeed, a three-tier structure is now proposed:-

Regulations, Codes of Practice, and Guidance

Notes:

(i) Regulations set down requirements and duties, and

procedures where no choice or alternative is acceptable.

They specify basic permissible levels of exposure, make provision for record

keeping, create a system of

recognition of qualified

experts, and deal in a general

way with the provision of

suitable plant, facilities and

specialised protection and

medical services.

(ii) Approved Codes of Practice

provide practical guidance as

to the general requirements to meet the Regulations. This

avoids making the Regulations

too lengthy, or too specific

where alternatives are possible. Such Codes occupy a

special position in the en- forcement of legal requirements. If a prosecution is taken under the Health and

Safety at Work etc Act, during

which a person is alleged to have failed to comply with the terms of the Code, then such

failure will be prima facie

evidence that he has not com- plied with the Regulations,

However, it will be open to him to show that he has met

the legislative requirement

in some other way which is equally effective. Thus a more flexible approach results,

which can take account of new

developments.

(iii) Guidance Notes may be provided

to give detailed advice in

considerable depth, where

appropriate. Such Notes can

relate to precautions in particular fields, such as

industry, teaching, medicine,

dentistry or veterinary work. Guidance Notes do not have a special legal status, but will

nevertheless reflect legal

requirements.

At this point I need to make reference to the impact in this area of the UK joining the European Community, an impact which will result

in new ionizing radiation regulations in the UK.

The European Directive and the HSC Consultative Document

On joining the European Community, the UK became subject to the provisions of the Treaty

establishing the European Atomic Energy Community,

or Buratom. This treaty requires that basic

standards should be laid down in the Community

for the health protection of workers and the general public against the dangers arising from

ionizing radiations, and the instrument chosen

has been a 'Directive', the contents of which

must be given effect in member states. The

Directive adopted on 1 June 1 976, (8) , reflected

the thinking of ICRP Publication 9, (9). More

recently, the ICRP have revised and updated their

philosophy, and in 1977 presented this in ICRP Publication 26, (10). In consequence, the Directive is also being revised, and proposals to amend the Directive have been circulated. In the meantime, another Directive issued in 1979, (11),

extends the time for implementation of the original 1976 Directive.

These Directives are having direct con- sequences on the UK scene. Fortunately, the

Health and Safety at Work etc Act, already pro- vides comprehensive powers to give effect to many

of the requirements of the Directive. Several

government departments are taking the necessary

steps, and in particular, the Health and Safety

Executive, HSE, is drafting new Ionizing Radiation

Regulations, along with Approved Codes of Practice and Guidance Notes for publication by

the Health and Safety Commission, HSC. A 'Con- sultative Document' was issued by HSC in 1978,

(12), and following comments received, and the updating of the Directive, a further Consultative

Document is expected later this year (198O).

Such a Consultative Document, making reference to all facets of the problem, enables all

interested parties to react to the proposals made,

in time for account to be taken prior to the final

version. To give just one example, there is need

to designate some individuals as 'Radiation Pro- tection Advisors' (RPAs) , 'Radiation Protection

Supervisors', and 'Qualified Experts', - with

specified responsibilities. Indeed, interested

bodies like the Society for Radiological Protection, SRP, and the Hospital Physicists' Association, HPA, have been busy devising schemes

to provide for the certification of members who may qualify as RPA's, etc.

According to the current draft proposals,

such Advisors and Experts will have a part to play in respect of traceability, as will the British Calibration Service, BCS, at different

stages in the calibration chain. However, while

consultations continue, I can only refer to some proposals currently under discussion. Thus, to ensure adequate performance and traceability in

respect of instrumentation, three levels of

21
testing are envisaged, type testing, acceptance

testing, and routine testing:

(i) Type testing relates to specimens of new instruments,

and comprises wide—ranging

tests of compliance with, or •conformance to' agreed specifications or criteria.

(ii) Acceptance testing relates to more restricted tests on individual instruments, prior

to "being put into service, and

(iii) Routine testing relates to simple periodic in-service

checks on performance.

We must now consider who should carry out these respective tests, and how the scheme can be monitored. Calibration may be regarded as a part

of testing, in so far as it constitutes one aspect, - though a vital aspect, of performance

under restricted, but specified conditions.

Let us return to the possible role of the

BCS, to which reference in regard to Laboratory

Approval, has already been made.

The British Calibration Service

The British Calibration Service, BCS, (6) was established by the government to provide

British Industry with a comprehensive service for

the calibration of instruments against recognised

standards, the calibration work being carried out in existing laboratories which have been specifically approved for the purpose. The Service

headquarters is now an integral part of NPL. An

Advisory Council on Calibration and Measurement

advises on the operation of the service, and a series of expert panels assist in each field of

activity, including the drawing up of criteria

for the approval of laboratories. At present,

some 80 laboratories are approved for measurements in electrical, mechanical, fluid, thermal

and optical fields, and they are currently

issuing certificates at a rate of about 30,000 per year, overall.

It had become clear, even before the forthcoming Ionizing Radiation Regulations were

drafted, that a national dissemination scheme was needed to calibrate the 20,000 or so monitors in use for protection measurements in the field in

the UK, To this end, 'Radiological Measurements'

was added to the BCS list of activities, another

Advisory Panel set up, and a series of criteria

prepared in respect of laboratory approval to act

as secondary standardising centres. These criteria, listed in Table 1

, relate to both protection and therapy—level instruments, and to their use for X, y, 3—rays and neutrons. Some details

regarding the approval procedure were summarised

by Dr M J Rossiter, of FPL, in a paper also

delivered at the Symposium held in Atlanta in

1977, (13).

TABLE 1

BCS RADIOLOGICAL CRITERIA, INSTRUMENT CALIBRATION

Document

Number Title

0802 General Criteria for Laboratory Approval. Calibration of Radiological

Instruments

.

0811 Supplementary Criteria for Laboratory

Approval. Calibration of Radiological

Protection-Level Instruments: X-, Gamma- and Beta-Rays

.

0812 Supplementary Criteria for Laboratory

Approval. Calibration of Radiological

Therapy-Level Instruments: X- and Gamma-Rays

.

0813 Supplementary Criteria for Laboratory

Approval. Calibration of Radiological

Protection-Level Instruments: Neutrons

DDU1 Calibration of Radiological Instruments

at Protection and Therapy Levels (Guid- ance Publication)

.

However, no such approvals have yet been

finalised, pending the outcome of the discussions

initiated by the HSC Consultative Document previously mentioned. Thus, it may now be necessary

for such secondary standardising laboratories to be formally approved by HSE, having met BCS

criteria. Moreover, there is now the additional matter of type testing, and laboratories carry- ing out this work may also require HSE approval,

such approval being based on the assessment of the laboratory by BCS in the light of appropriate

criteria for this purpose. Such criteria have

yet to be written, and it has been proposed that this should be done by the relevant BCS panel,

based no doubt on existing specifications such as the IEC standards now nearing completion.

Similar proposals are under discussion in

respect of acceptance and routine tests, the latter being carried out by means of standards,

either instruments or radioactive sources, and

in either case, they will need to be certified in

order to confirm traceability to national

standards. In regard to routine tests, the Radiological Protection Advisors, and others,

will clearly have a recognised part to play.

It is difficult to be sure how comprehensive

the final scheme will be, bearing in mind the costs of implementation, in the present economic

climate in the UK, as well as the need for safety. As far as BCS is concerned, the above proposals

extend its role beyond that of 'calibration'.

However, consideration is presently also being

given to setting up a broader-based 'national

Testing Laboratory Accreditation Scheme', NATLAS,

also to be based at HPL, which would involve the

22
TABLE 2

BCS RADIOLOGICAL CRITERIA, PERSONAL DOSIMETRY SERVICES

Document Number Title

0803 General Criteria for LaboratoryApproval. Provision of Personal

Dosimetry Services.

0821 Supplementary Criteria for

Laboratory Approval. Provision of

Personal Dosimetry Services using

Film Dosemeters for Beta, Gamma, X- and Thermal Neutron Radiations.

0822 Supplementary Criteria for

Laboratory Approval. Provision of

Personal Dosimetry using Nuclear

Emulsion Film Dosemeters for Neutron Radiations.

0823 Supplementary Criteria for

Laboratory Approval. Provision of

Personal Dosimetry Services using

Thermoluminescent Dosemeters for

Beta, Gamma, X- and Neutron

Radiations.

assessment of all kinds of testing laboratories

to establish whether they are competent to carry

out a wide variety of tests.

Personal Dosimetry

Before leaving the topic of radiation

hazards, mention must be made of one other area, namely, personal dosimetry services, using either

TLD or film badges, for X, y, (3—rays and neutron

radiations. At present, some 50 laboratories in

the UK supply such services, and these laboratories are now subject to HSE approval, based on criteria prepared by the BCS Technical Panel, as listed in Table 2. Traceability is ensured

through intercomparisons, and proposals for an NPL-based audit scheme are under discussion.

Radiotherapy Calibrations

Turning now to radiotherapy—levels, it will be appreciated that this field is subject to Codes of Practice, rather than regulations, which

have been elaborated over the years. Indeed, a nation-wide scheme for the calibration of X-ray

treatment machines was established well before

the BCS was set up. The scheme is comprehensive

in extent, in that it reaches 100 percent of the treatment machines in use in the UK, with the

possible exception of a few units in private

dermatological practice. On the other hand, the scheme depends on the expertise of the hospital

physicists involved with very limited central

verification.

The scheme was started in 1 950, soon after

the UK National Health Service, NHS, was launched,

when the demand for calibrations grew to a level in excess of the NFL capability to accept all the dosemeters submitted. Following joint consultations between the Department of Health and Social

Security, DHSS, the Hospital Physicists' Association, HPA, and the NFL, a series of Centres were designated as 'secondary standardizing centres* and a dosemeter from each one was selected as the

transfer instrument for calibration at NFL. There

are at present some 30 such centres within the

UK. Each centre became responsible for the calibration of all the dosemeters in use in its

region. Over the years, this scheme has been

elaborated by the introduction of an NFL—designed

secondary standard instrument, along with a Code

of Practice, agreed between DHSS, HPA and NFL, on

its use in the calibration of tertiary standards

or field instruments. The secondary standard was developed specifically as the link in the NHS dissemination chain, and is produced commercially. Some 30 instruments were centrally purchased by

DHSS, and allocated to the 30 designated centres. This approach, made possible by the operation of

the NHS, helped NFL to streamline its own procedures, and also provided for a certain measure

of control in the system. Thus, these instru- ments are specifically restricted for use as transfer devices only, and they must be returned,

complete with the log—book recording radioactive

check—source readings taken between calibrations,

to NFL for recalibration every three years. The

Code of Practice recommends in-phantom comparisons, and the necessary phantoms were also made

available to all the centres.

It must be stressed that the designated

centres are all within competent, long—established

hospital physics departments, but generally do not possess any X—ray equipment dedicated to standards work. Indeed, the secondary standard

instrument may be mobile in the region. There are no laboratory criteria or approval procedures

at present. Indeed, in the past there has been

some resistance to any form of inspection or audit. However, there have been occasional field

trials in which a number of centres irradiated TLD and/or Fricke capsules, supplied by NFL, under specified conditions with encouraging

results. For example, in 1 975» six radiotherapy

centres in the UK, all of which were actually

sub—centres of the secondary standardizing

centres, irradiated such capsules in a phantom

each using a single beam of cobalt 60 gamma rays. The results, taken from a paper by Dr Rossiter

(14) are shown in Table 3.

Recently, seven radiotherapy centres, this

time all possessing a secondary standard instrument, were interested in checking the dose

delivered as the basis of a clinical field trialt this time employing multiple field techniques.

This trial is not yet complete, but the available

results of measurements in a phantom, employing

various techniques, are given in Table 4-

We would be happy to see more such field

trials in the UK, along the lines of the excellent trials conducted both by NBS, and

23
TABLE 3

FIELD TRIAL. 1 975 (Rossiter, 1975)

UK

Nominal dose * Measured dose

Comment Centre

(mean)

ILL)

(mean)

Pri eke

1 0.944 0. 954 5$ error in ion

chamber reading

2 0.963 1.001 TLD discrepancyunresolved

3 0. 991 1.002 -

4 1.008 1.018

5 1.004 1.003

6 1.000 o. 991

* based on ionization chamber measurements.

TABLE 4

FIELD TRIAL. 1979-80 (not yet completed)

UK

Centre Machine NPL ' dose

stated

Revised

dose — Reason

A Co 60 O.964 0. 980 - Water/

Perspex correction, and

cobalt 60 decay

B

it 1.020 ? - Some evidence for being

1-2$ high

C

it 1.004

D

n

1 .016 1.006 - Soft tissue/water

correction

E

ii 1.012

F

ti 1.041 ? - Under study

G 4MV 1.020

through the AAPM Regional Laboratory scheme, — to be described later in this seminar.

Radioactivity Measurements

Next, a few words about the dissemination

of standards of activity in the UK. For many

years, NPL has provided absolute standards of

activity for many radionuclides, along with the determination of decay schemes. Such standards

are made available to the user, either by the despatch of the standards themselves, or through

the use of the commercially available ionization

chamber, type 1383A, developed at NFL, and for

which the Laboratory publishes calibration

factors. This latter approach is particularly

appropriate for short-lived nuclides, and indeed, an improved NPL calibrator will soon be available.

The Radiochemical Centre, TRC, also

provides standards, and traceability to national

standards has been maintained through periodic

two-way exchanges of standards between NPL and TRC for measurement for a large number of nuclides.

Recently, it has been proposed that BCS should be

directly concerned in regard to the certification

of sources (cobalt 60, caesium 1 37 and radium 226) which may be used for the routine testing of the large number of protection monitors in the field, as previously mentioned. Such sources are calibrated in terms of exposure rate, and it is of interest to note that the small discrepancy

found between exposure rate measurements and the activity of the NPL standard radium source, is

within the measurement uncertainties (Read, Burns and Liquorish, 1978, (15)).

From the legal standpoint, the main provisions of the legislation in respect of activity

relate to safety. The Euratom Directive has

called for some changes. For example the DHSS is setting up new procedures under the Medicines

Act, 1968, for the authorisation of persons entitled to administer radiopharmaceuticals.

However, the principal impact in regard to trace- ability concerns instrumentation for the measurement of surface and air contamination. The HSC Consultative Document lists levels of contamination which must not be exceeded, and hence there

is now a clear need for new reference standards

for the calibration of appropriate monitors. NPL

has now commenced a programme of work to this

end, though there is still a debate in relation

to the relative merits of surface 'activity 1 and

'emission rate' as the quantity of interest.

Industrial Radiation Processing

Facilities are available at NPL for the calibration of the type of dosemeter normally

used in radiation sterilization processes, such

as polymer, or polymer—dye combinations which

undergo change in optical absorption on irradiation. Uniform fields are available in the form

of annular arrays of cobalt 60 rod sources, and

these fields are calibrated in terms of absorbed

dose to water by means of chemical dosemetetrs,

which themselves are cross-checked against the NPL exposure standards. Plant operators can submit a sample, from a batch of dosemeters in

use, for irradiation to known dose levels prior

to assessment in their reader, and thus achieve

a calibration of their dosimetry system, ie,

dosemeter material and readout. Two types of

dosimetry material based on polymethylmethacrylate are made available by bulk purchase by

AERE Harwell, and by the 'UK Panel for Gamma and

Electron Irradiation', a body on which the DHSS,

24
industry and NFL have representatives. This panel

has also supported the requirement that sterile

goods supplied to the National Health Service

should receive a minimum dose of 2. 5 Mrad, or

25 kGy; although micro-hiological counts prior to sterilization must also he kept down to agreed

limits, the DHSS does not accept a safety index

system dependent on biological tests alone.

In addition to the calibration of the dosemeter material and readout, the establishment of traceability for the dose to the irradiated product depends also on the relation

between the test dose and the product dose, and

routine dosimetry must be carried out on each

batch of products put through the plant. The

adequacy of the dosimetric system employed, and

the competence of the staff, is assessed during

the commissioning of the plant, and test measurements are carried out periodically thereafter,

though no formal audit procedure is in use. If

the plant is to supply sterile goods to the NHS, DHSS will need to approve the plant prior to recommending the firm concerned as a recognised

source of supply. This approval is usually

exercised under contractual arrangements and is only statutory when the plant is used for those

few devices which have been deemed medicinal

products under the Medicines Act - and where

pharmaceutical products e.g. eye drops may be irradiated. Incidentally, UK legislation (The

Pood (Control of Irradiation) Regulation, 1 9^7)

prohibits the application of ionizing radiation

to food intended for sale for human consumption,

except in those cases receiving prior approval,

and in the case of sterile diets for patients

prescribed such diets.

International Links

I cannot close this talk without a brief

reference to certain international links, entailing NFL involvement, which have a bearing on traceability, with particular reference to the possibility of international recognition of

certification. (See Table 5).

I will assume that everyone present is

familiar with (i) the role of CIPM, through

CCEMRI and BIPM, in the comparison of national

standards, Sections I, II and III of CCEMRI covering the areas of dosimetry, activity and neutron measurements respectively. (ii) the role

of IEC and ISO in regard to specification

standards:- thus IEC Committees and Working

Parties have much to contribute to good measurement practice through improved instrumentation at both therapy - and protection - level, for

photons, beta rays, and neutron measurements.

ISO CoSimittees are recommending optimum reference

radiations, and so on.

The EEC involvement in such activities may

be less familiar to this audience. In addition

to the Euratom Directive, the EEC has set up

various programmes, such as the •Biology and

Health Protection Programme •', and more recently,

the 'Applied Metrology Programme ,

. NPL, and PTB

amongst others, participate as contractors on

such community projects as the comparison of

personal dosemeters for X, (3 rays and neutrons.

TABLE 5

CIPM - International Committee on Weights

and Measures

CCEMRI - Consultative Committee on Standards

for the Measurement of Ionizing

Radiations

BIPM — International Bureau on Weights and Measures

IEC - International Electrotechnical

Commission

ISO — International Standards Organisation

EEC — European Economic Community

PTB - Physikalisch-Technische Bundesanstalt

ICRU - International Commission on Radiation

Units and Measurements

ICRP — International Commission on Radiological Protection

IAEA - International Atomic Energy Agency

OIML — International Organisation for Legal

Metrology

WEMC - Western European Metrology Club

TABLE 6

FRACTION OP MAXIMUM PERMISSIBLE FLUENCE

EXPOSURE

AIR KERMA

ABSORBED DOSE TO AIR, free in air

ABSORBED DOSE TO TISSUE, free in air

ABSORBED DOSE INDEX

DOSE EQUIVALENT INDEX

SHALLOW DOSE EQUIVALENT INDEX

DEEP DOSE EQUIVALENT INDEX

SKIN DOSE EQUIVALENT

DEPTH DOSE EQUIVALENT

DOSE EQUIVALENT CEILING

AVERAGE DOSE EQUIVALENT

EFFECTIVE DOSE EQUIVALENT

25
Another group is discussing protection instrumentation, though they are currently still

debating the merits of various alternative field

quantities, as listed in Table 6, in respect of

their appropriateness for use with both personal

and environmental monitoring. This work overlaps

the interests of other bodies, and I trust that ICRU and ICRP will take the lead in resolving

these problems.

However, from the standpoint of traceability, the position can be dealt with. All

the 'dose equivalent' quantities can now be expressed in sieverts, and units for such

quantities can in principle be derived by the

application of appropriate conversion factors to the units of the more basic physical quantities

exposure, fluence or absorbed dose, which are realised by the Standards laboratories. A

similar position has arisen in radiotherapy

calibrations, where improved factors to convert from either exposure, or from absorbed dose in

graphite, to "absorbed dose in water under

specified conditions", will need to be established and agreed. The procedures for both

therapy—level and protection-level calibrations

may thus run along parallel lines.

The IAEA has a programme for the com- parison of high-dose measurement systems, and

the OIML has an interest in both radiation

instrumentation and calibration. Unlike IAEA

or BIPM, OIML has no central laboratory, so presumably their interest relates primarily to specifications and the contents of calibration

certificates, from the legal standpoint.

There is one informal body which has taken

a lead in regard to the international acceptance

of calibration certificates, and that is the West European Metrology Club, WEMC. This 'club*,

which is broader-based than EEC, comprises some

14 countries represented by the Directors of

national standards laboratories, or equivalent

establishments, in 'Western' Europe. Amongst its

activities, it has set up a Calibration Group,

and this provides a framework for the co- ordination of BCS—type activities, which are now being established in other countries, such as in

the Federal Republic of Germany and in the Netherlands.

It would clearly be advantageous if

calibration certificates issued through such

activities , were mutually acceptable between

countries. Initially, this would depend on the

comparison of the respective national standards

of the countries concerned, either through BUM,

or bi—laterally. For example, as regards the UK and the USA, tables listing comparisons relating

NPL and BBS measurements in respect of activity, neutron fluence and X-ray dosimetry have been

prepared, and all show excellent agreement.

Thus, there are many threads in the tapestry of traceability, — legal, technical,

scientific, political ... I believe that it is

indeed a tapestry, and not a tangled web?

References

Traceability — An Evolving Concept,

Brian C. Belanger, national Bureau of Standards, Washington, USA, 1979.

Some Aspects of Traceability, H. L. Daneman,

Metrology Consultant, 390 Meadowbrook Road,

II. Wales, PA 19454, USA. Paper presented to the Japan Industrial Technology Association,

Tokyo, 1975-

Assuring Accurate Measurement and Traceable

Standards, J.Landvater, Consultant,

Industrial Research Development, Part 1, p 97, July 1979; Part 2, p 35, August 1979! Part 3, p 129, September 1 979.

Glossary of terms used in Metrology, BS 5233,

item 4.4, British Standards Institution,

2 Park Street, London W1A 2BS, United

Kingdom.

Specification for Measurement and Calibration

Systems, BS 5781 , item 4.13, British

Standards Institution, 2 Park Street, London

W1A 2BS, United Kingdom.

The British Calibration Service, Document

0021 , BCS, National Physical Laboratory,

Teddington, Middlesex TW1 1 OLW, United

Kingdom.

Standardization in Radiation Dosimetry in the United Kingdom, W. A. Jennings, p 119,

Proceedings of a Symposium on 'National and

International Standardization of Radiation

Dosimetry, Atlanta, USA, 1977, Vol 1, International Atomic Energy Agency, Vienna,

1978.

Council Directive, 76/579/Euratom, laying

down the basic safety standards for the health protection of the general public and

workers against the dangers of ionizing radiation, Official Journal of the European

Communities, L187/P19 0 976).

Recommendations of the International Com- mission on Radiological Protection, ICRP Publication 9, Pergammon Press, Oxford, 1 966.

Recommendations of the International Com- mission on Radiological Protection, ICRP

Publication 26, Annals of the ICRP, Vol 1, No 3, Pergammon Press, Oxford, 1977.

Council Directive, 79/343/Euratom, amending

Council Directive 76/579/Euratom (see (8) above), Official Journal of the European

Communities, L83/pl8 (1979).

26
Ionizing Radiations, Proposals for Provisions

on Radiological Protection, A Consultative

Document, Health and Safety Commission, HMSO, 1978 (See (16) below).

Activities of the British Calibration

Service in the Radiological Field,

M.J. Rossi ter, p 1 33, Proceedings of a

Symposium or •National and International

Standardization of Radiation Dosimetry,

Atlanta, USA, 1977, Vol 1, International

Atomic Energy Agency, Vienna, 1978.

The Use of Precision Thermoluminescence

Dosimetry for Intercomparison of Absorbed

Dose, M. J.Rossiter, Physics in Medicine and

Biology, p 735, Vol 20, 1975.

Exposure-Rate Calibration of Small Radioactive Sources of °®Gof ^°Ra and 1 ^7(jB|

L.R.Read, J. E. Bums, and R. A. C. Liquorish,

Int. Journal of Applied Radiation and

Isotopes, p 21, Vol 29, 1978.

The Acts, Regulations, Codes of Practice and

Guidance Notes referred to in the text can be obtained from Her Majesty's Stationery

Office (HMSO); US Agents:- Pendragon House

of Connecticut Inc., P.O.Box 255, Old Mystic,

Connecticut 06372, USA. These Acts, etc

serve as examples only; there are many

others relevant to this field.

Acts and Regulations:

The Radioactive Substances Act, 1948 The Ionizing Radiations (Sealed

Sources), Regulations, 1969

The Ionizing Radiations (Unsealed

Radioactive Sources) Regulations,

1 968.

The Factories Act, 1961. The Health and Safety at Work, etc. Act, 1974. The Medicines Act, 1968. The Food and Drug Act, 1 955 The Food (Control of Irradiation)

Regulations, 1967.

Don-Statutory Codes of Practice and Guidance Notes

Code of Practice for the Protection of

Persons against Ionizing Radiations

arising from Medical and Dental Use,

1972.

Guidance Notes for the Protection of Persons exposed to Ionizing Radiations

in Research and Teaching, 1968.

27

NATIONAL STANDARDS FOR RADIATION DOSIMETRY

Robert Loevinger

Center for Radiation Research

National Bureau of Standards

Washington, DC 20234

NBS measurement standards for radiation dosimetry, the radiations with which they

are used, and the corresponding calibration uncertainties, are described briefly.

(Calorimeter; cavity ionization chamber; extrapolation chamber; free-air chamber;

ionizing radiation; measurement standards; radiation dosimetry; standards)

In radiation dosimetry we are concerned with

the physical quantities exposure, absorbed dose,

and (rarely) the mass of radium. The word "standard" is used here in the sense of measurement

standard, i.e., the physical realization of a unit

(of a physical quantity) in terms of its definition. Since the physical realization of a unit is independent of its magnitude, the question of

special units versus SI units is irrelevant to the

consideration of standards.

The quantity exposure is limited in its

application to photon beams with energies below a few MeV. The standards of exposure at the National Bureau of Standards (NBS) are of two

kinds. A free-air chamber measures the ionization

current in a known wall -less volume of air, under

approximately equilibrium conditions, hence the

name. The mean range of the secondary electrons

increases rapidly with energy, and increases more

rapidly with energy than the mean free path of the

photons. As a result, considerations of both size

and accuracy limit the NBS free-air chambers to photon beams with energies below several hundred

keV. For higher energy photons, the standard is a set of graphite cavity ionization chambers, each

of which determines the ionization in a known

volume of air in graphite. Using appropriate

physical factors, that ionization is converted to absorbed dose to graphite, then to absorbed dose

to air under equilibrium conditions, and then to

exposure.

A graphite calorimeter is the standard of

absorbed dose for photon beams, at present limited

to cobalt-60 gamma-ray beams, which have a photon energy of 1.25 MeV. Since it is absorbed dose to water, not to graphite, that is desired, pro- cedures have been developed for obtaining absorbed

dose to water traceable to a graphite calorimeter.

An extrapolation chamber is the standard of

absorbed dose for beta-particle sources and beams. This instrument measures the ionization current in

a small volume of air inside tissue-like materials, under circumstances where the results can

be interpreted as absorbed dose rate to water,

tissue, or similar material.

Gamma-ray brachytherapy sources are calibrated in terms of exposure rate at 1 meter, and

the standards are those of exposure described

above. An exception to this is radium-226, for

which the NBS standards are Honigschmid sources specified in terms of milligrams of radium. At present these play a relatively minor role in dosimetry standards activity at NBS.

The NBS dosimetry standards program has recently been described in detail [1]. The

table that follows illustrates the radiation

beams and sources that are used at NBS with the radiation dosimetry standards.

The uncertainties listed in the table are the

values associated with an instrument calibration

factor or a source strength obtained by comparison

with the relevant NBS primary standard. The

stated uncertainty represents a combination of the

uncertainty derived from statistical considerations with uncertainties obtained by other

methods. The uncertainties are intended to represent overall values that have a high probability of bracketing the final errors, very roughly corresponding to 95% confidence limits.

The method of obtaining these uncertainties has been described in part in [16]. The numbers given

in the table are recent estimates and will not in

all cases agree with values quoted in the refer- ences cited. The quoted uncertainties are subject

to revision, in light of new experience or techniques.

2 9
National Standard

Free-air chamber 1

Free-air chamber 2

Free-air chamber 3

Graphite cavity

chambers

Graphite cavity

chambers

Free-air chamber 2

Graphite calorimeter

Extrapolation chamber

Honigschmid sources

Physical

Quantity

Exposure

Absorbed

dose

Mass of radium

Radiation

10-60 kV x-ray beam

20-100 kV x-ray beam

60-250 kV x-ray beam

Cobalt-60 and cesium-137

Y-ray beam

Cobalt-60, cesium-137, and iridium-192 brachytherapy sources

Iodine- 125 brachytherapy sources

Cobalt-60 y-ray beam

(3-particle applicator and beams

Radium brachtherapy sources

Calibration

Uncertainty

(%)

1

1

1

1

2

1

5-10

1

Reference

2,3

4

4,5,6,7

8

9,10

11,12

13

14,15

References

[1] Loevinger, R. , Medical Dosimetry Standards

Programme of the National Bureau of Stan- dards, National and International Standardization of Radiation Dosimetry, IAEA-SM-222,

International Atomic Energy Agency, Vienna

(1978) 159.

[2] Lamperti, P.J., Wyckoff, H.O., J. Res.

Nat. Bur. Stand. (U.S.) 69C 1 (1965) 39.

[3] Boutillon, M. , Henry, W.H., Lamperti, P.J.,

Metrologia 5 1 (1969) 1.

[4] Ritz, V.H., Radiol. 73 6 (1959) 911; J. Res. Nat. Bur. Stand. (U.ST) 64C (.I960) 49.

[5] Wyckoff, H.O., Attix, F.H., Design of Free- air ionization Chambers, Bur. Stand. (U.S.)

Handbook 64 (1957).

[6] Wyckoff, H.O., Aston, G.H., Smith, E.E.,

Brit. J. Radiol. 27 (1954) 325.

[7] Aitken, J.H., DeLaVergne, L., Henry, W.H.,

Loftus, T.P., Brit. J. Radiol. 35 (1962) 65.

[8] Loftus, T.P., Weaver, J.T., J. Res. Nat.

Bur. Stand. (U.S.) 78A4 (1974) 465.

£9] Loftus, T.P., J. Res. Nat. Bur. Stand.

(U.S.) 74A 1 (1970) 1.

[10] Loftus, T.P., J. Res. Nat. Bur. Stand.

(U.S.) 85 1 (1980) 19.

£11] Domen, S.R., Lamperti, P.J., J. Res. Nat.

Bur. Stand. (U.S.) 78A 5 (1974) 595.

£12] Pruitt, J.S., Domen, S.R., Loevinger, R. , J. Res. Nat. Bur. Stand. 86 5 (1981) 495.

[13] Loevinger, R. , Trott, N.G., Int. J. App.

Rad. Isot. V7 2 (1966) 103.

[14] Honigschmid, 0., Anz. Akad. Wiss. Wien 82 8

and 9 (1945) 30.

[15] Loftus, T.P., Mann, W.B., Paolella, L.F.,

Stockmann, L.L., Youden, W.J., J. Res. Nat.

Bur. Stand. (U.S.) 58 4 (1957) 169.

[16] Loevinger, R. , and Loftus, T.P., Uncertainty

in the Delivery of Absorbed Dose, Ionizing

Radiation Metrology, (Ed. E. Casnati)

Editrice Campositori Bologna (1977) 459.
NATIONAL STANDARDS FOR RADIOACTIVITY MEASUREMENTS

L. M. Cavallo

National Bureau of Standards

Washington, DC 20234

The National Bureau of Standards provides the foundation of the National Radioactivity Measurements System: radioactivity Standard Reference Materials, calibration services, measurements

assurance programs, and traceability to the international radioactivity measurements system.

(Calibration; intercomparisons ; measurements; radioactivity; standards; system)

Introduction

Radioactivity Standard Reference Materials

(SRM's) are essential links in representing one facet of the national and international measurements systems. The critical part of the mission

of NBS is to provide a basis for a complete and consistent system of radioactivity measurements.

The responsibilities, in addition to the development and production of SRM's, include participation in the extension and improvement of the

international system, overall improvement in the state of the art of radioactivity measurements,

and maintenance of the system to meet national

needs. The systems approach is the only approach

that provides the requisites and flexibility

necessary to compensate for the lack of permanent

standards of radioactivity.

The specific functions of the Radioactivity

Group are the

1. development, production and distribution of well -characterized

standards of radioactivity,

2. provision of calibration, referee,

and special services,

3. provision of measurements-assurance

programs

,

4. participation in international com- parisons and studies programs, and

5. dissemination of information.

Radioactivity Standard Reference Materials (SRM's)

The preparation of good radioactivity SRM's requires considerable time and continuing effort. Those people experienced in SRM production can prepare standards with overall uncertainties of from 0.1 to 2%. In order to achieve the lesser

uncertainty, extensive knowledge and experience

are required because of

1. the chemical behavior of substances

at low concentrations, such as

a. hydrolysis resultng in gradual precipitation,

b. sorption of hydrolysis products,

c. polymerization,

d. oxidation of reducing agents by

dissolved oxygen,

e. change in pH if carbon dioxide

is or was present,

f. decomposition of some compounds

when exposed to light,

g. absorption of activity by microorganisms, and

h. solubility of glass,

2. the possible presence of radionuclide and radiochemical impurities,

3. complex decay schemes,

4. special requirements for source de- position, and

5. instrumentation problems.

There are many steps in the production and

distribution of NBS radioactivity SRM's. To begin with, information on needs is collected

from a wide spectrum of contacts. Because the

needs always surpass the Group's resources, a priority assessment is imperative to select

those SRM's which will be produced in a given

year. If there is no need for development work,

that is, if SRM's of a particular radionuclide

in a specific physical form have already been

developed and there is to be a reissue, then

one proceeds by procuring, processing, measuring

and certifying the material. If on the other

hand it is to be a new SRM, development work on preparation and stability must be tested, and a direct or near direct method of measurement de- cided upon. Implicit in the decision is the knowledge of the nature of the nuclear decay of the radionuclide in question and the assumption

that the attainable accuracy of the measurement

method is acceptable. Some fundamental or direct

methods of measurement of activity in radioactive

decay are: beta-gamma coincidence counting; 4it proportional counting; internal gas counting;
calorimetry; mass spectrometry; defined-sol id- angle-counting.

A radioactivity SRM must be meticulously

calibrated and described in a certificate, for

if it is to be used in an intelligent manner, the technical user must have a knowledge of the

following [1]:

1. the principal radionuclide,

2. the chemical and physical form of the SRM (where applicable: mass,

volume, density, pressure),

3. the stability of the solution or sample after opening,

4. the reference time and date,

5. the method of calibration,

6. the certified values (activity,

radioactivity concentration,

number of particles or photons of

a particular energy emitted per

unit time, where applicable),

7. the decay-scheme assumptions,

8. an assessment of radionucl idic and radiochemical purity, and

9. a detailed assessment of both random and systematic uncertainties.

When calibration and certification are completed, potential users of the SRM's are notified of their availability.

Since 1940, SRM's of 95 radionuclides have

been developed, prepared and "maintained". Some have been prepared in several physical forms

and in as many as 10 different activity levels to meet specific needs (radium-226). There are solution standards (e.g. cesium-137), electroplated standards (e.g. americium-241), auto- absorbed standards (e.g. polonium-210) , gaseous standards (e.g. krypton-85), solid standards of

the radioactive material implanted in a metal

(e.g. krypton-85), standards of material quantitatively dispensed onto a source mount and dried

(e.g. cesium-137). There are standards of alphaparticle-, beta-particle- and photon-emitting

radionuclides. These radioactivity SRM'S are used primarily to calibrate radiation-detection

instruments so that activities or emission rates can be computed from instrument readings. SRM's are used to check instrument calibrations,

especially after changes or repairs, and or, to extend the detector-calibration to other radionuclides, energy ranges, or types of radiation.

Even laboratories that specialize in relative measurements often need to determine radioactivity values if only to assess radiation

hazards from the use or discharge of radionuclides. SRM's are used to produce scientific

data which can then be referenced to a common

base; in the exchange of data it is important

that quantities be expressed so that they are understood. Nuclear properties such as fission

yields and decay schemes are determined by measurements for which very precise standards

of radioactivity are required. "Through the

use of standards, a cross section obtained in Vinca can be compared with one measured in Chalk

River without the necessity of moving equipment

or people from one place to another." [2]

Standards by themselves, do not guarantee meaningful measurements! They do not obviate the prerequisite for trained, experienced personnel!

As we cannot "freeze" time and keep it on hand for future reference, so too, radioactivity

standards cannot be salted away in some repository for future reference because every radionuclide has a decay scheme peculiar to it, and most importantly, radioactivity is ephemeral.

Standards of most radionuclides can be produced

"but keeping a continuous supply available at

all times, including standards of the shorterlived activities, is beyond the production" and financial "capacity of the national and commercial laboratories in most countries. Therefore,

throughout the world, the need for radioactivity

standards has been met by calibrated instruments

of greater or lesser degrees of complexity, all of which are normalized to the national or in- ternational radioactivity measurements systems

by calibrations using radioactivity standards over a wide spectrum of radionuclides with widely

different modes of decay. Thus the national stan- dard of iodine-131 in the U.S.A. is, for the

periods between calibrations, a "4tt"y ionization

chamber and a sealed radium-226 reference source

at NBS, and any laboratory that wishes to check the calibration of its own measuring equipment

for iodine-131 can, at any time, send a well- characterized solution of that radionuclide to

NBS for assay." [2]

Calibration Services

Throughout the U.S. there are private metrological laboratories which offer services to the

general public. [3] For those who must make measurements consistent with national standards

and who require higher accuracy calibrations,

there is available a variety of scheduled NBS calibration services for alpha-particle-, beta- particle-, and photon-emitting radionuclides.

Those for whom the scheduled services are insufficient may request special services, and if it can be demonstrated that a real need exists,

and if the service is within the capacity of the Group, it will be performed. The charges

will reflect the cost of the materials involved,

the time used to perform the services and to write a calibration or traceability report. Many

radionuclides in different sample configurations

and at different activity levels can be measured,

or prepared and measured, at reasonable costs,

but some requests are tantamount to research

projects and the costs may be prohibitati ve. Descriptions of scheduled calibration services can be found in NBS Special Publication 250. [4] For those who must show continually that their measurements are "in control", NBS offers several measurements-assurance programs.

32
Measurements-Assurance Programs

Measurements-assurance programs are the last links in the National Radioactivity Measurements

System and are essential to long-term reliability

because they yield information that can be used to initiate searches for sources of error. NBS is conducting formal radioactivity measurements-assurance programs with the Atomic Industrial Forum, the

Environmental Protection Agency's Environmental

Monitoring and Support Laboratory in Las Vegas,

the Food and Drug Administration, and the Nuclear

Regulatory Commisson's Health Services Laboratory

in Idaho Falls. Informal programs are conducted

with the College of American Pathologists and both the public (including industry and universities)

and government. All programs, except the latter

(the informal programs for the public and govern- ment will be discussed in detail by my colleagues.

Both the formal and informal programs involve

one or both of the following basic mechanisms:

1. A laboratory submits a radioactivity

sample (selected randomly from a prepared

series of samples) with complete documentation as to the activity or emission

rate at a specified time and date, error

analysis, method of measurement, assessment of radionucl idic purity, etc., to

NBS, and receives a report of measurement

which is expressed in percent as

laboratory value - NBS value x iqo. NBS value

If there is significant difference be- tween the laboratory's value and that of

NBS, the NBS value can be used to calibrate the laboratory's measuring system,

and we try to discover the source of error and to assist the laboratory in eradicating it.

2. NBS provides a radioactivity standard of undisclosed activity or emission rate to

a laboratory where measurements are per- formed on the sample. On returning the results and details of the measurements

to NBS the laboratory receives the rel- evant certificate and a report of measurement plus assistance if needed.

The first mechanism monitors the steps in the

production of radioactivity samples and provides a measure of the quality of samples that are pre- pared; the second checks the ability of those in a laboratory to make measurements that are consistent

with the national radioactivity measurements system. The following table illustrates the types of laboratories that have engaged in the informal measurements-assurance program, the radionuclides

measured by those laboratories, and the deviations

of the reported results from those of NBS.

Typical Results of Institutions Participating in Informal Measurement-Assurance Programs

TYPE OF LABORATORY YEAR RADIONUCLIDE DIFFERENCE FROMNBS VALUE (%)

Hospital 1978 Cobalt-57

Gold-198

Lead-203

0.80

1.84 5.16

Utilities Co. 1979 Ban' urn- 133 Xenon-13316.46

6.4

Commercial

Suppl ier 1979 Barium- 133 8.53

Utilities Co. 1979 Barium- 133 21.6

Hospital 1979 Thallium-201

Iodine-131

Technetium-99m

6.60

0.77

3.1

Commercial

Suppl ier 1979 Barium-133 3.70

State 1979 Iodine-125 3.84

Commercial

Suppl ier 1979 Barium-133 1.76

University 1979 Barium-133 0.95

Federal 1979 Iodine-131 0.72

33
cnO O

o o

137Cs - Activity concentration (Bq.mg_1

| 1978-12-01)

47i(PC)-V

4k y IC

relative %

counting

4rc(PC)-y

>

mO

m

>

4tf(PC)-Y

relative T

counting

O

2

4ji(pc)-Y

CDI

r- 47c(pc)-y |

4^(PPC)-^AC §

4Jr(PC)-tf 1

c —i -i s

«

Q- 9

O r+ 3

I

CO

&2

4ff(ppc)-KAC g

4jc(pc)-X i

4ir(PC)-* ^

4Jl(PPC,)-y 3

4Jt(PPC2 )-tfwell

Figure 1. Results of an International Intercomparison of 137

Cs

34
International Involvement

Since NBS provides the foundation of the

National Radioactivity Measurements System

(NRMS), and in the absence of permanent standards of radioactivity, it is incumbent on this agency to maintain traceability to the international radioactivity measurements system (IRMS), and to periodically demonstrate professional competence. NBS seeks to fulfill these obligations

through

1. participation in intercomparisons under

the aegis of the Bureau International

des Poids et Mesures (BIPM),

2. participation in both the International

Reference System for Measuring Activity

of Gamma-Ray-Emitting Nuclides (BIPM)

and the International Service of Calibrated Radioactive Solutions (International Atomic Energy Agency, IAEA), and

3. membership on the International Committee for Radionuclide Metrology (ICRM) and participation through membership

in its working groups.

International Comparisons and Standards Registries

Three-way intercomparative measurements of artificially prepared radionuclides were initiated

in the late 1940's by Canada, the United Kingdom

and the United States. Such intercomparisons

were extended to world-wide participation by the

International Commission on Radiological Units

and Measurements (ICRU) from 1955 until the

responsibilities for such measurements were as- sumed by the BIPM Consultative Committee for

Measurement of Standards of Ionizing Radiations

Section II (CCEMRI II). The goal of this Com- mittee is the improvement of the overall accu- racy and uniformity of measurements of activity,

which includes techniques of measurement, the determination of constants necessary for disintegration-rate measurements and their application. "The spread of results of an international

comparison of measurements carried out by com- petent laboratories is the traditional yardstick

by which accuracy can be gauged. However, it must

be emphasized that the results of such intercomparisons, even when the spread of results is con- sistent with the individual uncertainties, only

provide an estimate of the accuracy of that par- ticular measurement". [5] Since 1955, the fol- lowing radionuclides have been studied:

sodium-22, sodium-24, phosphorus-32 , sulfur-35,

potassium-42, manganese-54, iron-55, cobalt-60,

zinc-65, stronti um-90, iodine-131, cesium-134,

cesium-137, cerium- 139, mercury-203, thallium-204,

americium-241.

A graphical representation of the results

obtained by the ten participants in a recent

cesium-137 comparison [8], is shown in Figure 1:

It is stated in the BIPM Report [8] that "Mean values from international comparisons are often

difficult to interpret and may be misleading.

However, the request to "conserve" a representative result of the present comparison by means of the International Reference System for Activity

Measurements of y-ray emitters (SIR) made it nec- cessary to take an average value. Since the

weighted and unweighted means nearly coincided,

an intermediate value and its (external) standard

deviation were chosen:

A = (760.0 ± 4.0) Bq rug" 1 ."

In the report are described the different solution and source preparations, counting methods,

extrapolation procedures, and methods of calculating radioactivity concentration. It may be noted

that the range of results is 1.7%, and that the

NBS value differs by 0.5% from the "chosen value".

When results of intercomparisons showed

little or no improvement over those of earlier

studies of the same radionuclide, CCEMRI II or- ganized working groups to examine problems as- sociated with radionuclide metrology such as

1. principles of the coincidence method,

2. problems in microwei ghing,

3. procedures for accurately diluting and dispensing radioactive solutions, and

4. study of reference techniques for the

assay of radionuclides.

The object of these studies is the production

of a series of monographs to be used as guides to good laboratory practice.

The organization of intercomparions, the

collection and analysis of the data and the publication of the results require a great deal of work and time. W. B. Mann, the principal scientist in the Radioactivity Group, suggested that

international traceability could be maintained by

establishing stable ionization chambers at BIPM

for the purpose of measuring national standards

of photon-emitting radionuclides. [9] In this way consistency would be maintained between na- tional laboratories and also within individual

national laboratories over extended periods of time. Such chambers, "with calibrations de- rived from standards produced by many national

laboratories, could provide other countries with more limited facilities with calibrations for radionuclides that, because of complicated decay

schemes, might present serious problems in meas- urement". This scheme was adopted by the IAEA and first put into operation in 1973 followed by BIPM in 1975". [6]

The ionization current produced by the stan- uard submitted to BIPM or IAEA is compared to that

produced by a radium-226 reference source and the "equivalent activity" is calculated for the sub- mitted solution standard. The equivalent activity

(A e ) is the stated activity of the radionuclide

in the submitted standard that would have produced

the same ionization current as the radium-226 re- ference source, at a specified time. Both BIPM

35
and IAEA then issue registration tables for each

radionuclide in which is recorded the equivalent

activities for the samples submitted by the different laboratories. [7] "If in the course of the measurement and registration of any standards

serious discrepancies between national laboratories are revealed, then international measurements can be organized on split samples of the

same solution of that radionuclide in the hope of elucidating the nature of the discrepancy". [6].

The following information is taken from the BIPM Registration Table for "^Cs:

BIPM Registration Table for 134

C<

REPORTING LABORATORY MEASUREMENTS MADE AT BIPM

R(%) S(X) DATE u(%) Ae (k Bq) T.U. (k Bq) NPL 0.067 0.35 12/30/76 0.06 10087 36

BIPM 0.013 0.27 11/21/75 0.29 10047 40

AECL 0.014 0.32 5/23/77 0.07 10071 33

NBS 0.009 1.10 10/18/77 0.05 10117 111

IER 0.08 0.63 2/24/78 •0.09 10023 64

UVVVR 0.20 0.40 4/17/78 0.TJ7 10124 46

BIPM 0.025 0.13 11/13/78 0.05 10092 14

OMH 0.05 0.30 1/26/79 0.06 10124 31

AIEA 0.07 0.30 2/13/79 0.14 10159 34

R = random uncertainty, reporting laboratory (one standard error)

S = systematic uncertainty, reporting laboratory

U = random and systematic uncertainty, BIPM

T.U. = total uncertainty = [R 2 + S

2 + U2 ]^

International Committee for Radionuclide

Metrology "

In 1974, the International Committee for Radionuclide Metrology (ICRM) came into existence. It is an association of scientists re- presenting national laboratories producing radioactivity standards and international organizations

such as BIPM, IAEA and the EURAT0M Central Bureau

of Nuclear Measurements. The objectives formulated

by the ICRM are:

1. to promote the advancement of applied

radionuclide metrology,

2. to study metrological problems arising

from worldwide development of applied

radioactivity and nuclear energy,

3. to cooperate with other organizations

concerned with radionuclide metrology,

4. to engage in such activites as are con- ducive to the applications of radionuclide metrology, and

5. to disseminate knowledge pertinent to

such application.

The ICRM is operating through 5 working groups, concerned with

1. non-neutron nuclear data,

2. low-level techniques,

3. alpha-, beta- and gamma-ray spectrometry,

4. radionuclide-metrology needs in relation

to nuclear energy, and

5. radionuclide-metrology needs in the life

sciences.

The working group on low- level techniques

organized a symposium on environmental problems;

the need for natural-matrix (NM) standards for measurements assurance in monitoring for radioactivity in the environment was accentuated and work was initiated on NM standards containing

plutonium-239 in human lung, in human liver, in Rocky Flats soil, etc. The proceedings have been published in the International Journal of the Environment, 1, No. 1/2 1978. An intercomparison of the measurement of photon-emission rates

at energies between 120 and 1408 keV with germa- nium-spectrometer systems was arranged by the

36
spectrometry working group; a "best set of gamma- ray-emission probabilities per decay for the ten strongest lines of europium-152 were derived and details of the measuring and evaluation methods"

have been presented in a recent publication. [10]

In 1980 the life sciences working group distributed, worldwide, a questionnaire which is designed to identify those radionuclides which will be- come important in nuclear medicine so that the

metrologists can initiate programs of work to solve problems relating to decay schemes, standards and measuring equipment.

Other important functions of national labo- ratories are the accumulation and distribution of technical knowledge and skill and the dissemination of this knowledge and skill to other nations.

Many countries have learned to augment their re- sources by participating in training and technical

exchange programs with other national laboratories.

In the past three years, the Radioactivity Group

has had guest workers from Korea, Japan, India and France, as well as individuals from U.S. lab- oratories who spent from one to three days with

metrology personnel. Additionally, a revised

version of NBS Handbook 80, A Manual of Radioactivity Procedures , has been prepared with a con- siderable part written by members of the Radioactivity Group and entitled National Council on Radiation Protection and Measurements Report

(NCRP-58) A Handbook of Radioactivity Measurements

Procedures . The report includes nuclear data for

about 200 "biologically important" radionuclides.

References

[1] Certification of Standardized Radioactive

Sources, International Commission on Radiation

Units and Measurements, ICRU Report 12 (1968).

Needs for Radioactivity Standards and Measurements in Different Fields, L. M. Cavallo,

B. M. Coursey, S. B. Garfinkel, J.M.R.

Hutchinson, W. B. Mann, Nucl. Instrum. Methods

112 (2973)5.

C 3 3 A Directory of Standards Laboratories,

National Conference of Standards Laboratories

(1979).

[4] Calibration and Related Measurement Services

of the National Bureau of Standards, ed.

B. C. Belanger, National Bureau of Standards

Special Publicaton 250 (1978).

£ 5 3 The Work of the BIPM Consultative Comnittee

for Measurement Standards of Ionization

Radiations Section II, P. J. Campion, Nucl. Instrum. Methods 112 (1973)41.

The Radioactivity Standards Programme of the National Bureau of Standards, W. B. Mann,

National and International Standardization

of Radiation Dosimetry, IAEA I (1978)147.

[7] A Handbook of Radioactivity Measurements

Procedures, National Council of Radiation

Protection and Measurements, NCRP Report

No. 58 (1978).

[8] Activity Measurements of a Solution of l^Cs:

An International Comparison on Efficiency

Tracing by 134Cs, A. Rytz, Rapport BIPM-80/1

(March 1980).

t9] Radioactivity Calibration Standards, ed.

W. B. Mann and S. B. Garfinkel, National Bureau of Standards Special Publication 331 (1970)7.

1-10] international Intercomparison of Gamma-Ray

Emission-Rate Measurements by Means of Germanium Spectrometers and '^£u Sources,

Klaus Debertin, Nucl. Instrum. Methods 158 (1979)479.

37

NATIONAL STANDARDS FOR NEUTRON MEASUREMENTS

J. A. Grundl National Bureau of Standards

Washington, DC 20234

Brief description of NBS capabilities for neutron measurement standardization

is provided along with a characterization of these activities in the context

of traceability and measurement assurance.

(Calibration; neutrons; standardization)

Introduction

Neutron measurement requirements for modern

technology are diverse. The range of neutron

intensities is large, the detection methods may be sophisticated or primitive, and the needs for accuracy vary from beyond state-of-the-art to semiquantitative calibrations undertaken to maintain

reproducibility. The response of NBS to these

diverse requirements over the past decade has been

framed largely as a set of connections to National programs and priorities. Consequently, standardization in the context of traceability and measurement assurance is often a matter of individual

efforts tailored to specific needs.

Characteristics of Neutron Measurement

Standardization

Examples of these kinds of standards

activities are listed in Table 1. They are organized according to the characteristics of trace- ability discussed by E. H. Eisenhower in this

session:

Traceability

--direct versus indirect

--artifact versus measurement traceability or

equi valently, implied versus demonstrated

measurement consistency

Measurement Support System (MSS) Elements

Neutron Measurement Standardization

Capabilities at NBS

In spite of the concentration of specific

needs, some generally available neutron measure- ment standardization capabilities have been

developed. Two of them, which are most nearly

complete for purposes of traceability and for which there is a maturity of measurement assurance experience, are radioisotope neutron source strength determination and isotopic fission rate measurements. A brief description of these cap- abilities is given in Table 2. Also, over the past few years, a broad range of neutron fields

with established intensities and spectra have

become available. Three classes of these fields,

fission neutron sources, near-monoenergetic

filtered reactor beams, and Maxwell ian thermal neutron beams have seen substantial use for detector calibrations and measurement assurance

programs. Characteristics of these fields, seven

in all, are outlined in Table 3. Other neutron

fields associated with the Van de Graaff and with

the reactor ISNF facility also represent a con- siderable neutron standards development effort

but have been employed primarily for neutron

cross section measurements. Along with a new moderated 252 Cf fission source, these fields are expected to contribute to the growing need for improvement and standardization of neutron

personnel and therapy dosimetry. Characteristics

of these fields which are in early use for neutron neasurement standardization are given in Table 4.

--measurement standards: national or transfer

--calibrations

--measurement quality assurance program (MAP)

--field instruments

--procedures, training, and records

39
TABLE 1. EXAMPLES OF NEUTRON MEASUREMENT STANDARDIZATION ACTIVITIES AT NBS

(^traceability

(^ACTIVITY

Direct or IndirectArtifact or Measurement (^MSS ELEMENTS

(1) Radioactive neutron source calibrations at the

I 111 Da l*n ral I 1 I Ly . u

An msn, cal

(2) Calibration of rem-meters at the thermal and filtered reactor beams and the ^-^Cf Irradiation Facility. U

A msn, f inst

(3) Calibration of fission activation detectors for interlaboratory materials dosimetry. I A mst, cal , map

(4) Gold activations in the Thermal Neutron Flux Density

Standard. D A or M msn, cal

(5) Neutron fluence transfer to reactor pressure vessel mock-up and to pulsed reactor irradiations of

electronic components. D M mst, map, proc.

(6) Preparation of ASTM Standards for benchmark neutron

field recerencing of reactor dosimetry. I M map, proc.

(7) Joint pilot program of testing personnel dosimetry

services

.

I A msn, finst. , proc.

See Tables 2, 3, and 4 for description of facilities.

Direct traceability results from direct interaction with NBS; indirect traceability involves interaction with NBS through one or more intermediates. Artifact traceability refers to calibrations of

instruments or radiation sources either directly or indirectly, measurement traceability is the ability to quantify a total measurement uncertainty relative to a national or other designated

standard.

Measurement Support System (MSS) elements are (1) msn : national measurement standards; (2) mst : transfer national standards; (3) cal : calibration; (4) map : measurement quality assurance

program; (5) finst. : field instruments; (6) proc. : procedures , training or records.

40
TABLE 2. NBS FACILITIES FOR STANDARDIZATION OF NEUTRON SOURCE STRENGTHS AND ISOTOPIC FISSION RATES

NEUTRON EMISSION RATE OF RADIOISOTOPE SOURCES

(1) National Standard Radi urn- Beryl i urn Photoneutron Source (NBS-I)

o Primary artifact standard for all fast-neutron source strength determinations and related measurements of neutron fluence rates.

o Emission rate of 1.25 X 106 neutrons per second is established to an accuracy of + 1.0%

(la). Decay rate is 0.04% per year. Consistency among source strengths of similar

world standard neutron sources including NBS-I is +0.6% (la).

(2) Managanous-Sul fate Water Bath for Neutron Source Intercomparison

o Neutron source immersion system for comparing neutron emission rates based on observation

of neutron induced activity in manganese.

o Neutron sources with emission rates of up to 10 10 n/sec can be compared with NBS-I to an accuracy of + 0.4%.

o Source strength determinations have been rendered as "Report of Test" since 1952.

ISOTOPIC FISSION RATES

(1) Reference and Working Fissionable Deposits

o Artifact isotopic mass standards designed for measuring absolute isotopic fission rates

o Reference deposits have been established for eight fissionable isotopes with one standard deviation mass assay errors as follows: U238 U238

U235 (depleted) (natural

)

U233 Pu239 Pu240 Np237

0.25 0.25 0.23 0.12 0.10 0.15 0.12

1.0% 1.5% 1.5% 1 .5% 1 .0% 1 .5% 1 .7%

Mass (mg): 0.25 0.25 0.23 0.12 0.10 0.15 0.12 0.60

Error(Jan 1980): 1.0% 1.5% 1.5% 1.5% 1.0% 1.5% 1.7% 2.0%

o Collection of working deposits of various thicknesses, mass intercompared with the reference deposits, are available for measuring fission rates in NBS supported measurement

or for loan to outside users under cooperative agreement.

(2) Bouble Fission Ionization Chamber

o Back-to-back ionization chambers which record fission events in a fissionable deposit

with an intrinsic efficiency of better than 99.6%.

o Dynamic range: (1) fission rate: 10" 1 to 101* f/sec; (2) fluence rate: 10

1* to 10 11 n/cm2 sec. Negligible sensitivity to gamma-ray induced ionization at intensities up to 10 5 R/hr. Designed to small volume and light weight for wide range application.

o Operated with NBS fissionable deposits the chamber is an absolute measuring device

available for NBS programmatic measurements or for loan to outside users. Performance

maintenance is kept as an NBS responsibility.

41
TABLE 3. NEUTRON FIELDS IN SUBSTANTIAL USE FOR CALIBRATION AND MEASUREMENT ASSURANCE

Median Spectrum

Neutron Energy

Energy Range

Typical

Maximum

Fluence Rate Fluence

n/cm2 sec n/cm2 Accuracy (la)

(1) FISSION NEUTRON SPECTRA

*252Cf Irradiation Facility 1.7 MeV 0.3-6 MeV

Cavity 235

U Fission Source: 1.6 MeV 0.2-5 MeV

4 x 10°

(cm distance)^

2 x 10

10

Source strength, +1.1%

10

IJ based on NBS-I; fTuence

(@ 5cm) at 5cm distance, + 1.4%

1 X 10

15 Flux relative to 252Cf

Irradiation Facility,

+ 5%

(2) REACTOR FILTERED BEAMS

Scandium

Iron - Aluminum

Si 1 i con

2 keV + 0.3 keV 3.9 x 10

H

24.5 keV + 1 keV 3.6 x 10

144 keV + 12 kev 1.4 x 10

5

4

+ 5%

+ 10%

+ 10%

(3) THERMAL ENERGY FIELDS 0.005-0.4 eV Thermal Flux Density

Standard:

Reactor Thermal Column

External Beams:

4391

2 to 2000 x 10H

2 x 10

12

Flux density + 1.5%; internationally compared.

Incomplete thermal izati on

Fluence + 2% based on 235U fission chamber

moni tor

* Free-field fluence rate are rendered as "Report of Test."

42
TABLE 4. NEUTRON FIELDS IN PREPARATION OR USE FOR NEUTRON DATA MEASUREMENT STANDARDIZATION

Median

Neutron

Energy

Spectrum

Energy

Range

Fluence Rate

n/cirr'sec

Typical

Maximum

Fluence

n/cm2 Accuracy (la)

(1) MONOENERGETIC VAN DE GRAAFF

SOURCES

7 Li(p,n) 7Be target reaction: 0.2 to 1 MeV < + 20 keV discrete

3

H(

2H,n)4He target reaction: 14 MeV

600 - 2100

(@ 100cm)

1 x 10

5

(@ 10cm)

0.3-1 x 10"

1 x 10

9

+ 2%

(2) INTERMEDIATE-ENERGY STANDARD

NEUTRON FIELDS (ISNF)

Sub-MeV (ISNF-1):

Near-l/E (ISNF-CV)

0.6 MeV 0.003-3 MeV

0.17 MeV 6 eV - 3 MeV

10"

10"

10

14

10

14

Total fluence

< + 2.5%

spectrum

< + 5%

(3) PARTIALLY MODERATED FISSION SPECTRUM

Heavy Water Sphere 8.2 keV 5 eV - 3 MeV 0.5 x 10 Surrounding 2 ' 2 Cf Source: (@ 50cm)

43

NBS SERVICES FOR IONIZING RADIATION MEASUREMENTS

H.T. Heaton, II Center for Radiation Research

National Bureau of Standards

Washington, D.C. 20234

The NBS measurement support services relevant to establishing traceability to the national standards for ionizing radiation are described. These services can be grouped into four categories: calibrations, standard reference materials, measurement quality assurance services, and special services. Within each category,

the services for photon and electron dosimetry, radioactivity measurements, and neutron measurements are summarized.

(calibration, ionizing radiation, national standards, measurement, quality as- surance, standard reference material, traceability)

Introduction

The first three papers £1-3] in this publication describe various concepts of traceability

to national standards for ionizing radiation and

the kinds of mechanisms, including institutional,

by which this traceability can be established.

The next three papers 1.4-6] describe the national

standards for photon and electron dosimetry,

radioactivity measurements, and neutron measurements to which measurements can be traceable.

To make maximum use of NBS resources there

should be some kind of intermediate laboratory

between NBS and the ultimate user. This means

that measurements can still be traceable to NBS through the intermediate laboratory without a direct interaction with NBS. For those cases where a direct interaction with NBS is necessary,

this paper will summarize those services which

NBS offers which are useful in establishing

traceability for ionizing radiation measurements.

Additional information about these services may

be found in other papers in this publication.

For ionizing radiation measurements, the NBS services can be grouped into four categories:

°Calibrations

"Standard Reference Materials (SRM) "Measurement Assurance Program (MAP) or Measurement Quality Assurance CMQA)

Services

°Special Services

The first two categories are relevant for establishing what Eisenhower £1] called "artifact

traceability". This is the traditional concept

of traceability. The calibration services that

NBS offers are described in NBS SP 250 £7J. Similarly, currently available SRMs are listed in NBS SP 260 [8]. Both ot tnese publications are regularly updated with the latest editions being

respectively 1980 and 1979-80. Both publications

have appendices which contain the latest price

information. In addition to NBS SP 250 and SP 260, the Radioactivity Group also distributes

two documents which list the currently available

radioactivity SRMs £9a] and radioactivity calibration services £9b]. The former also includes

a schedule of when standards containing shortlived radionuclides will be issued.

The third category is relevant to what

Eisenhower £1] called "measurement traceability".

The programs and services in this category can be used to test the participant's entire measurement

system. In order to be listed as an "officially

recognized" NBS Measurement Assurance Program

service (I.e. to be listed as offering a MAP service in NBS SP 250) it historically has been necessary for the Statistical Engineering Division of NBS to have evaluated the participating

company's quality control procedure to ensure

that the process can be maintained in statistical

control. Measurement Quality Assurance services,

as used in this paper, are conceptually the same

as a MAP service with the exception that a par- ticipating company's quality control program need

not be evaluated by NBS. Only the term MQA ser- vice will be used throughout the remainder of

this paper since, in the area of ionizing radiation, there is no NBS evaluation of the participant's quality control program. Participants

should, however, still have a quality control program to make effective use of an MQA service.

The last is a broad category and the non- routine services listed could, for example, in- clude a short or long term interagency agreement,

an internal project which will result in a new calibration service, or a standard calibration of

an instrument using non-standard techniques.

Calibration Services

The various calibration services that NBS offers provide one way of achieving "artifact

traceability". In all of these services, some artifact (radioactive source, dosimeter, etc.) is sent to NBS and the response of that artifact is determined under specified conditions. NBS will calibrate certain instruments used in photon and electron dosimetry and in neutron measurements,

and will measure the radioactivity of samples

45
Dosimetry

which meet certain physical and chemical criteria.

Before any of the artifacts are sent to NBS for calibration, arrangements should be made in advance.

Loevinger [10] has previously discussed the calibration services offered by the Dosimetry

Group. These are summarized in Table 1* and are

Table 1 Summary of Dosimetry Services

Service Items Calibrated/Readout

Energy

Range*

(MeV)

Exposure or Absorbed Dose Range Comments

Exposure (Rate)

calibrations

1) Reference class instruments

which serve as user's "in-house"

standards

0.01-1.25 10" 6 - 10° R/s Not all intensities

are available at all energies

2) Instruments suitable for calibrating therapy units

0.01-1 .25 10" 6 - 10° R/s

3) TLD's (both personnel

and environmental) for calibrating user's readout unit

0.01-1 .25 10' 6 - 10° R/s This service is in- tended to provide

a known exposure which

can be used to characterize the user's readout systems and it is not intended to be

a large scale commercial TLD irradiation

service.

Absorbed dose

cal ibrations

1) Reference class instruments

which serve as user's "in-house"

standards

1.25 1 -2 rad/s Calibrations in terms of absorbed dose to water

2) Instruments suitable for calibrating therapy units1 .25 1 -2 rad/s

3) Radiochromic dye

dosimeters (film and liquid)

1.25 0.1-60 Mrad

4) Beta-particle sources •20-200 rad/s Surface absorbed dose

rate to graphite,

plastic , or water. Mainly tor ar- Y •ophthalmic (beta-ray)

appl icators

LApUbUl C l ale

at 1 meter

cal ibrations

LilCapSU 1 aUcU SOUPCGS OT

137 Cs, 60 Co, 192 Ir

i /inn mD /h i -huu mK/n Radium is calibrated in terms of equivalent

radium mass

Spectrophotometric

readout of customer

irrauiatcu dosi- meters

1) Ferrous sulfate (Fricke)

solution

5-50 5-8 krad This is part of an MQA service to check

consistency of high energy electron beams.

2) Radiochromic dye

dosimeters

0.1-60 Mrad Can readout optical

density at several wavelengths

Other 1) Determine temperature de- pendence of radiochromic dye

dosimeter in range -78°C to 100°C

2) Calibration of penetrameter

(Ardran -Crookes-type cassette)

*See Table 16 for conversion of special units to SI units.

46
presented in more detail in Tables 2-5. Table 2 lists the exposure and exposure rate services for

ionization chambers and passive dosimeters. Their

response is compared with that of a free air

ionization chamber for x rays or determined in standardized beams for gamma rays [11]. Before an instrument is calibrated, the ionization chamber

is tested for leakage, radiation induced leakage,

stabilization time, short term stability, re- combination loss, communication to the atmosphere, and guard electrode insulation (if applicable). The ionization chamber must have suf- ficient wall thickness to provide electron equilibrium for the highest energy photons selected

for calibration. If the ionization chamber is submitted with an associated electrometer, a dimensionless correction factor is provided forTable

scales marked in terms of exposure or exposure

rate. Otherwise, the ionization chamber is calibrated in terms of exposure per unit charge.

The calibrations can be made with polarizing

potentials of either polarity or with both polarities. Values of the ionization current at half

and full polarizing potentials are available. In Table 2, the homogeneity coefficient is the ratio

of the first half-value layer (HVL) of Al to the second HVL of Al . For monoenergetic beams this

coefficient is unity, hence the smaller the coefficient, the poorer the approximation that

the filtered x-ray beam can be represented by a monoenergetic photon beam. In many applications,

it is useful to think in terms of an "equivalent

energy"* of the filtered x-ray beam. Table 3

Exposure (Rate) Calibration Services

Beam Constant Added Filter Half-Value Homogeneity Equi va 1 ent Exposure Rate

Potential (mm ) Layer (mm) Coefficient Energy*

(kV) Pb Sn Cu ft

1

Cu Al IKev

;

min max

(R/s) (R/s)

Lightly Filtered X Ray d)

L-B 10 0 0 029 0 79 7.2 io- 6

1 .7 L-C 15 0 0.O50 0 74 9.1 10- 6 4.2

L-D 20 0 0.071 n 7fi 9.8 io- 6 3.3

L-E 20 0.5 0 23 0 78 13.6 in- 6 n i? L-G 30 0.5 0.36 0 64 16.8 io- 6 0.3

L-I 50 1.0 1.02 o 66 24.4 io- 6 0.4

L-K 75 1 .5 1.86 0 63 31.9 IO

-6 0.4

L-M 100 2.0 2 78 o 59 38.3 io- 6 0.4

Moderately Filtered X Rays'

MFB 60 0 0 1 62 0 68 28.5 7xl0- 3 0.12

MFC 60 0 2.50 0.090 2 79 0 .79 34.2 7xl0" 3 0.04

MFE 75 0 2.51 0.116 3 39 0 74 38.7 7xl0- 3 0.07

MFG 100 0 3.50 0.20 5 03 0 .73 48.5 1 .5xl0" 2 0.10

MFI 150 0.25 3.49 0.66 10 25 0 89 76.9 1 .5xl0- 2 0.13

MFK 200 0.50 3.49 1 .24 13 20 0 .92 101 3.0xl0- 2 0.22

MFM 250 1 .01 3.50 2.23 15 80 0 .92 131 4.0xl0- 2 0.28

MFO 250 3.20 3.47 3.25 18 30 0 .98 153 2.0xl0- 2 0.15

Heavily Filtered X Rays U) 1 HFC 50 0.10 0 0 2.50 0.14 4 19 38 3x10"" 1 .5xl0" 3 HFE 100 0.50 0 0 2.50 0.74 11 .20 70 8x10 4xl0- 3 HFG 150 0 1

.

51 4.00 2.50 2.45 16.96 117 7x10-" 4xl0- 3 HFI 200 0.77 4. 16 0.60 2.47 4.09 19 60 167 SxlO-" 4xl0- 3 HFK 250 2.72 1. 04 0.60 2.50 5.25 21 .55 210 5x10-" 4xl0- 3

Gamma Rays

Cs-137 10. 8^ } 662 1 .5xl0- 3 0.1 Co-60 14.9^ ) 1250 1 .5xl0" 3 2.5

(*) The inherent filtration is approximately 1.0 mm Be

( 2

) The inherent filtration is approximately 1.5 mm Al

( 3

) Calculated

*For lightly and moderately filtered x-ray

beam, the "equivalent energy" is the mean

energy for the exposure spectra as reported in Seelentag et al [12]. For heavily filtered x- rays, the "equivalent energy" is the "effective

energy" listed in the "Report of Calibration"

for the NBS Dosimetry Group and it is based on the initial slope of good geometry copper ab- sorption data. For gamma-rays, the "equivalent

energy" is the mean energy of the gamma-rays occuring in the radioactive decay.

47
lists the absorbed dose calibrations available:

calibration in a water phantom in a standardized

60 Co beam [13], calibration of radiochromic dye

dosimeters in a standardized 60 Co beam in an irradiation pool [14, 15] and calibration of

beta-particle sources in terms of surface ab- sorbed dose rate. Table 4 lists the sources which can be calibrated in terms of exposure rate

at one meter: 60 Co, i37 Cs £16] and ia2 Ir [17].

Radjum sources are calibrated in terms of equivalent radium mass. Table 5 lists the dosimeters

which can be irradiated by the user and sent to NBS for spectrophotometry readout to determine

the dose delivered to the dosimeter. Services

are available for reading ferrous sulfate CFricke)

solution dosimeters [18-20] irradiated according

to a prescribed protocol [21], and for spectrophotometrical ly reading irradiated radiochromic

dye dosimeters at specified wavelengths. [14,

15].

Table 3

Absorbed Dose Calibrations

Radiation Cal i brat ion Method

Items

Cal i bra ted Absorbed Dose Range Comments

60Co Standardized

beam and water

phantom

1) Ionization

chambers

2) Passive

dosimeters

1-2 rad/s Calibration is done in a water

phantom at a depth of 5 g/cm2 in a 10 cm x 10 cm field

60

Co Standardized

beam in an irradiator

pool

Radiochromic

dye dosimeters

0.1-60 Mrad Dosimeters are placed known

distances from a

60 Co source

at the bottom of an irradiation pool

.

Beta particles

Extrapolation

chamber

B-particle sources 20-200 rad/s Source calibrated for surface

absorbed dose rates.

Table 4

Exposure Rate at one Meter

Source Encapsulation Nominal Range Comments

mR/h at lm mCi 60

Co 0.4-400 0.3-300

137

Cs 0.4-400 1-1000

192

lr 0.1 mm platinumor

0.2 mm stainless

steel

0.4-400 0.8-800

Radium Corrections are made for the encap- sulation if it is specified

(0.5-250 mg

of radium

)

Calibration in terms of equivalent

mass of radium content measured

relative to the National Radium

Standard through comparison of gamma radiation.

Radioactivity

In addition to providing SRMs with known • activities, NBS will also measure the radioactivity

of y-ray, ^-particle and a-particle emitting

samples subject to certain conditions. Contact

the Radioactivity Group beTure sending any samples

to NBS to ensure that all physical and chemical

requirements of the sample are met, that resources

will be available to calibrate the sample when

it arrives, and that all possession and shipping

regulations are being followed. Tables 6-9 are

48
Table 5

Spectrophotometric Readout of Customer Irradiated Dosimeter

Dosimeter Application

Absorbed

Dose Range

Wavelength (s) of

Readout

Containers for

Dosimeters Comments

Ferrous sulfate

(Fricke) solution

high energy

electron beams

5-8 krad 304 nm Radiation resistant

sil ica-glass

spectrophotometric

i*ci i , puiysLyrene

mailing containers

to be irradiated in polystyrene phantom

Normally three

cells are shipped,

one as a control

anrl twn fnv i v— radiation, The

irradiation should

be performed ac- cording to a prescribed protocol (jReference

21)

Radiochromic dye commercial

irradiators

0.1-60

Mrad

ultraviolet and visible, depends on particular type of

dosimeter and amount of absorbed

dose

These dosimeters

are used to measure radiation in processes such as sterilizing medical

products, curing

plastics, etc.

Table 6 Calibration of Radioactive Samples

Y-ray a-particle 6-particle

Calibration

Instrument

"4n"f ionization

chamber

2lla proportional counter

0.8na definedsol id-angle

Liquid Scintillator

4110 proportional counter

Activity

Range

10-1500 uCi 0.04-300 nCi 5-300 nCi 0.5-50 mCi/L 0.5-50 mCi/L

Nominal

Uncertainty

0.8-3.4% 1 .5% 1.0% 1.5-2% 2-3%

Physical

Form solution sol id sol id solution solution

Sample

Container

Flame sealed

glass ampoule! 1

) Such that neither

the container nor packaging material

contacts the active surface

same flame sealed

glass ampoule! 1) flame sealed

glass ampoule! 1

)

Sample

Dimensions

5 or 50 mL diameter: 10 cm max

thickness; such that 99.5% of the

ct-particles are emitted with energy greater than 400

keV.

diameter: 1 .6 cm thickness: same

5 mL 5 mL

Radiation

Quantity

activity! 2

) Alpha-particle

emission rate into

2n steradians

activity activi ty activity

i 1

) appropriate borosi 1 icate-glass ampoules are available from NBS

( 2) calibrations for 65 Zn and 109 Cd - 109mAg are in terms of emission rate rather than activity.

49
based on information found in Radioactivity

Calibration Services of the National Bureau of

Standards 19b], This reference contains additional information on suggested chemical forms for the carrier and solution of the radionuclides

and information on the borosilicate glass am- poules used for radioactivity calibrations. For samples emitting y-rays, a-particles or 3- particles, Table 6 summarizes the type of instru- ment used for calibrating the sample, the nominal

activity range, nominal uncertainty, physical

form of the sample, sample container, limitations

on sample sizes and what radiation quantity is determined. The actual uncertainty depends on

the activity level, source geometry and chemical

form. It is the linear sum of the random uncer- tainty at the 99% confidence level plus the estimated maximum limits for all conceivable

sources of systematic uncertainty. Table 7

Table 7 Gamma-Ray Emitting Solution Samples

Radionucl ide Nominal Uncertainty (%)

22 Na 1 .6

21, Na 0.8

* 2 K 2.0

"Sc 0.8

51 Cr 1 .0

5 "Mn 1 .2 "Co 0.8

59pe 1 .4

60 Co 0.8

65 Zn(0 1 .7 67 Ga 1 .4 75 Se 2.4

85 Sr 2.0

88y 0.7 "Mo-"mTc 1.6 "mjc 1.5

109 Cd_109 mAg (l)

1 .7 iiomAg_noAg 0.9

J11

In . 1.3

113 Sn- 113 mi n 2.7

12

3l 1.5

131!

1 .3 133 Ba 1.5

13 "Cs 1 .0 137 Cs- 137mBa 1.5

139 Ce 1 .0 3.4

lkl Ce 2.0

i52 Eu 1 .6 15^ Eu 0.8

155 Eu 1.5

169 Yb 2.5

195Au 2.3

197 Hg 2.4

198 Au 1.3

201 T1 1 .9

20 3 Hg 1 .4

2 0 3p b 1 .7 226 Ra 1.1

lists 39 Y-ray-emitting radionuclides with the nominal calibration uncertainty. Table 8 pro- vides similar information for the 8 3-particleemitting radionuclides together with which

instrument is used for calibrating that radionuclide. Table 9 lists the 9 a-particleemitting radionuclides calibrated at NBS. In addition to the calibration services listed in Tables 6-9, some gaseous radionuclides can be calibrated by internal gas-counting measurements

and gamma-ray point sources and solution sources may be assayed with calibrated Ge(Li) spectrometers.

Table 8 Beta-Particle Emission Solution Samples

Radionucl ide Counting System^ 1

) Nominal

Uncertainty(%)

3 H L.S. 1.5 mc L.S. 2.5

32p 4116 (PC) 2.0

36 C1 L.S. 2.0

89 Sr 4113 (PC) 3.0

90 Sr _90 Y L.S. 2.5 ^Pm 4113 (PC) 3.0

20*

J-] L.S. 2.0 C) L.S. is Liquid Scintillation counter.

4113 (PC) is 4113 proportional counter.

Table 9 Alpha-Particle Emitting Solid Source Samples

Radionucl ide

Nominal Uncertainty (%)

2lTa proportional counter

~ 0.8Jla definedsol id-angle

11,8 Gd 1.5 1 .0 210po 1.5 1 .0

2 3 0 Th 1.5 1 .0

2 38 Pu 1.5 1 .0

2 3 9 Pu 1.5 1 .0 241 Am 1.5 1 .0

2 " 2 Pu 1.5 1 .0

21t3 Am 1 .5 1 .0 U 1.5 1 .0

01 in terms of gamma-ray-emission rate rather

than activity

50
Neutrons

Traditionally, the services NBS offered for neutron measurements included neutron source

strength determinations I22-23J and foil irradiations in a thermal neutron flux density £24-25].

These services are described in Table 10. Within the past several years, NBS has developed a set

of standardized neutron fields [26, 27] which can

be used to calibrate instruments and dosimeters or

can be used to evaluate their performance. These

fields are summarized in Table 11. The energy,Table

fluence rate, and uncertainty in the fluence rate

Cat the 67% confidence level) are listed. The

uncertainty does not include any components due to gamma rays which may be present in the neutron

beam. The gamma-ray component has been measured

for the filtered beams 1 27] and the gamma-ray

spectrum per unit mass of " 2 Cf is listed in ICRU

26 128] . In addition to the fields listed in Table 11, a 14 MeV facility using a d,T reaction

at the Van de Graaff will soon be available for calibration purposes.

10

Neutron Calibrations

Service Method Range Comments

Neutron source manganous 10

5 -TO^n.s- 1 Measure the saturated 56 Mn emission rate sulfate activity produced by neutron

(into 411) bath capture in the bath. Source composition and encapsulation

should be specified. Source

length must be less than

1.2 cm.

, Thermal neutron neutron standard 4000 n.cm

- 2 .s~

1 Dosimeters (gold foils) may dosimeter thermal neutron be irradiated both with and irradiation fl uence without cadmium covers. Response to gamma rays in the thermal beam is not provided.

Table 11

Standard Neutron Fields

Field Energy

(MeV)

Fluence rate

(n. cm2

. s1

) Uncertainty (%)^ •

252

Cf 2.1 2xl07

< 2

> 2 Van de Graaff 0.1-1.5 10

3

2 Cavity (Reactor)

235,

( 3) ISNF v ;

1 .6 0.62 x 10 10

10

9

5

3 Tnermal 2.5 x 10~8

10

11 2.5 Filtered Beams

10

5 <*> 4xl04 {h)

4xl04 W

Si 1 icon

Iron

0.144

0.026

10

10 Scandium 0.002 5 External Thermal 2.5 x 10"8

2 x 10

7

5 Thermal flux density std. 2.5 x 10"8 4 x 10

3

1 .5

t

2

i

( 2)

( 3) n

Uncertainty at the 67% confidence level any y's present in the beam

5 cm from the source

ISNF is Intermediate-energy Standard Neutron Field

225 cm from the reactor

51

It does not include the uncertainty components due to
Standard Reference Materials

Standard Reference Materials (SRMs) are materials which have been certified by NBS for specific chemical composition, chemical property

or physical property. Currently, the only SRMs developed at the Center for Radiation Research

are produced by the Radioactivity Group. In this case the activity or emission rate is certified.

Many of the SRMs have a short half-life and,

hence, are not always available. One can be put

on a mailing list, maintained by the Radioactivity Group, to be notified when a particular SRM

will be (re)issued. Information on ordering

these SRMs is given in NBS SP 260 [8] or may be obtained from the Radioactivity Group [9a].

Table 12 summarizes the radionuclides and

the classification in which they have been

issued as SRMs. A numerical entry in the Table

gives the nominal value (or range) of the ac- tivity or activity concentration of the SRM. In

a few cases a symbol appears in the parentheses

after the value. This indicates that the certification is for the emission rate of that par- ticle in the same units as the heading, i.e. for

239 Pu, 6 alpha particles s"

1 g" 1

. For the K x rays, the emission rate is per steradian. An

"*" in a column means that the SRM was originally

issued in that form but is temporarily out of

stock. The overall uncertainty (see section on Calibration Services) for most of the SRMs is 1 to 2%.

In addition to the SRMs listed in Table 12 the following SRMs are available in the special

form indicated:

Oxalic acid (for 11> e dating)

226 Ra solution (0.1 to 100 pg) 226 Ra for radon analysis (blank, 10" 8 10- 9

, 10-" g)

River sediment (12 certified radionuclides, an additional 18 values,

are listed but not certified)

Point-source and solution standard of

long-lived mixed radionuclide

( 12? Sb, "»Eu, 155 Eu)

Table 12 SRM Nominal Activity at Time of Calibration

RaHinnurl idp Classification of Standard

Solution Point faas- eous

-(adiopharmaceutical

r l i \

1 ,10,10

(s- 1

) (s- 1) (s- 1 g1

) 3 H

1 <+ Q 1 U , 1 U 22 Na 10 26A1 39

32p 1 U

36 C1 10

1* 37 Ar

3 9n r

1 n't 10 10^ (Kx)

1

0

5lt Mnin i 10

r c 10 (Kx) 10 1^x2 "Co * 1Q 5 59 Fe in 5

1 u

60 Co 1 (J 1 u

63 Ni 1 U 67 Ga l n 8

1 0 75 Se in 6

1 u

8 5|(r

1 a 5 1 a7 10- 1 0

1 A6 i r\l 10 ,io 7 85 Sr

88y 1 A 5 10

1 u

89 Sr *

9 0g r_9 0y 10 3 91»Mh l A3 10

9 9m„1*10- 9 9mT1,1

1 rC in 6

I u

9 9im-r

T a9 10

1 ^Cd- 1 09mAg 10 5 (y) 10 3 (y)

1 1 1 Inl n in 6

I u

1 1 3c n Oil _l 1 3IDT111n in 5

112 3 j in 7

1 u 125

j in 5

1 u 127 Xe i a6

1

0

129J *

131

j

1 0

1 3 3v p J;Q , 1

0

1

0

1

3

3 RaDa * *

1 3tr,

137 r<LS-- 137mRD33 10 1

0

1* ,10 s

1 39 Ce

i a5

mi i n 3

1 U

1 ^^(lA 1 U - 1 u 152 Eu in 5

1 u 1 u 169¥b 10 6 195Au 10 s 198 Au 10 6 zoi T1 10 6

2 0 3 Hg 10 6

2 0 3pb 10 6

2 0 7 Bi 10"

22e Ra C1

) 1 u — 1 u 228j h 10*

23 8pu 10 2 -10*

23 9p u 6 (a)

2.,op u 18 (a)

21,1 Am lO^lO6 2l,2 Pu 27 (a)

2 - 3 Am *

(

:

) mass of radium (g)

52
Measurement Quality Assurance Services

Currently there are measurement quality assurance services in the areas of photon and electron dosimetry and radioactivity measurements.

The advantage of an MQA service is that it tests

the participant's entire measurement system so that variation due to different personnel, "in house" standards, systematic procedures, etc., can become apparent. In principle, the MQA services

should be a true blind test of the participant's measurement capability but in practice the transport standard is often of significantly different

form so that special non-routine measurement

procedures must be used. Hence, one might argue

that this does not properly test the measurement

system. It does, however, demonstrate how well the user's sytem is performing under a specific

set of conditions at the time the MQA service is carried out. To make effective use of this type

of program, the participant must be making a conscious effort to maintain his own quality

control program. using "in-house" standards so that trends and abrupt changes in the measurement

process can be detected. If the participant's measurement system properly characterizes the transport standard, then there is demonstrable

evidence that the participant is able to maintain

calibration of his sytem and can use it to make

correct measurements. This assurance is further

built up with each successful participation in the MQA service, particularly if the transport

standard can be designed so that it will test the user's system under different conditions. The

long-term use of an MQA service, together with

the user's own quality control program, significantly reduces the chance that the correct values

of the transport standard was obtained as the result of a "lucky" measurement.

The MQA services for ionizing radiation

operate in the following modes:

°NBS sends a known but undisclosed

transport standard to be characterized

by the user.

°The user selects and characterizes a suitable item to serve as a transport

standard and sends it to NBS for analysis.

°NBS sends a transport standard to be given a predetermined irradiation by the user and then returned to NBS for analysis.

Conceptually these programs are very similar

to the types of programs in which NBS participates

with the National Standards Laboratories of other

countries to ensure that there is a common basis

for measurements on the international level

Tables 13 and 14 respectively summarize the Dosimetry and Radioactivity MQA services. The first columns in these tables identify the pro- gram and the participants in the NBS MQA services.

The second half of these tables gives the details

of the various programs including information on

the transport standards and results. The results

are expressed in slightly different form throughout the tables although all are in terms of A where

..-.^ Participant va lue , ,„» A

- 100 PS value ~ - 1

( % )

Since there were so few participants and so few

results in the first two programs of Table 13, the actual values of A are specified. Many more

results have been obtained for the last program

listed in Table 13 and for all the programs

listed in Table 14. For these cases, the per- centage of participants' results for various

ranges of A are specified, (e.g. for the electron beam dosimetry uniformity study in the years 1967-1975, 59% of the participants' values were within ±5% of the NBS value, A< 5).

53
Table 13

Dosimetry MQA Services

Program

Designation

Participants

with NBS Comments

AAPM RCL £29,30] The three RCL's accredited by

the AAPM

The RCL laboratories calibrate

instruments used for standardizing

therapy beams.

Federal Agency

(BRH) £31] Bureau of Radiological Heal th Cal i- bration Laboratory

This laboratory calibrates instruments

for FDA compliance inspections of x ray units and for state agencies for their

compliance and contract inspections.

State RCL£32] An RCL is being es- tablished in the State

of Illinois

This laboratory will calibrate instru- ments used in their radiological health programs and similar instruments for g other state agencies.

Electron Beam Dosimetry

Uniformity

study £18-20]

Actual users of

high energy

electron beam

therapy units

Program

Designation

/ear(s)

AAPM RCL

Federal Agency

(BRH)

State RCL (Illinois)

Electron Beam Dosimetry

Uniformity Study

Number

of

Participants

1976 1977 1978

1979

1980

1967-1975

1976-1979

59 124

Transport Standard

between NBS and Participant

Shonka 3 cm 3 ionization chamber

Victoreen 41 5B chamber

NEL Dosemeter and Farmer chamber

PTW 1 era

3 30-349 chamber

MDH-1015

Ferrous sulfate (Fricke)

solution in sealed

spectrophotometry cells

AA-mn " 100 1 Participant value , I m

[ NBS Value

1

| U)

A for medium

filtration x rays

-0.7 to 0.2 -0.3 to 0.1 -0.4 to 0.3

-0.6 to 0.2

A for 60 Co gamma -rays

-0.3 to 0.1 -0.1 to 0.3

0.0 to 0.2

-0.4 to 0.2

For 5 lightly filtered x ray techniques, A less than 1. For one medium filtered x ray technique A=l

Still under development

Percentage of measurements within various ranges of A*

A<»5 5<A$10 A>10

58 23 19

73 19 18

*These values of A are averaged over the time interval

participants in the specified range of A. The numerical values are the percentage of

54
Table 14

Radioactivity MQA Services

Program

Designation

Participants

with NBS Comments

EPA National

Quality Assurance

Program [33]

EPA Las Vegas

Laboratory

This laboratory provides both standard samples and samples

to be used in QA programs.

NRC Confirmatory Measurement [34] DOE Laboratory at

Idaho Falls

The DOE lab 1) provides radioactive

standards to the NRC for its use and

7\ at NRP rlirprtinn ^pnrl<; tp^t ^anrnlp^ to NRC licensees.

AIF [35-37] Radiochemical and radiopharmaceutical

manufacturers

Typically 7 companies plus FDA participate in monthly distribution

of high and low level SRMs

CAP "Q" Program

[35-37]

Hospital and

nuclear pharmacies

Typically 30 to 50 laboratories report

back results. Up to 1977 participants were asked to identify and quantify

the SRMs but after 1977 only to quantify.

Program

Designation Year(s)

Number of

different

test transport

standards

Transport Standard

between NBS

and participant

Percentage of sample measurements for various

ranges of A where

A=10olreported va1uP-i 1 *IUU|NBS value 1

1

(%)

EPA National

Quality Assurance

Program

1976-Present

38 NBS SRHs and specially'

calibrated sources.

As2 2<A$5 A>5

55 37 8

NRC Confirmatory

Measurement Program

1974-Present 87 NBS SRMs and specially

calibrated sources.

A^2 2<A<5 A>5 54 38 8

AIF 1975-1980 44 5 mL solutions in standard NBS borosilicate glass ampoules

Highlevel range: 1-300 mCi Low level range: 0.050-5 mCi

24 different radionuclides.

Each participant can submit

one calibrated sample per year

for measurement by NBS

A<5 5<A^10 A>10

77.4 16.1 6.5

CAP "Q" Program 1972-1979 16 5 mL solutions in standard NBS borosilicate glass ampoules

Typically in range: 0.05-5 mCi

A<10 A>10

55 45

1972* 1 50 mCi of 51 Cr with serum

bottle

A<20 A>20

81 19

*This was a one time test in which the participants were asked to inject a known amount of 51 Cr into

a serum bottle, return it, the syringe and needle to NBS.

55
the services requested, the NBS measurements in- volved, and results obtained are listed. The type of traceability resulting from cooperative

studies which use some NBS facilities or measurement systems (e.g. characterizing instruments

with the filtered beams of the rector) is some- where between "artifact" and "measurement" in that several facets of the user's measurement

system are involved but not .necessarily his whole

system in its normal environment.

i Table 15

Examples of Special Services

Source of

support

Project NBS Measurements

Percentage of measurement within

various ranges of A where

= 100

[measured value J

{%) (delivered value

J \

'

BRH L38.39] Voluntary survey of

60 Co teletherapy

units.

Evaluate dose delivered to CaF2:Mn TLD shipped in

a polystyrene block

A$5 5<A^10 A>10

83 13 4

NCI £10, 40] Calibration of beams u^pd U ^ VJ "frir 1 Ul thpranv bllCl U UJr inIII ad hospital setting.

Measurement of photon

l/cuiiid ud i iiy UIIC INL>*J portable graphite

calorimeter and an NBS calibrated ionization

chamber.

NRC [41-44] Test of a draft ANSI standard containing

a protocol for establishing a testing laboratory to deliver known doses

to personnel

monitors which

would then be re- turned to companies

providing this

dosimeter service.

Supply calibrated sources

and correction factors

to the pilot test laboratory.

Percentage of personnel dosimeter

readings within 50% of the dose

delivered by the pilot test lab- oratory

A<50%

80

LLL £27, 45] Remmeter and albedo

dosimeter response

to low energy mono^

energetic neutrons.

Joint NBS-LLL measurement

using the 2, 24, and 144 keV filter beams at the NBS reactor.

Information at 2 keV is new. Good agreement in region where

previous measurements exist.

Special Services

NBS will perform many measurements or calibrations which are not part of the regularly

offered services. Often these services are re- quests for calibrations beyond the range NBS normally offers Ce.g. calibrate neutron sources

with greater source strengths, determine the radioactivity in samples in non-standard con- figurations, etc.L Other examples of special

services result when some agency wants to develop

a joint program to test the measurement capa- bility of a particular measurement community.

Four examples of this type of special service are summarized in Table 15. Who requested the service,

Units

This paper is intended to provide the reader

with information on the wide range of radiation measurement services offered by NBS. It was felt

that this could best be accomplished by using

special units for the radiation quantities rather

than SI units. Table 16 provides the conversion

factors between SI units and the special units

used in this paper.

Table 16

Conversion Factor for Special to SI units

1 R/s 25.8 mA/kg

"1 mR/h 71.7 pA/kg

1 rad/s 0.01 Gy/s I

1 Ci 37 GBq 1

1 mCi/L 37 GBq/m3 10-" n.m-^s- 1

1 n. cm2

, s1

56
References

[ 1] Eisenhower, E.H., This publication

[ 2] Kathren, R.L., This publication

[ 3] Jennings, W.A., This publication

[ 4] Loevinger, R., This publication

[ 5] Cavallo, L.M., This publication

[ 6] Grundl , J. A., This publication

[ 7] Calibration and Related Measurement Service

of the National Bureau of Standards, 1980 Edition (Ed. B.C. Belanger) NBS SP 250

[ 8] NBS Standard Reference Material Catalog 1979- 1980 Edition, NBS SP 260

[ 9] References 9a and 9b are available from:

National Bureau of Standards

Radioactivity Group, Bldg. 245 Washington, D.C. 20234

[9a] NBS Radioactivity Standards for Science,

Industry, Environment and Health.

[9b] Radioactivity Calibration Services of the National Bureau of Standards

[10] Loevinger, R. Medical Dosimetry Standards

Programme of the National Bureau of Stan- dards, National and International Standards

for Radiation Dosimetry, IAEA-SM222 Inter- national Atomic Energy Agency, Vienna, (1978)

Vol I, 159

[11] Loftus, T.P., and Weaver. J.T. Standardization of the 6a Co and l57 Cs Gamma-Ray

Beams in Terms of Exposure, Journal of Re- search of the National Bureau of Standards,

Part A 78A (1974) 465

[12] Seelentag, W.W., Panzer, W., Drexler, G.,

Platz, L., and Santner, F., A Catalogue of

Spectra for the Calibration of Dosimeters,

GSF Bericht 560, Gesellschaft fur Strahlenund Umweltforschung mbH, Munchen (19791

II 3] Loevinger, R., National Measurement Standards

for Radiation Dosimetry, Lecture prepared for

the AAPM 1976 Summer School at Trinity College, Burlington, Vermont, July 1976

[14] McLaughlin, W.L., This publication

[15] McLaughlin, W.L., Radiation Sterilization of

Plastic Medical Devices, Radiat. Phys. Chem. 11 (1980) 9

[16] Loftus, T.P., Standardization of Cesium-137

Gamma-Ray Sources in Terms of Exposure Units

(Roentgens), Journal of Research of the National Bureau of Standards, Part A, 74A

(1970) 1

[17] Loftus, T.P., Standardization of Iridium-192

Gamma-Ray Sources in Terms of Exposure.

Journal of Research of the National Bureau of

Standards, 85 (1980) 19

[18] Soares, C.G., and Ehrlich, M., This publication

£19] Ehrlich, Margarete and Lamperti, P.J., Uniformity of High-Energy Electron-Beam Calibrations, Phys. Med. Biol U (1969) 305

[20] Ehrlich, M. and Lamperti, P.J., Electron

Therapy Dosimetry, Measurements for

the Safe Use of Radiation, (Ed. S.P. Fivozinsky) NBS Special Publication 454

(1976) 365

£21] Protocol for Dosimetry of High-Energy

Electrons Physics in Medicine and Biology, H (1966) 505

£22] Spiegel, V. Neutron Source Calibrations at NBS for Calibration Checks of Neutron Ra- diation Instruments, Measurements for the Safe Use of Radiation, (Ed. S.P. Fivozinsky)

NBS Special Publication 456 (1976) 87

£23] Noyce, R.H., Mosburg, E.R. Jr., Garfinkel,

S.B., and Caswell, R.S., Absolute Calibration of the National Bureau of Standards

Photoneutrons Source: III. Absorption in

a Heavy Water Solution of Manganous Sulfate. J. Nucl. Eng. 17_ (1963) 313

£24] De Juren, J. A. and Rosenwasser, H. Absolute

Calibration of the NBS Standard Thermal Neutron Density. J. Res. Nat. Bur. Stand. CDSI 52 0 954 ) 93

125] Mosburg, E.R. Jr., and Murphy, W.M., A Recalibration of the NBS Standard Thermal Neutron Flux, Reactor Science and Technology

CJ.N.E. Parts A/B) 14. (1961) 25

126] Wasson, O.A. NBS Facilities for Standardization of Neutron Dosimetry from 0.001 to

14 MeV, Neutron Standards and Applications

CEds. CD. Bowman, A<D. Carlson, H.O. Ltskien, and L, Stewart 1, NBS Special Pub- lication 493 09771 111

I27J Schwartz, R.B., and Grundl, J. A., NBS Standard Reference Neutron Fields for

Personnel Dosimetry Calibration, National

and International Standards for Radiation

Dosimetry, Proceeding of a Symposium,

Atlanta 5-9 December 1977, IAEA-SM-222,

International Atomic Energy Agency, Vienna

Vol. I 0978)

£28] Neutron Dosimetry for Biology and Medicine,

ICRD Report 26, International Commission on Radiation Units and Measurements, Washington,

DC 0977)

I29J Shalek, R.J., Humphries, L.J., andHanson

W.F., This publication
£30] Shalek, R.J., Kennedy, P., Stovall , M.

,

Andiff, J.H., Gagnon, W.F., Frant, W.III,

Hanson, W.F., Quality Assurance for Mea- surements in Therapy, Measurements for the Safe Use of Radiation, (Ed S.P. Fivozinsky)

NBS Special Publication 456 (1976) 111

[31] Ohlhaber, T.R. This publication.

[32] Neuweg, M., This publication

[33] Inn, K. G.W., This publication

[34] Cohen, L.K., This publication

[35] Colle R., AIF-NBS Radioactivity Measure- ments Assurance Program for the Radiopharmaceutical Industry, Measurements for

the Safe Use of Radiation, (Ed S.P. Fivozinsky) NBS Special Publication 456

(1976) 71

£36] Golas, D.B., This publication

[37] Cavallo, L, Ehrlich, M, Hutchinson, J.M.R.,

Traceability in Ionizing Radiation Mea- surement Systems, National and International

Standards for Radiation Dosimetry, Pro- ceedings of a Symposium, Atlanta, 5-9 December 1979, IAEA-SM-222, International

Atomic Energy Agency, Vienna Vol 1, 0978)

65

£38] Soares, C.G., and Ehrlich, M., National

Survey of Cobalt-60 Teletherapy

Dosimetry, NBS Technical Note 978 (1978)

£39] Thompson, D.L., Kearly, F.E., Wyckoff, H.O.,

Gitlin, J.N., Reffit, E.B., and Shangold,

E.J., National Survey of Cobalt-60 Teletherapy, Final Report, HHS Publication (FDA)

80-8130 (1980)

£40] Loevinger, R., private communication (1980)

[41] Plato, This publication

[42] Plato, P. and Hudson, G., Performance Testing of Personnel Dosimetry Services, Final Report of a Two- Year Pilot Study October

1977- September 1979, NUREG/CR-1064, U.S. Nuclear Regulatory Commission 0980)

[43] Plato, P., and Hudson, G., Performance

Testing of Personnel Dosimetry Services,

Supplementary Report of a Two-Year Pilot

Study, October 1977-September 1979, NUREG/CR1304, U.S. Nuclear Regulatory Commission

(1980)

[44] Plato, Phillip and Hudson, Glenn, Perfor- mance Testing of Personnel Dosimetry Ser- vices: Procedures Manual, NUREG/CR-1063,

U.S. Nuclear Regulatory Commission (1980).

£45] Hankins, D.E., Energy Dependence Measurements of Remmeters, and Albedo Dosimeters at Neutron Energies of Thermal, and Between 2 keV and 5.67 MeV, Proceeding International

Radiation Protection Association, IV th International Congress, Paris (1977) p. 533

(also preprint-UCRL-78307) (1977)

58
THE CALIBRATION PROGRAM OF THE BUREAU OF RADIOLOGICAL HEALTH

T. R. Ohlhaber

DHHS, PHS, FDA

Bureau of Radiological Health

Rockville, Maryland 20857

The x-ray calibration program of the Bureau of Radiological Health is described

including users, workload and relationship to Bureau programs. Traceability of field measurements to national standards through this laboratory are discussed.

(Calibration; instruments; measurements; standards; traceability; x-ray)

Introduction

In 1966, the Bureau of Radiological Health (BRH)

performed its first documented calibrations. It was

evident at that time that high quality measurements were

important if any conclusions were to be drawn from the work in the laboratory and applied to radiation reduction programs for the country.

The Bureau has operated under the Public Health

Service Act and its 1968 amendment, Public Law 90-602

"The Radiation Control for Health and Safety Act." The

intent of this legislation is "to provide for the protection

of the public health from radiation emissions from electronic products." [l] In 1976 the mission of the Bureau was expanded with the "Medical Device Amendments" to the "Food, Drug, and Cosmetic Act." [2] Under an agree- ment with the Bureau of Medical Devices, BRH performs

the lead role within the Food and Drug Administration

(FDA) for all medical devices which emit radiation.

In order to comply with the above legislation, BRH

must monitor possible radiation hazards from electronic products and medical devices. This entails measurement

of emissions from various products and devices in the

laboratory, factories, distributorships, and wherever used.

It is obvious that the quality of these measurements must

be assured if rational decisions are to result from the

data.

Under Public Law 90-602, various performance

standards have been promulgated as regulations of the FDA. Specific electronic products are monitored and

tested under these regulations and compliance i s mandatory. In the ionizing radiation area, standards exist for television receivers, cold cathode demonstration

tubes, diagnostic x-ray systems, and cabinet x-ray sys- tems. [3] In order to determine compliance with these

standards, a nationwide measurement program has been

established. The basis of this program rests with the FDA

field force and State Radiological Health Agencies.

In addition to compliance programs, the Bureau

conducts various voluntary programs (BENT, DENT, and

NEXT) [4-6] , in cooperation with State Agencies to reduce radiation exposure to the public and improve the

quality of radiographs used for medical diagnosis. Both

the compliance and voluntary programs use large numbers

of survey instruments and passive dosimeters.

Calibration Program

Services

The BRH ionizing radiation facility is directly

tailored to support the role of the Bureau in the medical

and electronic products area. Therefore, the services offered correspond to the typical energies and intensities found in diagnostic x-ray machines and consumer products such as color television. Table 1 lists the current

calibration beams and additional techniques under devel- opment. Since 1966, the calibration program has steadily increased. In 1979, approximately 1200 calibrations were

performed. For 1980, 1400 are anticipated. The Bureau

calibrates for Federal and State Agencies as shown in Table 2. Various Bureau programs are supported by the

calibration program. Table 3 shows a breakdown by program.

Table 1. BRH CALIBRATION TECHNIQUES

ASSOCIATED

NBS CODE CONSTANT

POTENTIAL

kV

HVL

Almm

HOMOGENEITY COEFFICIENT

EXPOSURE RATE

MIN. MAX

.

mR/Sec mR/Sec

L-E

L-G

L-I L-K

L-M MFG

HFC*

20

30

5075

100 100

50

0.2 0.4

1 .0 1.8

2.9

5.0 4.2

0.63

0.68

0.70

0.63

0.58

0.72

100

100

100 200 200

100 0.5 mR/hr 100

"TECHNIQUE IS UNDER DEVELOPMENT

59
Table 2. CALIBRATIONS LISTED BY AGENCIES Radiation Calibration

AGENCY NUMBER PERCENT

BRH 457 37 FDA Field 466 37 Army •J D

-30 Air Force 13 1 Navy 14 1

States 263 21 1248 100

Table 3. CALIBRATIONS LISTtD BY PROGRAM

Upon successful completion of the above tests, the instrument is set up on the x-ray calibration facility. The

technique used for calibration consists of a comparison

between the response of the laboratory standard and the instrument under test in a known radiation field.

The radiation field is produced by an industrial x-ray tube powered by a specially designed high voltage generator. The output of this system is gated by a pneumatic

shutter. Filters are inserted into the x-ray beam appropriate for each technique. Multiple collimators are used

to control beam size and reduce scatter (Figure 1).

AGENCY NUMBER PERCENT

Compl iance 437 35 BENT 245 20 NEXT 325 26 DENT 29 2 BRH Lab 212 17 1248 100

Instruments Calibrated

Any reasonable quality instrument which is consistent with the calibration techniques listed above is accepted for calibration. Examples of these are electrometer and ion chamber sets such as MDH Model

1015, Victoreen Model 666, Keithley Model 35020 etc.; Condensor-R sets and pocket dosimeters such as Victoreen Model 570, DCA Model 002, Capintec Model

SEQ6 etc.; passive dosimeters such as TLD and film; and

other instruments such as G-M and scintillation detectors.

All active instruments are checked for proper

operation upon receipt. These checks depend on the

ability to separate functions such as electrical response and radiation response. Usually, manufacturers suggested

checks and adjustments are performed.

For instruments with separable ionization chambers

and electrometers, electrical calibration of the elec- trometer may be performed. This is routine on all MDH

Model 1015 and Victoreen Model 666 instruments. This calibration determines proper electrical operation on all modes and scales of measurement and adjusts all elec- trometers for equal response to charge and current.

The equipment used for electrical calibration is a

Keithley Model 261 Picoampere Source and a BRH constructed charge source. The Picoampere Source is used

to provide precise currents simulating the current from

an ionization chamber being used for an exposure rate measurement. The charge source provides a known

amount of charge to test the integrated exposure

function.

For instruments which are prone to chamber or high

impedance cable leakage, a charge leakage test is per- formed by exposing the instrument to radiation and then monitoring the leakage of charge in the integrate mode.

The leakage rate is compared to the manufacturer specification to determine whether the chamber, cable or integrate capacitor is faulty.

If an instrument exhibits erratic readings or does not

function and minor repairs are indicated, these will be

performed in-house. For major repairs, the symptoms are noted and the instrument is returned.

X-Ray Tube Shutter

Filter Wheel

Main Ion Collimator Chambers n

-I tlii i i i

[•I

_

Control and Readout Equipment

Figure 1. Radiation Calibration Range

The standard is composed of a high quality ionization chamber and a readout system. Most commonly used is a low energy secondary standard such as a Victoreen Model

415-A. The laboratory also maintains Models 415-B, 415- D and Exradin Models A5 and A6 chambers. These chambers provide complete coverage of energies employed in diagnostic x-ray machines.

The readout system is composed of a Keithley Model

616 electrometer with a General Radio Model 1403 Standard Air Capacitor inserted in the feedback loop. This configuration provides an integrating electrometer

with a low leakage and precise capacitance (Figure 2).

G R Modal 1403

lh

Chamber

Keithley

Model 616

Figure 2. Charge Collection System

Because the measurement is a comparison of the response of two devices, a positioner is used at the

calibration site which allows precise positioning of the standard and device under test, with standard mounts to hold the most commonly calibrated instruments

(Figure 3). Temperature and pressure are recorded

60
because a correction for air density must be performed

for all the standards and most instruments containing vented ionization chambers.

Cstp ^ calculated from T (ambient temperature in °C) and P (ambient pressure in mm of mercury) as follows:

Figure 3. Positioner With Two Chambers and

TLD Holder Mounted

Associated Calculations

All phases of calibration involve the production or measurement of a physical or electrical property and,

therefore, errors are inherent in each phase of calibration. The calculations used in radiation calibration are

straightforward.

CF =

Where:

(1)

CF is the correction factor for the instrument under test; X5 is the response of the radiation standard

in Roentgens per second;

Xj is the response of the instrument in Roentgens per second. X$ is calculated at STP by;

q cStp

XS= (RCCF) (2)

Where: Q is the integrated charge in Coulomb

RCCF is the NBS conversion factor for the standard chamber in R/coulomb

C5TP ' s tne correction factor for air density at standard temperature and

pressure and;

t is the exposure time in seconds.

For the equipment used in this laboratory, Q is measured as the product of voltage (V) and

capacitance (C).CV (3)

'STP

/273.15 + T\ /760 \

\ 273.15 / \ P /

Combining equation (2), (3), and (4) and applying to the standard chamber (S):

CV /273.15 + Tc\ /760\

XS

= (RCCF)— ( ]( (5)

*s\

273 15 Av For a typical instrument which measures directly in Roentgens the term CV (RCCF) reduces to the instrument reading in Roentgens (rj). Thus:

I

'273.15 + T T\ /760

273.15

(6)

If the instrument has a sealed chamber, the terms

containing T and P are dropped indicating no correction

for air density.

There are basic assumptions in the above equations.

The most important assumption is that both the standard and the instrument under calibration are exposed to identical radiation, both in energy spectrum and intensity.

Also, it is assumed that effects from other variables such

as charge leakage, relative humidity, air composition

(pollutants) and electromagnetic fields are negligible.

The parameters in equations (5) and (6) must be

measured with reasonable accuracy to maintain an overall accuracy sufficient for the calibration of field instru- ments and dosimeters. Table <f lists the equipment used

to measure the parameters. Table 5 provides the specifications of the radiation source.

The instruments are typically used indoors at room

temperature. Therefore, all correction factors are recalculated for 22 °C.

CF22° = CF

273.15 + 22

273.15

(7)

Table 4. RADIATION CALIBRATION MEASUREMENT

EQUIPMENT

PARAMETER MEASURED EQUIPMENT

V (Voltage) Keithley Model 616 Electrometer

C (Capacitance) General Radio Model 1403 Capacitor

t (Time)

P (Pressure)

ERC Model 2612-33

Timer, Operating with

BRH Constructed

Shutter Controller

Sensotec Model Z Transducer and ERC

Model 3501 Readout

T (Temperature) ERC Model 9300-C

Thermometer

61
Table 5. SPECIFICATIONS OF RADIATION SOURCE

Generator Model Manufacturer

Output D.C. Regulation

Stability

Metering

Emission Current Emission Control Regulation

Stabil ity

Metering

Tube Model Manufacturer

Continuous Rating

Inherent

Filtration

BRE-150-20-DHEW1

Universal Voltronics

10-150 kV 0.1%

0.1 kV/hr

+0.5%

0.01 - 30 mA Active Feedback Loop

+5% 0.01 - 0.299 mA

+1% 0.30 - 30.0 mA

+1%

+2% or +0.01 mA {Whichever is Less)

MG-150

Phillips

3000 Watts

3 mm Be

On the intermediate level, various approaches can be

used. Traceability can be achieved for each individual component of the measurement system. This usually

results in a long and torturous chain to the national standard. An example of this can be shown for the measurement of charge in this laboratory. This measurement is a product of capacitance and voltage. The

air capacitor is calibrated directly by NBS. The voltage

measured by the Keithley Model 616 electrometer is traceable through a Fluke Model 335D voltage calibrator and Fluke Calibration Center standards. This is also verified at BRH by directly measuring a set of saturated standard cells (Eppley Model 121) which are calibrated by NBS. The combination of the capacitor and electrometer

is also checked by a Keithley Model 261 picoampere

source and a BRH constructed charge source. The

Keithley picoampere source is traceable through Keithley

to NBS. Figure k outlines the relationship of measure- ment of charge at BRH to NBS. It is obvious that errors or equipment failure could occur at any point in this complicated system. Although redundancy is present, a systematic error could be present and undetected.

Traceability NBS

National Standard

The above measurements with associated internal quality control provide a consistent measure of "exposure." If BRH were the only facility performing these measurements, this would be sufficient. However,

"exposure" is measured at a multitude of facilities and

calibrations must relate to a single standard if meaningful measurements are to be performed. In this country, the National Bureau of Standards is the only facility

empowered to maintain the national standard of "exposure." All measurements and calibrations must be traceable to this standard within the necessary accuracy of the measurement.

Reasons for Traceability

BRH is responsible for enforcing performance

standards which involve radiation measurements. In order

to determine compliance with these standards numerous

field and laboratory measurements are performed across the nation. These measurements must provide data which

can be defended. In other words, the data must relate to the national standard and provide evidence "beyond

reasonable doubt" that the product does not comply with

the performance standard. These measurements have to be made with the thought that they may have to be

legally defensible.

In addition to measurements made to determine

compliance with Federal performance standards, the

States use these instruments to determine compliance

with State laws protecting the public health and safety.

Again, the measurements must relate to the national standard and might have to be legally defensible.

Traceability Mechanisms

Various approaches can be used to achieve agreement

between field measurements and the national standard. The most direct would be to compare each instrument to the standard. This is obviously impossible since thousands

or tens of thousands of instruments are involved. This indicates the need for intermediate laboratories to provide reliable calibration services.

Fluke Cat. Center I

77

Keithley Cal. Center

Fluke 335D

Eppley 121 Keithley 616 Keithley 261 General Radio 1403

BRH

Charge Source ure \

*~

Primary traceability Secondary check

Figure 4. Traceability of Measurement

of Charge

The final output of this process yields a measurement

system for charge which documents that the instruments used in this system are traceable to a national standard.

It does not ensure that the use of these instruments will yield an accurate measurement of charge.

Extensive quality control systems can be implemented for each instrument involved in the measurement. However, it is still possible for the final product to deviate from the national standard. A far better program to determine agreement with

the national standard is to test the total operation of the

calibration laboratory. Not only are the calibration instrument errors detected but also human, calculational and systematic errors. All of these contribute to the

total disagreement from the national standard.

Since the final output of this laboratory is the

calibration of survey meters and passive dosimeters at diagnostic x-ray energies, the test for determination of agreement with the national standard should involve the

calibration of an instrument at both BRH (using the

62
normal laboratory protocol) and at NBS. Disagreement

between these calibrations will indicate the typical

performance of the laboratory as related to the national standard. This should be an on-going program continually

documenting the performance.

In addition, cross calibrations between intermediate

laboratories serve a useful purpose. Measurements showing agreement between two or more laboratories would

indicate that the national measurement system is operating properly at the intermediate level. If the cross

calibrations disagree, a need for improvement is indicated.

Tests of Agreement

Since 1976 a specific Condensor-R electrometer and chamber have been used to monitor the output of the BRH facility. This instrument has been calibrated at both NBS and BRH. Figure 5 contains both sets of data for the instrument. Variations in the BRH data result from

several sources:

1. Standards in the laboratory are interchanged and

returned for recalibration on 7- to 8-month

schedules. The disagreement between the standards amounts to 2% or less. BRH View of Traceability

The instruments calibrated by this facility are used

to enforce Federal and State laws for the protection of the public and, therefore, the measurements made with

these instruments must be accurate and defensible. It is the intention of BRH to provide calibrations of sufficient accuracy so that the field instruments can be used to

their full potential with confidence in the measurements. At present this can be interpreted as meaning the calibrations must exhibit less than 5% error. This number is based on the accuracy of present field instruments and on

the reported needs of the States. [7]

2. Various operators have performed these calibrations. Since the display for this instrument is an analog system, variability has occurred in their readings. This can amount to differences as much as 2%.

3. The basic errors in the set-up, measurement and

generation of the beams can amount to approximately 1%.

In spite of these errors most BRH points fall within 3% of the NBS points.

The goal of the laboratory is to maintain an overall error of 3% or less. This provides a comfortable margin

of safety for unexpected errors. In order to maintain

such a limit, an active quality assurance program must

exist. To be most effective, NBS should be an integral part of this program. The program should include testing of the BRH facility by checking instruments calibrated in the normal manner at BRH against the national standard and providing a report documenting the degree of agree- ment. This should be performed on a regular basis, preferably twice a year. As of this date, such a comparison

has been performed.

An MDH Model 1015 instrument was calibrated at BRH following the normal laboratory protocol. The

instrument and associated BRH calibration report were

sent to NBS for comparison to the National Standard. The results of this test are present in Table 6. Excellent agreement was obtained, verifying a reasonable transfer

of the National Standard to the intermediate level.

This program does not replace any in-house quality assurance program nor does it alleviate the need for calibration of the individual components of the cali- bration system. The program is an independent measure

of the total system.

1.20rFigure 5. Calibration of Victoreen

Condensor-R Chamber Model 70-5

Table 6. BLIND COMPARISON OF MDH MODEL 1015 INSTRUMENT CALIBRATED AT BRH TO NATIONAL STANDARD

TECHNIQUE BRH VALUE NBS VALUE PERCENT DISAGREEMENT

To eliminate some of the inherent errors in the above

test, an independent Keithley electrometer system and

standard chamber were compared to the laboratory

system. The results of these tests verify the sources of errors in routine calibration. L-E 1 n 1 11 * L-G 1 05 1 05 * The two systems were compared at five different L-I 0 99 0 99 * techniques. Then the chambers were interchanged and L-K 0 98 0 98 * the comparisons were rerun. Two general assumptions

L-M 0 99 0 99 * were made, namely that the radiation delivered to each MFG 1 01 1 .00 U system was identical and that the spectrum of energies was a reasonable approximation to the NBS techniques. *N0 APPARANT DISAGREEMENT WITHIN ACCURACY OF Both of these assumptions have been shown to be TEST INSTRUMENT reasonable from other tests.

63
Calculations were then performed to determine the

deviation in readout systems and the deviation in chamber

response from the NBS calibration of each chamber.

Table 7 summarizes the results of these comparisons.

Table 7. PERCENT DISAGREEMENT OF TWO MEASURING

SYSTEMS LISTED BY CALIBRATION TECHNIQUE

CHARGE CHAMBER TECHNIQUE COLLECTION RESPONSE

L-E 0 28% 2 21%

L-G 0 29% 1 13%

L-I 0 33% 1 20% L-K 0 13% 1 20%

L-M 0 32% 2 07%

As can be seen, the difference between the two

charge collection systems amounts to approximately

0.3%. The amount of difference between the two chambers seems excessive. The worst point was repeated with both chambers used on the same charge collection system. Again, the difference in response, using the NBS

calibration factors was 2.2%.

It appears that the greatest error in the BRH calibration facility can be traced to the transfer chambers. It is believed that this error may be attributed to changes in the volume of the chambers because of small movements

of the thin window.

This effect has been noted by changes in the NBS

reports for these chambers. It appears that the dis- agreement shown in this analysis represents the maximum

chamber error. Of the chambers used by BRH, the two

chosen for this test represent the two extremes of change

in NBS reports. Any other combination of chambers

chosen for this test should result in a smaller disagreement.

Because of realization of this effect, more extensive

tests will be performed to determine if these changes

occur while the chamber is in use or only while it is being

transported and exposed to varying environmental

conditions.

Field Measurement Traceability

The traceability of intermediate laboratories is only one step in the establishment of field measurements

which are traceable to the national standard. After

calibration by an intermediate lab, the instrument must

be transported properly, set up properly and used

properly. BRH has attempted to solve these problems by

supplying simple to use instruments coupled with training

and written test procedures. All programs the Bureau

initiates or cooperates in have a manual which documents

the needed measurements and equipment.

The step from the intermediate laboratory to the

final field measurement is the most difficult portion of the traceability. Usually, direct control is lost and even

though procedures exist, these may be ignored at the time

of the measurement.

Instruments purchased from or repaired at the manufacturer may be assumed to be calibrated when, in fact, they may not be traceable to a reliable standard. Such calibrations should be verified and repeated if necessary.

Conclusion

In order to achieve traceability for field measurements, all facilities in the chain of calibration must be traceable to the national standard. There must

be an active measurement assurance program to docu- ment continued agreement to the national standard.

Also, a mechanism should be developed to extend measurement assurance to the field level. This may be

accomplished by a more general revision or compilation

of existing procedures.

BRH is an active participant in diagnostic x-ray measurements for the public health and safety. Since

1966, BRH has served as an intermediate laboratory for diagnostic x-ray energies resulting in over 5000 documented calibrations. It is anticipated that this program

will continue with increasing demand for services and

with more emphasis on total traceability of field measurements.

References

[1] Radiation Control for Health and Safety Act of 1968, Public Law 90-602, H2 U.S.C., (1968)

[2] Medical Device Amendments of 1976, Public Law 9*-

295, 21 U.S.C., (1976)

[3] Regulations for the Administration and Enforcement

of the Radiation Control for Health and Safety Act

of 1968, HEW Publication (FDA 79-8035), (1978)

M Reduced Dose Mammography - Results of a Nationwide Study, R.G. Tans and T.R. Ohlhaber; Proceedings of the Second Reduced - Dose Mammography Meeting, Roswell Park Institute, Buffalo,

New York, (1978)

W Dental Exposure Normalization Technique (DENT)

Instruction Manual, HEW Publication (FDA 76-

80*2), (1976)

[6] Nationwide Evaluation of X-Ray Trends: Organ Dose Index System, HEW Publication (FDA 77-

8006), (1977)

[7] Ionizing Radiation Measurement Criteria for Regulatory Purposes, Conference of Radiation Control Program Directors, Inc., NBS Publication (GCR 79-174), (1979)

The mention of commercial products, their sources,

or their use in connection with material reported herein is not to be construed as either an actual or implied

endorsement of such products by the Department of Health and Human Services (HHS).

64
The EPA National Quality Assurance Program

A. N. Jarvis

Office of Quality Assurance-Radiation

National Environmental Research Center

U.S. Environmental Protection Agency

Las Vegas, NV 89114

The speaker submitted neither an abstract nor written version

of his talk for inclusion in the proceedings of this seminar. For further information, contact the speaker directly.

65

THE LLL CALIBRATION AND STANDARDS FACILITY*

George W. Campbell

Jack H. Elliott

Hazards Control Department

Lawrence Livermore Laboratory

University of California

P.O. Box 5505 Livermore, California 94550

The capabilities of Lawrence Livermore Laboratory's Calibration and Standards Facility are delineated. We describe the facility's ability to provide radiation fields and measurements for a variety of radiation safety

applications and the available radiation measurement equipment. The need for

national laboratory calibration labs to maintain traceability to a national

standard are discussed as well as the areas where improved standards and standardization techniques are needed.

(Standards; calibrations; traceability; calibration instruments; calibration

techniques.)

Introduction

The Lawrence Livermore Laboratory Calibration

and Standards Laboratory is operated by the Dosimetry Group of the Hazards Control Department's Radiation Safety Division. The purpose of the facility is to maintain radiation standards

for LLL and to offer radioactive sources that provide x- and gamma rays, neutrons and beta

particles so that all instruments at LLL may be standardized [1].

The functions of this facility include:

• Providing accurate measurements and calibration of radioactive gamma (>1 mCi) and neutron sources, and providing in situ measurements of photon fields produced by x-ray machines.

• Providing accurate irradiations using

fields of gamma rays, x-rays, beta and neutrons over a wide range of energy and

i ntensity.

• Performing routine calibrations for the Personnel Dosimetry program.

t Performing high-level (>10^ rad)

irradiations for radiation damage and dosimetry development programs.

• Maintaining radiation instrumentation

standards and neutron source standards for accurate comparisons with other radiation

instruments and neutrons sources within the Laboratory.

• Evaluating new and old radiation detection

instruments.

• Maintaining portable radiation survey in- struments.

Facility Description

The facility is composed of a low scatter

cell (Cell A), an x-ray cell (Cell B), a source

storage cell (Cell C), a control room, a dosimetry

laboratory, and a portable instrument calibration

laboratory as shown in Fig. 1. An elevation of cells A, B and C is shown in Fig. 2.

Neutron and gamma sources are pneumatically

fired from Cell C to Cell A. Table 1 lists the sources available in the pneumatic transfer system.

Cell A has an aluminum grating floor that is 3 m

above the solid concrete floor and 5 m below the concrete ceiling. The locations of the neutron

and gamma irradiation heads in Cell A are shown in Figs. 3 and 4. The heads are positioned 1 m above

the aluminum-grating which is as far from the ceiling and walls as possible to reduce the effects of scattering. Boggs [2D has shown that the aluminumgrating contributes little to neutron scattering

and that the major contribution to scattering is from the ceiling and walls. To keep the scattering

to 1% or less the source should be less than 140 cm from the detector, greater than 50 cm from the false floor, and greater than 200 cm from the

walls.

Blockhouse

with boreholes

Office

Cell A

183 A

Control panel and consoles

Instrument'

calibration shop

Dosimetry laboratory and counting room

Chemical hood

Cell C

183 C

Offices North

FIG. 1. Sketch of Hazards Control Standards and Cal'bration Laboratory in bldg. 255 (not to scale).

This work was performed under the auspices of the U.S. Department of Energy

by the Lawrence Livermore Laboratory under contract number W-7405-ENG-48.

67
FIG. 2. Cross section of cells A, B, and C.

TABLE 1. Available source choices in the gamma and neutron pneumatic source-transfer

systems.

Gamma system Neutron system

Source3 Dose rate at

1 m (mR/min) D Half life(yr) Source Dose rate at1 m (n/s) Half life

(yr)

60co 136 5.263 252 Cf 1.316 x 109 b 2.646

60Co 29.2 5.263 238 PuBe 7.8 x 10? c 86.4

137 Cs 406 30 238p U Be 1.6 x 108 86.4

137 Cs 12.9 30 Photoneutron Short

source storage

a Isotopes.

bDose rate as of 1 June 1978.

c Dose rate as of 28 February 1973.

0.61 m

-9 mFIG. 3. Locations of pneumatic source- transfer heads and neutron generator

in Cell A. See the heads, generator,

and aluminum-grating floor in Fig. 4.

Gamma

head

68

FIG. 4. Pneumatic source-transfer

heads and neutron generator shown in place in Cell A.
Note that Cell A also contains a neutron gen- erator suspended below the aluminum-grating floor

as shown in Fig. 5. This neutron generator can produce 14.6 MeV neutrons through the T(d,n)^He

reaction and 2.8 MeV neutrons through the D(d,n)3He

reaction. More detailed information can be found

in the operation manual developed by Elliott. [3D.

The exposure rate from the gamma sources is measured with Shonka-type ionization chambers calibrated by the NBS, [4], The pneumatic 252 Cf source was calibrated by NBS and the ANISN code

has been used to characterize the neutron fields

in Cell A. The neutron flux in Cell A can also be measured using a dePangher modified precision long counter. The long counter (Fig. 6) has been calibrated from 2 keV to 19 MeV by Slaughter. [5]

Cell A also contains a television camera and remote screwdriver to calibrate high range survey

instruments as shown in Fig. 7.

Cell B contains three x-ray systems, a manganese sulfate bath for neutron source calibrations,

and a beta exposure range.

One x-ray system is a 150 kV, 10-mA x-ray

unit used to produce filtered x-ray spectra. The

other two systems are transmission anode x-ray

tubes (TRAX) [6]. These TRAX tubes produce x rays characteristic of the anode material giving a fairly discrete or narrow band of energy depending

on the anode materials. We presently have tubes

with copper, silver, neodymium, tungsten and uranium targets with principal energies of 8, 22,

38, 60 and 107 keV, respectively.

FIG. 5. Neutron-generator accelerator

suspended below aluminum-grating

floor of Cell A.

FIG. 6. Top target portion of neutron generator shown with de Pangher

precision long counter and shadow

shield.

FIG. 7. The kiloroentgen/hour scales on portable survey instruments are calibrated with

pneumatically transferred sources, a remote

screwdriver, and a television monitor (inset).

69
The manganese sulfate bath is used to calibrate neutron sources using a NBS calibrated

neutron source as a reference (see Table 2) [7].

Table 3 lists the beta sources that are available.

These beta sources are used to calibrate portable

survey instruments and TLD's. We need some type

of NBS calibration for these sources.

Cell C is used to store the sources listed in Tables 1 and 5; however, the most intense source

is located at the bottom of the 60 Co pool. The irradiation pool (Fig. 8) is about 2 m in diameter

and 6 m deep. The source consists of 72 pencil

shaped, encapsulated G^Co rods arranged vertically in a wire basket so they form a circle

approximately 25 cm in diameter. Table 4 lists the dose rate at different positions in the pool. The pool water is kept pure by continuous recirculation of the water through a resin deionizer and filters. These filters are continuously monitored

for radioactivity as a leak test mechanism.

FIG. 8. A pneumatic sample capsule transfers

samples to the source at the bottom of the 6-m-deep 60r, o irradiation pool in Cell C. The blue glow is produced by high-intensity

gamma rays causing Cerenkov radiation.

TABLE 2. Calibration of neutron sources.

Uses Method Reference Standard Standard Calibration

All low level neutron

sources used for

- dosimeter exposure

- detector & spectro- meter development

Intensity (n/s) by

activation comparison

Mn SO4 Bath

Estimated error-counting

statistics +1% max. combined with source

error +2%

238 Pu-Be (a, n) #300094

NBS Emission rate, n/s 1.7% standard error

TABLE 3. Beta-source choices in the standards and calibrations laboratory beta-source range.

E E(keV)Calibration Dose rate

Isotope (keV) (mCi) Date Wi ndow Y (R/h) a

147 Pm 70 224 2.62 0.39 + 0.4/sr

4.9 + 0.5 9/75 Aluminum 514 keV (0.4%) 0.075

85 Kr 249 672 10.76 -13 9/75 0.002-in.-

stainless

thick

steel None,

samarium x rays

2.2

90 Sr/90 Y 200/931 546/2270 28 21 + 10% 10/75 0.002-in.-

titanium

•thick Significant

bremsstrahlung

18.2

aDose rate of 25 February 1977, using JUNO at -25 cm with all shields open.

70
The portable survey instrument calibration

laboratory mai ntai ns the radioactive-source blockhouse [8] shown in Fig. 9. The two main sources

used are l"Cs and 252r,f t This source range

is calibrated using IAEA transfer standard tech- niques and the Cell A sources (see Table 5) [9].

Typical Calibration Fields and Uses

The accuracy required in most of our uses is +5%. In some cases we can do better than this

value, but we strive not to exceed it.

Table 6 lists some uses and calibration tech- niques for the 252cf and PuBe neutron sources.

We can moderate these sources with Al, polyethelene, D2O and water to provide a variety of spectral distributions (Fig. 10). Our 252Cf source was calibrated by NBS. Our largest PuBe

source is calibrated by the activation comparison

method and is traceable to NBS.

Table 7 lists albedo dosimeters, neutron

remmeters, spectrometers and neutron activation

detectors as typical uses for the neutron generator. The neutron generator was calibrated

using the dePangher long counter.

Table 8 lists possible uses for the betasource fields including dosimeter exposures and instrument response checks. Note that we need to

be able to calibrate these sources and we hope NBS

will provide this much needed service in the near future.

FIG. 9. Radioactive-source blockhouse

for calibrating portable survey

instruments. Sources are stored at the bottom of vertical holes 4 m below the top surface.

Table 9 lists some typical uses for gamma

fields. The calibration instruments are Shonka

chambers with air equivalent walls that have been calibrated by NBS.

Table 10 lists the type of x-ray fields we

can produce. The exposure rate can be measured

using Victoreen Radocon probes, free-air

ionization chambers, or Shonka chambers.

TABLE 4. Sample dose rates at three. 60Co source positions as of May 1980.

Position Dose Rate (rads/s)

A Center

B Pneumatic

C Outer ring

1710 + 171

1664 + 166

278 + 39

TABLE 5. Portable survey instruments calibration range.

Uses Method Calibration Fields Calibrated

All portable survey

instruments gamma

and neutron

IAEA transferstandard method

Placement of transfer

standard in known radiation fields

(gamma or neutron)

Estimated errors 2.5%

if pulses integrated (y)

Gamma source fields

determined by NBS calibrated Shonka

Chamber

71
FIG. 10. A variety of neutron source moderators

are available to simulate the variety of spectra

workers might be exposed to. Moderator materials

available are polyethylene, water, D2O, and solid aluminum. A hydraulic jack positions the spheres about the source head.

TABLE 6. Neutron fields.

Uses Source Dose Rate Calibration

Albedo TLD Badge

Calibration & Development

Remmeter Calibration

(& Transfer Std. for

Cal. Range)

As Above

Moderators Available

Cf-252

PuBe #300084

Based on Decay Program

by Fabricator ORNL for emission rate

and

ANISN code or similar

code for lowscatter-cell

to give rem/neutron,

Emission rate & ANISN

(or similar) Code

Uses Code

NBS Emission Rate n/s 1.6% standard error

Activation comparison

method traceable to NBS

TABLE 7. Neutron generator fields.

Uses Sources Calibration Instrument Calibration

Albedo Dosimeters D(d,n) 3 He 2.8 MeV

Neutron Remmeters T(d,n) 4 He 14.6 MeV

Spectrometers

dePangher precision

long counter

Neutron Activation

Detectors

Slaughter & Rueppel

Nuc. Instr. & Meth.

145 (1977) 315-320

relative to Std. differential reaction

cross sections, except

at 2 keV, where the scandium filtered beam

at the NBS reactor was

used. (Rate based on calibrated BF3 counter.

)

Efficiency relative

to a calibrated

238 Pu-Be (a, n) source.

72
TABLE 8. Beta-source fields.

Uses Fields From Instrument Cal i brati on

Dosimeter

Exposures

147 Pm

85 Kr

Beta Extrapolation Not Available

Chamber

Instrument Response checks

90 Sr/ 90 Y

TABLE 9. Y 'fields.

Uses Location Calibration Instrument Calibration

Calibrated doses to TLD's

High Range Calibration

of Portable Survey

Instrument

Calibrate Transfer

Standards for Survey

Instrument Calibration

Range

Low Scatter Cell fields from

137 Cs, 60 Co sources

Shonka Chambers ionization

chambers with air equivalent

plastic wall

Error Estimates

Electrometer readings +1% Distance measurements +0.5%

NBS calibration +2% Combined, +2.3%

NBS

137 Cs , 60 Co accuracy within 2%

TABLE 10. X-Ray fields.

Instrument Cal i brati on

Low Energy Fields produced by

Transmission Anode

X-ray Tubes 8, 22 & 38 keV

Radocon 10LA keV +3.8%Victoreen Corp

fields

Traceability to NBS

Above

5-40 keV range

or

Free-air ionization

chamber

we estimate +1.4%

optimum

Victoreen claims

+0.6% based on NBS HB 64

no traceability

High Energy Fields over

40 keV Shonka Chamberest. +2.3% combined

NBS

G> 37 keV & 115 keV effective

accuracy within 2%

Above

40-250 keV range

or

Free-air ionization

chamber

Est. +1.4%

Victoreen claims

+0.54%.

Cross check with

Shonka chamber.

no traceability

73
TABLE 11. 60Co irradiation pool.

Uses Calibration Methods NBS

High dose rate dosimeter studies

Radiation Damage

- Light pipes

- epoxy plates

- batteries

- granite

TLD's Chemical dosimetry

Nylon film

Current value TLD's +10% est.

Offers calibration

service for Nylon film

Table 11 lists some uses and calibration

methods for the ^Co pool. The uses are usually

high dose rate dosimeter studies or radiation

damage studies. The pool has been calibrated

using TLD's, chemical dosimeters and Nylon film.

Nylon film can be calibrated by NBS, and we plan

to use their service.

Traceabi nty

As we have shown in Tables 6-11 many of our source calibrations are directly traceable to NBS. That is, either the emission rate from the source or the calibration instrument must have been calibrated by NBS. Experience has shown us that this level of traceability is necessary, be- cause we have found that instruments calibrated by someone other than NBS may be calibrated incorrectly. In such a case, a well equipped facility

such as ours will usually discover an incorrectly

calibrated instrument and return it to the manu- facturer for recalibration. However, many small laboratories cannot afford the number of over- lapping instruments that we maintain. It is,

therefore, imperative that NBS provide an in- strument and source calibration service for all types of radiation, or at a minimum certify

several laboratories to provide secondary

calibrations.

Do national labs need to be traceable to national standards? Since national labs are re- quired to meet essentially the same standards as other users of radioactive sources, we feel it is

a necessity for all national labs standards to be related to NBS standards. For example, the new

ANSI standard for personnel dosimetry performance

testing is being implemented by the NRC, and DOE intends to use the same testing lab and standards.

In order to pass this standard each national lab will need sources and instruments calibrated by NBS to properly calibrate their personnel dosimeters and to relate to the NBS calibrated sources

that the testing lab will use.

NBS Calibration Services

should provide standard filter packs that are equivalent to those used at NBS. They should also provide a source of monoenergetic x-rays for calibration of instruments at specific energies. For example, the filtered x-ray calibration offered by NBS is not useful for instruments used to calibrate

our TRAX systems. That is, we need a correction

factor for a specific energy, not a range of energies.

The other area where we Teel a calibration

service is needed is for beta sources. This service could be either calibrating the users' source

or providing NBS calibrated sources. At a minimum

we need calibrated beta sources for personnel do- simetry and portable survey instrument exposure and energy response tests. In short, this troublesome

area needs immediate help.

Summary

We have described the LLL Standards and Calibration facility. It is composed of a low scatter

cell, an x-ray cell, a source storage cell, and a portable survey instrument calibration facility.

Several typical uses for the facility were de- scribed as well as the typical calibration in- strumentation and techniques that are used. We

discussed the traceability of our radioactive

sources. Finally we stated that national labs do need to maintain a traceability to the NBS and that

national standards are needed for x-ray and beta

sources.

References

CI] Elliott, Jack H., "Tour of the Standards & Calibrations Laboratory," LLL, UCRL-52537

(1978).

C2J" Boggs, J. V., "Neutron Scattering in the Hazards Control Low Scatter Cell," Hazards

Control Progress Report No. 34 , LLL, UCRL-50007-69-2 (1969).

Elliott, Jack H., "Operation of the Hazards

Control Calibration Facility Neutron Gen- erator," LLL, UCID-17215 (1976).

We feel that the NBS needs to increase or im- [3] prove their services in two areas. One is the area

of x-ray calibration. For filtered x-rays NBS

74
Elliott, Jack H., "Shonka Chamber Calibrations Procedures," LLL, UCID-17788 (1978).

Slaughter, D. R. and Rueppel, D. W., "Calibration of a dePangher Long Counter from 2 keV to

19 MeV," Nucl. Instr. and Meth. , 145, 315

(1977).

Cate, J. L., "Transmission Anode X-ray Tube

Development," Hazards Control Progress Report

N o. 53 , LLL, UCRL-50007-76-2 (1976).

[7J" Elliott, Jack H., "Neutron Source Calibration

Procedure by Activation Comparison," LLL, UCID-17216 (1976).

[8] Boggs, J. V., "The Hazards Control Instrument Calibration Facility," LLL, UCRL-51049 (1971).

[9] "Handbook on Calibration of Radiation Pro- tection Monitoring Instruments," IAEA, Vienna, 1971.

75

STATE OF ILLINOIS REGIONAL CALIBRATION LABORATORY

Maury Neuweg

Division of Radiation Protection

Illinois Department of Public Health

Springfield, Illinois 62761

The State of Illinois, Department of Public Health, is engaged in a pilot project with

the National Bureau of Standards to establish a regional calibration facility. The

objective of this project is to provide calibration services for state radiation

control programs for radiation measurement instruments utilized in the diagnostic x-ray

energy range. Rationale for the pilot project and the design and implementation

phases of the calibration laboratory facility are discussed.

(Facility design, future plans, implementation, objectives, purpose)

Introduction

One of the most fundamental requirements in the conduct of state radiation control programs

which protect the public from the hazards of ex- cessive and unnecessary exposure to radiation is the capability to make measurements of radiation

fields with adequate accuracy and reliability.

This requires the use of measuring instruments with

calibration traceable to the national measurement

standards maintained by the National Bureau of

Standards (NBS). The calibration chain which

provides traceability to NBS standards for state radiation control programs should be short and

direct because of the major impact which measurements made in state programs have on public health

and safety.

Ideally, radiation measuring instruments used

in state radiation programs should have no more

than 2 calibration steps between them and the NBS standards. The first step is represented by an instrument calibration against NBS standard. This

instrument plays the role of a transfer standard,

and serves as a secondary reference standard in a regional standards laboratory. The second step is to calibrate field instruments against the secon- dary reference standard, some of which could serve

as tertiary standards.

To complete the chain of traceability in a satisfactory manner, the calibration system must be tested periodically to verify that all calibrations

are being performed satisfactorily with adequate

accuracy. This measurement assurance function is a necessary part of a satisfactory calibration and measurement system. Unfortunately, a system which

will provide the needed calibration traceability to NBS standards does not exist at this time. As a result, many measurements are made in state ra- diation control programs with unknown and unspecified accuracy. In many cases, such measurements

are made with instruments that have no verified

traceability to NBS standards.

Purpose

Realizing this very important void in our radiation control program, we agreed to enter into

an agreement with NBS to design and implement

a regional calibration laboratory as a pilot project. The laboratory is designed to serve the calibration needs for the Illinois Radiation Control Program, specifically relating to measurements of x-ray meachines unker 150 kVp. It will also provide calibration services for other state radiation control programs, especially, for the states surrounding Illinois and in the Midwest

region who desire to take advantage of this service. It is clearly indicated that one of the most serious applications of radiation, in terms

of significant exposure of a relatively large per- centage of the public, is the practice of diagnostic radiology. Therefore, the laboratory will concentrate on the range of x-ray energies and in- tensities utilized for that purpose. However,

this range also covers many additional applications of x-rays in other medical and industrial

applications. Once the procedures and techniques

are established for calibrating instruments within

the diagnostic x-ray range, it is proposed that an expansion of the laboratory will be necessary to calibrate instruments measuring energies and in- tensities above the 150 kVp range.

Objectives

In cooperation with NBS, this project will test the concept of having a state radiation

control program serve as a regional calibration

laboratory. The laboratory will also serve as a model facility which could be duplicated in other

states or regions in an attempt to provide crucial

traceability standards for radiation measuring

instruments. It is not the intent of our Depart- ment either to duplicate or interfere with com- mercial companies or other organizations or pri- vate entities regarding calibration of radiation

instruments. But rather, to provide a supplement

to the existing calibration services available

either locally in Illinois or throughout the nation. The Department of Public Health is placing major emphasis on this project, since it was

the only new initiative approved by the Bureau of

the Budget for an appropriation to fund the pro- ject during FY 80 within the Department. The Director of the Department has been personally

involved in project negotiations, and the Governor

77
is also aware of the project and supports this new initiative.

Implementation of the Project

Administrators with NBS and the State Health

Department formulated the ideal of initiating a regional calibration laboratory in 1978. Depart- ment administrative staff was extremely supportive

in promoting the project, since the need for such

service has been demonstrated numerous times

through diagnostic x-ray inspection and enforcement activities. In 1973, the Department initiated a rather innovative approach to reduce un- necessary radiation exposure to patients from

diagnostic x-ray procedures. This approach re- lates to the concept of placing a limit on the exposure per radiographic film for certain diagnostic x-ray examinations. Illinois was the first

state to initiate this method to reduce unnecessary patient exposure by limiting exposures for

dental bitewing examinations. In 1975, Illinois

became the first state to establish limits on 4 specific medical radiologic examinations. Com- pliance with these limits is determined by making

actual measurements at medical and dental facilities throughout the State with appropriate

radiation measuring instruments. It is easily

recognized that accuracy and reliability of the instrument readings are paramount to regulate and enforce the exposure limit standards properly. If radiation measuring instruments are not calibrated

and traceable to a national standard, enforcement

action could be challenged and subject to possible

legal proceedings. This was the Department's

prime reason for initiating the calibration

laboratory within the State of Illinois.

Other states, and the Federal Environmental

Protection Agency, have since either established

patient exposure limits or recommendations utilizing the rationale developed within the Illinois State Health Department. The Conference of Ra- diation Control Program Directors, Inc., and the Food and Drug Administration, Bureau of Radiological Health, are currently interested in the development of patient exposure guidelines as a method of reducing unnecessary patient exposure

throughout the nation. Measurement results, how- ever, are only as good as the reliability and accuracy of the measuring instrument. Therefore,

calibration within the diagnostic x-ray range is critical in properly assessing exposure to pa- tients and accurately determining compliance

through regulatory activities. Since it is neither possible nor practical for MBS to calibrate all instruments used in field application,

especially if other states implement this concept,

it is appropriate to establish regional calibration centers for the convenience of the states desiring these services. Thus, the Illinois pilot

project is especially important because it will test the viability of this concept. If it is successful, it will then serve as a model for

similar facilities in other regions of the country.

FACILITY DESIGN AND OPERATION

The agreement to develop the calibration

laboratory with NBS specified that the Department

of Public Health would be responsible for pro- viding the necessary space for and components of the structure, including construction of a shielded room, adequate electricity and water

supply, and of course, appropriate temperature,

humidity and ventilation control. The Department

would also provide the operating staff to perform

the calibrations and handle the accountability and record keeping procedures.

NBS would provide all equipment necessary to implement the laboratory, including a 150 kVp, 20 mA constant potential industrial x-ray unit and

all auxiliary equipment such as electrometers,

standard ion chambers, power supplies, laser system, visual monitoring system, etc. The Bureau would also provide training for the operating

staff, conduct periodic comparisons of the Illinois standard with the national standard for exposure measurement, and conduct periodic testing

of performance of the laboratory to maintain

qual ity control

The laboratory is located within the Depart- ment of Public Health office complex at 525 West Jefferson, Springfield, Illinois, on the ground

floor level. Two existing walls of the outside

structure of the building provide excellent en- vironmental shielding since one side wall is solid

concrete, approximately 18 inches thick at the bottom, and tapers to approximately 10 inches at the ceiling of the shielded room. The other wall

has approximately 15 feet of compacted earth, sand and concrete which provides excellent shielding.

The shielded room was constructed so that the direct beam of the radiation source would be aimed

toward this end wall. To reduce radiation scatter, we also constructed a 7' x 7' sheet of onequarter-tnch. lead on the inside of the end wall whtch was then covered with plaster board. The interior walls of the shielded room consist of one-quarter-inch thickness of lead sheeting im- pregnated onto sheet rock which extends to the ceiling. All openings cut in the lead shielding

for electrical outlets, and all nail and screw

holes to support the shielding, were individually

covered with additional lead to provide necessary exposure reduction and radiation protection. The

floor above the shielded room within the structure

consists of a 6-inch thickness of concrete. An oversized door to the shielded room is steel constructed and leads into a maze to further

reduce environmental exposure. The entire lab- oratory consists of approximately 800 square feet. The shielded room is approximately 250 square

feet. The remaining area of the laboratory contains an office, x-ray control area, and work area for instrument maintenance and repair, and suf- ficient space for radiation survey instrument

shipments

The x-ray unit was installed in January,

1980. However, the optical bench and auxiliary

supporting equipment have not yet been received

from NBS. We expect to receive the additional

equipment within the next month so we can begin

operation by June or July. Once all the quipment

is installed, a thorough, detailed environmental

monitoring of the shielded room and the laboratory

will be conducted, utilizing thermoluminescent

dosimeters (TLD), to verify integrity of the

78
shielding and conformance to state and national

radiation protection standards.

FUTURE PLANS AND EXPECTATIONS

Calibration procedures and methodology will

be formatted into standard operating procedures

with assistance from NBS staff. We plan to per- fect the system utilizing our own radiation

measuring instruments prior to initiating calibration services for other state radiation control programs. Once the procedures and techniques have

been developed, tested and approved by the National Bureau of Standards, we will then contact

state radiation control program directors advising them of the services available. We expect

to assess nominal fees to other state programs to offset operating expenses the Department will in- cur through personal services, overhead expenses

and transportation costs. The fee structure has not as yet been determined.

The Bureau has expressed interest in ob- taining a Cesium-137 source of approximately 3-5 curies to provide calibration services for in- struments of higher energy ranges. It is an- ticipated this will be the second phase of the project to provide a broader range of calibration

capabilities on a regional basis.

There will be routine evaluations of the operating procedures by the Department and NBS to assure quality control of the calibration system.

Operating staff of the facility will be provided

with the best training available through NBS. Continuing education will also be stressed to assure that the calibration system will be con- ducted with high quality standards in the ever- increasing complexity and technological advancement in the radiation protection field, especially

as it relates to radiation measuring instrumentation utilized by state radiation control programs.

79

THE AMERICAN ASSOCIATION OF PHYSICISTS IN MEDICINE'S

REGIONAL CALIBRATION LABORATORY SYSTEM

Robert J. Shalek, Leroy J. Humphries and William F. Hanson

Physics Department

The University of Texas System Cancer Center

M. D. Anderson Hospital and Tumor Institute

Houston, Texas

Three Regional Calibration Laboratories have been established

primarily for the dissemination of national radiation standards

for radiation therapy. The National Bureau of Standards together

with the regional laboratories have a calibration capacity in rough equilibrium with the demand. However, if all instrument

users had field instruments calibrated regularly the demand might

exceed present calibration capacity. Various data are adduced to demonstrate that commercially available field instruments can maintain calibrations for periods longer than the generally

recommended 2 year interval.

Introduction

It is estimated that there are 1322 radiation therapy facilities in the United States

and that a minimum of 1057 field instruments

require calibration in order to service these

facilities [1]. At present the National Bureau of Standards calibrates less than 100 field instruments per year. In order to close

the gap between need and calibration capacity,

it was suggested that secondary radiation

standardizing laboratories be established just

as secondary laboratories exist for the dissemination of electrical and other standards.

Robert Loevinger of the National Bureau of

Standards recommended that the American

Association of Physicists in Medicine (AAPM)

become the accrediting agency for the establishment of Regional Calibration Laboratories

(RCL) [2]. The AAPM accepted the suggestion

in 1970 and appointed Task Group #3 of the Radiation Therapy Committee to establish

criteria for the initiation and operation of

the laboratories, to review applications for

laboratory accreditation, to select laboratories and to continue in the supervision of

the laboratories.

To date, three Regional Calibration

Laboratories have been accredited by the AAPM. These facilities are located at Memorial SloanKettering Cancer Center (MSK) in New York,

The University of Texas System Cancer Center

M. D. Anderson Hospital and Tumor Institute

(MDA) in Houston, and Victoreen Instrument

Division (VIC) in Cleveland. It has been re- commended that at least one additional RCL

be established at a distance from the other

laboratories [1].

In the discussion here, some of the re- quirements and capabilities of the regional

laboratories will be considered together with

an indication of the quality assurance procedures between the National Bureau of Standards and the regional laboratories. The distribution of work load between the laboratories and the types of instruments now used

as field instruments will be discussed. In addition, the frequency of calibration of

field instruments used for the calibration

of radiation therapy machines will be con- sidered from the view of what is occurring

and what may be required for the satisfactory

use of the instruments.

The information derives from Task Group

#3 reports, from a Report of the Committee on Radiation Calibration Needs in Therapy of the American Association of Physicists in Medicine

(L. Lanzl , Chairman) [1], from the operating

experience of the M. D. Anderson RCL, and from

data collected by the Radiological Physics Center (RPC). The latter organization reviews

radiation measurements and calculations re- lating to radiation therapy at institutions

participating in interinstitutional clincial

trials and thus has the opportunity for ob- serving the operation of field instruments by the user.

Requirements For and Operation of Regional Calibration Laboratories

The specific requirements for operation

of an RCL are presently being reviewed by a subcommittee of Task Group #3 [3] . It is likely that the RCLs will be required to pro- vide instrument calibrations that agree with

the national standards to within the limits

specified in Table I. These overall require- ments will replace present specific require- ments upon various steps in the calibration

process. In this paper only instruments for

the calibration of therapy machines will be considered.

81
Table I Table III

Proposed Criteria for Calibration Agreement Radiation Beam Qualities Available

Between at NBS and the RCLs (1980)

an RCL and NBS _____________

a Co X ray __

6 ° Co X Ray (HVL/kV) *Fi1t.

Reference-class instruments

suitable for calibration of other

instruments to a precision of 0.1%

Field-class instruments

suitable for therapy beam

cal ibration

Field-class instruments suitable

for diagnostic x-ray calibration

Field-class instruments suitable

for health physics survey measurements

±0.5% ±1.0%

±1.0% ±2.0%

±5.0% ±5.0%

±10% ±10%

NBS Yes

MDA Yes

MSK Yes

VIC Yes

0.03-2. 78mm Al/10-100 kVcp L

1 6mm Al-3.2mm Cu/60-250 kVcp M

4 2mm Al-5.2mm Cu/50-150 kVcp H 0.07-2. 4mm Al/20-100 kVp L

2 0mm Al-3.0mm Cu/75-250 kVp M 0.03- 1.95mm Al/10- 60 kVp L

3 0mm Al-2.1mm Cu/60-250 kVcp M

0.9- 1.6mm Al/50- 75 kVp L

2 8mm Al-3.2mm Cu/60-250 kVcp M

* Filtration: Light, L; Moderate, M; Heavy, H

NBS also calibrates at 137 Cs energy

Table II

Secondary Standard Instrumentation

at the MDA RCL

Exposure Standards: (NBS calibration biennially)

Shonka-Wyckoff , 3.6cc, 0.25mm AE wall Exradin Model A-3, 3.6cc, 2.54mm AE wall Victoreen Model 415A. 2cc, 2mil mylar window

Nuclear Enterprises Model 2561 (NPL Secondary

Standard), 0.3cc, 0.5mm graphite wall

Capacitance Standards: (NBS traceable calibration biennially)

General Radio Type 1404-A, 1000 pF General Radio Type 1404-B, 100 pF

Voltage Standards: (*NBS traceable calibration biennially)

Keithley Model 240A, Regulated HV supply,

0 to 1.2kV *Data Precision Model 3500, Sh digit, DNM Data Precision Model 245, 4% digit, DWI *Eppley Model 100, Standard Cell

Other RCL Instruments: Keithley Model 602 electrometers

Keithley Model 261 picoampere source Taylor Model 6204M aneroid barometer

Fisher Model 15-043A thermometer, 1 to 51°C,

0.1°C/div.

Alumini zed-mylar transmission monitor chamber

Table IV

RCL Measurement Assurance Tests by NBS

Medium Energy X Ray(b ) Devi a tip 1(a) eo Co Year RCL Mean : 'Max Deviation

(

a )

MDA -1 3 - 4 -3 1976 MSK +2 1 + 4 -1 VIC -7 2 -11 +1

MDA -5 - 5 -1 1977 MSK -3 - 3 +3

VIC +2 3 + 8 +2

MDA -4 5 -11 +2

1978 MSK -2 1 - 4 0 VIC +3 2 + 6 +1

MDA -5 2 - 8 +2

1979 MSK + 2 4 + 9 -1 VIC -6 4 -12 -4

(a) Deviation: Parts per thousand

[(RCL/NBS)-1] x 1000

(b) 60-250kV; 1.86mm Al to 3.2mm Cu HVLs

(c) One standard deviation

Intercomparison Instrument

1976: Shonka 3cm 3 ion chamber

1977: Victoreen 2cm 3 415B chamber

1978: NEL Dosemeter and Farmer Chamber

1979: PTW 1cm 3 30-349 chamber

82
In Table II, the equipment employed at

the MDA RCL is listed. This equipment is commercially available and for the most part

capable of performing with a reproducibility

of 0.1%. The range of beam qualities available for calibaration at NBS and at each RCL are shown in Table III.

The ionization chambers maintained as secondary standards by an RCL are calibrated

at NBS at least biennially for each calibration energy offered by an RCL. Other instruments

such as standard capacitor, standard voltage

cell, barometer, thermomether and voltmeter

have calibrations documented as traceable to NBS. In addition NBS circulates a chamber or dosimeter system with undisclosed calibration

annually to each RCL for calibration. The re- sults from four years of these measurement

assurance tests are shown in Table IV. In each year the calibration at cobalt-60 and the mean

of the calibrations in the x-ray range were

within the criteria defined in Table I. In two isoloated x-ray cases, the deviation from the national standard exceeded the 1% proposed for

reference-class instruments, however, the worst

case was only 1.2%.

Table V shows the distribution of instru- ment calibrations among the various laboratories.

Data comes from two sources, the questionnaries

circulated by the Lanzl committee [1] and from

RCL records. 80% of the responders to the

Lanzl committee questionnaire had calibrations

from NBS or an RCL. Although the word Azgional

appears in the name of the secondary laboratories, instruments come for calibration to the RCLs from distant parts of the country and some foreign countries.

Table V

Laboratory of Last Calibration

and RCL Workload

Laboratory Respondents (a) # Instruments

(

b ) % 7/78 - 6/79

NBS 19 MDA RCL 24 102 MSK RCL 21 65 VIC RCL 16 75 Manufacturer

or other 20

Directly Traceable to NBS

The first definition of dixzcXly tnaczablz

appeared in the 1971 protocol of the AAPM Scientific Committee on Radiation Dosimetry

(SCRAD) [4] as follows, "for the purposes of

this protocol, an instrument with a calibration

factor directly traceable to the National Bureau of Standards has been calibrated either

at NBS or against a reference instrument which

has itself been calibrated at NBS." Robert

Loevinger of NBS has proposed that the definition of dixzcAly tna.czja.bZz be tightened as follows [5]. A {iztd initAumznt uiiXk a calibnaution {acXoA cUAzctly tAac.za.blz to tkz

National BuAz.au. ofi StandaAdi hot, bzzn caJLL- bnatzd against tkz national. itandaxd maintainzd

at NBS oA again&t a AzcondaAy itandaAd maintainzd at a Rzgional CaJLibAation LabonatoAy.

Implicit in this definition is the recognition

that a izaondoAy itandand is more than a re- ference-class instrument calibrated at NBS be- cause of the quality assurance requirements

placed upon an RCL by the AAPM.

The Frequency of Calibration

of Field Instruments

The Nuclear Regulatory Commission requires

that licencees of cobalt-60 teletherapy units

perform calibrations with dosimetry systems

calibrated by NBS or an RCL within the pre- vious two years [6] . Some states and other

agencies require annual recal ibration. A time period of two years between calibrations

of field instruments accords reasonably well with current practices as shown in Table VI.

Table VI

Frequency of securing a calibration

From Lanzl Report From MDA RCL Data

Time

(years)

(

a ) Frequency

% Time

(years)

(

b ) Frequency

%

<1 3 0.5 9

1 33 1 29

2 30 1.5 32

3 13 2 18

4 7 2.5 4

5 4 3 4

6 4 3.5 3

7 2 4 1 8 2 >8 3

(a) Number of respondents to this Average time: 2.5 year 1.5 year question was 520; number of 3 3 y radiotherapy centers is Mean time : 1.5 year 1.2 year approximately 1,322.[1]

(b) From RCL reports a) Time since last calibration

b) Time between calibrations by

an institution

83
The median time indicated by respondents to the Lanzl questionnaire [1] or users of the MDA RCL is approximately 1.5 years. Despite

the agreement between the practices of users

and the federal regulation, the frequency of

calibration necessary for field instruments is worth consideration. Information to be addressed here suggests that the time period

between the calibrations of field instruments

could be longer than two years if suitable

other tests upon the instrument are performed

by the user.

During visits to institutions to review measurements and calculations relating to radiation therapy, the RPC usually makes an intercomparison in air in a °^Co beam between

the institution ' s field instrument and the RPC instrument. Since September, 1970 the RPC instrument consisted of one of several Farmer

chambers and a Keithley 602 electrometer. As

an indication of RPC precision, seventy-five

constancy checks over a three-year period

using the RPC field instrument showed a stan- dard deviation of 0.4% for individual measurements, with a maximum deviation of 1%, where

°°Co irradiator or a commercial 9 Sr checker

was the radiation source [7] . In some intercomparisons prior to September 1970, the RPC used a Farmer Secondary Standard model 2502 electrometer and chamber that showed a stan- dard deviation of 0.7% for individual measurements in 17 measurements over a two- year period [7] .

In Figure 1 a bar graph indicates the types of chambers the institutions visited by the RPC employed during various two-year inter- vals from 1968 to 1979. It is clear that

Farmer-type chambers are being used more and that Victoreen R-Meters are being used less as time passes. However, the stability of the

various instruments in holding their calibration appears to be comparable as is shown in Table VII. Here RPC intercomparisons with in- struments which had calibrations from NBS or

an RCL show no great difference according to instrument type. The lapsed time between the calibration of the instrument and the intercomparison with RPC was a median 13 months for

Victoreen R-Meters and 10 months for Farmer

type instruments. In tables whicn follow, no distinction is made between different types of

instruments.

In Table VIII, the results of RPC intercomparisons are shown according to calibration

source before 1976 and after 1976. It is clear that prior to 1976 instruments which were calibrated by a manufacturer or had an uncertain

calibration history (other) were suspect; after

1976 few instruments with suspect calibrations

were found regardless of the method of calibration; however, there are not enough manu- facturer or other calibrations after 1976 to demonstrate a conclusive improvement. It is noteworthy that field instruments intercompared with other instruments which were calibrated at NBS or an RCL appear to have calibration factors which are not significantly

less reliable than those calibrated by NBS or

an RCL. Many of these instruments were an institution's instrument for everyday use which

has been compared to the institution's standard

instrument calibrated at NBS or an RCL. Prior

to about 1976, intercomparison with the institution's chamber was usually made only when the

RPC differed by more than 2% in the calibration

of a therapy machine. After that time intercomparisons were made whenever the institution's

instrument was available during review visits.

Thus some bias in the direction of causing

the earlier data to appear less consistent has been introduced by RPC procedures.

HS Victoreen Farmer Type

Other

n n I in In 70 71 72 73 74 75 YEAR OF COMPARISON

76 77 78 79

Figure 1: Number of chamber intercomparisons

performed by the RPC, by year, for Victoreen

R-Meters, 0.6cc Farmer type chambers and for other chambers

.

Table VII

Intercomparison of the RPC instrument with

instruments calibrated at NBS or

an RCL, distinguishing the type

of instrument (1968 - 1980)

Instrument

Victoreen

R Meters

Farmer-type

chambers

Other

Number of Intercomparisons

57

56

10

Mean RPC/Inst

1.000

1.000

1.016

0.014

0.009 0

0.033

a) One standard deviation

b) Number of chambers whose factor differed from

the RPC by more than 3%

84
Properly maintained therapy field instru- ments appear to maintain their calibration

factors over long periods of time. The time

since instrument calibration does not seem to play a role in the reliability of the chamber

calibration factor as seen in RPC intercomparisons in Table IX. These instruments were calibrated at NBS or an RCL and thus started

with a calibration directly traceable to NBS.

Further data on long term stability of

instruments comes from the MDA RCL. Table X shows data on 5 chambers which have been calibrated by MDA RCL 3 times or more since 1976. The checks indicate the year of initial calibration and the values are the ratio of the calibration factor determined in subsequent

calibrations relative to that determined in the original calibration. The maximum deviation

seen in the calibrations was 0.3%.

Forty-two other chambers were calibrated

twice by MDA RCL since 1976. The time interval

between calibrations varied from one to three years. The results are shown in Figure 2. The mean ratio between the new and original caliTable IX

Interconparison of the RPC instrument with

institution's instrument as a function

of the time since instrument was calibrated

at NBS or an RCL

Table VIII

Intercomparison of the RPC instrument

with institution's instruments

calibrated by various laboratories

Calibration

Source

Number

of

Intercom- parisons

Mean

RPC/

Inst.

,(a)

In&tfum&nti aaLibJuvteA b&{,oi& J 976

NBS

RCL

Compared to chamber calibrated at NBS or RCL

Chamber

manufacturer

Jnttsuuntrvti aitibAate.d in 1976 on. tat&l

Other

NBS

RCL

Compared to chamber calibrated at NBS

or RCL

Chamber

Manufacturer

Other

29

35

20

44

25

1.001

1.003

0.017

0.020

1.005 0.013

1.016

1.009

0.030

0.031

13

6

9

40

24

4

5

1.000

0.999

0.009

0.011

0.998 0.018

1.017

1.005

0.053

0.014

a) One standard deviation.

b) Number of instruments with calibration

factor differing from the RPC by more

than 3%

Time since Number of calibration Intercom- Mean

(months) parisons RPC/inst. ,(a) Number

>3%

0 - 12 60 1.003 0.018 2

13 - 24 29 0.997 0.010 0

25 - 36 10 0.996 0.008 0

37 - 48 10 1.008 0.016 0

49 - 60 1 0.990 0

>60 3 0.993 0.021 0

a) One standard deviation.

b) Number of instruments with calibration

factor differing from RPC by more than 3%.

Table X

Repeated Calibrations by MDA RCL

(new calibration factor)/

(original calibration factor)

Dosimeter '76 '77 '78 '79 _80

K-F .999 999 .999 1 000

K-F / 1 000 0 999

K-F / 1 000 1 002

F / 0.999 1 002

Vict R 0 999 1 000

K-F - Farmer 0.6 cc graphite chamber with

Keithley model 602 or 616 electrometer

F - Farmer 0.6 cc graphite chamber

Vict R - Victoreen model 131 chamber with

model 570 electrometer

85
bration factors was 1.002 with a standard

deviation of 0.3%. A maximum deviation of 0.7%

was seen in three chambers. There was no difference between the results for Victoreen R-Meters

and Farmer type instruments.

The MDA RCL data indicate that instruments

are even more stable and reliable than indicated

by the RPC data above. These differences stem

from several factors including: the RPC data

are from field intercomaprisons with field in- struments, the institution may be using the in- strument in a different manner from that em- ployed by the calibrating laboratory, or the instrument may have been modified since calibration. Although the data indicate good long term stability, there are two 0.6cc Farmer

chambers (with nylon thimbles), belonging to the authors, each of which have experienced

unexplained changes in calibration of 1 to 2%.

Discussion of the Time Between Calibrations of Field Instruments

If NBS and each RCL presently in operation were to calibrate 85 instruments per year, the

1057 instruments requiring calibration [1]

could on the average be calibrated every 3.1 years. If another RCL was activated the average time between calibrations could be 2.5 years. However, there are a number of calibrations required following repair of instru- ments or purchase of new instruments. The fact

that the average time between calibrations by

an institution at the MDA RCL is 1.5 years

suggests that some institutions or individuals may be overly conscientious in calibration of instruments while others allow longer periods

of time between calibrations of their instruments.

From the instrument user's view, an instru- ment calibration is essential if he feels uncer0 994 — mean = 1 002 — a

= 003

0 996 n

= 42

0 998

1 000

1 002

1 004

1 .006

Frequency

Figure 2: Histogram of the ratio of the

calibration factor assigned by the MDA RCL on

a subsequent calibration, relative to that

assigned when the chamber had been previouslycalibrated by MDA RCL one to three years

earlier.

tain about his current calibration. However,

if the user is confident of his instrument

calibration, a recalibration according to a time schedule is usually not welcome, since

there is risk to the instrument in transport

and the absence of the instrument may be a serious inconvenience. In addition, the cost of

calibration is sometimes a problem.

Techniques Available to Assure Reliability of Assigned

Calibration Factors -

Since therapy field instruments appear to maintain their calibration factors over extended periods of time, the instrument user can maintain confidence in his instrument calibration through periodic constancy checks. Grant,

et al . [7] discuss the use of a cobalt-60

therapy unit or a strontium-90 constancy check source device to perform routine checks on

the performance of the instrument. Both tech- niques appear comparable. The 9 Sr data are reproduced in Figure 3, showing all checks to

be within + 1% of the mean.

Another important constancy check pro- cure is an intercomparison with instruments

from other institutions that have chambers

calibrated by NBS or an RCL. Table XI shows

the results of intercomparisons carried out in conjunction with meetings of Southwest, Midwest

and Missouri Valley chapters of the AAPM

[8, 9, 10]. These intercomaprisons uncovered

erroneous factors on two chambers whose factors were from questionable sources, and verified suspected problems with two RCL calibrated chambers. Periodic intercomparisons of

several chamber electrometer systems (last 5 lines of Table XI) again demonstrate the long term stability of these dosimetry system.

It is important to remember that any calibration laboratory can provide an erroneous calibration factor and that instruments may

2cr = 0.8%

i.oi r

m% 0 99

S 098

100 200 300 400 500 600 TOO

Number of Days (1-18-73, Day I)

Figure 3: Constancy check of an RPC Farmer- Keithley dosimetry system over a 21 month

period using a 9°Sr constancy check device. From Grant et al . [7 ]

86
undergo change during transport. A physicist

should therefore challenge, in every way

possible, any calibration factor obtained

from NBS and an RCL. These challenges can include; comparing the new factor with the old

factor, a constancy check on the instrument be- fore and after calibration, and intercomparison

with other instruments calibrated at NBS or an

RCL.

Conclusions and Recommendations

The Regional Calibration Laboratories

appear to be sucessfully filling an important

need in the radiological community. The users

of therapy field instruments who respond to

Table XI

Intercomparison of Chambers with

a Reference Chamber that had been Recently Calibrated

by NBS or an RCL< a )

Time Since Cal ibration

Last Factor

Cal ibration Type of Cal i bra ted Institution/

(Months) Dosimeter by Reference

40

38

36

34

3125

21

18

15

7

1

1?

?

41420

1933

F-K

Vict R Vict R Cap

Vict R F-K

Vict R F-Cap F-K

Vict R Cap F-K

EG&G-K F-K

F-K

F-K

RCL

RCL

?RCL

RCL

RCL

RCL

RCL

RCL RCL

RCL

RCL

? Inter- comparison

Inter- comparison

Inter- comparison

1.000

1.001

1.042

1.001 0.981 0.998

0.996

0.980

0.993 0.997

1.003 0.994

1.027 0.994

0.998

0.998

1.000 0.994

0.993

(b)

(c)

(c)

(b)

id)

(d)

F-K, Farmer 0.6cc chamber with Keithley

model 602 or 616 electrometer

Vict R; Victoreen model 621 or 131 chamber with model 570 electrometer

Cap; Capintec model 192 chamber with

model 192a electrometer

EG&G; EG&G model 586 A chamber

a) Data from various regional chapters

of the AAPM [7,8,9].

b) The chamber factor in use for these two chambers was of unknown or questionable

origin.

c) Problem with the correction factor was suspected by the institution.

d) The same institution on several occasions.

questionnaires and have their instruments

calibrated regularly have calibrations at a mean interval of about 1.5 years. However, from

an estimate of potential users and the current capacity of NBS and 3 RCLs it is suggested that

only one calibration every three years would be possible for each user if all of the instruments were calibrated at the same interval.

Data from various sources support the conclusion that commerical field instruments

are capable of maintaining their calibrations

for many years. It is suggested here that there

be a reconsideration of the time interval be- tween calibration required by federal or state

policy. If a user who has a calibration factor

directly traceable to NBS verifies the constancy

of this instrument monthly by measurements on

a cobalt-60 irradiator or strontium-90 constancy

checker and if he verifies the instrument con- stancy at least every two years by an intercomparison with other instruments with calibrations

directly traceable to NBS, it should be possible

to space calibrations at NBS or an RCL to periods of 3 to 5 years. The user would always use

the factor assigned by NBS or an RCL and employ

the monthly constancy checks and biennial intercomparison checks as indications for recalibration of his instrument when consistent discrepancies of 2% are found in the checks. This

suggestion seems warranted by the performance

characteristics of the available instruments

if coupled with reliable checks and adequate

documentation.

[1]

[2]

[3]

[4]

[5]

[6]

References

Lanzl , L. H. (Principal Investigator) Report

of the Committee on Calibration Needs in Therapy of the American Association of Physicists in Medicine, Chicago, Illinois

(1979).

Rosenfeld, M. (Chairman), Task Group #3 of the American Association of Physicists

in Medicine. It has been recommended that

the regional laboratories be renamed,

Accredited Dosimetry Calibration Laboratory

(ADCL), but the AAPM has not as yet approved the name change.

McCarthy, W. A., Chairman of Subcommittee

of Task Group #3 of the American Association

of Physicists in Medicine. Report in draft

(private communication).

Scientific Committee on Radiation Dosimetry

(SCRAD) of the American Association of

Physicists in Medicine. "Protocol for the Dosimetry of X- and Gamma Ray Beams with

Maximum Energies between 0.6 and 50 MeV."

Phys Med Biol 16 (1971): 379-396.

Loevinger R., NBS, Private Communication.

Federal Register 44, 5, 1722-1725, (Janaury

8, 1975).

87
^ Grant III, W. , Cundiff, J., Hanson, W.,

Gagnon, W., and Shalek, R., Calibration

Instrumentation used by the AAPM Radiological Physics Center. Med Phys 3, p. 353-4,

(1976).

^

Southwest chapter of AAPM (Humphries, L. J.)

unpublished data. ^

Missouri Valley chapter of AAPM (Purdy J. A., and Feldman, A.) unpublished data.

^ 10 ^Midwest chapter of AAPM (Hrejsa, A. F.)

unpublished data.

This work supported in part by DHEW NCI grant CA 10953.

88
NBS TRACEABILITY PROGRAMS FOR RADIATION THERAPY

Christopher G. Soares and Margarete Ehrlich

National Bureau of Standards

Washington, D.C. 20234

Traceability of the calibration of radiation therapy machines to the national

dosimetry standard may be verified by means of a measurement assurance program. Such a program often involves the use of rugged dosimetry systems for establishing a direct link between the user and the primary calibration laboratory

without personal visits. In this paper, procedures common to this type of

therapy dosimetry survey systems are discussed. Then, to illustrate these pro- cedures, three of these systems are treated in detail: (1) the ferrous sulfate

(Fricke) dosimetry system used at NBS in an ongoing survey of electron-therapy

dosimetry, (2) a TLD system that was used by NBS in a one-time study of

cobalt-60 teletherapy dosimetry, and (3) a second TLD system proposed for sur- veying megavoltage bremsstrahlung therapy dosimetry.

(Cobalt-60 gamma radiation; dosimetry; ferrous sulfate dosimetry; high-energy

bremsstrahlung; high-energy electrons; measurement assurance; radiation therapy;

survey; teletherapy; thermoluminescence dosimetry; traceability)

Introduction

Users of teletherapy equipment rely on a calibration chain for an assessment of the radiation output from their units. The steps in this

chain involve calibration of a secondary standard

instrument against a primary standard and then a measurement of the therapy beam output either

with this secondary standard or with a tertiary

instrument calibrated against the secondary standard. It is the aim of NBS measurement assurance

programs to test this chain by a direct comparison between the primary standards laboratory and

the user, with a suitable detector. Such a com- parison may be carried out initially by means of

shipped dosimetry systems sufficiently rugged and compact to withstand rough handling and variations

in ambient conditions likely to be encountered

during shipment. Subsequent follow-ups through

personal contacts may be required.

All surveys involving shipped dosimeters

have certain features in common in their conception and execution. First, a survey objective must be stated, defining what is to be measured

and to what accuracy. Then an administrative

procedure for obtaining participants and reporting results must be set up. In developing the mechanism for the survey, an irradiation protocol must be decided upon and its feasibility tested. Along with this goes the selection of a suitable

dosimeter. Handling and readout procedures for

the dosimeter must be developed and tested, and

some information about the accuracy of dose determination must be gathered. Once these preliminary

steps have been completed, the survey can be performed.

In actual practice, each round of a typical survey (such as those described here) contains

three distinct phases. They are (a) a dosimeter

characterization phase, in which the relative

response of all dosimeters is determined prior to shipment; (b) shipment in suitable irradiation

holders of the dosimeters required by the survey participants, and calibration of the remaining

dosimeters in the surveying facility; and (c) after return of the shipped dosimeters, readout

of all dosimeters in one session and evaluation,

from the dosimeter responses, of doses delivered

by the participants. Each of these phases is discussed in greater detail below.

(a) Dosimeter Characterization Phase

Dosimeters may be characterized by their response to a known irradiation level. If, in a given batch, dosimeter identity is maintained,

this response may be used to correct for variations in the response characteristics of individual dosimeters during the survey. This

procedure may be referred to as individual

dosimeter characterization . If, on the other

hand, dosimeter identity is not maintained, the batch of dosimeters may be characterized by the mean and the standard deviation from the mean of

the responses of the members of the batch. This

procedure may be referred to as batch characterization . The way in which dosimeters are characterized determines overall uncertainty in dose

interpretation. Batch characterization is suf- ficient when dosimeters have similar response

characteristics. However, when the spread in response among the dosimeters within the batch is comparable to or larger than the reproducibility

of the response of individual dosimeters in the

batch, then the increased effort involved in maintaining dosimeter identity and using individual characterizations often pays off in increased accuracy. Examples are discussed in

a later section.

89
(b) Dosimeter Shipping and Calibration Phase

Participants are shipped dosimeters each con- sisting of a passive radiation measuring device in

a holder of a material with atomic number close to water (and soft tissue). They are also given

instructions for the irradiation of these dosi- meters in their therapy beams. A portion of the characterized dosimeters remain in the surveying

facility for calibration during the survey round. This calibration consists of delivering known

absorbed doses to individual dosimeters in a geometry identical to that to be used by the par- ticipants. A sufficient number of different

absorbed-dose levels are used to establish a calibration curve over the range of doses likely to

be delivered by the participants. This calibration curve forms the basis for the dose interpretation from the response of the dosimeters

irradiated by the participants.

(c) Dosimeter Readout and Dose Evaluation Phase

When dosimeters have been returned to the surveying facility, they are "read out" along with

the dosimeters that remained for calibration

(i.e., the radiation effect is measured). Readout

of all dosimeters at the same time is important

since it eliminates corrections for possible dayto-day variations in readout apparatus. Dose interpretations may then be made from dosimeter

responses via the calibration curve, if necessary after appropriate corrections.

This completes a single survey round. If the survey consists of several rounds and the same dosimeters are to be used throughout, recharacterization of the dosimeters may be required

between consecutive rounds.

To illustrate how these procedures work in practice, traceability surveys with three types

of mailable dosimeters are discussed in the following sections. First, the NBS ferrous sul- fate (Fricke) dosimetry service of megavoltage

electron therapy dosimetry is discussed in detail

Next, a one-time thermoluminescence dosimetry

(TLD) traceability survey of cobalt-60 tele- therapy dosimetry is discussed and finally, a second TLD system is described which has been tested for use in a proposed traceability sur- vey of megavoltage bremsstrahlung dosimetry.

Megavoltage-Electron Dosimetry Traceability

The ferrous sulfate (Fricke) system is used

in an ongoing NBS service to provide users with

assistance with absorbed-dose measurements in high-energy electron beams. This is a fee service, performed twice a year. It is not meant

to take the place of a beam calibration, but is only to provide information on uniformity of dose

delivery throughout the country.

Procedure

Megavoltage electron beam users contact NBS

if they wish to receive dosimeters for the next survey round. Fresh dosimeter solution is prepared for each survey round and each dosimeter is characterized individually. The desired number of

dosimeters is shipped to the participants along

with a shipping control and the rest kept at NBS

as in-house controls. Most dosimeters are returned within the next six weeks. All dosi- meters are then read out together and dose interpretations are made. Results for all dosimeters

shipped and irradiated by the participants in one

round are reported to each participant, with only

his own identified.

The sensitive volume of the dosimeter is 2.5 cm3 of Fricke solution. This is contained in

a ground-glass stoppered quartz spectrophotometer

cell, encased securely in a polystyrene block as shown in figure 1. The participants are in- structed to insert this block into an appropriate

cutout in a 30 cm x 30 cm x 30 cm polystyrene

phantom as prescribed in the Protocol of the Therapy Committee of the American Association of Physicists in Medicine II]. The center of the block is to be at the center of a 10 cm x 10 cm

field, at a depth in the phantom at or slightly

beyond that corresponding to maximum depth dose. (The prescribed depth is 1 cm for electrons of energy between 5 and 10 MeV, 1.5 cm for electrons

between 10 and 25 MeV, and 3.5 cm for electrons

between 25 and 50 MeV.) The participants are further instructed to deliver 50-80 Gy (5000-

8000 rad) to water to all but one of the dosi- meter blocks and then to return all blocks to

NBS, along with their assessment of dose

delivered. The change in ferric- ion concentration in the returned dosimeter solution is evaluated spectrophotometrical ly and related to absorbed dose. The report mailed to each participant includes a record of the G-value used in the dose interpretation.

Figure 1 Ferrous Sulfate (Fricke) Dosimeter

Assembly

Principle of Fricke Dosimetry

The radiation-chemical yield, or G-value

(defined as the number of stable atoms or ions formed per 100 eV of absorbed energy), is one of

the quantities of fundamental importance in the

use of the ferrous sulfate (Fricke) dosimeter. For the ferrous-ferric reaction initiated by

irradiation, G(Fe+++

) = 100 n/D, where n is the

90
number of Fe+++ ions formed in a unit mass and D is the radiation energy in eV absorbed in the same unit mass. When expressed in terms of

molar concentration M (in moles per liter) and

absorbed dose D (in grays), this becomes

G(Fe

+++

) = 0.9426 x 107

JJ (1)

when the density of the Fricke solution is set

equal to 1.024 g/cm3

. The radiation chemistry

of the Fricke system has been studied in detail and the G-value of the reactions leading to the oxidation of the ferrous ions has been determined over a relatively wide range of linear energy transfers I2J. Since the change in ferric- ion concentration causes a marked change in the ultraviolet

absorption spectrum of the Fricke solution, a chemical evaluation of this change may be replaced by a simple spectrophotometric measurement of the change in the absorption pro- perties in the main absorption peak (304 nm).

Absorbance, A (which is the transmission density

corrected for losses through scattering in the optics of the spectrophotometer), is related to the molar concentration, M, by Beer's law

A = e M d (2) where d is the optical path length, and e the molar extinction coefficient.

Combining equations (1) and (2) yields

D = 0.9426 x 10

7 (3) Ae G(Fe ) d

where AA is the change in absorbance before and

after irradiation to an absorbed dose D and

Ae = e(Fe+++

) - e(Fe++

). When the measurement

is made at the conventional wavelength of

304 nm, e(Fe++

) = 0 and, as a consequence,

Ae « e(Fe*++

).

Rather than to rely on the theoretical value

for the molar extinction coefficient, it is good

practice to measure this coefficient for one's

own spectrophotometer, using Fe+++ solutions of *

a number of different known molar concentrations.

Temperature control during optical density

measurements is important since the extinction

coefficient has a temperature dependence of

^.7 percent per °C [3].

Dosimeter Preparation

The Fricke solution used at NBS consists of

0.001 M Fe(NHlt ) 2 (S0 4 ) 2 , dissolved in 0.8 N H 2 S0 k , well aerated, and

0.001 N NaCl.

Having recently replaced our spectrophotometer

with a new model, we made this measurement in our new instrument and obtained a value of

2188 M

-1 cm

-1 at 25.0°C, which agrees well with

the theoretical value of 2197 M

_1 cm

-1

.

The NaCl is added to desensitize the system

against organic impurities. Because the addition of NaCl causes an increase in the rate dependence of the G-value, we recommend that the participants do not exceed instantaneous dose

rates of 103 Gy/s. Irradiation of this solution

produces free radicals and molecular products

which cause oxidation of Fe++ to Fe+++

. Spon- taneous oxidation also occurs at room temperature

even in the absence of organic impurities. This must be taken into account when there are delays

of more than two or three days between the initial dosimeter readout during the characterization phase and the final dosimeter readout, as

is usually the case in a mailed survey. Cleanliness of glassware used in preparing

and storing the solution is of great importance.

Organic contaminants cause massive spontaneous

oxidation of stored solution rendering it useless

for dosimetry. At NBS the spectrophotometer cells were initially cleaned with detergent in an ultra- sonic cleaner and since then have been kept filled

with Fricke solution. Other glassware was ini- tially cleaned with hot concentrated sulfuric acid

and since then has been kept filled with either

Fricke solution or distilled water. No plastics

are ever allowed in contact with the Fricke solution.

The purity of the water used both in cleaning

and making the Fricke solution is crucial to the performance of the system, freedom from organic

impurities being one of the main requirements.

Satisfactory water has been obtained at NBS by

permanganate distillation [4]. Over the years,

NBS has also had a number of satisfactory com- mercial sources for water.

Dosimeter Characterization

The cleaned and filled cells are all irradiated with cobalt-60 gamma radiation to a level of ^50 Gy to water and read out spectrophotometrically. These readings characterize each

individual dosimeter in the batch and furnish the base line from which changes in optical density

due to irradiation are measured, as well as the base line from which corrections for the spon- taneous growth of optical density are determined.

The procedure also identifies dosimeters with

anomalous characteristics, which then are eliminated from further use; it also provides for a rough check on the G-value of the particular

Fricke batch for cobalt-60 gamma radiation, cal- culated from the average of the optical densities of the irradiated cells and a knowledge of

the dose delivered. No further calibration is performed.

Dosimeter Evaluation

The returned dosimeters are read out together

and the change in optical density is determined

for each dosimeter. Correction of the readings

of the irradiated dosimeters for spontaneous

density growth is made by subtracting the average

density growth of all unirradiated control dosi- meters (shipped and unshipped). Since growth

varies somewhat with individual dosimeters, this

procedure adds an additional uncertainty to the

91
dose interpretations, which in our procedure

amounts to about 1 percent. Finally, the dose

delivered to the dosimeters is determined from

the corrected change in optical density by

eq (3) using the molar extinction coefficient

measured for the spectrophotometer employed, and

published G-values.*

Uncertainty

We estimate that the total uncertainty in dose interpretation in the NBS survey procedure is about 4 percent. We feel that this uncertainty

could be reduced by using a sealed Fricke dosimetry system instead of the present open system.

We are presently attempting to adapt such a system

to our program.

Results

Overall performance of the participants did

not improve noticeably between 1967, when the ser- vice was initiated, and 1975. Table 1 shows that,

through 1975, only 58 percent of the dose interpretations were within 5 percent of the dose

assigned by participants. In the last four years,

this fraction is seen to have risen to 73 percent.

This improvement has been accompanied by a large

increase in the number of dosimeters shipped,

which indicates an increased awareness in the radiation-therapy community of the importance of accurate dosimetry.

Table 1

Performance Results of All Participants

in Electron Beam Dosimetry Uniformity Study

Calendar Year Number of Dosimeters |&| < 5%

Number of Dosimeters with

Difference A of

5% < |A| x

< 10% |4| > 10%

1967 50 33 (66%) 14 (28%) 3 (6%)

1968 81 39 (48%) 24 (30%) 18 (22%)

1969 65 25 (45%) 16 (29%) 14 (25%)

147(1 61 34 (56%) 12 (20%) 15 (25%)

1971 58 30 (52%) 13 (22%) 15 (26%)

1972 47 35 (74%) 5 (11%) 7 (15%)

1973 60 38 (63%) 9 (15%) 13 (22%)

1974 49 38 (78%) 6 (12%) 5 (10%)

1975 74 38 (51%) 24 (32%) 12 (16%)

1976 99 76 (77%) 19 (19%) 4 (4%)

1977 109 77 (71%) 21 (19%) 11 (10%)

1978 142 107 (75%) 25 (18%) 10 (7%)

1979 148 103 (70%) 29 (20%) 16 (11%)

Cobalt- 60 Teletherapy Dosimetry Traceability

The major objective of the cobalt-60 tele- therapy survey was to assess the ability of users

to deliver a requested absorbed dose. This was

accomplished- by a survey of teletherapy dosimetry,

conducted by the National Bureau of Standards

(NBS), supported in part by the Bureau of Radiological Health (BRH). Similar studies have been

(and are being) performed, elsewhere I5-8J.

Presently, we are using a G-value of 15.5/100 eV for both cobalt-60 gamma and high-energy electron

irradiations.

Procedure

Names and addresses of licensees were sup- plied to NBS by BRH, and each licensee was sent an invitation to participate free of charge. If there was no response, a single follow-up invitation was sent. In this way, over 700 or about

two- thirds of all licensed users agreed to participate in the survey.

Because of limited facilities, NBS could only

survey about 40 participants at a time, which made

dosimeter re-use mandatory. Dosimeters were

shipped every six weeks, being kept at NBS for

readout and re-characterization only one week

between mailings. Also shipped with the dosi- meters was a three-page information form, which

asked for calibration details of the unit surveyed

and for steps in the calculation of the dose to be delivered. This information was used by NBS to check the participants' dose calculations. The

results of this check as well as the dose interpretations from the response of the irradiated

dosimeters were sent to participants in a report

covering all dosimeters involved in each mailing.

All results were kept confidential; the participant to whom the report was sent had only his own dosimeters identified. Results and information

from returned forms, which were given to BRH without participant identification, formed the data base for a later BRH statistical study £9].

Each participant was sent six dosimeter

blocks. Five were to be irradiated in separate

exposures, the sixth was to be left unirradiated

as a control. The participants were to place one block at a time on the shipping container and

position the center of the block at their normal treatment distance, with a 10 cm x 10 cm field

size. They were to calculate the time necessary

to deliver 3 Gy to water at this distance, at a depth of 1 cm in a water phantom, and then to irradiate the block in air for the calculated

time. Setups and irradiations were to be per- formed by persons routinely involved in patient

irradiations.

Choice of Dosimeters

Several considerations went into the choice

of the type of dosimeter for use in this survey. The necessity for dosimeter re-use with minimal

re-calibration, the limited manpower available for performing the work at NBS, and the need to re- strict overall uncertainty in dose interpretation

to less than 5 percent, all pointed towards the

use of thermoluminescence dosimetry (TLD) for the

survey. CaF2:Mn was chosen as the TL phosphor

because of the relatively small dependence of its response on annealing and irradiation history.

Also, because all irradiations were to be performed with cobalt-60 gamma rays, one could

ignore the energy dependence of its response which is large compared with that of other com- monly used but otherwise less desirable phosphors

(such as LiF and U2B14O7). Normal handling difficulties involved in TLD work were overcome by

obtaining the TLD phosphor in a commercially

available configuration in which two pieces of

hot- pressed CaF2:Mn, held in contact with a me- tallic heating strip, are sealed in a glass bulb

92
containing a neutral atmosphere. Each dosimeter

consisted of the commercial TLD bulb enclosed in

a black polystyrene block. The block protected

the bulb during shipment and participant han- dling, shielded it from ultraviolet radiation,

and provided electron equilibrium during cobalt-60

gamma irradiation. An exploded view of the dosi- meter is shown in figure 2.

The TLD readout system consisted of a com- mercial unit in which the metallic strip of the TLD bulb was heated resistively, and the resulting

thermoluminescence emission was collected by a cooled photomultiplier tube (PMT). The current

signal from the PMT was fed to a current integrator, which was gated by a timer to allow cutoff

of integration after readout was complete, but

prior to emission of the thermal signal generated

during subsequent annealing. On completion of

the readout, the integrated signal was punched

on paper tape for off-line analysis.

Figure 2

Principle

Schematic Diagram of Bulb Dosimeter

Assembly

The crystal lattice of some solids--in par- ticular those containing certain impurity cen- ters—are capable of storing radiation energy and,

upon subsequent heating, releasing it in the form

of light or ultraviolet radiation. This phe- nomenon is referred to as thermoluminescence (TL).

In many phosphors, TL output increases monotonically--and over a limited range essentially

1 inearily--with the amount of radiation energy

stored, prior to the onset of saturation effects.

This is one of the major prerequisites for the application of TL in radiation dosimetry. Inten- sive research and development over the past

decades has led to a number of TLD phosphors

suited for the practical dosimetry of electrons,

photons, and neutrons over a wide range of radiation energies and irradiation levels, a subject

that has been extensively treated in the literature £10].

Repeated use of most TL phosphors requires

some form of heat treatment (annealing) after

readout, particularly at dose levels above a few hundredths of one gray. Insufficient annealing

causes accumulation of unwanted residual re- sponse in subsequent readouts. This is a problem particularly when a low dose is used in the laboratory to characterize the dosimeter response

and then a high dose is delivsred in the field.

For this survey, in which CaF 2 :Mn was used up

to dose levels of about 3.0 Gy, it was found to be sufficient to anneal the TLD bulbs in the reader for a few seconds after readout. The

temperatures developed during this procedure

were found to reduce residuals sufficiently to necessitate only minor corrections (discussed

below)

Characterization

Dosimeter identity was maintained throughout

the entire survey, permitting the characterization of the response of each individual TLD bulb. Initially, a base-line characterization was obtained in terms of the average response of each

bulb to identical reference irradiations (3 - 5 R) and subsequent readouts. This also yielded the information on the reproducibility of the TLD system required for an estimate of the uncer- tainty in the dose interpretation from the re- sponse to irradiations by the participants. Since

some residual response had been found to be present after irradiation at the 3.0-Gy level and subsequent readout with annealing, all bulbs were read out twice after each mailing (the second

readout five days after the first) to establish

the level of the residual response. This proce- dure was followed by two further sets of identical

reference irradiations and readouts. The average

relative response of the bulbs to these irradiations, suitably adjusted for residual response, was used as a correction in the computation of

the dose interpretations from the response of each

of the dosimeters irradiated in the preceding survey round. Throughout the survey, a record was kept of any change in the bulb characterization

from the initial base line.

Mailing and Calibration

All but about 40 of the 300 bulb dosimeters were mailed to participants for irradiation. The

remainder were used at NBS for establishing the current response-versus-dose relationship, and

to monitor fading characteristics of the batch.

Initially, the calibration was done at several levels around 3.0 Gy, and a second order

polynomial was fitted to the individually cor- rected responses. Dose interpretations were then made via this curve. In later rounds of the survey, calibration was done only at the 3.0-Gy

level, since in the narrow range in which most of

the bulbs were irradiated (within ±10% of 3.0 Gy), response was proportional to dose.

In order to be able to correct for fading

between irradiation and readout, dosimeters also were irradiated at a known level at several different times during each survey round, and read out with the other dosimeters at the end of the

round. Also, a record was kept of the participants' irradiation dates. With a knowledge of

these dates and of response as a function of fading time, we were able to correct the dose interpretations for fading. The fading function

reproduced well over the entire survey, with

typical corrections for four weeks of fading

having been of the order of 5 percent.

93
Readout and Evaluation

After readout, corrections were applied for

variations in individual response and for fading

of the response between irradiation and readout. Because of changes in PMT response during the two

to three hours required for readout of the 300 dosimeter bulbs (probably caused by insufficient

PMT cooling), a further correction, amounting to up to 2 percent, was necessary.

Dose interpretations were made from the cor- rected readings via the results of the similarly

corrected calibration data (response- versus-NBS delivered dose relationship). Establishing a new calibration for each survey round made it possible

to eliminate the influence of reader variations

and changes in dosimeter response.

Uncertainty

Sources of uncertainty in the dose interpretation are shown in table 2. The systematic

uncertainties shown are estimated upper bounds. The random uncertainties are taken as three times

the relative standard deviation of the mean of

dosimeter readings after repeated irradiations and

readouts. This table is discussed in detail in the comprehensive report on this survey published

elsewhere 111]. We feel that the quoted overall

uncertainty of 4 percent is probably conserva- tively high.

Uncertainties in NBS Method of Determining Absorbed Dose from Dosimeter Response

Systematic Uncertainty

NBS exposure calibration of Co-60 gamma-ray source 0.7%

Uncertainty in dosimeter calibration 0.7%

Uncertainty in dosimeter fading correction 1.0%*

Total (summed linearly) 2.4%

Total (summed in quadrature) 1.4%

Random Uncertainty

Reproducibility of individual dosimeter response .... 2.4%

Correction for sensitivity variation between dosimeters 2.4%

Total for corrected individual dosimeter response 3.4%

Total for average corrected response of five

dosimeters (summed in quadrature) 1 .5%

Total uncertainty in dose interpretation from average of

five dosimeters (summed linearly) ^.0%

(summed in quadrature) 2.8%

Chosen for NBS evaluation

Results

The overall results of the survey are shown

in figure 3. Plotted are percent differences

between individual dose interpretations and the dose to be delivered (3.0 Gy). Eighty- three

percent of the dose interpretations were within

-20 -10 0 10 20 PERCENT DIFFERENCE FROM DOSE TO BE DELIVERED

Figure 3 Performance of Participants Involved

in the Cobalt-60 Teletherapy Survey.

Shown is the difference, in percent,

between the dose to be delivered by the participants and the NBS dose in- terpretation from the average of the responses of the five irradiated

dosimeters. Total number of participants: 812; total number of sets:

906.

5 percent of the requested dose, with only 4 per- cent differing by more than 10 percent. From the figure it is apparent that there is a positive

bias in the data, the average deviation for all dosimeters shown being +0.7 percent. This could

be significant, and has been explained by the fact

that most participants used the conversion factor

from exposure to absorbed dose to soft tissue

(0.957) rather than that to water (0.965), which

was used in the NBS dosimeter calibrations.

Follow-up

Two follow-up studies were performed as sta- tistical checks on the results of the initial

study. The first of these studies involved resur- veying a random sample (about one-fifth) of the original participants. The second involved a sur- vey of a random sample (about one-tenth) of the initial non-participants. The results of these

follow-up studies, while of limited statistical

validity, tended to confirm the results of the

initial study.

Preparations for a Survey of High-Energy

Bremsstrahlung Therapy Dosimetry

There has long been interest in extending the survey of therapy dosimetry to include megavoltage

bremsstrahlung. Because of the much wider variation in spectral quality of these bremsstrahlung

sources as compared to cobalt-60 gamma-ray

sources, energy dependence of the dosimeter

response becomes an important consideration.

Therefore it was felt that a different system

than that used in the cobalt-60 teletherapydosimetry survey would have to be developed.

94
Procedure, Choice of Dosimeters and Irradiation

Protocol

This study will be carried out by BRH. While the administrative procedure for this survey has yet to be worked out by BRH, an irradiation protocol has been developed and its feasibility tested by NBS at some length I12J. At this time, it is envisioned that participants

will be sent a cubic polymethyl methacrylate

(PMMA) phantom with sides 20 cm in length,

loaded at several depths with hot- pressed LiF

samples. The participants will be asked to deliver a certain dose (1.0 Gy) to water at a 10- cm depth, treating the phantom for dose

calculation as if it were water. This procedure

will provide information on accuracy of dose

delivery and may also yield some information

obtained with the aid of TLD response at the different depths.

The response of LiF has a relatively low energy dependence; this makes LiF desirable for

a survey involving wide spectral variations.

Advances in reader technology have overcome

difficulties once encountered with this phosphor, such as spurious readings. For use in the medical dose range (> 0.1 Gy), furnace annealing

was required with the chosen reader. We investigated this system using the conventional

annealing cycle of one hour at 400°C, cooling

for one-half hour, followed by one hour at

100°C. In addition, all samples were given a post-irradiation anneal at 100°C for 10 minutes

prior to readout. They were never exposed to direct sunlight or other sources of illumination

containing a large ultraviolet component. A vacuum pickup was used for all sample manipulations. For readout, an automated reader was employed, in which the samples are heated by hot nitrogen and which allows the readout of 50

samples in rapid sequence. The readout signals were fed directly into a microcomputer system

for storage and later retrieval for off-line

analysis.

Several investigations were carried out to assess the feasibility of such a system using

the protocol described. Fading under laboratory

conditions was found to be almost negligible,

with only about 2 percent being evident over a period of three weeks. Also investigated was

the influence of phantom dimensions upon dosi- meter response at the depth of interest. Several phantom sizes and shapes from 15 cm 3 to 20 cm3 were investigated, and no significant effect

was measured. The influence on the response of

samples at a 10-cm depth in the presence of

samples located on the axis above and below this

depth was investigated as a function of phantom

size and beam energy. The results of these

investigations are shown in table 3. Response

of dosimeters at a depth of 10 cm in the pre- sence or absence of dosimeters at other depths

is compared. There is a trend towards slightly

reduced responses in the presence of other

dosimeters, however its significance is questionable. In view of these results it was concluded

that it was feasible to irradiate dosimeters at more than one depth simultaneously.

BRH plans to have the first phase of the survey include sources of up to 10 MeV in photon energy. We therefore made measurements of the response of LiF as a function of absorbed

dose with bremsstrahlung produced at exciting

potentials of 4, 6, and 10 MV as well as with

cobalt-60 gamma radiation. Dose-versus-response

data from this determination are shown in figure

4. The samples show the same degree of supra- linearity, regardless of energy. Of particular

interest is a comparison of response for difTable 3. Influence on Dosimeter Response of the Presence of Dosimeters 1n Other Depths

AVERAGE DOSIMETER RESPONSE FOR DOSIMETERS AT A 10-cm DEPTH IN

TYPE

OF RADIATION

Cube, 15 cm sides, with dosimeters at Cube, 20 cm sides with dosimeters at Paral leleplped,

15 cm x 15 cm x with dosimeters20 cm deep

at

10-cm depth only 2.5-, 5- and 10-cm depths

10-cm depth only 2.5-. 5-. 10- and

15-cm depths

10-cm depth only

2.5-, 5-, 10- and 15-cm depths

Cobalt-60

gamna rad. 0.581 ± 0.002 0.578 t 0.004 0.589 ± 0.003 0.588 t 0.004

4 MV bremsstr. 0.607 0.003 0.601 t 0.004

6 MV bremsstr. 0.552 i 0.003 0.552 t 0.003

10 MV bremsstr. 0.681 ± 0.003 0.680 i 0.004 0.685 i 0.004 0.683 * 0.005 0.683 ± 0.004 0.685 i 0.003

95
200 ABSORBED DOSE . rod

Figure 4 LiF Response in PMMA as a Function of

Absorbed Dose. Dashed line - linear

relationship between response and ab- sorbed dose.

ferent beam energies at one particular dose

level. The level used was 1 Gy, chosen because

higher levels induce residual TL signal which is difficult to remove with conventional annealing

techniques. Table 4 shows measured values of

the ratio of responses to 1 Gy irradiations of

high-energy bremsstrahlung and cobalt-60 gamma

radiation. As is seen from the table, the ratio

is unity within the uncertainty of the determination. Therefore, no correction for beam energy (at least up to 10 MeV) will be required

in the survey. In addition, it will be possible

to perform calibrations during the mailing round

with cobalt-60 gamma rays, without any further

corrections.

Finally, exposures were made to assess the feasibility of measuring depth-dose profiles

using the planned irradiation geometry. Results

of these measurements are shown in figure 5. Data were normalized to those at the 10-cm

depth, and are seen to be adequate—at least in

Table 4

Ratio of Dosimeter Response in PMMA to Megavoltage Bremsstrahlung

and Dosimeter Response in PMMA to Cobalt-60 Gamma Rays,

for 1 Gy Absorbed Dose to Water

Radiation Source Nominal Peak Enerqy Ratio

Varian Clinac-4 4 MeV 0.991

Siemens Mevatron VI 6 MeV 1.001

Varian Clinac-18 10 MeV 0.979

Siemens Mevatron XII 10 MeV 1.000

principle--for distinguishing between the energies employed.

Expected Uncertainty

The number of dosimeters to be included per measurement point greatly influences the overall

uncertainty in dose interpretation. Of impor- tance also is whether the dosimeters are calibrated individually or as a batch. We have

determined that associated with the response of

individually calibrated dosimeters is a standard

deviation of about 1 percent, as compared with

a practical lower limit of 1.5 percent asso- ciated with batch-calibrated dosimeters. Since

the survey will be performed by BRH personnel

using large numbers of dosimeters, batch calibration probably will be used. In this case, nine dosimeters per measurement point lead to a combined random and systematic uncertainty of

about 4 percent in dose interpretation £12].

Individual calibration would lower this value by

about 1 percent.

Plans for Extension of Current Programs

Our future plans in therapy dosimetry

traceability include extensions of the proposed

high-energy survey to bremsstrahlung energies up

to 50 MeV. This will involve further phantomsize and energy-dependence studies.

We are presently involved in preliminary

work on devising a TLD system for use in a high- energy electron dosimetry survey. As a first

step, we are trying to determine whether a system similar to that employed for the high- energy bremsstrahlung survey would be satisfactory or whether charge-up effects will make

it necessary to switch from a plastic to a water

phantom.

DEPTH , cm

Figure 5 Absorbed Dose to Water as a Function

of Depth in the PMMA Phantom, Computed

from Dosimeter Response. The absorbed

dose data were normalized to those ob- tained at a depth of 10 cm in PMMA

(arrows)

.

96
References

[1]

[2]

[3]

[4]

[5]

[6]

The Subcommittee on Radiation Dosimetry of

the AAPM (SCRAD), "Protocol for the Dosimetry

of High Energy Electrons", Physics in Medicine

and Biology 11_, 505 (1966).

See e.g., Fricke, H., and Hart, E.J., "Chemical

Dosimetry" in Radiation Dosimetry, Vol. II, Attix, F.H., Roesch, W.C., editors, Academic

Press, New York (1966) or SCRAD Protocol

(ref. 1) or "Radiation Dosimetry: Electrons

with Initial Energies Between 1 and 50 MeV",

I.C.R.U. Report 21, International Commission

on Radiation Units and Measurements, Washington,

D.C. (1972).

Scharf, K., and Lee, R.M., "Investigations of

the Spectrophotometry Method of Measuring

the Ferric Ion Yield in the Ferrous Sulfate

Dosimeter", Radiation Research 1J5, 115 (1962).

Chesler, S.N., Gump, B.H., Hertz, H.S.,

et al . , "Trace Hydrocarbon Analysis", p. 49,

Appendix A, NBS 889, U.S. Department of

Commerce, National Bureau of Standards (1976).

Shalek, R.J., Kennedy, P., et al., "Quality Assurance for Measurements in Therapy", Pro- ceedings of the Symposium on Measurements for

the Safe Use of Radiation, NBS SP 456, 111-118,

U.S. Department of Commerce, National Bureau

of Standards (1976).

Sundara Rao, I.S., Naik, S.B., et al., "Evalu- ation of Dosimetry Accuracy and Uniformity

for 60Co Radiation Therapy", Proceedings of

the International Symposium on National and International Standardization of Radiation

Dosimetry, Atlanta, Ga. (1977).

[7]

C8J

[9]

DO]

[11]

[12]

Eisenlohr, H.H., and Jayaraman, J., "IAEA-WHO Cobalt-60 Teletherapy Dosimetry Service Using

Marked Dosimeters. A Survey of Results

Obtained during 1970-75", Phys. Med. Biol. 22, 18-28 (1977).

Dicey, B.B., Moe, H.J., and Tongue, T.M.,

"Nationwide Evaluation of 60 Co Teletherapy

Calibrations", Medical Physics 5, 434 (1978).

Thompson, D., Kearly, F., Wyckoff, H., and GUI in, J., "Nationwide Survey of 60Co Teletherapy: Final Report", to be published as a Bureau of Radiological Health Technical

Report.

See, e.g., Fowler, J.F., and Attix, F.H.,

"Solid State Integrating Dosimeters", in Radiation Dosimetry, Vol. II, Attix, F.H.,

Roesch, W.C., editors, Academic Press, New York Q966).

Soares, C.G., and Ehrlich, M., "Nationwide

Survey of Cobalt-60 Teletherapy Dosimetry",

NBS TN 978, U.S. Department of Commerce,

National Bureau of Standards (1978).

Ehrlich, M., and Soares, C.G., "A Thermoluminescence Dosimetry System for Use in a Survey

of High-Energy Bremsstrahlung Dosimetry",

NBS TN 1119, U.S. Department of Commerce,

National Bureau of Standards (1980).

97

TRACEABI L I TY PROGRAMS FOR NUCLEAR MEDICINE

D. B. Golas

Atomic Industrial Forum, Inc. Washington, D.C. 20014

and National Bureau of Standards

Washington, D.C. 20234

The National Bureau of Standards (NBS) supervises and administers two measurements

assurance programs: one on behalf of the Atomic Industrial Forum (AIF), re- presenting several manufacturers of radiopharmaceuticals; and the other with the

College of American Pathologists (CAP), representing hospitals and final users of radiopharmaceuticals. Each program is described and the results of measurements

of samples of known, but undisclosed, activity are presented.

(Assurance; measurements; radioactivity; radiopharmaceutical; standards; traceability)

Introduction

The National Bureau of Standards (NBS) currently

supervises and administers two programs for measurements assurance in the field of nuclear medicine.

The research-associate program of the Atomic

Industrial Forum (AIF) involves several of the major

bulk suppliers of radiochemicals and producers

of radiopharmaceuticals; the College of American

Pathologists (CAP) quality assurance "Q" pro- gram involves the hospitals and nuclear pharmacies

which comprise the users of radiopharmaceuticals.

Together, these two programs encompass the radiopharmaceutical spectrum from manufacture to use. The programs are a help in satisfying the increasing

regulatory requirements to demonstrate traceability

to NBS, through the distribution of samples

(Standard Reference Materials) of known, but un- disclosed, activity ("blinds") which are measured

by the participants. The comparison of the participant's measured activity to that certified by NBS

is a measure of the competence of the participant

to quantify an unknown amount of radioactive

material accurately. In the case of the AIF researchassociate program, a Report of Measurement is then

issued which states the difference between the participant's reported value and the NBS certified value, thereby establishing traceability to within that limit, for that particular radionuclide,

at that time. In the CAP program, a Report of Calibration giving the NBS certified activity value

is sent to each participant upon return of their

results, and when all values are in, a report is issued which gives the results for the entire group

of participants. If a participant has a problem

measuring the unknown, the activity value is usually

given by telephone, in advance of sending a certificate, so that the participant can make use of the

NBS reference material to derive a calibration factor

for his dose calibrator or other measuring system.

The AIF-NBS research-associate program is of great value to the manufacturers of radiopharmaceuticals because it helps to minimize measurement uncertainty and demonstrate traceability to NBS.

This in turn reduces some of the problems

they have in satisfying application require- ments when filing New Drug Applications

with the Food and Drug Administration (FDA),

as well as saving time and paperwork when complying with requirements of the Nuclear

Regulatory Commission (NRC) and other Federal and State agencies. Participation in the program also

helps the participants when questions arise be- tween the companies and their customers. For ex- ample, when the quantity of radioactive material

measured by the customer does not agree with that

of the supplier, the supplier often uses results

of measurement tests to defend its value.

The CAP "Q" program is valuable to the users

of radiopharmaceuticals because it enables them

to determine if the calibration of their dose calibrator or other measuring system is correct for

each radionuclide that they receive. In addition

they can obtain help if they have problems in the

measurement of these radioactive materials. The CAP program is limited, however, by the number of par- ticipants who receive the samples for measurement.

This will become more apparent later, when this program is described in detail.

AIF-NBS Standards Program for the RadioPharmaceutical Industry

The AIF-NBS radioactivity measurements-assurance program evolved in response to a number of

problems facing the commercial suppliers of radionuclides. In 1973, Seidel and Brantley [1] de- scribed some of these problems: lack of standard

reference materials for about 75 percent of the more than 100 radionuclides commercially produced

at that time, the sometimes inconvenient physical

form, and the insufficient activity levels of some of the standards that were available. Another

reason, important economically, was that one company's activity differed from that of another

due to the use of different decay-scheme para- meters. After several pilot distributions begun in 1972, and at the request of two AIF committees,

99
namely the Committee on Radioisotope Production

and Distribution and the Committee on Radiopharmaceuticals, the Atomic Industrial Forum entered into

an agreement with the National Bureau of Standards

in November 1974. The agreement established a re- search-associate program to help satisfy the needs

of the radiopharmaceutical industry and solve the

problems described above. Past and present industry

participants are listed in Table 1. Con- currently, the FDA is provided with similar

services through an interagency agreement.

TABLE I

PARTICIPANTS IN THE AIF-NBS STANDARDS PROGRAM FOR THE RADIOPHARMACEUTICAL INDUSTRY

Food and Drug Administration

Bureau of Drugs

Division of Drug Chemistry

Washington, D. C.

Atomic Industrial Forum Participants

Atomic Energy of Canada, Ltd. Ottawa, Canada

General Electric Company3 Pleasanton, California

Mallinckrodt Nuclear

St. Louis, Missouri

Medi-Physics, Inc. Emeryville, California

New England Nuclear

North Billerica, Massachusetts

E. R. Squibb & Sons, Inc. New Brunswick, New Jersey

Union Carbide Corporation

Tuxedo, New York

Amersham/Searle Corporation'3 Arlington Heights, Illinois

Currently a partial member

''Participation terminated November 1975

The major objectives of the AIF-NBS researchassociate program are to: 1) provide a monthly

distribution of both high-level (multi-millicurie)

and low-level (multi-microcurie) Standard Reference

Materials (SRMs); 2) provide current decay-scheme

data through the Evaluated Nuclear Structure Data

File at the Oak Ridge National Laboratory; and 3) assist participants with any difficulties or problems in the measurement of these SRMs.

The SRMs consist of approximately 5 milliliters of solution in standard NBS borosi 1 icateglass ampoules, except for xenon-133 which is distributed as an uncompressed gas in a pyrex ampoule having a volume of approximately 5 milliliters. The activity ranges are from 1 to 300

mi Hi curies for the high levels and from approx- imately 50 microcuries to 5 millicuries for the

low levels depending on the radionuclide and its half life. A steering committee composed of one representative from each participating company

and NBS, and the AIF-NBS research associate

selects the radionuclides to be distributed each

year. Several radionuclides currently more im- portant in nuclear medicine, such as molybdenum-99

,

technetium-99m, iodine-125, iodine-131, and xenon-133 are distributed yearly and others of lesser im- portance are supplied every other year. Table 2 list those radionuclides which have been issued by NBS through April 1980.

TABLE 2

STANDARD REFERENCE MATERIALS PREPARED FOR THE AIF-NBS STANDARDS PROGRAM

FOR THE RADIOPHARMACEUTICAL INDUSTRY

FROM APRIL 1975 TO APRIL 1930

SRM NO. RADIONUCLIDE

4400-C* 51 Cr

4401 -F 131 J 4402-B 113 Sn-U3mIn 4403-B 85 Sr 4404-C 201 T1 4405-B 198 Au 4406-D 32p

4407-E 125j

4408-B 57 Co 4409-C 7 5Se 4410-E 9 9mj

c 4411 -B 59 Fe 4412-E "Mo

4413 197 Hg

4414-B 123 J 4415-D 133 Xe 4416 67 Ga 4417 ni In 4418 203 H g 4419 169y 5 4420 203pb 4421 195Au 4422 36 C1

*The letter after the SRM number indicates

the number of times the radionuclide has been distributed since the beginning of the program. (B means it has been

distributed twice; C, three times; etc.)

100
The SRMs are usually dispatched as "knowns"

the first time, and as "blinds" subsequently. A questionnaire is included with each blind in order to check the measuring procedures used by each participant. If the reported activity value is greatly different from the NBS value, it is often

possible to ascertain where an error occurred or what caused the discrepancy, by examining the questionnaire. As previously stated, the

"blinds" are used to demonstrate traceability to

NBS within stated limits prescribed by the U.S. Pharmacopeia. Although the particpants have the

option of not receiving the SRMs as blind sources

if they do not produce or market the particular

assessment. Participants have usually submitted a radionuclide that they have had difficulty

measuring in the past; one whose activity value

has been claimed to be incorrect by a customer or another producer; or one that they market but which has not been distributed by NBS for some

time.

Figure 1 shows how the participants'

reported values compared with the NBS-measured ac- tivity values for both the high-level and low-level

samples distributed since the beginning of the program. Twenty-eight of the 429 values used in the histogram are beyond the 10-percent

AIF High and Low Lsvel Rocults for Round* I Through XLIV

All Values Reported As Of 4/23/80

Vcluas Not Shown

1.136

1.151 1.156

1.161

1.241 1.244

1.254

1.281 1.297

1.985 10.119

.880 .890 .900 .910 .920 .930 .940 .950 .960 .970 .960 .990 1.000 1.010 1.020 1.030 1.040 1.050 1.060 1.070 1.080 1.090 1.100

Tnbs X/NBS

radionuclide, many companies elect to receive them

as blinds to test their instrument response or measuring procedures. The first radionuclide

distributed as a part of this program was chromium-51 issued in April 1975. A different SRM

has been distributed almost every month since then,

usually as a blind. The results of the blind distributions, with the exception of those from the

FDA and Amersham/Searl e Corporation, are summarized in Tables 3, 4, and 5 and in Figures 1,

2, and 3. The results are not given in the same order as the listing of companies in Table 1.

Beginning in 1979, two distributions per year

were replaced by two "open" months to allow

participants greater flexibility in their choice

as to what radionuclide they would like to measure. During the open months, each participant submits a calibrated sample of their choice giving the activity, solution composition, and impurity

limit (5 percent for iodine-125) imposed by the

U.S. Pharmacopeia for radiopharmaceuticals. This

is 6.5 percent of the values, a higher percentage

than would be expected if the differences were

strictly random; however, the trend has been to- ward a reduction in the number of outliers. For

example: in 1975 and 1976, there were 6 values

outside the 10-percent limits; in 1977, there were

7; in 1978, 5; in 1979, 4; so far in 1980, none. Some of these outliers occurred when the participants asked for the SRMs as blinds during the

first distribution of that particular radionuclide,

so that the values reported were not based on any previous NBS standard. The negatively skewed

distribution indicates that there is a bias in the results and that the participants tend to measure

less activity in the SRM than is certified by NBS. This bias can be seen even more clearly in Figure 2, where the average results are pre- sented chronologically.

101
In Figure 2 the results are averages presented for the group of AIF participants as a whole,

for each radionuclide distributed each month. Ex- cept in a few cases, the results are lower than the

NBS certified value; one or two large outliers

which are not representative of the group as a whole are usually responsible for results greater

than those of NBS. For example, the difference

between the high-level and low-level results for

tin-113-indium-113m (SRM 4402B) is caused by one

low-level outlier which was almost 100 percent

greater than the NBS value. Figure 2 shows that

there is little difference between the results for

the high-level and the low-level blinds; this

tends to indicate that the differences are due to calibration errors or source-preparation techniques

rather than to problems in making dilutions.

Figure 3 is similar to Figure 2 except that the direction of the deviation from the NBS value

is eliminated by taking the absolute value of the difference before averaging the participants'

values. The results show that the average absolute

deviation from the NBS value has not noticeably

improved with time, and is generally within five

percent. Table 4 shows, however, that there are

FIGURE 2

Average x/NBS by SRM Distribution

All Values Received as of 3/3/80

Note: one low level value in March, 1979 (441 2D) omitted

(high by a factor of 10)

BD 0 CD OOOOt-t-OOO n s n «s t- n r r^to ajcomcoocoooocococDOOoa OC40>C0i-<T^<0OTCMI0Nt-C0 Ot-OOOOOOt-t-Ot-t-OO omoocaoooouiiuujo t>»inooT-c>oi(WTr*-h-o<OiSRM Number

102
FIGURE 3

Average Deviation from NBS by SRM Distribution

All Values Received as of 3/3/80

Note: one low level value In March, 1979 (4412D) omitted

(high by a factor of 10)

0.0 I I I I I I I I I I I

I I I I I I I I

CD N S O IO r (O t- O O O O T- -7- © O Q

QD CO CQ CO 00 coocoooocacocooQ ©OOOOi-t-Ot-i-OC 33333333333?

SRM Number

CO Q CO Q O CO U QUO

3f333§33333333

103
cases where the results have improved with time. The sharp peaks in certain areas of Figure 3 are again usually caused by one or two large outliers

and are not representative of the group as a whole.

Figure 3 shows that the participants usually do slightly better with the high-level blinds.

This could be due to the fact that the high-level

blinds are closer to the usual activity levels measured by most participants. Table 3 illustrates

this trend more clearly.

TABLE 3

AVERAGE DEVIATION FROM NBS VALUE

FOR ROUNDS I THROUGH XLI (Results received as of February 28, 1980)

PARTICIPANT HIGH LEVEL i C\i i i r-

\ # I— i LOW LEVEL

ALL 3.892% 4.616%

(215) (191

A 3.58% 2.81%

(48) (41)

R 3 34% 3 79% 09) 07)

c 7.45% 6.20%

(43) (40)

D 2.91% 3.96%

(32) (32)

E 2.36% 2.53%

(37) (34)

F 1.68% 1.66%

(19) (16)

G 4.06% 19.52%

(17) (ID

*Number of values in average.

The overall deviation for the participants is approximately 4 percent for the high-level blinds

and 4.6 percent for the low-level blinds. The re- sults for individual participants listed by letter

in Table 3 show that some participants do a better

job than others. The order of the participants

in this table is not the same as that in Table 1. The high value for the low-level results of participant G is due to one or two outliers, and to the

small number of results reported to NBS by the

participant. However, these numbers do not show

that the participant's performance has improved

with time, and that the average is still largely

affected by some earlier bad results. Currently, more time is being expended to find and suggest

changes in each participant's measuring procedure

that could give better results. In most cases,

however, suggestions would not be implemented un- less the cost or time spent in making the measurement is similar to that presently being used. Substantial changes in the amount of training re- quired by the personnel making the measurements

would also hinder any changes from taking place.

Tables 4 and 5 give the ratios of each participant's value to that of NBS for individual

radionuclides and show how they have changed with

repeated distributions. Only molybdenum-99 and iodine-131 are tabulated as examples. When more

than one value is shown for a particular company

for a single distribution, it indicates that the participant reported the activity measured in two different ways.

The values in Table 4 show that there has been some improvement with time for molybdenum-99,

and the deviation has leveled off in the past two years so that it is less than 1.5 percent different from the NBS value for the group as a whole. There is no guarantee however that the results in subsequent years will remain as good. The ratios

for iodine-131 in Table 5 illustrate this; the average for the first year is better than those

for the next two years. From this, one could con- clude that any new improvement would have to be the result of a change in the method or technique

used to perform the measurements. For example,

most of the participants determine the activity

by counting sources which are made from a dilution

of the solution in the ampoule. The dilutions in most cases are made by volume using pipets which

are quite often uncalibrated. Improvements could

be made by calibrating the pipets using solutions

which are the same density as the solutions in the

SRMs, by applying volume corrections for changes

in temperature and pressure, or better yet, by

making the dilutions by mass. Most participants,

however, cannot justify the changes that NBS would

suggest, because some of these improvements might

take more time than the methods currently employed.

If they are already within the requirements imposed

by the regulatory agencies, there is no economic in- centive to improve. This is one reason why it is un likely that there will be any significant change in the future unless the regulatory agencies demand an improvement. Secondly, companies that have employees who belong to certain unions must see that the radiation exposure is divided equally

among the personnel performing the measurements.

This results in many different people making the

measurements, which means that relatively simple

procedures must be used. This must not be interpreted, however, to mean that only a minimum of training is necessary. Unfortunately, training is frequently inadequate.

104
TABLE 4

AIF-NBS STANDARDS PROGRAM FOR THE RADIOPHARMACEUTICAL INDUSTRY

INDIVIDUAL RESULTS FOR MOLYBDENUM-99

PARTICIPANTS' REPORTED ACTIVITY VALUES/NBS ACTIVITY VALUE

(X/NBS)

PARTICIPATING

COMPANY 3 SRM

DATE

441 2B

2/77

441 2C

4/78

441 2D

3/79

441 2E

3/80

A H° 0.9355, 0.9394 0.8651, 0.9262 0.9924 0.9730

L 0.9260, 0.9600 0.9354, 0.9833 0.9932 0.9934

B H 0.9946 1.0109 1.0016 1.0256

L 0.9885 0.9981 0.9976 0.9984

C H 0.9485 0.9825, 0.9528 0.9894 0.9690

L 0.9591 0.9673, 0.9540 0.9872 0.9845

D H 0.9448 0.9947 1.0128 0.9930

L 0.9541 0.9927 1.0138 1.0126

E H 0.9609 1.0081 0.9593 1.0061

L 0.9592 0.9716 1.0090

F H 0.9297 0.9838 0.9986 0.9805

L 0.9061 1.0471 10.119

G H 0.9877 0.9842 1.0039 1.0008

L 0.9970 0.9862 0.9927 0.9874

Average X/NBS 0.9557 0.9748 0.9934c 0.9949

Average absolute deviation

from NBS

4.43% 3.29% 1.1 5%c 1.35%

a. The order of the participants does not correspond to that in Table 1. The FDA and Amersham/Searle are not represented in this tabulation.

b. H = High Level. L = Low Level.

c. 10.119 outlier not included.

105
TABLE 5

AIF-NBS STANDARDS PROGRAM FOR THE RADIOPHARMACEUTICAL INDUSTRY INDIVIDUAL RESULTS FOR IODINE-131

PARTICIPANTS' REPORTED ACTIVITY VALUES/NBS ACTIVITY VALUE

(X/NBS)

PARTICIPATING

COMPANY 3 SRM

DATE

440 IB

5/76

440 1C

5/77

4401D

5/78

4401

E

7/79

A H»> 0.9866, 0.9599 0.9798 1.0439 0.9785

L 0.9859, 0.9908 1.0100 0.962b 1.0006

B H 1.0036 0.9586 1.0137 1.0138

L 1.0012 0.9538 0.9964 1.0081

C H 0.9923 1.0290 1.0083 1.0258

L 1.0280 0.9937 1.0081

D H 1.0067 1.0166 1.0094 1.0289

L 1.0145 1.0239 1.0108 1.0297

E H 0.9603, 0.9919 0.9888 1.0319, 0.9337 0.9602

L 0.9760, 0.9637 0.9917 1.0219, 0.9621 0.9836

F H 0.9742 0.9078 1.0013

L 0.5534 0.8767 1.0024

Average X/NBS 0.9872 0.9590

(0.99591c 0.9838 1.0034

Average absolute deviation

from NBS

1.68% 5.89%

(2.37%)c 3.62% 1.64%

a. The order of the participants does not correspond to that in Table 1. The FDA and Amersham/Searle are not represented in this tabulation.

b. H = High Level. L = Low Level.

c. 0.5534 outlier not included.

106
College of American Pathologists Quality

Assurance "Q" Program

The College of American Pathologists quality- assurance program was developed as a result of a survey taken in 1970 by the Nuclear Medicine Subcommittee of the College. Out of 1300 laboratories

responding to a questionnaire, 560 users of radioactive materials were identified, and an interest

in quality assurance was seen.

In the fall of 1970 a pilot study was con- ducted with 25 participants who responded to the questionnaire. NBS was asked to prepare and distribute solution standards of iron-59 and participants were asked to identify and quantify the ra- dionuclide. Fourteen laboratories identified the material correctly, six incorrectly, two said that they were too busy to participate, one had no in- terest, one was unable to identify the peaks and one did not respond. No one reported a cobalt-60

impurity in the sample. Nine of the fourteen

correct identifications were within five percent

of the NBS value. The results of this exercise

showed that identification of the radionuclide

presented a larger problem than the assay of the activity.

In 1972, a new pilot study was performed to determine the accuracy with which a measured quan- tity of radioactivity could be administered to a patient. The purpose of this exercise was to determine how good the participant's laboratory

performance was on a routine basis. Seventy-six

percent of the participants that completed this

study indicated that the procedure used in the

test was indeed routine.

Participating laboratories were asked to in- ject a known activity of approximately 50 microcuries of chromium-51 into a serum bottle (the

"patient") and return the bottle, syringe, and needle to NBS. Data were received from 33 out of

46 participants. Reported activities were based either on dose-calibrator measurements and, or, the value supplied on the vial by the manufacturer.

Eighty-one percent of the reported values were

TABLE 6

OVERVIEW OF THE CAP QUALITY ASSURANCE "Q" PROGRAM

YEAR RADIONUCLIDE SAMPLES

Ui orM 1 UntU

PARTICIPANTS REPORTING

pre 1 II TC

CORRECT

IDENTIFITATTHMC

VALUES WITHIN 10%

Ur NtSo VALUt

- % OF REPORTED

VALUES WITHIN

1 Cio/ nr mdc

lU/o Ur NBb

1972

131

j 50 28 25 20 71%

125 J 56 3R 1

1

i i

1973

57 Co 50 24 23 12 50%

203 Hg 51 27 17 10 37%

1974

75 Se 48 25 21 12 48%

59 Fe 45 22 21 14 64%

1975

60 Co 117 39 27 16 41%

85 Sr 110 38 32 17 45%

1976

75 Se 123 48 46 26 54%

125j 120 43 41 15 35%

1977

133 Xe 83 42 20 48%

201 T1 83 55 28 51%

1978

67 Ga 80 40 30 75%

169 Yb 82 43 24 56%

1979

!11 In

131 j

6368

3842

314082%

95%

107
within twenty percent of the NBS-measured values. Noticeable differences from NBS were seen among participants who used the same type of dose calibrator, and consistently low values were reported

from participants that purchased their material

from one particular supplier. The results ranged

from 0.60 to 1.36 of the NBS-measured values with one extreme of 3.68. Careless arithmetic and re- porting of results or incorrect decay corrections were found in one-third of the reported results.

Eighty-two percent stated that they never checked

for radionuclide impurities and six percent never checked the suppliers' values.

In 1972, as a result of these two studies, the

CAP quality-assurance "Q" program was begun, and continues in much the same form today. Two calibrated radioactivity samples are provided by NBS per year to each subscriber. For the first ten distributions (5 years), the participants were

asked to identify and quantify the unknown radionuclide, but beginning with xenon-133 (distributed

in saline solution) in the spring of 1977, the participants were asked only to quantify the amount of radioactive material present. A summary of these distributions is presented in Table 6.

The data in the table show that a large num- ber of participants do not report results. Some of the explanations for not completing the exercise

after receipt of the material range from "not enough time to measure the sample", to "no setting

on the dose calibrator for the particular radionuclide", to "the ampoule was too big to fit in the Nal(Tl) well crystal". The results in the last three columns indicate that there is much room for

improvement in both identification and quantification of an unknown radionuclide. It is important

to know that the patient receive the correct

material for a specific study, and that the patient

be administered only the amount necessary for that

study. Better training of the personnel, better

equipment, and more careful computation and re- porting skills would all help to improve the

results.

TABLE 7

COLLEGE OF AMERICAN PATHOLOGISTS

1979 RADIONUCLIDE STUDY SERIES Q-B

I0DINE-131

SUMMARY OF ALL PARTICIPANTS nUHDLK miimrfd nrUr PARTICIPANTS

Number of Participants 43

Participants suspecting

radionucl idic impurities* 7

Selenium-75 3 Cobalt-57 2 Iodine-125 2 Cobalt-60 1 Indium-113 1

No photon-emitting impurities were found by

NBS.

*Two participants noted the presence of

xenon-131m which is, however, a decay

product of iodine-131.

TABLE a

!: June 1972

Reported Activity as % Deviation from NBS Valus

Overall Performance <-20

-20 to 15.1•15 to

-10.1

-10 to

-5.1

•5to0

0

to+ 5

+ 5.1 to + 10+ 10.1 to + 15+ 15.1 to + 20 > + 20

No. of Samples

Dispatched

No. of Participants Reporting

50 30* R R r-i

"1 identified sample as Cr

133

1 identified sample as Ba

42.86% of results reported were within 5% of NBS value. 71.43% of results reported were within 10% of NBS value.

108
Table 7 shows some of the results of radionuclidlc-impurity identification for the iodine-131

samples distributed in 1979. Little improvement has occurred in the identification of impurities since

the first pilot study in 1970. In fact, in 1979,

sixteen percent found radionucl idic impurities in the iodine-131 when there were none.

Tables 8 and 9 give a comparison between re- sults for iodine-131 distributed in 1972 and again

in 1979. The overall performance seems to have

improved in the past seven years but this could be

a coincidence as the participants reporting their

"esults in 1979 may not be the same as those re- Dorting in 1972. In the past seven years, however,

;he equipment has most likely improved, and as the

)ld equipment is replaced by the new, results should

improve as well. Whether or not the people who

nade the measurements were better trained in 1979

is a matter of speculation. The results obtained

vith dose calibrator S would tend to indicate that

:he equipment and not the personnel, is in question, but the results of the impurity assesslent would suggest just the opposite. In any case,

improved training of personnel and calibration of

:he dose calibrators would substantially improve

the results. It is probable that the participants

in this program are more aware of the need for

making accurate measurements than the average user

of radiopharmaceuticals due to their interest in participation in the program. Even so, the results

show much room for improvement and one can only

guess as to how well the other 97 percent of

the 3200 [2] or more hospitals with diagnostic

radioisotope facilities can measure a given amount

of radioactive material.

Conclusion

The AIF-NBS Research Associate Program and the

CAP Quality Assurance "Q" Program are beneficial

for those associated with the practice of nuclear

medicine because they provide both hospitals and radiopharmaceutical suppliers with SRMs for the

calibration of their measuring systems, and at the

same time, help them to satisfy the increasing re- gulatory requirements for traceability to the

National Bureau of Standards. However, 85 percent

of the diagnostic procedures performed utilize

technetium-99m-labeled compounds and the measured

dose is usually determined in the hospital's

nuclear-medicine department or nuclear pharmacy.

TABLE 9

I: November 1979

Reported Activity as % Deviation from NBS Value

Overall Performance <-20

20

to

•15.1

•15 to

•10.1

•10 to

•5.1

•5too

0

to+ 5

+ 5.1 to + 10

+ 10.1 to + 15

+ 15.1 to + 20 > + 20

Dose Number of Calibrator Participants

R 30

r—i R m

A

R R

D 5 H r—

i

S 3 H

%of

Participants 2% 14% 62% 19% 2%

76.19% of results reported were within 5% of NBS value. 95.24% of results reported were within 10% of NBS value. 109
The AIF program is limited in this area because

technetium- 99m is not sold in its final prepared

form due to its six-hour half life, but rather

milked from a molybdenum-99-technetium-99m generator

in a hospital laboratory. The CAP "Q" program is limited due to the fact that less than 100 hospitals out of the approximately 3200 hospitals

with diagnostic radioisotope facilities participate

in the program. Also, the radionuclide which is presently of greatest importance in diagnostic

nuclear medicine, tech net ium-99m, has not been

distributed to the CAP participants due to the

cost and the great effort required to supply it to each participant in a short enough time for it to

be useful. In spite of the shortcomings, these pro- grams are important steps toward assuring that the correct dose is given to a patient for a diagnostic

procedure. Because of the AIF-NBS research-associate program, the suppliers of radiopharmaceuticals can give greater assurance to their customers

that the products they sell contain the amount of activity stated on the label, and this helps the

hospital pharmacist provide more accurate doses. The participants in the AIF-NBS Research Associate

Program and the CAP program are helped by being

able to assess their routine measuring techniques

with each blind received from NBS, and are benefited by having a standard to calibrate their in- struments once the activity is disclosed.

From the patient's point of view, to ensure

that the correct dose of a radiopharmaceutical is given, important steps would be (1) improve

training of the personnel in the nuclear-medicine

departments across the country and (2) involve the companies that manufacture dose calibrators in one

of these traceability programs administered by the National Bureau of Standards.

References

C. W. Seidel and J. C. Brantley, "Activities

of Commercial Radionuclide Producers" in Activities and Needs Related to Radioactivity

Standards for Environmental Measurements,

Environmental Protection Agency Rpt. No. EPA-670/4-75-006, 39 (U.S. Printing Office,

Washington, D.C., 1975).

[2] Hospital Statistics, American Hospital Associ

ation Hospital Data Center (1979).

no
THE ROLE OF CALIBRATION STANDARDS IN ENVIRONMENTAL THERMOLUMINESCENCE DOSIMETRY

Thomas F. Gesell and Mary Feild Jones

The University of Texas School of Public Health

P.O. Box 20186

Houston, Texas 77025

and

Gail de Planque

U. S. Department of Energy

Environmental Measurements Laboratory

376 Hudson Street New York, N.Y. 10014

The nature of the environmental radiation field is briefly reviewed and its complexity of composition and energy emphasized. The needs and appropriate standards for environ- mental dosimetry are discussed and calibration procedures are examined. The international environmental dosimeter intercomparison program is reviewed. Data from the intercomparison program are used to show that only a small part of the error associated with environmental TLD measurements is likely to be due to uncertainty in the calibration standard. Other problems of the calibration process are discussed.

(Calibration; dosimetry; environmental; intercomparison; standards; thermoluminescence)

.

Introduction

Penetrating Environmental Radiation

Penetrating environmental radiation arises

from several sources, naturally occurring primordial radionuclides and their daughter products,

cosmogenic radionuclides generated in the atmosphere by cosmic radiation, cosmic radiation itself, and man-made radionuclides and radiation

devices (1) . The primoridal radionuclides and

their daughter products give rise to a complex

penetrating component of the environmental ra- diation field consisting of gamma rays, x-rays

and beta particles. These radiations arise not

only in the rocks and soils but also in the atmosphere because there is transport of naturally

occurring radon isotopes from the soil to the atmosphere. Another major component of penetrating environmental radiation arises from cosmic

rays. Although primary cosmic radiation consists

almost entirely of protons, few of these reach

ground level due to attenuation in the atmosphere. Instead nuclear reactions in the atmosphere produce high energy muons and electrons

which reach ground level. The ground level air

ionization produced by these muons and electrons

is roughly equivalent to that produced by

typical soil concentrations of the primordial

radionuclides. Cosmogenic radionuclides do not

make a significant contribution to penetrating

environmental radiation field. In addition to radiation arising from natural radionuclides

distributed in a natural fashion, there are manmade contributions. These anthropogenic contributions arise from man-made radioisotopes

and devices as well from the re-distribution of

naturally occurring isotopes (2) . Anthropogenic

sources contribute gamma rays , x-rays and beta

particles to the penetrating environmental radiation field.

Measurement of penetrating environmental

radiation is required for a number of reasons which include basic and applied research, regu- latory compliance and health effects studies.

When the requirement is for an integrated measure- ment over a period of time of a few days to a year or so, passive environmental dosimeters,

usually thermoluminescence dosimeters (TLDs) are often employed. These devices are well described in the literature (3, 4) and are widely

employed. While no exact ccunt of the users of

these devices is available, approximately 100 laboratories throughout the world have participated in the series of voluntary environmental

dosimetry intercomparisons conducted over the last several years by the University of Texas School of Public Health and by the U. S. Depart- ment Energy. Environmental TLDs are in universal

use around U.S. nuclear facilities and figured

prominently in the assessment of the population

radiation dose to the residents in the vicinity

of Three Mile Island Nuclear Station (5)

.

Standards for Environmental TLD

The complexity of the radiation fields to which environmental TLDs are exposed as well as the often harsh environmental conditions in which they are used create special problems for

111
their calibration and handling. These special

problems have been addressed in the American

National Standards Institute Standard ANSI N

545-1975, "performance, testing, and procedural

specifications for thermoluminescence dosimetry

(environmental applications > " (6) . This stan- dard has been adopted with minor changes by the

United States Nuclear Regulatory Commission (7) and therefore serves as guidance to the Com- mission's licencees. The ANSI standard specifies (among other things) that the calibration

exposure given to a TLD shall be known to within 5% and that acceptable methods of calibration include comparison with calibrated

equipment or radioactive sources traceable to

the National Bureau of Standards (U.S. A) or similar national institutions in other countries.

The purposes of this paper are to examine

how environmental TLDs are calibrated, the degree of agreement that exists among users of en- vironmental TLDs, the problems of calibration

and the importance of standards in the overall accuracy of environmental TLD measurements. This paper draws heavily on the several international

intercomparisons of environmental dosimeters,

(8,9,10,11) especially the most recent (11) in

addressing these questions.

Calibration of Environmental TLDs

While TLDs in the environment are subject

to a variety of kinds and energies of charged

particles and a rather broad spectrum of photon

energies, calibration is usually performed with

one or at best a few photon sources. Cesium-137,

Cobalt-60 and Radium-226 are specifically mentioned in the ANSI Standard (6) and reported as being used by most of the intercomparison participants. The calibration is usually expressed

in exposure units, Roentgens or more recently

Grays. The environmental measurements on the

other hand cannot be strictly expressed in exposure units because exposure is strictly defined

only for photon radiation. Thus when an environmental measurement is expressed in exposure units

it is understood that the result is equivalent to that obtained from a specified exposure from the

calibration source. Theoretical and some experi- ment evidence indicates that TLD phosphors underrespond to cosmic ray muons (12). The packaging

of typical environmental dosimeters is sufficiently thick to exclude some to all of the

environmental beta particles. Many users however

utilize a package of sufficient thickness to ex- clude all beta particles. This approach has the additional advantage of assuring charged particle

equilibrium for gamma rays during calibration.

In this case, only the photon and cosmic radiations are being measured however.

Another intrinsic problem with TLDs con- cerns energy dependence. While some phosphors

such as those whose major component is LiF and Li. B4O7 are nearly energy independent, the more

sensitive phosphors such as those based on

CaSC>4 and CaF2 exhibit a severe over -response to photon radiation at low energies. Some users compensate for this over-response with an energy

compensating shield or filter. The following

discussion of calibration should be interpreted

with the above limitations in mind.

Basic calibration is effected in one of two

ways. In one technique an NBS traceable instrument

is used to measure the radiation exposure rate in some small volume in a radiation field and a calibration dosimeter substituted for the instrument

for an appropriate length of time to achieve the desired exposure. In another approach an NBS traceable source is arranged with the calibration

dosimeter in an approximation of "free air" geometry. The calibration exposure is then calculated using the known source strength, the gamma

ray constant of the source and the inverse square

law. Within this basic frame-work a variety of

calibration schemes are employed. Some laboratories calibrate each dosimeter individually;

others select batches of dosimeters with similar response and calibrate only a random sample of

the whole batch; others combine these techniques

and perform batch calibrations but use individual

dosimeter correction factors

The International Environmental Dosimeter

Intercomparison Program

Procedures

Much of the information contained in this paper derives from the series of international

intercomparisons of environmental dosimeters so a discussion of them is appropriate. The intercomparisons originated in 1973 with a highly

informal pilot intercomparison at Oak Ridge

National Laboratory involving 12 sets cf dosi- meters from 5 laboratories (13) . The poor results of this informal study were sufficiently

alarming that a more formal study with good control

for radiation exposure acquired in transit was conducted in 1974 (8) . Dubbed the "first international intercomparison of integrating environmental dosimeters" it has been followed by three

others using similar protocols. The fifth intercomparison is to be held in Idaho Falls in 1980. The recent intercomparisons have typically attracted 125 sets of dosimeters from 100 laboratories

located in 25 countries. For each set to be

tested in the intercomparisons, each participant

sends several pairs of dosimeters to the test

location. One pair of dosimeters is designated

as "control", one pair is designated as "field"

and the third and sometimes fourth pairs are designated as "laboratory". Upon receipt at the test site the dosimeters are stored in a low

background radiation shield until the beginning

of the field test period. At the beginning of

the field test period the "field" dosimeters are removed from the storage shield and deployed in close physical proximity in an environmental

radiation field. Both natural (first, second,

fourth intercomparisons) and artificially en- hanced (pilot, third intercomparisons) fields have

been employed. Usually a field test period of

three months is used but shorter times have occ- asionally been employed. Except for the pilot

study, high pressure ionization chambers have

been operated at the field site for the entire

duration of the field exposures to give an independent assessment of the field exposure. Approximately half way through the field period,

112
the "laboratory" dosimeters are removed and ex- posed to a known but unrevealed quantity of gamma

radiation. Cobalt-60, Cesium-137 and Radium-226

have been employed in the several intercomparisons

.

In the fourth intercomparison, two laboratory

pairs of dosimeters were solicited from the participants . One set was given a "low" exposure

on the order of a typical field period

exposure to natural radiation; the other pair

was given a "high" exposure approximately four

times the "low" exposure. In all but the pilot

study, control dosimeters were used to isolate

the actual laboratory and field exposures from

the exposures acquired in transit and storage

.

The control dosimeters also allowed estimation

of the transit exposures. The results of the

intercomparisons have been analyzed statistically

and a number of factors contributing to random

and systematic errors identified.

Selected Results of the Intercomparisons

30

as

^ 20

I 15

• LABORATORY

* FIELD

4

\ INTERCOMPARISON _ i y

1 HOUSTON 1974 2 NEW YORK 1976

: 2 \ 3 OAK RI06E 1977 — z\ 43

I*** •—

4 HOUSTON 1979

4

i i 1 1 1

3

1 1 1 1 1 10 20 30 40 50 60 70 EXPOSURE (mR)

80 90 100

Figure 2. Relationship between percent

standard deviation and delivered exposure

for all tests in four intercomparisons

.

The general results of the fourth intercomparison are shown in figure 1. The estimated

delivered laboratory and field exposures are

shown for comparison. Two levels of laboratory

exposure were used to help determine if pre- viously observed differences in dispersion of

the results could be related to exposure level,

to differences between laboratory and field

conditions or to improved performance. These

data on dispersion are combined with data from

the previous intercomparisons, and presented

in figure 2. These results strongly suggest

that the dispersion is related to the exposure

level. The only point not lying on the smooth

curve is the value for the field exposure during

the third (Oak Ridge) intercomparison. This

particular field exposure involved an artifically enhanced source with a large low energy- scattered radiation component causing unusual

response problems.

The Importance of the Calibration Source

In Environmental TLD Measurements

The importance of the accuracy of the calibration source in environmental TLD can be illustrated using data from the fourth intercomparison (11) . Figure 3 shows the degradation of estimated accuracy from the standard itself to the

field measurement. The uppermost histogram is the hypothetical distribution of accuracies of laboratory standards available to participants. For purposes of illustration it is assumed that all users could have a laboratory standard with an accuracy of 2%. This could be either a calibrated source or a calibrated instrument. The next lower histogram is the distribution of

overall calibration accuracy estimated by participants (participants were asked to estimate

accuracy as two standard deviations) . This distribution is clearly much broader and reflects

additional uncertainties in the calibration process beyond the uncertainty of the source. These

113
additional uncertainties are introduced by

errors of positioning of the calibration

dosimeters, timing of the exposure, and, especially with calibrated sources, errors associated

with scattered radiation. The lower three histograms represent the distribution of estimated accuracy reported by the participants for the

"high" laboratory test, the "low" laboratory

test, and the field test (participants were

again asked to estimate accuracy as two standard

deviations) . Those distributions are in turn broader than the distribution of accuracy

of calibration. The additional breadth results

from known additional sources of measurement

error such as random variation of dosimeter

response, energy dependence, directional dependence, signal fading, and self irradiation (14) as well as the additional error introduced by

the requirement for subtracting transit exposures.

> z

HYPOTHETICAL DISTRIBUTION OF THE ACCURACY OF LABORATORY STANDARDS AVAILABLE TO PARTICIPANTS

>

ui3oUJ 20 AC

>-O

z »

DISTRIBUTION OF THE OVERALL ACCURACY OF

CALIBRATION REPORTED BY PARTICIPANTS

DISTRIBUTION OF THE OVERALL ACCURACY OF MEASUREMENT REPORTED BY PARTICIPANTS FOR THE

"HIGH" LABORATORY TEST

D=EL 10 2030 4050 60 70 80 90 DISTRIBUTION OF THE OVERALL ACCURACY OF MEASUREMENT REPORTED BY PARTICIPANTS FOR THE "LOW" LABORATORY TEST

DISTRIBUTION OF THE OVERALL ACCURACY OF MEASUREMENT REPORTED BY PARTICIPANTS FOR THE FIELD TEST

PERCENT

Figure 3. Frequency distributions showing

the hypothetical distribution of accuracy of

laboratory standards available to environmental TLD users, the distribution of reported overall calibration accuracies and the distributions of reported overall accuracies

of measurement for the three tests carried

out in the fourth intercomparison.

It should be stressed that figure 3 discussed above consists of a hypothetical distribution of laboratory standard accuracies

plus distributions of estimated accuracies re- ported by environmental TLD users. At this point

we can turn to actual performance in the intercomparison tests. Figure 4 illustrates the

absolute percent difference between participants '

3 20 O

LABORATORY TEST- HIGH"

QZtZL

>-o

z

ui3 » O

,0 2030 4090 00708090

LABORATORY TEST ' LOW"

0=. r~r—r~i m ,—,

10 20 30 5> soin 60fin 537n anso oneo

5' *' 3m»ioo

FIELD TEST

anf—nan 'lh* m_inn ABSOLUTE PERCENT DIFFERENCE BETWEEN

PARTICIPANT S RESULT AND THE DELIVERED EXPOSURE

Figure 4. Frequency distributions showing

actual deviations ( in %) of the participants' results from the delivered exposures for the three tests carried out in the fourth intercomparison.

results and the estimated delivered exposure for all three tests . Performance is seen to be better

for a the "high" laboratory test than for either

the "low" laboratory of "field" tests. This performance is in general consistant with the estimated accuracies shown in figure 3.

Figure 5 examines more directly the ability

of users to estimate the error of their laboratory and field measurements. The quantity

displayed on the abcissa is the error estimated by the participants ( in %) subtraced

from the actual difference ( in %) between

the participants' results and the estimated delivered exposure. Positive results occur when

the actual error exceeds the estimated error. These cases of underestimating of error are shaded for emphasis. Approximately 30 percent

of the participants' results differed from the delivered exposure by more than their estimated

error. The estimated accuracy of the delivered

exposures was 10%.

The uncertainties estimated by environmental

TLD users (figure 3) as well as the deviations

from the delivered exposures (figure 4) are much

larger than the estimated uncertainties of

currently available laboratory standards traceable to the National Bureau of Standards or equivalent standards groups in other countries

114
LABORATORY TEST-"HIGH"

«> -80 -40 -20 0 20 40 80 80

j—

|—I LABORATORY TEST "LOW"

: 100 -100 -80 -80 -to X 0 20 40 00 80 100

FIELD TEST

= 100 -100 -80 -80 u-40 -20 0 20 40 BO 80 >100 DIFFERENCE BETWEEN ACTUAL ERROR (%) AND

ESTIMATED ERROR (X)

Figure 5. Frequency distributions of the differences between the errors estimated by the participants ( in %) and the actual deviations

of the participants 'results from the delivered

exposures ( in %) . The positive (shaded)

results represent cases in which the deviation from the delivered exposure was greater

than the error estimated by the participant.

Furthermore many users are apparently underestimating their overall uncertainties (figure

5) . It thus appears that little would be gained

by improving the 1-2% accuracy already available

in the calibration standards.

There are however several problems associated with calibration which have been elucidated

by the intercomparison program, but which are

not necessarily connected directly with the accuracy of the calibration source. When the

data for the second intercomparison (9) was

analyzed it was noted that the standard deviation of the results of participants who calculated their calibration exposures from known

source strengths was larger by a factor of two than the standard deviation of the results of

participants who measured their calibration exposures directly. It was believed that

this additional error may be due to unaccounted

-for room scattering, air attenuation and effects

of the source capsule or support. This effect

was somewhat diminished in the subsequent intercomparisonsf but still persisted.

Another calibration problem which has persisted through the four international intercomparisons is the systematic difference in results among uses of the three most common calibration isotopes. Users of Cobalfc-60 calibration sources typically exhibit average laboratory test results a few percent higher

than those using Cesium--137. Users of Radium-226

calibration sources exhibit average laboratory

test results a few percent lower than either

Cobalt-60 or Cesium-137 users. No satisfactory

explanation has been found for these differences.

Conclusions

At the present time the collective errors associated with making environmental TLD measure- ments are much larger than the error associated

with laboratory standards traceable to the National Bureau of Standards or equivalent stan- dards groups in other countries . It would

therefore seem that the standard sources and

standardized instruments available to the users

are of sufficient accuracy in view of the state

of the art. Use of standard sources rather

than standardized instruments can lead to additional calibration errors due to uncertainties in scatter, attenuation and source holder

effects . While environmental TLD users will

nearly always wish to use a locally available

calibration facility for routine operations, it may be desirable to have a service similar to that provided by the international program available to users at their convenience rather than

at the fixed and rather infrequent intervals

presently available. This service could con- ceivably be provided by the National Bureau of

Standards, another government agency or a contractor. This scheme could allow users to test the effectiveness of their own calibration

systems at reasonable expenditure of time and money

References

(1) National Background Radiation in the United

States, National Council on Radiation

Protection and Measurements Report NCRP 45,

Washington, D.C. (1975)

(2) The Technologically Enhanced Natural Radiation Environment, T. F. Gesell and

H. M Prichard, Health Physics 28 361-366

(1957),

(3) Thermoluminescent Dosimetry , J. R. Cameron,

N. Suntharalingam, and G. N. Kenney,

The University of Wisconson, Press, Madison,

Wisconson (1968) .

(4) Solid State Dosimetry, K. Becker, CRC

press, Cleveland, Ohio (1973).

(5) Staff Reports to the Presidents Commission

on the Accident at Three Mile Island; Reports of the Public Health and Safety

Task Force, ed. Jacob I. Fabricant, Sup. Doc. Washington, D.C. (1979)

(6) Performance, testing and procedural specifications for thermoluminescence dosimetry

(environmental applications), ANSI N 545-1975.

115
American National Standards Institute,

1430 Broadway, New York (1975)

(7) Performance, testing and procedural specifications for thermoluminescence dosimetry; environmental applications, U.S. Nuclear Regulatory Commission, Regulatory

Guide 4.13, Washington, D.C. (1976).

(8) An International Intercomparison of Environmental Dosimeters, Thomas F. Gesell, Gail

de Planque Burke and Klaus Becker, Health

Physics 30, p. 125-133 (1976)

(9) Second International Intercomparison of

Environmental Dosimeters, Gail de Planque

and Thomas F. Gesell, Health Physics 36 p. 221-233 (1979)

(10) Third International Intercomparison of

Environmental Dosimeters under Field and

Laboratory Conditions, T. F. Gesell,

R. B. Gammage and G. de Planque, Presented

to the 23rd Annual Meeting of the Health

Physics Society, Minneapolis, Minnesota,

18-23 June, 1978 Abstract: Health Physics

35, p. 909-910 (1978)

(11) Highlights of the Fourth International

Intercomparison of Environmental Dosimeters

under field and laboratory conditions,

Thomas F. Gesell and Gail de Planque,

Nuclear Instruments and Methods (in press)

(12) The Response of LiF Thermoluminescence

Dosimeters to Natural Environmental

Radiation, Wayne M. Lowder and Gail de Planque, Energy Research and Develop- ment Agency Report HASL-313 New York, N.Y.

(1977)

(13) Tenth Dosimetry Intercomparison, H. W. Dickson, F. F. Haywood and K. Becker,

Oak Ridge National Laboratory Report

#ORNL-TM-4566, Oak Ridge, Tennessee

(1975)

(14) Error Analysis of Environmental Radiation Measurements made with Integrating

Detectors, Gail de Planque Burke and

Thomas F. Gesell, Proceedings of the

Symposium on measurements for the safe use of radiation, ed. S.P. Fivozinsky,

National Bureau of Standards Special

Publication 456, p. 187-198 (1976)

116
THE NATIONAL BUREAU OF STANDARDS

LOW-LEVEL RADIOACTIVITY-MEASUREMENTS PROGRAM

K. G. W. Inn

J. R. Noyce

National Bureau of Standards

Washington, D.C. 20234

The National Bureau of Standards low-level radioactivity measurements

program is oriented towards the production of reference materials for environmental radioactivity measurements needs. These reference

materials are used 1) for calibration of instruments, and 2) as test sources for analytical procedure evaluation. These endeavors are designed to provide the nation with a means of assessing the quality

of environmental radioactivity measurements and relating them to

national and international radioactivity standards. The present status

of these efforts is discussed along with possible future plans.

(Calibration, environment, natural material, radioactivity, radionuclide,

standard, traceabil ity)

Introduction

The need for environmental radiological

studies has been and will continue to be of great importance to the public. The protection of the puDlic from excessive exposure to radiation and basic scientific understanding

of the environment are the two primary reasons

for these studies. Some of the programs that

are concerned with environmental radiological

studies are listed in Table 1. Regulatory

requirements have been established for public

safety and require radiation monitoring around

nuclear-power plants, uranium mines, nuclearfuel manufacturing plants, nuclear-waste repositories, as well as the air we breath, the water

we drink, and the food we eat. Basic scientific

environmental investigations, on the other hand,

use radioactive tracers as a sensitive means for studying the environment. Careful radiometric measurements have aided in transport studies of the atmosphere, oceans, and the lithosphere, dating studies as well as cosmological and biological studies. The objective of the low-level ra- dioactivity-measurements program at the National Bureau of Standards (NBS) is to produce reference

materials suitable for environmental radioactivity-measurements needs. These materials are used for 1) calibration of instruments and 2) as test sources for analytical -procedure evaluation. In this paper the status and requirements

regarding reference materials and test samples

needed in traceability programs will be discussed.

Table 1

General categories of low-level radioactivity measurements with examples.

Public Safety :

Routine monitoring:

Radioactive waste studies:

Coal-burning power plants, uranium mines, uranium

mills, nuclear-power plants, Clean Water Act, Clean

Air Act.

High-level contaminated sites, nuclear-waste repositories, uranium-mill tailings and slag.

Scientific Knowledge :

Transport studies:

Dating studies:

Cosmological studies:

Meteorology, oceanography, water resources.

Archeology, geology, cosmology.

Lunar samples, polar ice, deep-sea sediments, meteorites.
Radioactive Standard Reference Materials

The selection of radioactive Standard Refer- ence Materials (SRM) to be produced has been, to

a large degree, influenced by requests from agen- cies such as the Environmental Protection Agency

(EPA) and the Nuclear Regulatory Commission

(NRC), reports from knowledgeable groups such as the International Committee for Radiological Me- trology (ICRM), NBS questionnaires, evaluation

of regulations and surveys of the literature.

Table 2 lists some of the users of the resulting

NBS SRMs.

Presently, approximately seventy radioactive

SRMs of nearly forty radionuclides are available

from NBS [1], many of which are useful for environmentally related work [2]„ .Table 3 includes

the various types of SRMs produced by the Radioactivity Group at NBS. These sources come in various forms namely as liquids, point sources, gases and solids. Most of these SRMs are used to calibrate instruments for detection efficiencies while

some are used to monitor the stability of instrumental response [3], These SRMs also play an im- portant role in traceability considerations.

Table 2

NBS standards users and examples.

Operating nuclear-power stations

Preoperational nuclear-power stations

Research reactors Major nuclear facilities:

Nevada Test Site

Idaho National Engineering Laboratory

Richland, Washington

Oak Ridge National Laboratory

Savannah River Plant

Rocky Flats Plant

Mound Laboratory

Paducah, Kentucky

Cimarron, Oklahoma

Federal Agencies:

Environmental Protection Agency

Nuclear Regulatory Commission

Department of Energy

States with active environmental

surveillance programs: New York, Pennsylvania, South Carolina

University based research projects:

Berkeley

Miami

Arkansas

Institutions:

Woods Hole Oceanographic Institution

Scripps Oceanographic Institution

Battelle NW

Environmental radiation consulting firms:

Radiation Management Corporation

Nuclear Environmental Services

United States Testing Company

Westinghouse NES

Cities, counties, other sub-state govern- mental bodies: New York City

Table 3

Types of National Bureau of Standards radioactivity Standard Reference Materials and examples.

Source Type

alpha-particle,

solution

beta-particle,

solution

photon-emitting,

solution

Examples

239 PUj 242 Pu

3 H, 14 C, 63Ni,

5*Mn, 60 Co 109 cd 137^.137*1^ 226^ a

alpha-particle, point 148Gd, 238Pu, 241 Am

55 Fe 85Kr 133 Ba 139 Ce> 152 Eu

beta-particle, photon- 3 H, 3 '7 Ar. 3 ^Ar. emitting, gas 85 Kr, 13lmXe, * 33Xe

photon-emitting,

point

sol id River Sediment

Measurements Traceability

In environmental measurements, one is inter- ested in establishing the ability to make consistently accurate assays. That is to say, the goal

is to establish a consistently accurate analytical scheme which begins with the collection of

samples and continues until the data are finally

reported. Measurements-traceabi 1 ity programs for

environmental radioactivity provide a basis by

which laboratory measurements can be related to

national radioactivity standards. Through a trace- ability program, data quality can be assessed,

and a firm foundation for policy decision and scientific discussion can be established. In many

cases traceability may be recommended or required

under regulations, agreements, regulatory guides,

licensing, or recommended practices. One can visualize a three-phase traceability scheme which

would test:

118
1) Instrument calibration

2) Radiochemical procedures

3) Sampling, preparation, and storage methods.

The first phase of traceabil ity is concerned

with the accuracy of instrumental response.

The second phase of traceabil ity evaluates

radiochemical procedures for significant

chemical biases. And finally, the third

phase provides some assurance that a laboratory is able to collect and prepare samples

for assay, and store them without affecting

their integrity.

Calibrations of Instruments

The first phase, instrumental traceability, is propagated through the Traceability System [4,5,6,7,8,9] shown in Figure

1. NBS maintains traceability internationally

through interaction with the International

Bureau of Weights and Measures, the International Atomic Energy Agency and other na- tional laboratories. Domestically, NBS establishes instrumental traceability to Quality

Assurance (QA) laboratories through Measure- ments-Assurance Programs [10,11,12,13]. Some

of the SRMs produced by the Radioactivity

Group at NBS are used in these programs as test samples, of undisclosed value, to establish the traceability link between NBS and QA organizations.

The Environmental Protection Agency (EPA)

is responsible for radiological monitoring of the environment outside nuclear-fuel-cycle

facilities. To assist in the accomplishment of EPA's mission, the EPA-NBS traceability program

consists of both implicit and explicit [14] trace- ability measurements for alpha- and beta-particle

and gamma-ray-emitting nuclides. Tests on twentyeight radionuclides have been made so far, and EPA's performance demonstrates its instrumental

traceability to NBS for these radionuclides (Figure 2). Because it has been able to assay a va- riety of radionuclides accurately, it has developed a reputation for consistent and competent

activity-concentration measurements. Nuclides

which may be added to its list of traceable nu- clides by the end of 1980 are 46 Sc, 57 Co, and 125 Sb .

In addition to EPA's traceability program,

a Radiological Pollutant Quality Assurance Pro- gram was established in 1975 to provide NBS ref- erence materials for radionuclides released to the environment by coal-burning and nuclear power

plants. The sources, produced in quantity for EPA's distribution as calibrated materials [15]

or as test samples in their Environmental Radioactivity Laboratory Intercomparison Studies Program (cross-check program) [16], are listed in Table 4. When used in EPA's cross-check program, these materials provide traceability to the user

level for nuclides that have not been included in the formal traceability program between NBS and

EPA. Several of the calibrated radioactivity

sources in this list are environmental matrix

materials. A more complete discussion on the

natural material sources follows in the next section.

INTERNATIONAL AND NATIONAL RADIOACTIVITY

MEASUREMENTS "TRACEABILITY TREE"

BIPM

IAEA

DOE NRC EPA

I 1 i

HHS

(fda'.brh) *

DOD AIF CAP

1 I

ETC

1

STATES, UNIVERSITIES, HOSPITALS, GOVERNMENT AGENCIES, INDUSTRIAL GROUPS AND OTHERS

INTERNATIONAL

ETC NATIONAL

LABORATORIES

QUALITY CONTROL AND

REGULATORY BODIES

USERS

Figure 1

119
Table 4

Radioactivity-calibrated materials pre- pared by the National Bureau of Standards

for the Environmental Protection Agency

under the Radiological Pollutant Quality Assurance Program (1976-1980).

Solutions:

210Po

232Th

239Pu

241 Pu Mixed Radionuclide Solutions:

Mixed gamma-ray emitting ("Cr.

Natural uranium ( 234U, 235U, 238U)

and ?38iU)

Solids: Mancos Shale ( 226Ra and 228Ra)

Pttery Clay («7n 88Y> 113cn 13mIn> 137 Cs.137mBa> and 139cCe)

Fly Ash from coal combustion

( 22gRa and 228Ra)

The responsibility of the NRC is to moni- tor nuclear-fuel -cycle facilities, and its traceability program with NBS is implemented

through the Radiological and Environmental

Sciences Laboratory (RESL) at Idaho Falls.

Since the program was established in 1974, cal- ibrated sources of forty-six radionuclides have

been commonly measured by NBS and RESL and the

results of the measurements are shown in Figure

3. RESL has demonstrated throughout the program

a high level of instrumental reproducibility and stability, and operator competence for a broad

range of alpha-, beta-particle, and photon-emitting nuclides, some of the radionuclides being

assayed more than once. Scandium-46, l 33Xe, 228Tn .208Tlj and 240Pu are i nc i uded in the RESL traceability program for 1980.

Another program in the national traceability

effort was established by agreement between EPA

and NRC. The NRC Regulatory Guide 4.15 [17]

requires the nuclear-power plants in the United

States to participate in interlaboratory comparison programs, such as the EPA cross-check program

for environmental samples [16], to establish

links to the national traceability program [18]. To evaluate the level of analytical performance

of the power plants, EPA has agreed to develop

a number of test samples for the NRC. Calibrated

samples of radionuclides such as ,1, natural uranium, 210Pb, 210Po, 226Ra, and 230Th in air,

food and water are desired. NBS may prepare some

of these standards to help implement the EPA-NRC

agreement.

The College of American Pathologists (CAP) and the Atomic Industrial Forum (AIF) also have

traceability programs with NBS. These programs

have previously been discussed by Golas [19], and

will not be addressed here.

0.90 0.92 0.94 0.96 0.9S 1.00 1.02 1.04 tPA VAlUt

NBS VALUE

1.06 1.08 1.10 1.12

Figure 2 Results of the EPA-NBS Radioactivity-Measurements Traceability Program from its inception through March, 1980.

120
Sr- Nisi) c*3

IIOm 9©

SrAm241

iX'g. 2©C

Am241

Am

243

Zn- Co- os -IS 1 1 0.90 0.92 0.94 0.96 0.98 1.00 1.02 1.04 1.06 1.08 1.10 1.12 1.14 RES1 VALUE NBS VALUE

Figure 3 Results of the RESL-NBS Radioactivity Measurements Traceability Program from its inception through March, 1980.

NBS provides two additional services that

are designed to provide implicit instrumental

traceability to interested parties. First, SRMs

can be obtained by customers, for a small extra

fee, as "blind" test sources. These "blinds"

are issued without disclosure of their certified emission-rate or activity-concentration

values. The purchaser measures one or other of these quantities and reports his value to NBS,

which then issues a Report of Measurement

giving the certified value, the purchaser's

value, and the percentage difference from the certified value. By using the "blinds" the purchaser can test the performance of his in- strumentation, but not necessarily his radioanalytical techniques.

NBS also provides traceability services

for a large number of radionuclides submitted

by the customer. Sources must be submitted in forms which meet certain criteria for chemical

composition, geometry, and activity. The cus- tomer provides his measured value for the cal- ibration of the emission rate or activity con- centration. After NBS completes the calibration of the source, the supplier receives a Report of Calibration which states the certified emission rate or activity concentration

of the source, the customer's value, the per- centage difference, the uncertainties in the

NBS assay, and the methods and nuclear param- eters used.

In addition, NBS provides an explicit trace- ability mechanism to other laboratories, that produce and distribute radioactivity standards,

through their submission of a few samples of each

batch to NBS for corroborative measurement. In the past NBS produced SRMs which contained a mixture of nine photon-emitting radionuclides:

"Co, 60 Co , 85Sr , 88Y> 109 Cd> 113 Sn> 137 Cs> l-^Ce, an(j 203^. jn

-j s mixture was provided in the forms of point sources and as solutions in

5-, 50-, and 450-ml containers. These SRMs have found wide application in calibrating detectors

for gamma-ray spectrometry [20,21], Recently,

similar standards or reference sources have been

distributed by the Amersham Corporation and Analytics, Incorporated. Whenever these companies

have produced a set of such standards, they have

sent several randomly selected samples from the

set to NBS for confirmation of emission rates per gram at 10 or 11 gamma-ray energies. The explicit traceability mechanism, therefore, provides

for the continual availability of mixed gamma- ray-emitting reference sources that are traceable

to NBS.

NBS is presently working on another mixed

gamma-ray-emitting reference source consisting of the relatively long-lived radionuclides l^Sb

(t 1/2= 2.77 Y*), l%u (t 1/2 = 8.6 Y), and

* One mean tropical year equals 365.2422 days.

121
1"eu (ti/2 ~ 4.69 Y). The new mixture will provide more gamma-ray photopeaks in the lower- energy region than the earlier mixture and a longer usable life.

Tests of Radiochemical Procedures

The second phase of environmental tracea- bility is implemented through calibrated test samples containing specific radioanalytical

problems. These test samples fall into two

general catagories: 1) SRM solutions with par- ticular chemical challenges and 2) NaturalMatrix Standards (NMSs) which present peculiar

matrix problems. Several test samples with

chemical and other interferences have been distributed in the past by NBS and are listed in Table 5.

Table 5

Test sources with interferences.

losses of material during dry ashing. Losses

of material may be the result of selective

volatilization, co-precipitation, or even diffusion into the container wall. Hamilton et al

[27] observed selective volatilization of As in spiked serum. When the serum was spiked i n vitro , 28% of the As volatilized during ashing, but when

the serum was spiked in vivo , as much as 86% of

the As volatilized. This showed that metabolized

As was considerably more volatile than As added

as a yield monitor. Thus, if a tracer is added

in vitro as a radiochemical yield monitor for As determination in serum, chemical equilibration

between the sample and the tracer would not be achieved during ashing, thereby resulting in un- reliable data.

Accordingly, reference materials closer in composition to environmental samples should pro- vide more rigorous tests of analytical systems.

Natural-Matrix Standards (NMSs) serve as test

samples for environmental radiochemical assays.

An NMS has been defined by Noyce [28] as

Assayed

radionucl ides 89 Sr, solution

90Sr.90Y> solution

232jh, solution

Natural uranium,

solution

Mixed photon-emitting

spiked pottery clay

Interferences

90 Sr, Ca2+

133Ba, Ca2+

230-rh

234

y> 235y 238u

(interfere with

each other)

Matrix

Although these test sources with interferences present considerable challenges to the

analyst's skill, they are relatively "clean" samples. Environmental samples, on the other

hand, are very complex materials and contain an abundant store of insidious difficulties. Some

of the obstacles facing the analyst are: in- terfering ions [22], chelating ligands [22],

grain size of the host matrix, organic decomposition [23], mineralogical variability, radionuclide volatility [23,24], contamination of the samples [22,25], density variability, varying chemical species and valence states of the

nuclides [e.g., 26], and the variability of the radionuclide distribution in the matrix.

Particularly important is the attainment

of equilibrium between the radionuclides in the

matrix and the tracers and carriers being used

as radiochemical yield monitors. Without this

condition, quantitative assays of the radionuclides will be forfeited before the analyst has had the opportunity to work the sample. Gorsuch

[23], for example, warned against selective

... a solid, liquid, or gas found in or closely derived from nature. It is homogeneous and contains one or more

radionuclides, present from environmental processes or by addition in the laboratory, whose concentrations have

been rigorously assayed and certified...

For those materials in which the radionuclides

were introduced into the matrix by environmental processes we further designate here as Environmentally Quasi-equilibrated Materials (EQMs)

while those materials in which the radionuclides

were introduced by delibrate addition in the lab- oratory we call Spiked Materials (SMs). The NMSs

can be used to develop new wet-chemical procedures, to evaluate chemical procedures already in use, calibrate instruments, act as materials for

interlaboratory comparisons, test the competence of technicians to do chemical assays, and demonstrate

that data outputs are reliable [28].

To date, NBS has produced four NMSs: the River Sediment, Mancos Shale, Pottery Clay, and

Fly Ash from coal combustion (from Tables 3 and

4). SRM 4350, the River Sediment, is an example

of an EQM. The radionuclides certified by NBS include the alpha-particle emitters 239p., p] us 2^0p U) the pure beta-particle emitters ^Sr and

9j?Y, and^the ganma-ray^ emittersJ^Jk, 54Mn, 60 _ gamma-ray £_... Co, 137 r , r52 E(Jj 154 E u, and 228 Zn, Ac [29]. 1J/ Cs,

The Mancos Shale and Fly Ash are also EQMs,

and both are certified for 226p a ancj 228p a rac(i 0_ activity concentrations.

An example of a calibrated Spiked Material is the Pottery Clay mixed-gamma-ray emission-rate stan- dard. In this case, the material was quantitatively spiked with calibrated solutions of five radionuclides ( 65 Zn, 88Y, 113 Sn, 13 7r,s, and l39ce).

122
There has been some discussion about which

type of NMS is preferable for presenting ra- dioanalytical problems. Some of the factors

affecting the suitability of EQMs and SMs will now be addressed.

When using NMSs, it is important to keep

in mind the mechanism of nuclide addition to the material [29,30,31,32,33]. For EQMs, it is presumed that if the radionuclides have been in the environment for some time, natural pro- cesses would have brought them into chemical

equilibrium. Strontium-90 and cesium-137, for example, require only a relatively short time

to reach an equilibrium state in the environment. Many radionuclides, however, require

long periods of exposure to the environment to attain chemical equilibrium. Plutonium dioxide,

for example, is highly resistant to weathering

and is likely to require extremely long exposure times before it could be considered equilibrated with the environment.

Other problems concerned with the production of EQMs are that the desired matrix material may be limited in quantity, the activity

levels may not be suitable, there is no prior

knowledge of the concentration of the radionuclides, and because of the low radioactivityconcentrations the possibility of confirmation

by independent methods is limited.

The SMs, in principle, have considerably

greater flexibility than EQMs. There is control over the concentration and composition of the radionuclides being added (particularly

useful for short-lived radionuclides), known

analytical problems can be "built into" the

material, and the cost may be lower because the calibration and characterization of the material may require less effort.

Does the chemical form of the radionuclides in an environmental sample significantly

affect the assay? Herein lies a presumed limi- tation of SMs as test samples which are to be subjected to destructive analysis. In most

cases it is probable that spiking results in chemical species which do not correspond to those found in the environment. Furthermore,

since environmental speciation of the radionuclides are often not well known or characterized, duplication of the chemical forms of the radionuclides in environmental samples by

spiking may not be possible. Thus, the spiked

radionuclides may not behave in the same way

during radiochemical analysis as those nuclides

which were incorporated by natural processes.

For some purposes, chemical equivalence is of no consequence. For example, if the material is to be assayed by Nal(Tl)- or Ge(Li)-

detector spectrometry, the chemical speciation

of the radionuclides does not significantly af- fect the quality of the assay. However, if selective chemical leaching is the method of choice,

it is important that the radionuclide of interest

be as close to its environmental state as pos- sible to justify the validity of the assay. Even with these limitations on EQMs and SMs, we feel that NMSs will still serve as valid test samples

for many environmental -radioassay methods.

The calibrated River Sediment, Fly Ash, Mancos Shale, and Pottery Clay, of course, cannot cover all the existing needs for environmentalradioactivity-reference materials. Other NMSs

are also needed. The Low-Level Techniques Working Group of the ICRM is comprised of representatives from a number of national and international

metrology and standards laboratories. The Working Group held an international symposium in Paris, in 1976, to identify problems in low-level radioactivity measurements [34,35], 11977, an- other conference was convened at Woods Hole Ocean- ographic Institution (WHOI). The needs for NMSs

and assignment of priorities for their production were the topics of this meeting. The list of highpriority materials as human organs, foods, water,

sediments, soils, and air particulates. These

materials are to be calibrated for activation and fission products as well as a number of natural radionuclides, and alpha-particle emitters when

found to be present.

One of the more important considerations was

that these materials provide a long-term comparison base for measurement quality-assurance pro- grams. Consequently, quantities of materials of the order of several-hundred kilograms are needed. The production of such large quantities of calibrated materials by individual QA laboratories

would have been nearly impossible not only be- cause the requirements for manpower, time, and calibration equipment would be prohibitive, but also specialized materials-handling equipment

and expertise would also be needed. NBS, therefore, has undertaken the responsibility for pro- ducing some of the requested NMSs with the coop- eration of other domestic and national laboratories.

From the initial list of requested materials

in Table 6, seven materials were selected to be produced first. These materials are listed in Table 7, along with their production progress [36].

The Human Lung and Liver are plutonium-contaminated tissue. The Rocky Flats Soils - East and West - are low-calcium soils with moderate levels

of plutonium. The Columbia River Sediment is a fresh water, low-calcium river sediment containing activation and fission products and alphaparticle emitters at low concentrations. Gyttja

is a freshwater-lake sediment of high-organic

content that contains moderate levels of activation and fission products. And, the Peruvian

Soil will represent a background "blank" because

it is expected to be nearly free of fallout

radionuclides. All of the collecting, milling,

bottling, and homogeneity measurements

123
Table 6

Calibrated materials needed for environmental

radioactivity measurements.

Matrix

Soil:

High Ca

Low Ca

Sediments:

High Ca

Low Ca

Mill

tailings

Water:

Biological

Lung

Liver

Bone

Food

Milk

Sea clam

Sea hare

Seaweed

Air:Filters

Radionucl ides

alpha-particle

emitters

90

sr, i 37 cs, 2l0p b

alpha- and beta- particle

emitters, photonemitters

natural radionuclides,

alpha-particle

JSfRu. ^Cs!

alpha-particle

emitters, 3H,

14C, fission

products,

activation

products

natural radionuclides

Ten-year

requirements

5,000

al iquants

(1-kg

samples)

1,600

al iquants

(100-g

samples)

Several

thousand

al iquants

(50- to

100-ml samples)

Several

hundred

aliquants

Tests of Sampling, Preparation, and Storage Pro- cedures

The third phase of the traceability scheme

has not yet been implemented and will be left for

future discussion.

Future Plans

Future efforts by the low-level radioactivity measurements group at NBS will include con- tinuing traceability programs with RESL and EPA,

particularly for those radionuclides that they distribute but are not as yet traceable to

NBS. We hope to develop new solution SRMs of

99Tc , 208Po or 209 Po> 210Pb> 227ACj and 232u# There will also be continued development of NMSs which may include matrices such as animal bone,

vegetation, air filters, and uranium-mill tailings. It is also anticipated that reference

sources of noble gases for the calibration of

thermoluminescent dosimeters (TLDs) will be de- veloped. Charcoal traps containing 85>Kr, 133x 6) and l-"Xe W1 n be produced in addition to the present gaseous SRMs. And lastly, methods are to

be developed for exposing TLDs to ^Kr an(j 133j( e>

Acknowl edgments

The authors thank Dr. J.M.R. Hutchinson, who

is the coordinator of the Low-Level Measurement- Technique Group, ICRM, and Dr. W. B. Mann for their comments on the manuscript.

References

[1] L.M. Cavallo, National Standards for Radioactivity Measurements, Traceability for Ionizing Radiation Measurements, May 8-9, 1980,

National Bureau of Standards, U.S. Department

of Commerce, these proceedings.

have been completed for these materials.

Assays of the various radionuclides is just be- ginning and will be a fairly lengthy process. Confirmatory and additional assays will be carried out by other domestic and national lab- oratories such as Battelle NW, Environmental

Monitoring Laboratory, Los Alamos Scientific

Laboratory, RESL, Service Central de Protection

Contre les Rayonnements Ionisants, and WHOI. We are grateful for the efforts of these moral and financial support of the EPA, NRC, and the U.S. Department of Energy.

B.M. Coursey, J.M.R. Hutchinson, L.L. Lucas,

W.B. Mann, T. Matsumura, and J.R. Noyce, Radioactivity Standards for Environmental Monitoring, J. Radioanal. Chem. , 43, 451, (1978).

J.M.R. Hutchinson, W.B. Mann, and R.W. Perkins,

Low-Level Radioactivity Measurements, Nucl

Inst. Methods, JQ2, 305 (1973).

124
TABLE 7 Status of Calibrated Environmental Material Rocky Flats

Soil -West Rocky Flats

Soil -East Peruvian

Soil Columbia River

Sediments Gyttja

Human

Liver

Human

Lung Remarks Collected / J / / J / Several hundred kilograms

Dried / J /

Freeze

Dried Freeze Dried

Freeze

Dried

Freeze DriedAir dried or freeze dried at <38 C shelf temperature

Milled J

* *

/

* * /

* /

*+

/

** •Average Particle Diameter i5u, milled by pancake air Jet mill with Internal classification. "Wiled by cryogenic hanmermill

> 80% -200 mesh

61 ended / 109 kg /

132 kg

/

50 kg 190 kg 59 kg /

34 kg /

10 kg

"V" blender used w/intensifier

bar, blended for 30 m1n. HaT Homogeneity

Determination / / / / J N/A N/A Inhomogeneity < 0.31 (3s)

Prel 1m1 nary Assay

/ / /

N/A N/A Ge(L1) spectroscopy S radlochemistry

Bottled / / J / /

Semi-Quantitative

Elemental Determlniation

/ / / / N/A N/A Measurements by emission spectroscopy

Assay

[4] L.M. Cavallo, M. Ehrlich, and J.M.R. Hutchinson, Traceability in Ionizing Radiation Measurements Systems, Proceedings of "IAEA International Symposium on National

and International Standardization of Radiation Dosimetry," Atlanta, Georgia, December

5-9, 1977, IAEA-SM-222/18, Vienna (1978).

[5] W.B. Mann, Radionuclide Metrology and Quality

Assurance, Environmental Monitoring Series,

EPA-670/4-75-006 (June, 1975), Proceedings

of "Activities and Needs Related to Radioactivity Standards for Environmental Measurements", U.S. Environmental Protection Agency,

Washington, D.C., August 21, 1973.

[6] L.M. Cavallo, B.M. Coursey, S.B. Garfinkel,

J.M.R. Hutchinson, and W.B. Mann, Needs for Radioactivity Standards and Measurements in Different Fields, Nucl. Inst. Methods,

112, 5 (1973).

[7] W.B. Mann, and J. P. Cali, Traceability and Standard Reference Materials, Proceedings of "Standardization, Performance and Quality

Control in Nuclear Medicine", June 12-14,

1975, National Bureau of Standards, Washington,

D.C., The C.V. Mosby Company, Saint Louis,

Missouri, (1975).

[8]

W.B. Mann, Reliability and Traceability in Radioactivity Measurements, Proceedings of "Southeastern Workshop on the Utilization

and Interpretation of Environmental Radiation

Data", Orlando, Florida, March 1-3, 1976.

[9]

W.B. Mann, The Radioactivity Standards Program of the National Bureau of Standards,

Proceedings of "IAEA International Symposium

on National and International Standardization

of Radiation Dosimetry," Atlanta, Georgia,

December 5-9, 1977, IAEA-SM-222/1 1

, Vienna

(1978).

[10]

B.M. Coursey, J.R. Noyce, and J.M.R. Hutchinson, Interlaboratory Intercomparisons

of Radioactivity Measurements using National Bureau of Standards Mixed Radionuclide Test Solutions, National Bureau of Standards

Technical Note 875, U.S. Department of Commerce, Washington, D.C. (1975).

[11] H.L. Volchok and M. Feiner, A Radioanalytical Laboratory Intercomparison Exercise,

EML-366, Environmental Measurements Laboratory, U.S. Department of Energy, New York, New York (October, 1979).

125
[12]

A.N. Jarvis, The EPA National Quality Assurance Program, Traceability for Ion- izing Radiation Measurements, May 8-9, 1980,

National Bureau of Standards, U.S. Department of Commerce, these proceedings.

[13]

L.K. Cohen, NRC Traceability Concerns in its Inspection and Enforcement Program,

Traceability for Ionizing Radiation Measurements, May 8-9, 1980, National Bureau of Standards, U.S. Department of Commerce,

these proceedings.

[14]

National Council on Radiation Protection

and Measurements, A Handbook of Radioactivity Meaurements Procedures, NRCP Report No. 58, Chapter 8, Natl. Council Radiat. Protection Measurements, Washington, D.C.

(1978).

[15] L.H. Ziegler, Radioactivity Standards Distribution Program 1978-1979, EPA-600/4-78-

033, U.S. Environmental Protection Agency,

Environmental Monitoring and Support Laboratory, Las Vegas, Nevada (1978).

[16]

Quality Assurance Branch, Environmental

Radioactivity Laboratory Intercomparison

Studies Program 1978-1979, EPA-600/4-78-032,

U.S. Environmental Protection Agency, Environmental Monitoring and Support Laboratory,

Las Vegas, Nevada (1978).

[17] U.S. Nuclear Regulatory Commission, Quality

Assurance for Radiological Monitoring Pro- grams (Normal Operations) - Effluent Streams and the Environment, Regulatory

Guide 4.15, Office of Standards Development,

U.S. Nuclear Regulatory Commission, Washington, D.C. (February, 1979).

[18] L.K. Cohen, Quality Assurance for Effluent

and Environmental Monitoring - A Nuclear

Regulatory Commission Overview, ASTM Special Technical Publication 698, J.J. Kelly,

ed., Amer. Soc. Testing Materials, Philadelphia, Pennsylvania, 282 (1980).

[19]

D. Golas, Traceability Programs for Nuclear

Medicine, Traceability for Ionizing Radiation

Measurements, May 8-9, 1980, National Bureau

of Standards, U.S. Department of Commerce,

these proceedings.

[20]

B.M. Coursey, J.M.R. Hutchinson, and M.P. Unterweger, Calibration of Ge(Li) Gamma-Ray

Spectrometers for the Measurement of Radioactive Noble Gases, Int. J. Appl. Rad. Isotopes, 28, 551 (1977).

[21]

B. M. Coursey, Use of NBS Mixed-Radionucl ide

Gamma-Ray Standards for Calibration of Ge(Li) Detectors Used in the Assay of Environmental

Radioactivity, Proceedings of "Symposium

for the Safe Use of Radiation", National Bureau of Standards Special Publication 456 (November, 1976), U.S. Department of Commerce,

173, March 1-4, 1976.

[22]

C. W. Sill, Problems in Sample Treatment in Trace Analysis, Accuracy in Trace Analysis:

Sampling, Sample Handling, Analysis, NBS Special Publication 422, P.D. LaFleur, ed., U.S. Department of Commerce, Washington,

D. C, Vol. 1 , 463 (1976).

[23]

T.T. Gorsuch, Dissolution of Organic Materials, Accuracy in Trace Analysis: Sampling,

Sample Handling, Analysis, NBS Special Publication 422, P.D. LaFleur, ed., U.S. Department

of Commerce, Washington, D.C, Vol. 1, 491 (1976).

[24]

International Atomic Energy Agency, Reference

Methods for Marine Radioactivity Studies,

Technical Reports Series No. 118, Vienna

(1970).

[25]

T.J. Murphy, The Role of the Analytical Blank

in Accurate Trace Analysis, Accuracy in Trace

Analysis: Sampling, Sample Handl ing, Analysis, NBS Special Publication 422, P.D. LaFleur, ed. , U.S. Department of Commerce,

Washington, D.C, Vol. 1 , 509 (1976).

[26]

K.M. Wong, T.A. Jokela, and V.E. Noshkin,

Problems Associated with Transuranium Deter- mination of Suspended Solids in Seawater

Samples, Radioelement Analysis Progress and Problems, Proceedings of "Twenty-Third

Conference on Analytical Chemistry in Energy

Technology", W.S. Lyon, ed., Ann Arbor Science

Publishers Inc., Ann Arbor, Michigan, 207 (1967).

126
[27]

E.I. Hamilton, M.J. Minski, and J.J. Cleary,

The Loss of Elements During Decomposition

of Biological Materials, with Special Ref- erence to Arsenic, Sodium, Strontium and Zinc, Analyst, 92, 257 (1967).

[28]J.R. Noyce, Standards for the Assay of Radionuclides in Solid Environmental Sam- ples, Effluent and Environmental Radiation

Surveillance, ASTM Special Technical Pub- lication 698, J.J. Kelly, ed., Amer. Soc. Testing Materials, Philadelphia, Pennsylvania, 309 (1980).

[29] J.R. Noyce, J.M.R. Hutchinson, W.B. Mann, and P. A. Mullen, Development of a National Bureau of Standards Environmental Radioactivity Standard: River Sediment, Pro- ceedings of "International Conference on Environmental Sensing and Assessment", Las

Vegas, Nevada, Sept. 15-19, 1975, IEEE,

Inc., Annals No. 75CH1004-I 19-5.

[30]

V.T. Bowen, Natural Matrix Standards, Envi- ronment International, 1_, 35 (1978).

[31]

C. W. Sill, The Case Against Natural

Matrix Standards, Twenty-Fifth Annual Con- ference on Bioassay, Environmental, and Analytical Chemistry, Las Vegas, Nevada,

October 31 - November 1, 1979.

[32]

V.T. Bowen and H.L. Volchok, Spiked Sample

Standards: Their Uses and Disadvantages in Analytical Quality Control, Environmental

International, in press (1980).

[33]

D. G. Olson, Synthesized Standards in Natural Matrices, Environment International,

in press (1980).

[34] J.M.R. Hutchinson and W.B. Mann, ed., Metrology

Needs in the Measurement of Environmental

Radioactivity, Environment International , 2,

I (1978).

[35] J.M.R. Hutchinson, Possible Areas of Effort

by the International Committee on Radionuclide Metrology in the Field of Low-Level

Radioactivity, Environment International, 1,

II (1978).

[36]

H.L. Volchok, M. Feiner, K.G.W. Inn, and J.F. Mclnroy, Development of Some Natural Matrix

Standards - Progress Report, Environment

International, in press (1980).

127

NRC TRACEABILITY CONCERNS IN ITS INSPECTION AND ENFORCEMENT PROGRAM

Lawrence K. Cohen

U. S. Nuclear Regulatory Commission

Washington, D.C. 20555

This paper discusses NRC's traceability requirements in the licensing process and in its inspection programs. It describes the approach and direction NRC has taken to achieve

traceability for its own program and to provide a means for the licensee as well.

(Enforcement; inspections; NRC; radiation measurements; regulations; regulatory guides;

traceability)

Introduction

In the area of radiation measurements, the

U.S. Nuclear Regulatory Commission (NRC) has imposed upon their licensees technical specifications and license conditions to protect the radiation worker and general public from ex- cessive radiation exposure from facilities. Among these requirements, it is stated that radiation standards and measurements systems be "traceable." This requirement of traceability,

however, is not limited to only NRC licensees. NRC has also invoked similar requirements on its own radiation measurements programs being con- ducted by the NRC Office of Inspection and Enforcement (OIE).

"Traceability" is a term that often

triggers a spectrum of responses, especially

from licensees, ranging from confusion and perplexity on the one hand to frustration on the

other. We all know that traceability is perhaps

a noble, idealistic goal for which one should

strive and achieve, but many people are unsure what needs to be done, how to do it, or what traceability really means. The concept of traceability is mostly undefined, vague, often generating misunderstanding. There is an abundance of discussions, definitions, and papers covering the subject, with no apparent

consensus of opinion.

Traceabi 1 ity

Traceability Requirements in the Regulatory

Process

When writing regulations, technical specifications, and regulatory guides, regulators feel compelled to include, for example, some ambiguous statement about traceability to the National Bureau of Standards Radiation Measurement System.

Figure 1 provides a sampling of some of the statements that have been found in earlier regu- latory guides and technical specifications.

Regulatory Guide 1.21 (on measuring effluents from power reactors), P. 5, Section 1 1C:

"Calibrations of measuring equipment should be performed using reference standards certified by *he National Bureau

of Standards or. standards that have been calibrated against standards certified by the National Bureau of Standards."

Regulatory Guide 4.14 (on measuring effluents from uranium mills), P. 4, Section 4.3: "To the extent possible, calibrations of measuring equipment should be performed by using radioactive sources that have been calibrated by a measurement system traceable to the National Bureau of Standards' radiation measurements

system. . . .Functional tests, i.e., routine checks performed to demonstrate that a given instrument is in working condition, may be performed using sources that are not calibrated by a system traceable to the National Bureau of Standards."

Regulatory Guide 4.15 (on quality assurance for radiological effluent and environmental monitoring), P. 4, Section 6.1: "Radionuclide standards that have been certified by the NBS, or standards that have been standardized using a measure- ment system that is traceable to that of the NBS, should be used when such standards are available. Otherwise standards should be obtained from other reputable suppliers."

Figure 1. Statements concerning calibrations, traceability, and NBS in NRC Regulatory Guides and Technical

Specifications.

129
Regulatory Guide 4.15 (on quality control for continuous effluent monitoring systems), P. 7, Section 7:

"Initial calibration of each measuring system should be performed using one or more of the reference standards thai

are certified by the National Bureau of Standards or that are calibrated by a measurement system that is traceable to

that of the National Bureau of Standards."

10 CFR 50, Appendix I, Technical Specifications for PWRs, Table 4.3-1 1, Radioactive Liquid Effluent Monitoring

Instrumentation Surveillance Requirements, P. 3/4 3-53: "The CHANNEL CALIBRATION shall include the use of a known (traceable to the National Bureau of Standards

radiation measurement system) liquid radioactive source positioned in a reproducible geometry with respect to the

sensor and emitting beta and gamma radiation with fluences and energies in the ranges measured by the channel

during normal operation." (A similar statement is made regarding gaseous effluent monitoring.)

Example of a type of statement no longer being used by NRC:

"All liquid effluent radiation monitors shall be calibrated at least quarterly by means of a radioactive source which

has been calibrated to a National Bureau of Standards source."

Figure 1 (continued)

For those who are responsible for the inspection and enforcement of these requirements

and ensuring that the licensee is complying with

them, namely the NRC inspectors, these require- ments present a very difficult burden. There

have been many attempts to solve this problem. One solution was to replace the word "traceable" with "relatable;" i.e., "Standards that are relatable to the NBS, etc." As one would expect, this was no solution. It merely produced additional confusion.

In February 1979, the revision to Regulatory

Guide 4.15, "Quality Assurance for Radiological

Monitoring Programs (Normal Operations) — Ef- fluent Streams and the Environment," was issued

to ensure that radiation reference standards used

by the licensee were indeed traced back to NBS. We believe that this is an important aspect of a good quality assurance program. To prevent con- fusion, we deleted the term "traceable" in reference to standards and replaced it with a paragraph that, although more wordy, was more meaningful, practical, and useful. The paragraph

spelled out exactly what had to be done. This paragraph is shown in Figure 2. Similar phrasing

was used, incidentally, in the Standard Effluent

Technical Specifications shown in Figure 3.

U.S. NUCLEAR REGULATORY COMMISSION

Ravlilon 1 Fsbruiry 1979 REGULATORY GUIDE

OFFICE OF STANDARDS DEVELOPMENT

REGULATORY GUIDE 4.16 QUALITY ASSURANCE FOR RADIOLOGICAL MONITORING PROGRAMS

(NORMAL OPERATIONS) - EFFLUENT STREAMS AND THE ENVIRONMENT

" RADIONUCLIDE STANDARDS THAT HAVE BEEN CERTIFIED BY NBS OR STANDARDS THAT HAVE BEEN

OBTAINED FROM SUPPLIERS WHO PARTICIPATE IN IfASUREMENT ASSURANCE ACTIVITIES WITH NBS

"

A FOOT NOTE FOLLOWING THIS PHRASE DESCRIBES THE PeSUREMENT ASSURANCE PROGRAM (MAP) :

(1) THE SUPPLIER SUBMITS A CALIBRATED RADIOACTIVITY SOURCE TO NBS FOR CONFIRMATION

(2) NBS PROVIDES CALIBRATED RADIOACTIVITY SOURCES OF UNDISCLOSED ACTIVITY TO THE

SUPPLIER.

Figure 2. Standard statement from Regulatory Guide 4.15.

130
(3) The initial CHANNEL CALIBRATION shall he performed using one or more of ihe reference standards certified by the National Bureau of Standards or using standards that have been obtained from suppliers that participate in measurement assurance activities with NBS. These standards shall permit calibrating the system over its intended

range of energy and measurement range. For subsequent CHANNEL CALIBRATION, sources that have been

related to the initial calibration shall be used. (Operating plants may substitute previously established calibration procedures for this requirement.)

Figure 3. Standard statement from Standard Effluent Technical Specifications.

In subsequent discussions with suppliers of radioactive standards, they appeared to under- stand procedures and mechanisms. However, they

did complain about the cost of the service. Several speakers have already discussed the Measurement Assurance Program (MAP) to which

this paragraph refers, so I do not see any need for a further elaboration. I would like to thank NBS for their assistance in writing this section of the guide.

Traceability in the NRC Measurement Program

It is very important that radiation measurements made by NRC in the course of an inspection,

investigation, or in response to emergencies be accurate and reproducible. We must be able to demonstrate that our values are correct and will withstand a rigorous technical and judicious

review. We must be able to establish a level of credibility with the public. Those considerations are becoming more and more important as NRC expands its Independent Measurements Program

(IMP) in the Office of Inspection and Enforcement. Increasing emphasis is being placed on independent measurements to complement the traditional inspection techniques of records and procedures review, evaluation, discussion, and direct observation. Independent measurements

provide convincing direct evidence of the licensee's performance and are congruent with

the other techniques. Independent measurements

are being included in all routine inspections at

all NRC- licensed facilities. They cover reactors,

fuel facilities, byproduct material processors

and users, and medical users. At these facilities, inspectors or NRC contractors take and analyze inplant samples, such as effluents, or collect environmental media samples in the

environs. Similarly, they also take direct

radiation measurements in the plant and environs.

The RESL Connection

Since the beginning of a quasi -formal measurements program in 1972, the Radiological and Environmental Sciences Laboratory

(RESL) in Idaho Falls (formerly HSL) acted as the NRC reference laboratory and performed the radiological analyses. At the present time, RESL performs over 2000 analyses of over 800 samples a year submitted by the regional

inspectors. It was realized at the beginning of the program that some assurance was needed to demonstrate that the analytical results were

accurate.

In January 1973, NRC entered into a contract with NBS to develop the traceability of the NRC reference laboratory (RESL) to the NBS system

[National Radioactivity Measurements System

(NRMS)]. Here we are talking about "direct

traceability." The mechanism to achieve this was by means of a predetermined program of

tests. This program required the NRC reference laboratory to annually assay 8 to 12 prepared

NBS solutions of preselected radionuclides of unknown activity. Included in the selection were

alpha emitters, beta emitters, and single

gamma- ray emitters. Under the agreement between

RESL and NBS, RESL will report its measurements

to NBS. NBS will then issue a report of the test presenting the ratio of the RESL-to-NBS radioactivities concentration values. If the ratio lies within the range of 5 percent, the report will state that RESL has demonstrated traceability to the NBS to within 5 percent.

Figure 4 shows a histogram of the results of past tests since the inception of the program. The graph shows that the RESL measurements have consistently clustered within 1 percent of the NBS value.

As part of the agreement with the NRC,. NBS measures randomly selected samples from batches

of standards provided by RESL to regional offices

and NRC contractors (i.e., States). Periodically, NBS also distributes to RESL, NRC con- tractors, and regional offices special standards

such as Kr-85, Xe-127 and Xe-133 gas samples.

However, all of these types of samples sent to RESL are blind samples that are used in calibration and testing.

The NRC Indirect Traceability Connection

In the last two years, NRC has been developing its own capability to perform radiation

measurements. We have provided each of the five regions with mobile laboratories and propose to equip each regional office with additional

laboratory instrumentation. RESL will play an important role in a rigorous quality assurance

program, as well as provide the radiochemical

capability that is required.

Interrelationship Between NRC, NBS, RESL and Other Laboratories

Figure 5 shows the interrelationship that

exists between the various laboratories. Although

the intercomparisons and other efforts do not constitute traceability, they help to improve

the quality of the measurements performed.

131
i

1 1 1 r

Pu- 242

H-3

U- 234 Am241

X131 Pu- 238

Sr- 89

Sr- 90

Co139 Co- 60

«o- 226

Y68P- 32Sr- 89 Mo99Co- 57

Y88

Cf. 137 Co- 58

U- 238

P- 32

C14Cr51 Sn113 U- 235

Y88

Sr- 89

Nl63

Co139 Pb- 203 Au198 Bo140

Ci- 137

Pu- 239

CI36 Am243

Co

141 Y88

Co- 60

Cd109 H-3 U- 236

Pu- 242Cr51 Pm147

Cr51 Co139

I- 131 H-3 Am- w«

Zn- 65 Od148 Pm147

Co139 Noll

Po210 Zn- 65

Cl- 137

Cr51 Po- 239I- 125

Sr- 90

Ag110m

Sr- 90

H-3 Cd109 Hg203

Co144 Mn54

Sr- 85 Zn- 65

Sr. Ni- 90 63

C14

C»- 137

Se- 75 Mn54

Ct- 137

Ci- 134 Sn113 Mn54

Co- 60

Sr- 90

Y-88

Zn- 65

Co- 45

Pu241

1 1 0.90 0.92 0.94 0.96 0.98 1.00 1.0? 1.04 1.06 1.08 1.10 1.12 1.14 RESL VALUE

NBS VALUE

Figure 4. Historical comparison of traceability measurements.

Traceability in the Area of Direct Radiation Measurements

As previously indicated, we have also developed our capability to perform radiation

surveys in the plant and monitor the facilities

environs. It became apparent after losing an enforcement case over the inadequate calibration

of an NRC survey meter that a similar arrange- ment was needed in the field of direct radiation

measurements. I would like to divide the subject

into the calibration of radiation protection

instruments and the thermoluminescent dosimeter

(TLD) devices. For radiation protection instru- ments, I would like to see the establishment of regional calibration facilities directly trace- able to NBS as was done for medical instrumentation. At present, we are looking into the establishment of an NRC calibration facility to handle our needs. Another speaker will discuss

the question of traceability of these instruments. Figure 6 shows the proposed traceability

pathways.

After the accident at TMI, the OIE initiated

an NRC TLD Direct Radiation Monitoring Network,

which was a departure from our previous position.

In this program, up to fifty dosimeters will be placed around all operating reactor sites and

1

eventually will apply to other major licensees. This will provide, for the first time, consistent

and accurate measurements of the ambient radia- tion levels throughout the country. To ensure

the accuracy of this statement, I am developing

a direct traceability protocol with NBS.

Conclusion

In conclusion, our interest in the subject

of traceability is our desire to improve the quality of radiation measurements performed by

licensees as well as by NRC employees. We approach this objectivity by the following

means:

1. Imposing upon radiation users well- written, clear, and meaningful regulations and requirements.

2. Developing an effective and efficient

inspection program.

3. Establishing a mechanism for users of radioactivity to enter into a program to demon- strate the accuracy of these measurements.


RADON AND RADON DAUGHTER FIELD MEASUREMENTS

Andreas C. George

Environmental Measurements Laboratory

U. S. Department of Energy

New York, NY 10014

Practical methods for measuring the concentration of radon

and radon daughters in air are reviewed, and procedures

and instruments are recommended for reliable field measurements

(environmental measurements; radon; radon daughters)

Introduction

Radon and its daughters is causing increasing

concern to many investigators involved in research

and situations where diagnostic measurements for source identification and quantification are needed.

While radon-222 and its daughters contribute

the highest fraction of the natural radiation dose

to man, we have been more concerned by certain

special cases of exposure. These include the occu- pational exposure of uranium miners and uranium

mill workers, the general public in and around

areas of enhanced radiation, and more recently

inside houses built with materials with high

radium-226

The concentration of radon and its daughters

and their contribution to human dose cannot be

adequately measured and assessed unless all compo- nents of measurement systems are accurately

calibrated. Little has been published describing

the different calibration methods of all the equip- ment presently used for radon and radon daughter

measurements. The American National Standards

Institute (ANSI) issued a standard [1] with specific application in radiation protection in uranium

mines. The ANSI procedures do not specify any accuracy requirements. A more comprehensive

publication dealing with calibration procedures for radon and radon daughter measurement equipment was

issued by the Department of the Interior. [2] The report stresses the necessity for the proper calibration of the radon and radon daughter measurement instrumentation to assure accurate evaluation of the radiation hazard. Although the publication was intended for uranium mining it is very useful for other environments.

The instrumentation developed for measurements

in uranium mines has evolved with respect to sensitivity and convenience. The widespread need

of these instruments in other environments with

much lower concentrations necessitated further

improvement

Knowledge of the various kinds of errors encountered in physical measurements is necessary

for reliable data interpretation and comparison.

In this report I will describe some methods and

instruments employed in the determination of radon

and radon daughters as well as their applications

and limitations so one may be able to choose one method over another for a particular application.

Lmportance of Radon and Radon Daughter Measurements

The main reason for the high interest in radon and its daughters is their effect on human

health. An important stimulus for this interest

is the radon releases from the nuclear fuel cycle.

Although studies of radon and radon daughters

provide us with natural radiation data which can be used as a standard to evaluate health effects • to human populations from man-made radionuclides,

recently there have been extensive measurement

programs in all sources of radon in the environment. Some of the areas of interest are:

Nuclear Energy Industry

Uranium and its decay products are found in all industrial activities associated with uranium

mining and milling operations. Although the biological hazard data from the uranium mine popu- lation were investigated extensively, the evaluation of possible radiological hazards from the waste products of uranium mill tailings is just

beginning. Radon measurements are important for determining the adequacy of reclamation programs

at uranium tailings

Phosphate Mining and Processing

The concentration of natural uranium in 135
phosphate ores ranges from 10 to 400 ppm. [3] The assessment of the radiological impact of phosphate

mining, processing and use is being investigated

and appropriate standards and guides will be

established. In Florida more than 25,000 acres of

mined lands have been reclaimed for residential

development and the potential higher levels of airborne radiation warrant additional studies to define the scope and extent of this problem.

Radon in Natural Gas

Radon is being considered as another source

of exposure of inhabitants of buildings as a result of combustion of natural gas in unvented

appliances. The concentration of radon in natural

gas depends on the well head concentration and

transmission time to consumption point. Concentrations of radon ranging from 1 to 1,500 pCi/A have

been reported. [4]

Radon In Indoor Environments

Radon diffuses out of building materials

(brick, concrete, stone and interior walls) and to a greater extent from the soil under the floor and

from the domestic water supply. [10] In regions

with large deposits of radioactive materials,

indoor levels become elevated. In recent years,

the construction of energy-efficient homes re- sulted in elevated concentrations of radon and

other pollutants, many times over that found

outdoors. In the late 1970's, active solar heating

systems were installed in residential and commercial structures for space heating. To make the system more efficient, the heat is stored in rock

bins until needed. Since the natural radioactivity

of rocks in different geographical areas differs,

the impact of these rocks on the concentration of

indoor radon levels must be investigated.

Radon in Natural Caves

Every year in the United States an excess of

1 million persons visit some of the large caves. Usually exposure to tourists will not be large but measurements show that the radiation dose to regular cave workers is likely to reach or exceed

the maximum permissible dose. [5]

Radon and Geo thermal Resources Application

High radon concentrations in the waste

streams of geothermal electric power plants were

measured. It is suspected that elevated exposures to radon and its daughters would occur at

the plant and in the surrounding vicinity. Non- electrical applications of geothermal resources

are widespread especially in the western United

States [6] for space heating, domestic hot water

sources and for recreational purposes . Their

radiological health implications should be

investigated by measuring radon concentrations

inside structures which use geothermal fluids.

Instruments and Methods for Radon and Radon

Daughter Measurements

Measurements of the airborne concentrations of

radon and radon daughters are usually categorized

by application. Technology is sufficiently developed to meet most demands encountered in field measurements. Choice of the instrument and method

depends on the levels to be measured, the accuracy

required, equipment availability and convenience.

There is an abundance of available instruments for routine laboratory and field applications and

recently complex instruments have been introduced

for research purposes

There are methods for prompt or instantaneous

or grab sampling, continuous, and time-integrating

that yield average concentrations for an extended

time period usually for a week or more. Tables 1 and 2 list the most commonly used instruments and

methods for radon and radon daughter measurements. Detailed procedures of each method are described

in the listed references.

Earthquake Prediction

Radon measurements in sub-surface waters are being investigated in earthquake prediction. It

is suggested that the tectonic strain of the rock

formations may increase the rate of release of radon to the ground wa ter . [ 7

]

Radon in Atmospheric Tracer Studies

Since the half-life of radon is sufficiently

long to allow transport over thousands of miles,

it is used to trace continental air masses over

the oceans for as long as two weeks . It is also

used to study air currents, diffusion and cloud

formation and behavior .[8,9]

How Well Can Radon and Radon Daughter Measurements

be Made in the Field?

The errors of most monitoring techniques are acceptably small, when instruments are calibrated

and operated properly. The basic errors encountered in environmental measurements are:

Personal errors due to human failure. This can be traced to deviation from prescribed procedures. In the field, shortcuts in operating pro- cedures usually result in errors which can be eliminated through experience.

Statistical errors due to the random nature

of radioactivity. The resulting random errors cannot be prevented but they can be reduced and be

accounted for by the application of the proper

136
TABLE 1 . INSTRUMENTS AND METHODS FOR MEASURING RADON

Instrument

and Method Application Principle of Operation Sensitivity Reference

Scintillation flask

Two filter

Track etch

Passive

Plastic bag

Passive monitor

Grab or continuous sampling

Grab or continuous sampling

Pulse ionization Grab (laboratory only)

Continuous

Continuous

Time integrating

Time integrating

Scintillation alpha count

Decay of radon and collection

of daughter products on second

filter; alpha count

Sample transferred Into Ion chamber; pulse ion count

Alpha sensitive films register

tracks when etched in NaOH

Radon diffusion into sensitive

volume. Po-218 collected on scintillation counter electrostatically

Collection of ambient air

in bag. Transfer In scintillation flask; alpha count

Radon diffusion into sensitive

volume. Po-218 collection on

TLD electrostatically

< 0.1 pCi/i

0.01 - 5 pCi/i

< 0.05 pCl/i

0.2 pCi - month/i

0.5 pCi/i

< 0.1 pCi/i

0.03 pCi/A

11, 12

13, 14

15

16, 17

18

19

20

TABLE 2 . INSTRUMENTS AND METHODS FOR MEASURING RADON DAUGHTERS

Instrument

and Method Application Principle of Operation Sensitivity Reference

Kusnetz and Rolle Grab sample for working level only Collect sample on filter; alpha count 0.0005 WL* 21, 22

Tsivoglou and modificationsGrab sample for individual radon

daughters and working

level

Collect sample on filter alpha count

0.1 pCi/i each

of RaA, RaB and

RaC - 0.O005 WL

23, 24, 25, and 26

Alpha spectrometry Grab sample for indi- vidual radon daughters and working levelCollect sample on filter, count in alpha spectrometer

0.5 pCl/l each

of RaA, RaB and

RaC - 0.002 WL

27, 28

Instant working

level monitor

Grab sample for indi- vidual radon daughters and working levels

Automatic sample collection,

alpha or alpha and beta count

1 pCi/i each of

RaA, RaB and RaC 0.01 WL

29

Working level monitorTime -Integra ting radon

daughter concentration

Collect sample on filter (1-2 weeks). Detect with

thermoluminescent material

0.0005 WL in a week

30, 31, 32

*1 WL (working level) is the concentration of radon daughters in 1 £ of air that will release

1.3 x 10s MeV of alpha energy upon complete decay through Po-214.

137
statistical methods. In measuring environmental

levels of radioactivity, the primary goal is to accumulate statistically meaningful counts within

a reasonable period of time. By using the best

combination of sensitive volume, pumping rate and

counting times we can obtain the required precision. Measurement precision can be determined

experimentally by comparing the results of a series of replicate measurements. Usually, measurement precision between 10% and 20% is satisfactory.

Systematic errors usually result from malfunctioning instruments and from improper calibration of equipment. The accuracy of a method is measured by calibration against a standard method

or by a reliable method traceable to NBS as near

as possible to the actual deployment use in the field. Test calibrations should be conducted in large chambers in which the ambient conditions of temperature, relative humidity and dust loading

can be simulated for different times of exposure.

Our experience at the Environmental Measurements Laboratory (EML) is not to accept the calibration

of an instrument as received from a supplier.

Although instruments are usually constructed well,

we found that they are not necessarily calibrated

properly

Radon Measurements

Scintillation Flask

For grab samples, the scintillation flask

method is one of the oldest, most reliable and

widely used both in the laboratory and in the field. Basic equipment consists of a scintillation flask, a vacuum system or pump and a photomultiplier tube counter. Measurement errors with this method may arise due to the following.

Improper flask calibration . In intercalibration exercises in which several agencies and

universities participated, we found that the disparity of some of the data was the result of improper calibration. In one exercise in which 12 groups took part, the reported values of four

participants were low by 20 to 35% and in another

two cases were 20$ higher than the expected value.

Leaking flasks . Scintillation flasks from

the same production batch that deviate substantially from the ideal calibration are associated

with leakage. This is more common with the evacuated type. It is essential that flasks

should be leak-tested before calibration and that

they be recounted for several days after calibration to observe any deviation from the expected

value

Alpha counting equipment . A radon scintillation flask should be calibrated with the counting

equipment intended for the field application.

Flasks counted on different counters can differ

substantially because of different operating

voltage plateaus and their accompanying noise

levels. This can be very troublesome when

measuring environmental levels of radon.

Two-Filter Method for Radon

Although this method is not used as much as

the scintillation flask it can be designed for a variety of specific applications. The two-filter

sensitive volume may range from .05 I to 1000 I depending on the required sensitivity. By varying

the sampling flow rate, tube volume, and sampling

time, radon concentrations as low as .01 pCi/# can

be determined.

The common errors encountered are: any leakage around the front filter will tend to in- crease the radioactivity on the exit filter and

overestimate the radon concentration. To avoid

this, it is prudent to push rather than draw air

through the two-filter device; in this manner the leaks are outwards from the device. The front

filter should have essentially 100$ collection

efficiency for radon daughter products and the exit filter should have good surface characteristics for the collection of Po-218.

The counting equipment should be standardized

with an alpha standard that has the same geometric

configuration as the exit filter and approximately

the same alpha energy emission. Calibration under

different conditions of flow rate, collection time and concentration should be conducted to test the linearity of the system before it is deployed in the field.

Continuous Measurement of Radon

Continuous reading radon monitors have been

found useful for measuring varying concentrations

of radon over a long period of time. These types

of measurements are more meaningful than grab

samples in estimating average exposures. Several

kinds of continuously reading radon monitors have

been developed to serve this purpose. However,

this extra information is derived at a considerable increase in instrument size, complexity and

additional cost. The most commonly used continuous radon monitors are:

Radon flask monitor . This instrument is based on the counting of alpha disintegrations

produced from radon circulated through a scintillation flask mounted on a PM tube. Previous

monitors neglected to take into consideration

deposition of radon daughters in the scintillation flask and this resulted in questionable

measurements. To avoid this discrepancy, the monitor must be calibrated taking into consideration the total number of counts obtained in

138
successive equal time intervals, the detection

volume of the scintillation flask, counting

efficiency, and correction for the previously

deposited radon daughters .[ 14,33] When this pro- cedure is applied, the radon flask monitor is capable of measuring varying radon concentrations

accurately for an indefinite length of time.

Two-filter monitor . The instrument can be

designed to measure environmental levels of radon

(as low as 0.01 pCi/£) . Like the scintillation

flask monitor, it must be calibrated in the same manner as intended for field measurements.

Corrections for the radioactivity from the pre- vious samples must be made for accurate radon

determination. A source of error is that which

arises from the contribution of thoron activity on

the fixed exit filter. This can be eliminated by

passing the ambient air containing radon and thoron through a delay chamber upstream from the two- filter sensitive volume, which it will allow thoron

(Tj5 = 55 seconds) to decay but will have no effect

on the radon.

A modification [34] of the two-filter continuous radon monitor uses an automatic drive that changes the exit filter every hour and transports

it into a scintillation counter, thus eliminating

the accumulation of thoron daughter products and

the need for corrections from the previous hourlong sample

.

Passive electrostatic monitor . In principle

the monitor is continuously detecting the ambient

radon concentration. But as in the case of the scintillation flask and the two-filter monitors,

the changes in ambient radon concentration are masked by the previously deposited radon daughters.

So far a procedure for correction for the activity

associated with radon daughters deposited in previous counting intervals has not been incorporated in the calibration of this instrument.

Another deficiency in this instrument that may

result in error is the dependence of the instru- ment on humidity. Tests at EML with similar

monitors showed a humidity dependence, namely a 6f> decrease in sensitivity for a 10% increase in relative humidity .[35]

Time-Integrating Radon Monitor

Another type of instrument that measures

radon concentration over long periods of time is the time-integrating monitor which obtains a single number representing the average concentration during the period of observation.

Plastic bag method . Air is sampled continuously for 48 hours by pumping ambient air into a 40 & bag at a rate of 10 m£/min.[19] This method

requires additional analytical steps by trans- ferring the radon from the bag into a scintillation flask. In addition to errors encountered by

the flask method, correction for the decay of radon during the course of sampling are somewhat

difficult to make since it is not known exactly

when the radon was accumulated In the bag.

Passive environmental monitor . Its principle

of measurement [20] is similar to the passiveelectrostatic monitor in that it samples by

molecular diffusion. Air diffuses through a desiccant into the sensitive volume thus eliminating the effect of humidity on the instrument's

performance

.

The alpha activity that accumulates on the electrode is detected continuously during exposure by a thin thermoluminescence detector (TLD) . After

exposure the TLD chip is read in a thermoluminescence reader and its reading is proportional to the time -Integra ted radon concentration. Calibration of the monitor under different conditions

simulating field atmospheres is necessary.

The response of the monitor lags about 5 hours, which is the diffusion period through the desiccant, but over long monitoring periods

(usually one week or more) the average concentration in the sensitive volume will equal the average ambient concentration even in varying

radon atmospheres.

Radon Daughter Measurements

All measurement methods for radon daughters

are based on collecting a known volume of air

through a filter in a known time and by counting

the activity on the filter during or after

sampling. A number of different samplingcounting regimes may be used and the choice

depends on the amount of information one seeks. The simplest methods involve a single alpha count and yield a result in WL only. The more sophisticated methods involve several counts and yield

the individual air concentrations of the three daughter products, including the WL.

The methods listed in Table 2 for measuring

radon daughter concentrations by grab sampling

are well established. Details of each method are given in the references

.

Errors in determining individual radon

daughter and WL concentrations result from:

1. measurement of sample volume,

2. filter media characteristics,

3. measurement of collected radioactivity

directly on a filter or indirectly on a detector close to the filter.

All three are subject to several sources of errors.

139
Measurement of Sample Volume

Inaccuracies in measurements of air sample

volume results from improper calibration of flowmeters, unstable air samplers, filter holder

integrity and incorrect timing period.

Air pump flowmeters should be calibrated for each application. Their calibration is density

dependent and care must be taken when used at different altitudes. The pump -flowmeter- train

assembly should be calibrated at the same conditions of elevation and at the same resistance

caused by the filter and the other component parts

in the sampling train. During field sampling an open face filter or filter holder assembly suitable for particulates should be used to prevent

radon daughter losses due to plate out. Plate-out

losses may be significant in atmospheres with low concentrations of particles (less than 5,000

particles per cm

3 ). Some instruments tested by EML were found to be unsuitable for radon daughter

sampling. Plate out was high either because the filter was situated at the wrong place during

sampling or because of plate out on surfaces

upstream from the filter.

Sample timing is very important in the usually short sampling periods used for grab

sampling. Errors may be significant if an operator relies on his wristwatch and on his memory. A one-minute mistake in timing causes a 20% error

in air volume alone for a nominal five-minute

sample

The sensitivity of the different grab

sampling methods depend on sampling rate, the delay between sampling and counting, and the counting interval. For low concentrations of radon daughters, such as those encountered outdoors, the precision of the measurement can be

improved considerably by sampling a larger volume

of air. This can be accomplished by increasing

the flowrate and the size of the collection

surface. Sample flowrates from 10 Z/m±n to 300

JL/m±n can be achieved with available commercial

air samplers, and filters ranging in size from 4 cm

3 to 80 cm

3 can be accommodated with existing

samplers and alpha counters. Buildup of filter

resistance from dust loading is unimportant for

the short sampling periods of 5 to 10 min.

If alpha spectrometry is used for counting,

the volume of air is limited because solid state detectors are very small and can handle small filters only. Better sensitivity can be achieved

when counting total alpha as in alpha scintillation detectors which are not limited to sample

volume. A word of caution in using high volume

samplers indoors - if one wants to measure the ambient air, care should be taken not to disturb

it during sampling. A high volume sampler,

operating at 300 i./min in a small room, will

introduce particulates from its exhaust air. This

will disturb the state of equilibrium and attach- ment of the radon daughters, although it will not affect the radon concentration. However, with the proper positioning, high volume samplers can be

used inside large rooms and outdoors.

Filter Media Characteristics

Filters for radon daughter sampling Should

have high collection efficiency and good surface

deposition characteristics. Membrane filters, < 0.8 urn pore size, were found to be suitable.

Tests done at EML with both membrane, 0.8 um pore

size, and glass fiber filters showed collection

efficiencies of virtually 100$ for radon daughters.

Any other type of filter should be investigated

similarly before deployment in the field.

Measurement of Collected Radioactivity

Errors in counting radon daughter samples

result from incorrect calibration of the counting

equipment and from counting errors.

Several types of laboratory and field counters are commercially available; some have more desirable features than others. Scintillation

type detectors are the most popular. Alpha

spectrometry is used in special research applications with limited use in the field.

The counting efficiency of a detector is a function of geometry and energy level. The

geometric configuration of the counter depends on

the distance of the detector from the sample and

the relative size and shape of the detector and

sample. It is essential that alpha counters be

calibrated with an alpha standard having the same size and shape as the sample to be counted.

Usually, Po-218 and Po-214 sampled on a membrane

filter offer the most suitable alpha source. Instruments with thick windows were found to be energy dependent and their detection efficiency

with a monoenergetic alpha calibration source of

5 MeV to be as low as half of that for radon

daughters from Po-218 and Po-214. Alpha counters with windows need to be calibrated with radon

daughters against a windowless counting system. Once the counting efficiency of a counter is determined with radon daughters collected on a membrane filter, any alpha standard may be used as

a reference check source to verify the instru- ment's counting efficiency in the field.

Alpha self -absorption in membrane filters

counted with alpha scintillation counters was

found to be nil. Comparative measurements made by EML on glass fiber and membrane filters show self- absorption in glass fiber filters to be < 5% if the linear velocity across the filter is maintained below 100 cm/s . If any other filter is used, the alpha energy attenuation in the filter

140
should be investigated by making comparative measurements with thin membrane filters or by

using the procedure described in the ANSI standard.

[1]

Counting errors result because of the random

nature of radioactive decay and the larger the number of counts detected the smaller the uncertainty of the measurement. In most of the methods

listed on Tables 1 and 2, there is room for flexibility to reduce counting errors . This can

be accomplished by sampling a larger volume of air on a larger filter, by using a larger or more

sensitive detector, and by counting during and

after sampling.

Radon and Radon Daughter Measurements with

Thermoluminescent Detectors

Thermoluminescence dosimetry (TLD) is gaining

wide acceptance in environmental measurements.

There is an abundance of scientific papers in the literature that cover dosimetry using TLDs and an ANSI standard [36] was issued which considers the performance of TLD systems when used to measure x- and gamma radiation. To our knowledge, there are

no recommended procedures for TLD systems used for measurement of radon and radon daughter radiation

exposures. However, the same performance specifications and testing procedures used in x- and

gamma dosimetry will apply equally well in alphadosimetry

In alpha dosimetry the phosphors that have

been widely used are LiF, CaF2 and CaS04 . These

materials in combination with manganese or dysprosium as activators have adequate sensitivity

for monitoring radon and radon daughters

The short range of alpha rays in matter

insures total deposition of the incident a-ray

energy in the TLD material. Energetic beta and

gamma rays deposit only a portion of their energy

and this prejudices the registered signal in favor

of a-ray energy deposition - a desirable characteristic .

At EML, alpha TLD work began in the late

1960 's during testing and evaluation of personal

dosimeters for uranium miners. We selected LiF

because it has adequate sensitivity and found it

to be less troublesome in environmental measurements. CaFs and CaS04 have better sensitivities

but require energy response and fading corrections - both undesirable characteristics. Since TLD respond to beta and gamma radiation, it is desirable to minimize this response by using a thin dosimeter chip. Our tests indicate that LiF-700 (| x f X .015 in.) minimized response to beta and gamma radiation, and in field measurements the gamma radiation is readily corrected for by a second control TLD chip which is not exposed

to the alpha radiation.

Besides the practical reasons for choosing a TLD system, such as cost and system flexibility, a system with adequate sensitivity over the anticipated range of exposures should be selected. The ANSI standard [36] recommends testing and calibration procedures which are invaluable in selecting

the appropriate TLD system. The key to proper

testing is the simulation of the environmental

conditions under which the system will be used.

The EML Procedures Manual [15] devotes a whole section to the rmo luminescence dosimetry

procedures which will be of particular help to those who plan to incorporate TLD dosimetry in their programs. One of the most critical

parameters that can affect the measurements of radon and radon daughters is uniformity of TLD

response among dosimeters. At EML we found that LiF-700 chips from the same supplier but from

different production lots can vary by as much as a factor of two. Response of TLD chips from the same

lot is usually very good (standard deviation ±5$>) . The uniformity is usually measured by exposing TLD chips to alpha radiation for the same length

of time. From our experience, we found it less troublesome to purchase a large quantity of chips

from the same production lot and use them in our entire program.

Both of the integrating monitors designed by EML for measuring radon and radon daughters, using

LiF-700 chips (f x | X .015 in.) as the sensing

devices, are calibrated in the exact configuration

in which they are used in the field. Calibrations

are performed in a large chamber (20 m

3

) in which

radon and radon daughter exposure conditions can

be simulated. By varying the concentration over periods of one week or more and the normal length

of the field exposure, the sensitivity of the system over a range of exposures can be achieved.

Traceability of Measurements

Radon Measurements

The common methods for measuring radon con- centration are usually calibrated against a secondary standard traceable to a primary NBS standard; this is usually done in large laboratories. At EML, the pulse ionization chamber is the standard against which all other methods are compared. The 2 I pulse ionization chamber is standardized several times a year with radon from

an NBS SRM Ra-226 solution. The solution is diluted (by weight), split into aliquots and placed in radon bubblers from which the radon

standard is transferred to the pulse ionization

by emanation. The chamber has an overall counting

efficiency of 85$.

141
Radon Daughter Measurements

Standard electrodeposited alpha sources of

the same size as the filters are usually used to obtain the counting efficiency of the alpha

detector. At EML, the detection efficiency of 2lT proportional counters is determined by measuring

an NBS certified U3 08 standard source. The activity strength of other sources prepared at EML

or procured commercially is calculated based on

the detector efficiency determined with the NBS standard source. The counting efficiency of radon

daughter detectors is readily determined by

counting Rac' (Po-214) collected on a filter

alternately in a windowless counter and in the detector to be tested.

References

[10]

[1]

[2]

[3]

[4]

[5]

[6]

[7]

[8]

[9]

Radiation Protection in Uranium Mines, American

National Standards Institute, ANSI N13.8 (1973).

Calibration Procedures for Radon and Radon

Daughter Measurement Equipment, R. T. Beckman,

Mining Enforcement Safety Administration

Report MESA I.R. 1005 (1975).

Radiation Exposures in the Florida Phosphate

Industry, W. A. Mills, R. J. Guimond and S. T. Windham, Proceedings IV International Congress,

IRPA, Paris, April (1977).

Assessment of Potential Radiological Health

Effects from Radon in Natural Gas, G. W. Johnson, D. E. Bernhardt, D. E. Nelson and

H. W. Calley, U. S. Environmental Protection

Agency Report EPA 520/1-75-004 (1973)

Measurements of Seasonal and Daily Radon

Daughter Concentration Fluctuations in National Park Service Caves, K. A. Yarborough,

Radon Workshop, ed. A. J. Breslin, U. S. Energy

Research and Development Administration Report

HASL-325, New York (1977).

Radioactivity Associated with Geothermal Waters

in the Western United States, M. F. O'Connell

and G. A. Gilgan, U. S. Environmental Protection Agency Report ORP/LV-75-8B, April (1978)

Investigation of Radon-222 in Subsurface Waters

as an Earthquake Predictor, R. A. Smith, H. R. Bowman and D. F. Mosier, JEFE Transaction on Nuclear Science, NS-23, 694-698 (1976).

The Vertical Distribution of Radon-222, Radon220 and Their Decay Products in the Atmosphere,

W. Jacob i and K. Andre, J. Geophys . Res., 68, 3799 (1963).

Radon-222 Concentrations in the Convective

Patterns of a Mountain Environment, M. H.

[11]

[12]

[13]

[14]

[15]

[16]

[17]

[18]

[19]

[20]

[21]

Wilkening, J. Geophys. Res., 75, 1733 (1970).

The Distribution of Ambient Radon and Radon

Daughters in Residential Buildings in the New Jersey-New York Area, A. C. George and A. J. Breslin, Presented at the D0E/UT Symposium on

the Natural Radiation Environment III, Houston, Texas, April 23-28 (1978).

Improved Low-Level Alpha Scintillation -.(Counter for Radon, H. F. Lucas, Review Sci. Instrum.,

28, 680 (1957).

Scintillation Flasks for the Determination of Low Level Concentrations of Radon, A. C. George, Proceedings of Ninth Midyear Health

Physics Symposium, Denver, Colorado, Feb.

(1976) .

A Study of the Two-Filter Method for Radon-222,

J. W. Thomas and P. C. LeClare, Health Phys .

,

18, 113 (1970).

Development and Operation of Continuous Radon

Monitors 1974-77, J. W. Thomas, U. S. Depart- ment of Energy, Environmental Measurements

Laboratory, unpublished report (1977).

EML Procedures Manual, ed. John H. Harley,

U. S. Department of Energy Report HASL-300,

updated annually (1972).

Dosimetry of Environmental Radon. Methods and

Theory for Low-Dose Integrated Measurements,

R. L. Fleischer, General Electric Research and

Development Center, Schenectady, NY, unpublished report (1980)

Improved Type Track Etch Detector Calibration

Results, H. W. Alter, Terradex Corp., Walnut

Creek, CA, unpublished report (1980).

Design and Application of a Continuous,

Digital-Output Environmental Radon Measuring

Instrument, H. Spitz and M. W. Wrenn, Radon

Workshop, ed . A. J. Breslin, U. S. Energy

Research and Development Administration Report

HASL-325, New York (1977).

An Integrating Air Sampler for Determination

of Radon-222, C. W. Sill, Health Phys., 16, 371 (1969).

Measurement of Environmental Radon with

Integrating Instruments, A. C. George and

A. J. Breslin, Workshop of Methods for Measuring Radiation in and Around Uranium

Mills, ed. E. D. Harward, Atomic Industrial

Forum, Inc., Program Report, Vol. 3 (1977).

Radon Daughters in Mine Atmospheres - A Field

Method for Determining Concentrations, H. L. Kusnetz, Am. Ind. Hyg. Assoc. J., 17,85(1956).

142
[22]

[23]

[24]

[25]

[26]

[27]

[28]

[29]

[30]

[31]

[32]

[33]

[34]

Rapid Working Level Monitoring, R. Rolle,

Health Phys . , 22, 233 (1972).

Occurence of Nonequilibrium Atomospheric

Mixtures of Radon and Its Daughters, E. C. Tsivoglou, H. E. Ayer and D. A. Holaday,

Nucleonics, 1, 40 (1953).

Measurement of Radon Daughters in Air, J. W. Thomas, Health Physics, 23, 783 (1972).

A Radon Daughter Monitor for Use in Mines,

A. C. James and J. C. Strong, Proceedings 3rd International Congress, IRPA, Washington, D.C., USAEC CONF-730907, p. 932 (1973).

Analysis of the Activity of Radon Daughter

Samples by Weighted Least Squares, 0. G. Raabe

and M. E. Wrenn, Health Phys., 17, 593(1969).

Analysis of Atmospheric Concentrations of RaA, RaB and RaC by Alpha Spectroscopy, D. E. Martz,

D. F. Holleman, D. E. McCurdy and K. J. Schiager, Health Phys., 17, 131 (1969).

The Measurement of Low-Concentrations of the Short-Lived Radon-22 Daughters in the Air by

Alpha Spectroscopy, N. Jonassen and E. I. Hayes, Health Phys., 26, 104 (1974).

A Microprocessor-Assisted Calibration for a Remote Working Level Monitor, W. B. McDowell,

D. J. Keefe, P. G. Groer and R. T. Witek,

IEEE Trans. Nucl. Sci., NS-24:1, Feb. (1977).

Integrating Radon Progeny Air Sampler, K. J. Schiager, Am. Ind. Hyg. Assoc. J., 35, 165

(1974) .

A Working Level Dosimeter for Uranium Miners,

A. J. Breslin, S. F. Guggenheim, A. C. George

and R. T. Graveson, U. S. Department of Energy

Report EML-333, New York (1977).

A Time -Integra ting Environmental Radon

Daughter, S. F. Guggenheim, A. C. George,

R. T. Graveson and A. J. Breslin, Health Phys.,

36, 452 (1979) .

Interpretation of the Response of Continuous

Radon Monitors to Transient Radon Concentrations, A. Busigin, A. W. Van Der Vooren and

C. R. Phillips, Health Phys., 37, 659 (1979).

A Two-Filter Environmental Monitor with an Automatic Drive that Changes the Exit Filter,

V. C. Negro, U. S. Department of Energy

Report EML-367, p. 244 (1979).

[35]

[36]

FUNGI - A Radon Measuring Instrument with Fast Response, V. C. Negro and S. Watnick, IEEE Trans. Nucl. Sci., NS-25, p. 757 (1978).

Performance, Testing and Procedural Specifications for Thermoluminescence Dosimetry

(Environmental Applications), American

National Standards Institute, ANSI N545

(1975).

143
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the
PERFORMANCE TESTING OF PERSONNEL DOSIMETRY SERVICES

Phillip A. Plato

C. Glenn Hudson

The University of Michigan

Ann Arbor, MI 48109

From 1977 to 1979, The University of Michigan conducted a pilot study of a dosimetry

performance testing standard that the Nuclear Regulatory Commission is considering

as the basis of a mandatory testing program for dosimetry processors that service

their licensees. This paper discusses the traceability of the radiation sources used

in the pilot study to the National Bureau of Standards and summarizes the results of

the pilot study.

(dosimeters, NRC, pilot study, sources, standard, traceability)

Introduction

There have been many attempts during the past

twenty years to test the performance of personnel

dosimetry processors in the United States. Customers and competitors of commercial dosimetry

processors continuously design tests to examine

the competence of a given processor. Unfortunately, the competence of the testing group has often been worse than the competence of the pro- cessor being tested, which created more problems

than were solved. The National Sanitation Foundation [1] (NSF) has operated an annual dosimetry

testing program since 1966. However, participation in the NSF testing program is on a voluntary basis and, as a result, attracts a maximum of only a half dozen commercial processors

on a regular basis. In 1972, the American

National Standards Institute published a standard [2] that could be used to test the performance

of film badge processors. Due to a variety of criticisms [3], the standard was never used.

Thus, in reviewing the past efforts to test the performance of dosimetry processors, one common observation is apparent; none was successful.

In 1975, the Health Physics Society Standards

Committee (HPSSC) formed Working Group 1.4,

chaired by Dr. Margarette Ehrlich, to prepare a new standard that could be used to test dosimetry

processors. There was one primary reason to hope

that this standard would succeed as a useful docu- ment whereas other similar dosimetry standards had

received either modest support nationally or no support at all. That reason was cooperation among

a variety of regulatory agencies that would make

use of the HPSSC Standard once it had passed peer- review processes

.

The impetus for the development of a new standard came initially from the Conference of State Radiation Program Directors. The idea was

endorsed by the US Nuclear Regulatory Commission

(NRC) which expressed an interest in amending

10 CFR 20 to require performance testing of do- simetry processors that serve NRC licensees. An Interagency Policy Committee was formed to monitor

the progress of Working Group 1.4 and to coordinate the efforts of the various regulatory agencies

concerning future mandatory testing of processors.

The Interagency Policy Committee included members of the NRC, the Department of Energy (DOE), the Department of Defense, the National Bureau of Standards, the Bureau of Radiological Health, and

a representative from the States. Although no regulatory agency could commit itself in 1975 to the adoption of the standard that would be pro- duced by Working Group 1.4, it was the hope of many people that the standard would someday be

adopted by all the regulatory agencies involved

as the basis of a uniform, nationally-recognized,

mandatory testing program for all personnel do- simetry processors in the United States.

By late 1976, the first draft of the HPSSC

Standard [4] was available for public comment.

In a public meeting held at the end of 1976, con- cern was expressed by a number of people that regulatory agencies might adopt the Standard

without first seeing how it would work in a test situation. Thus, the NRC sponsored a two-year

pilot study of the Standard beginning in October,

1977. The contract to conduct the pilot study was awarded to The University of Michigan. Any

organization in the United States that processed

personnel dosimeters used for primary dose

records was permitted to participate in the pilot

study on a voluntary basis at no charge. A total

of 59 organizations chose to participate. These

included large and small commercial processors, most of the National Laboratories, a number of prime DOE contractors, many nuclear power plants,

the military, and a few medical facilities and universities

.

The purpose of this paper is to discuss the traceability of the radiation sources used in the pilot study to the National Bureau of Standards

(NBS), and to summarize the results of the pilot

s tudy

.

145
Radiation Sources

Table 1 is a summary of the radiation sources

used during the two-year pilot study and the pro- cedures used to determine if a processor passed

or failed any radiation category (type of radiation) within the Standard. A detailed description

of calibration and irradiation procedures has been

published [5] . Four types of radiation are re- quired for the Standard as shown in Table 1: gamma-rays (cobalt-60), standard NBS X-ray techniques (specific combinations of voltage and filtration), beta particles (strontium-90) , and neutrons (californium-252) . When the NRC contract' was awarded to The University of Michigan, we

had seven months to obtain the required sources, calibrate the sources, and develop the operational

and administrative procedures required to test each processor according to the Standard. At the same time the NRC awarded the contract to The University of Michigan, they awarded a second

contract to NBS to provide calibrations and other

technical services to The University of Michigan

to insure that all irradiations done for the pilot

study would be accurate to within ±5% as specified

in the Standard.

Two cobalt-60 sources, 5 Ci and 2700 Ci, were

used for the pilot study. Two Shonka-Wyckof

ionization chambers, 3 cm3 and 100 cm^, were cal- ibrated to cobalt-60 by NBS. These chambers were

then used to calibrate the exposure rate from

the two University of Michigan sources. Half-life

corrections were made on a daily basis after each source was calibrated.

The same two ionization chambers were also

calibrated by NBS to several standard NBS X-ray

techniques . The chambers were used to calibrate

an X-ray beam before and after dosimeters were

irradiated on a given day. A beam monitor con- nected to a strip chart recorder was used to determine if the exposure rate of the beam changed

during the working day.

A 40 mCi strontium-90 beta-particle source was calibrated by both NBS and The University of Michigan using extrapolation chambers. Half-life

corrections were made on a monthly basis after

calibration.

The californium-252 neutron source was cal- ibrated by NBS with their manganese sulphate

bath calibrator. The neutron emission rate de- termined by NBS was combined with a dose con- version factor given in the Standard to calculate

a dose equivalent rate at a given distance from

the source.

Results

each depth of each interval (dose range) shown

in Table 1. Thus, to pass Category IV, a pro- cessor had to pass only two statistical tests. However, to pass Category II, a processor had to pass seven statistical tests. The statistical

criteria are summarized on the bottom of Table 1 and are discussed in detail in the Final Re- port [6] of the pilot study.

The results of the pilot study showed that only about one-third of the categories tested were passed. The passing rate for the intervals

tested was considerably better, although a pro- cessor passes a category only if all the dose

intervals within the category are passed.

As part of an additional analysis of the results of the pilot study, the performance of each individual dosimeter irradiated during the pilot study was examined. This analysis, which

is discussed in detail in a Supplementary Re- port [7] following the completion of the pilot

study, is not part of the statistical requirements

of the Standard. However, this analysis permits

an observation of the percent of dosimeters that had a reported dose within ±10% of the actual

delivered dose, ±30%, ±50%, etc. The results of this analysis showed that approximately 80% of

the 23,000 dosimeters irradiated during the two- year pilot study had a reported dose that was within ±50% of the delivered dose.

Conclusion

The NRC and the other relevant regulatory

agencies are currently evaluating the results of

the pilot study to determine if a mandatory

testing program is necessary and feasible for all dosimetry processors in the United States. Operationally, a mandatory testing program ap- pears to be feasible. The radiation sources required by the Standard can be calibrated and used to provide delivered doses within ±5% re- quirement of the Standard. The cost of a mandatory testing program does not appear to be

prohibitive, probably around $3,000 for a com- plete test of a processor. Administratively,

the problems are immense. Answers are currently

being sought to questions such as;

How many tests should a processor be re- quired to pass within a given time

period?

What should be the qualifications of a testing laboratory?

How many testing laboratories should be

permitted?

How should a testing laboratory be monitored

Each processor was permitted to be tested technically to insure credability?

twice during the pilot study. In each test, a processor could choose to be tested in any or Who should mediate a dispute between a all of the radiation categories shown in Table 1. testing laboratory and a processor?

To pass each category, a processor had to pass

146
Should a processor that fails a test be

given a probationary period to correct

problems while still being permitted to provide dosimeters to radiation workers?

The relatively easy work of the pilot study

has baen completed. The difficult task of im- plementing the Standard is now at hand.

[1]

[2]

References

National Sanitation Foundation Standard No. 16 Relating to Dosimetry Services. The National

Sanitation Foundation, P.O. Box 1468, Ann

Arbor, MI, 48106 (1966)

.

American National Standards Institute, inc.,

American National Standard Criteria for Film .t" Badge Performance, ANSI N13.7 - 1972. 1430 3roadway, New York, NY (1972).

[3]

[4]

[5]

[6]

[7]

Plato, P. Evaluation of "Criteria for Film

Badge Performance" ANSI N13.7 - 1972. Am . Ind. Hygiene Assoc. Journal , 38:41-45 (1977).

Criteria for testing personnel dosimetry performance. Proposed standard prepared by the Health Physics Society Standards Committee,

4720 Montgomery Lane, Suite 506, Bethesda, MD 20014 (November 30, 1977). This Standard

is also published by the American National

Standards Institute as Draft ANSI N13.ll.

Plato, P. and Hudson, G. Procedures manual

for performance testing of personnel dosimetry

services, NUREG/CR-1063, National Technical

Information Service, Springfield, Virginia

22161 (January, 1980).

Plato, P. and Hudson, G. Final report for performance testing of personnel dosimetry

services, NUREG/CR-1064, National Technical

Information Service, Springfield, Virginia

22161 (January, 1980).

Plato, P. and Hudson, G. Supplementary re- port for performance testing of personnel

dosimetry services, NUREG/CR-1304, National

Technical Information Service, Springfield,

Virginia 22161 (April, 1980).

147
TabLe 1. Summary of the HPSSC Standard used in the pilot study.

Tolerance Level (!) Number of

Dosimeters

(see f o: tnote s) Radiation Shallow De - r Ca t ego r

Interval Test Range Per Test ( 7 ms? / ctq^ ") (1000 -z/c-.~ 1

I. Gatoa 1 Accident: 10-SQ0 rad 10 no test a (Co-60) 2 Protection: 30-100 mrem 10 no test b

3 101-300 10 no test b

4 301-10 000 mr em 10 no test b

II

X Ray 1 Accident: 10-800 rad 10 no test a (30-300 keV) 2 Protection: 30—100 mrem 10 c c

3 101-300 mrem 10 c c

4 301-10,000 mrem 10 c c

III. X Ray Accident: no test (15-30 keV) 1 Protection - 150—300 mrem 10 c c

2 701 Jul -in1U)UUU ODD 10 c c

IV. Beta Accident: no test (Sr-90) 1 Prnfprfinn' 1 5H— TOD mrem 10 c no test

2 Jul J. v )UUU mrem 10 c no test

V. Man r rAn

Accident: no test (Cf-252) 1 Protection: 100-300 mrem 10 no test c

2 301-5,000 mrem 10 no test c

VI. Photon Mixtures Accident: no test

(Cat. I & II) 1 Protection: 50-100 mrem 10 c c

2 101-300 mrem 10 c c

3 301-10,000 mrem 10 c c

VII. Photon and Beta Accident: no test Mixtures 1 Protection: 200-300 mrem 10 c c (Cat. I or II&IV) 2 301-10,000 mrem 10 c c

VIII. Photon and Neutron Accident: no test Mixtures 1 Protection: 150-300 mrem 10 no test c (Cat. I & V) 2 301-5,000 mrem 10 no test c

For each dosimeter, a performance index is calculated by: H' - H

P -

H where: H = delivered quantity

h' = reported quantity

For each depth of each interval, an average performance index, P, and its standard

deviation, S, are calculated.

A processor passes a category if, for each depth of each interval:

|P| + 2S 1 L where:

a: L = 0.3

b- L = 0.3 or 6//rf whichever is larger

c: L 0.5 or 15/ /lT whichever is larger

148
OCCUPATIONAL EXPOSURE MEASUREMENTS IN MRC REGULATORY GUIDES*

Allen Brodsky

Occupational Health Standards Branch

Office of Standards Development

U.S. Nuclear Regulatory Commission

Washington, D.C. 20555

Since the formation of the Nuclear Regulatory Commission (NRC), a series of guides

on occupational radiation protection standards have been developed. These guides

include information on acceptable accuracy and quality control of most types of

radiation survey measurements for internal and external exposure assessment. How- ever, more complete specifications of precision, accuracy, and traceability

requirements are under development, and programs are underway to establish measurement systems for monitoring and certifying licensee compliance with quality control and accuracy standards. Many fundamental measurement principles and radiation

protection concepts are involved in these developments, and they must be better

understood and applied to properly establish these systems.

(Accuracy, bioassay performance, occupational radiation protection standards, performance

criteria, quality control, radiation instrument performance, radiation measurements,

ragulatory standards)

I. Introduction

In recent years, a fairly extensive body of

NRC regulatory guides [1-31] has been published to assist the NRC licensee in establishing acceptable

ways of meeting regulatory standards for radiation

protection and the measurements and surveys required to ensure compliance with the exposure

standards [32]. However, the specific accuracy

and quality control performance criteria for the radiation or radioactivity measurements to be made

for occupational health protection still require

further development, although considerable progress

has already been made — particularly in regard to the development of personnel dosimetry performance

criteria. Preceding papers have described some of

this development, but some more recent progress in developing bioassay performance criteria will be summarized here. NRC programs for implementing

performance testing of personnel dosimetry are already underway [33-37], and similar programs for implementing the performance testing of survey meter calibrations and radiobioassay services are

planned. Many of the agencies and scientists

participating in this meeting have been very helpful to NRC in the development of these programs

and standards.

In developing its guidance, the NRC has encouraged public and licensee participation, and

has followed the government policies of supporting

the development of national consensus standards

through the American National Standards Institute

(ANSI) wherever possible [38,39]. A number of

these standards [40-73], in addition to the recom- mendations of professional and scientific organizations [74-80], are now available to guide the establishment of good radiation measurement and

survey practices. Where appropriate for regulatory

purposes, some of the provisions of the ANSI have

been incorporated by reference into NRC guides.

The NRC staff is supporting and participating in the development of further ANSI standards that are expected to be used in regulatory guidance and rule making on measurement accuracy and performance.

The participation of all government agencies in the development and use of consensus standards, in order to expedite the development of reasonable and effective regulatory requirements without unnecessary duplication of effort by the Federal agencies,

has been further encouraged by a recent Office of

Management and Budget circular [81], Considering

the complexities of scientific methods, measurement principles, radiation protection philosophies,

government-industry employee-public relations, and radiation protection management principles, which

all interact in the development of adequate per- formance testing systems, it is essential that

participation of all concerned and expert parties

be well coordinated during the implementation of

these systems. Thus, this is a subject worthy of

considerable further discussion. Only a few current developments can be mentioned here. There

are also many technical and policy questions that must be answered before the complete implementation

of a comprehensive national system of performance

testing can be accomplished, which will ensure the reliability and accuracy of measurements used for radiation protection purposes. Hopefully, the talks

and discussions at this conference, and their

publication for further study, will stimulate

progress in answering these questions.

Presented at the Seminar on Traceability for Ionizing Radiation Measurements, National Bureau of

Standards, Washington, D.C. 20234, May 8-9, 1980, to be published. This paper was prepared by an employee of the U.S. Nuclear Regulatory Commission. It presents information that does not necessarily

currently represent an agreed-upon staff position, but the author believes it to be consistent with current NRC plans and policies. NRC has neither approved nor disapproved its technical content.

149

*
II . Types of Occupational Exposure Measurements

Required for Employee Health Protection

The types of radiation exposure measurements

required by NRC regulations [32] to ensure compliance with regulatory limits of exposure may be divided into the following categories: personnel

dosimetry for external exposure monitoring; bioassay measurements for estimating internal exposures

(including in vivo or whole body counting); air

monitoring Tmeasurements of concentrations of

radioactivity in air in work areas); and surveys of external radiation levels and surface contamination. The regulatory guides related to occupational protection and license application requirements [1-31] now provide rather comprehensive

information and references that identify acceptable

radiation protection and survey practices for many

different types of installations, although the series is not complete in all respects. Most of

the guidance is procedural so far, but some information on accuracy requirements over necessary ranges of measurement have been developed based on recommendations of professional consensus standards

and regulatory experience. The present status of

NRC efforts to define, and subsequently monitor

compliance with, accuracy requirements for occupational exposure measurements will be reviewed.

However, the NRC programs to improve measurement

accuracies will either depend upon or will be assisted by, the current national and international

efforts to define and improve both "artifact

traceabil ity" and "measurement traceabil ity" as described by Eisenhower [111], or equivalently

"direct" and "indirect" traceabil ity (including

documentation) as defined by Kathren [112]. Thus,

some remarks will also be made about the NRC 1 s interest in the subject of traceabil ity, and its relationship to the overall quality control of

radiation protection measurements of various types.

A. Personnel Monitoring

The development of standards of performance for personnel monitoring services, and the completion

of tests of the feasibility of establishing a laboratory to certify compliance with such standards, represents in my opinion a major advance

in recent years toward national systems to assure

the best state-of-the-art accuracy in -Field measurements for radiation protection purposes.

Dr. Plato has ably described the progress of this program in the preceding paper of this seminar,

and in his reports [34-36]. He and Dr. Margarete

Ehrlich, who chaired the Health Physics Society WG

that produced the recent draft performance standard [37], deserve commendation and gratitude for their scientific and professional leadership in these projects.

Also, much credit is due R. E. Alexander and R. B. Minogue who recognized the need for NRC initiative

in providing the funding and technical direction

to implement this important program. Despite so many years and so many previous scientific efforts

to develop performance criteria [82-86], the implementation of a nationwide program to certify

personnel dosimeter processors had foundered until

now. Hopefully, the forthcoming public meeting

[33] on personnel dosimetry will help resolve the remaining technical and operational questions, and

a national system of quality assurance for

personnel dosimetry will be established and operating within the next few years. This system may

then serve as a model for establishing national

quality control over the other measurements made

for radiation protection: bioassay measurements

for internal exposure assessments; measurement of

air concentrations of radioactivity to evaluate

and control sources of internal radiation exposure

in the work environment; and surveys with field

instruments to measure ambient external radiation

exposure levels or surface contamination in work areas

B . Bioassay

Although a formal system of certifying the accuracy

and quality control of bioassay services has not yet been implemented, there has been considerable

progress in establishing a consensus of good pracice in the form of draft or final ANSI standards

for the important nuclides encountered in industry

and medicine. These ANSI standards have been pre- pared by working groups of the Health Physics

Society Standards Committee (HPSSC).

Information in one of the earlier drafts of the uranium bioassay standard was used in preparing

NRC Regulatory Guide 8.11 [11], published together

with an NRC NUREG report [126], which provides

analytical methods for evaluating internal radiation exposures from uranium bioassay data. Additional experimental work is underway at the University of Rochester to provide data that will allow the extension of these analytical methods in cases of exposure to UFg or its hydrolysis products.

One of the earlier working groups, composed of

health physicists involved in radiochemical bio- assay and whole body counting from various types of reactor installations, industry users, commercial

analytical laboratories, and the NRC, completed

development of an ANSI standard on bioassay of

fission products- and activation products [43].

This standard provides conditions requiring bio- assay, advice on selection of personnel to be bioassayed, frequencies of bioassay, and action

levels and actions to be taken, for various radionuclides — both for radiochemical procedures and

in vivo counting. It also provides, in appendices,

data and information useful for quantitatively

converting some types of bioassay data into esti- mates of internal organ doses. This ANSI standard

was well received by NRC technical staff, and was incorporated into a proposed Regulatory Guide,

published for comment in 1979 with only minor

interpretive additions. Comments received indi- cate that the parts of the standard dealing with

establishing, operating, and quality control of

fission product/activation product bioassay services are acceptable, but requests have been made

to update information on methods of dose evaluation. Publication of the regulatory guide in final form as Regulatory Guide 8.26 is expected in 1980, with relatively minor revisions and additional references to more recent literature on internal dose calculations and their relationships

to excretion analysis.

Since many detailed refinements in internal dosimetry modeling and calculation methods are underway

[104-106], in particular a complete revision of

the ICPP 10 series that provides methods of

150
relating bioassay data to internal doses [107], the user of the guide will be reminded to examine current literature for new information when examining individual cases with appreciable internal exposure. After all, in bioassay data evaluation,

each case of significant human exposure requires more than a single measurement, and is usually a research effort worthy of publication. Although

for fission and activation products, in vivo detection limits are usually far below the activities

that would deliver maximum permissible internal organ doses, even for equilibrium situations where

the internal burdens are continuously maintained

(see Table 1 and Reference 43), interpretation of

the actual burden of each organ and projected dose

commitments still require considerable skill of

measurement and analysis. Usually, a number of measurements by several independent methods over

time, selection of the proper mathematical models

of organ retention and body distribution vs. time,

and experienced judgment in pooling results to obtain the best dose commitment estimates, are required. This, combined with the inherent complexity and variability in assessing biological risk

factors per unit dose, makes the statement of accuracy and quality control requirements for bio- assay of numerous and/or mixed radionuclides

extremely difficult. The specification in advance

of a single mathematical model for utilizing bio- assay data to evaluate internal exposures in individual human cases even with varying parameters for each nuclide and form -- is impossible at the present time.

ANSI standards for bioassay of two other nuclides,

plutonium and tritium, have been completed in draft

form by Health Physics Society working groups. Again, both of these standards provide recommended

methods and programs for: managing bioassay

services; deciding which employees are to be bioassayed, under what working conditions, levels of exposure to air concentrations, or quantities of

material handled in unsealed form; what frequencies

of bioassay are appropriate; and what actions

should be taken when bioassay measurements exceed

selected action levels. In both documents, mathematical models and calculation methods for evaluating internal radiation exposures based on the bioassay measurements are presented only as examples of state-of-the-art methods. References are

also given to provide an introduction to important

published data and methods that may be used in individual human cases to obtain initial and follow

up estimates of internal radiation doses and dose

commitments. Criteria for evaluating measurement

accuracy, and defining and calculating statistical

limits of detection are provided in each document.

These criteria are based in each case on a judgment

of state-of-the-art measurement capabilities, as

well as on radiation protection requirements for optimum detection and measurement of internal burdens of H-3 or Pu-239 (and Am-241 ) under the specified programs and frequencies of sampling.

Although both the H-3 and Pu-239 standards have

been approved by the Health Physics Society Standards Committee for over a year, neither standard

has yet been approved by the ANSI Ml 3 Committee

and submitted for ANSI board approval. However,

in 1977 the NRC staff utilized some of the earlier

work on the H-3 draft standard to develop a concise

staff position, which is utilized by the Material

Licensing Branch of NRC, and available from that

Branch. This staff position provides criteria for judginq when it is appropriate to require bioassay

for tritium, and provides methods acceptable to NPC staff for selecting: employees to be assayed,

frequencies of bioassay, action levels in terms of

measured urine concentrations of tritium, and actions to be taken when specified concentrations

are exceeded. The draft plutonium standard has also been used informally by NRC licensinq staff

for guidance in evaluating bioassay programs in fuel cycle facilities.

While there are many important differences in the measurement and radioanalytic techniques of bioassay

for the many different radionuclides, and their

varied physico-chemical forms, there are also many

common aspects of bioassay proqram management:

quality control; statistical definitions accuracy, precision, bias and lower limit of detection:

record keeping; and types of actions to be taken in following up exposed employees whose bioassay measurements have exceeded action levels. Thus, in order to establish standards of bioassay performance

upon which a uniform national program of performance

testing can be based, which will enable NRC to ensure

that any radionuclide bioassays required of NRC licensees are sufficiently reliable and accurate for internal exposure monitoring purposes, the Office

of Standards Development requested the Health Phys- ics Society to establish another working group. In 1979, Working Group 2.5, "Criteria for Testing

Radiobioassay Performance," was established under

the chairmanship of Kenneth Heid. Excellent progress has been made and a first complete draft will

be examined for coherence and edited by the full Working Group at the 19B0 annual meeting of the Health Physics Society. The purpose and scope of

this standard, as currently agreed to and tenta- tively drafted for the Working Group, is as follows:

"1 . PURPOSE AND SCOPE

1 .1 Purpose

The purpose of this standard is to provide:

quantitative performance criteria for the accuracy

of measurements ('radiobioassay') of radioactivity

in humans occupational ly exposed to the intake of

radioactive materials and biological matrices

sampled from these humans; procedures for testing

radiobioassay service laboratories to determine

that their analyses conform adequately to these

performance criteria, for a selection of important

and representative radionuclides; and selected

quality control criteria and procedures of a non- quantitative nature that are necessary to ensure continued reliability of both the radiobioassay

source laboratories and the laboratories conducting

the testing programs.

"1 .2 Scope

This standard provides quantitative per- formance criteria for the accuracy and precision

of radiobioassays of selected radionuclides in the bodies of, or in biological samples from, persons occupationally exposed to the intake of radioactive materials. It also provides standard quality

control procedures for the internal quality assurance programs of radiobioassay laboratories, and procedures to be used by testing laboratories for

151
testing the conformance of radiobioassay service

laboratories to both the quantitative performance

criteria for accuracy and precision and the standard quality control procedures.

"Specifications are given for:

1. Accuracy and precision of both direct ( in vivo ) and indirect measurements of concentrations and quantities of selected important radionuclides

in humans and biological samples.

2. Acceptable detection limits for both routine

and emergency analyses, in terms of standard

definitions of acceptable 'minimum detectable

amounts (MDA) .

3. Ranges of concentration and amounts to be measured

4. Acceptable time limits for reporting analytical

resul ts

5. Standard methods of reporting analytical

resul ts

6. Standard procedures for internal quality control

in radiobioassay laboratories, including proce- dures for:

a. obtaining and handling samples

b. preliminary sample preparation and monitoring for external contamination

c. showering, clothing, and monitoring persons

prior to vn vivo counting

d. quality control and calibration of radioactivity counting equipment

e. providing suitable 'blank' and 'control' samples of measurement,

f. maintenance of records of all data and pro- cedures used in radiochemical and radiometric

analyses

7. Standard procedures for preparation and distribution of test samples and/or phantoms by the testing laboratories, for both 'blind' and 'non- blind' test programs.

8. Standard procedures for reporting test evaluations to the testing laboratories.

9. Standard procedures for evaluating and reporting

of test results by the testing laboratories.

"Criteria and procedures pertaining to direct

( in vivo ) radiobioassay are given in separate sec- tions of this standard from criteria and procedures

for indirect radiobioassay, since different testing

laboratories may be concerned with the different

types of radiobioassay. In addition, examples to clarify concepts and methods described in this

standard, and information that may be useful in implementing this standard, are presented in appen- dices to this standard. The appendices are illustrative and are not a part of the standard.

The scope of this standard does not include:

1. detailed radiochemical methods for extracting

radionuclides from biological samples,

2. detailed procedures for radiometric measurement

of in^ vivo and vn vitro samples.

3. metabolic data and mathematical models for converting radiobioassay results into absorbed

dose and dose equivalent,

4. radiation protection program management aspects

of radiobioassay sampling and services described

in standards for specific nuclides.

"Analytical methods are not currently

standardized, but are available in the literature

and are provided in summaries and references

appended to this standard and to standards for specific nuclides. Standard methods for converting

radiobioassay results into dose and risk estimates

are provided in publications of the International

Commission on Radiological Protection (ICRP), the National Council on Radiation Protection and Measurements (NCRP), and the International Commission on Radiological Units and Measurements (ICRU).

Recommendations of the ICRP, NCRP, and ICRU, and experience with the practical application of these

recommendations to the conduct of radiobioassay

services and the interpretation and use of bioassay

results in radiation protection programs, have been considered in the development of this standard.

Appendices to other standards on the provision and management of bioassay programs for specific radionuclides include information useful for interpreting and using bioassay results for radiation pro- tection purposes. The purpose of the present

standard is primarily to ensure the accuracy and reliability of the analytical results."

The purpose and scope alone illustrate the complexity of determining the content of a broad performance standard covering the area of bioassay measurements. Anyone wanting to maintain liaison

with this working group, or contribute experience

or ideas toward its goals, should contact the Chairman [113].

In addition to progress in improving and standardizing bioassay performance through participation in ANSI activities, the NRC develops its own criteria

to meet priority needs. Regulatory Guide 8.20 [18] was developed by NRC scientific staff to meet an urgent need for guidance on when 1-131 and 1-125 bioassay services should be provided to employees,

who should be monitored, and what action levels and actions are appropriate when positive indications

of internal 1-131 or 1-125 radioactivity are obtained. Since many of the compounds of iodine

nuclides used in medicine, industry and research

tend to be more volatile and/or dispersible than compounds of other nuclides, and upon inhalation or ingestion iodine tends to be absorbed into the body

and concentrated in the thyroid, the radioactive

iodine compounds have been involved in numerous questions regarding the need for, and interpretation

of, bioassay measurements in NRC-licensed establish- ments. Thus, the revision of Regulatory Guide 8.20

required not only a consideration of the many com- ments on the draft version, but visits to many

hospitals and industrial establishments to obtain

specific information on the likelihood of employee exposure in different situations, and on practicable

152
methods of carrying out bioassay programs.

During these visits, it was apparent that the guidance should not include specific measuring

equipment, nor radioanalytic or radiochemical pro- cedures, but only some selected references for persons establishing new bioassay measuring systems

for 1-131 and 1-125. Many different systems were

found to be in use and adequate for detection and measurements of 1-131 and/or 1-125, depending in some cases on what equipment or funds were available and what I-containing materials were involved

in the exposures. Also, it was evident that a scientist experienced in radiochemical or iji vivo measurements would need to be employed by a licensee to at least set up the equipment and pro- cedures for bioassay of radioiodines . This conclusion is similar to those of the ANSI committees,

which have each concluded that specific radioanalytic and measurement techniques should not be a part

of the standard. General guidance on instrumentation and radioactivity measurements is available

in References 78 and 79.

When the development of basic written criteria for accuracy and performance testing of radiobioassay

services is complete, the implementation of perform- ance testing will still require answers to many

questions, including:

(1) What additional procedures will need to be developed by a testing laboratory to provide "blind" and/or "double blind" tests

by sending radiochemical ly spiked samples

or phantoms to laboratories around the country?

(2) What additional radiochemical and physical

requirements need to be imposed on samples

to be prepared for shipment?

(3) What type of laboratory and/or laboratory

facilities would be appropriate for assuming

the role of the testing laboratory?

(4) How will the performance of the testing

laboratory itself be monitored, and how

will its own measurements be made "trace- able to the National Bureau of Standards"?

(5) What initial trial program of testing will

be necessary to ascertain both that the established laboratory is ready to carry out

a formal testing and certification program,

and that the basic standard of performance

is indeed sufficient and appropriate as a basis for testing the variety of laboratories

offering bioassay measurement services?

(6) What agencies will participate in the funding and supervision of the implementation

of this program, and how will the funding

be provided for the several stages of implementation?

Some guidance in answering these questions will come from the professional community of chemists,

physicists, and health physicists involved in radiobioassay, some will come from the early experience in NRC's program for performance testing of

personnel dosimetry services [34-37], and some will come from programs for testing performance of

radioanalytical services in measurinq environmental

samples [96-103, 114]. However, some additional

applied research in preparation of properly

simulating biological samples containing known quan- tities of radionuclides to be assayed will probably

be needed. Also, a pilot program that actually

sets up and implements a testing program for a trial period of three years will be needed to solve, and weave into a workable system, all of the management,

sample preparation, measurement, statistical, and

legal questions involved in an on-going radiobioassay performance testing and certification program.

C. Instrumentation, Surveys, and Air Monitoring

Regulatory guidance does not so far provide

detailed criteria for the accuracy and performance

of instruments used in surveys and air monitoring,

other than some general statements of accuracy in licensing and survey guides [4, 14, 19, 21, 22, 24- 31]. Some of these statements are under revision

to include suggestions for improvement contained

in recent public comments, and can be expected to be more uniform in future guides. However, they do not contain the rigorous statistical definitions

of accuracy and performance nor the procedural

specifications for instrument usage that would en- sure adequate survey measurements.

Calibration frequencies and some limited specification of ranges of calibration required for instru- ments used to monitor external radiation are con- tained in these guides. The Occupational Health

Standards Branch plans to recommend a rule and guide

specifying in more detail NRC's calibration

requirements and acceptable ways of calibrating

radiation survey instruments. Several acceptable

methods of calibration have been drafted, with the advice of National Bureau of Standards staff, and are presented in Appendix A for illustration only. The draft in Appendix A takes into account the facts

as explained by Elmer Eisenhower [111] at this

conference, that the National Bureau of Standards

maintains the standards but does not define methods

for making measurements by others "traceable to NBS"; it is each agency's responsibility to define

"traceable" for each measurement according to its requirements. Also, as pointed out by Ron Colle' [115], one can not define "traceable" without

actually stating "what you do" to make a measurement traceable; and when "what you do" is spelled

out, the word "traceable" may no longer be needed--

unless it is useful for repetitive reference.

Some of the examples in Appendix A may suffice to show how the specification of "acceptable methods"

of calibration may be used, in lieu of a vague requirement to make measurements (or sources)

traceable to NBS. The goal is to define what is to be done to ensure good practice in the calibration of radiation survey instruments.

153
The types of procedures in Appendix A for "acceptable calibrations," if carried out regularly by the licensee or company responsible for monitoring

its employees, would themselves provide considerable confidence that monitoring instruments used

for surveys were operable and sufficiently accurate

for radiation hazard assessment. However, an independent testing program might still be neces- sary for testing independent companies or agencies

performing calibration services for NRC licensees,

and perhaps for testing a licensee's own capabilities as appropriate. Recently another working

group has been formed under the Health Physics

Society Standards Committee to develop an ANSI standard on the testing of radiation survey instru- ment performance. Also, the NRC Office of Standards

Development is planning to implement a pilot program

for testing the performance of survey instruments

against the draft ANSI standard when it becomes

avail a bl e.

General guidance for many aspects of these programs may be obtained from some of the regulatory guides

[100-103] and the standards and recommendations

[74-80] already available. Specifications and performance standards in some of the current ANSI standards [41, 42, 44, 45, 46, 53, 54, 55, 57, 59-

62] may also be adaptable for use in implementing

a national testing program. The experience in the

NRC pilot program for testing personnel dosimetry

services [33-37], and the British experience and specifications developed for radiation survey meter

performance testing [116, 127-130] are likely to be invaluable in implementing a radiation survey

(and monitoring) instrument performance testing

program in the United States. Developments in the NRC Inspection and Enforcement programs for quality

control of surveys made by NRC inspectors [117] may also be invaluable to implementing certain

aspects of quality control programs for licensees.

III. NRC's Interest in "Traceabil ity" of Radia - tion Sources and Radiation Measurements to NBS

agencies who supply instruments and/or

services related to the licensee's radiation protection program. These are

internal quality control procedures.

(3) Procedures and requirements to be followed

by licensees and/or their subcontractors

to participate in a national performance

testing and certification program that

independently monitors overall performance

and accuracy of radiation surveys, and to provide any data and information necessary

to the continued improvement of radiation

monitoring and surveys for protection pur- poses. These are the external quality

control programs that have yet to be implemented .

Is is my impression, from the privilege of

participating in some of these developments at NRC during the past 5 years, that major progress has been made in developing the consensus standards

and guides necessary for (1) and (2) above. I believe that sufficient information, knowledge,

and experience is now at hand within the professional health physics and nuclear science

community — representing government, industry,

medicine, and research establishments — to com- plete tasks related to (1) and (2) within the next 3-5 years.

However, tasks related to implementation phases

of (3) above will, in my opinion, require con- siderable further technical assistance, applied

research, and systems development. This research

and development may — and probably should -- be carried out in parallel with pilot performance

testing programs of national scope. These pro- grams should involve all of the managerial and technical aspects -- administrative, measurement

science, statistical evaluation, record systems

and legal -- that would comprise the ongoing

national performance testing and certification

programs. When tasks (l)-(3) are accomplished to provide the necessary ongoing quality control of

radiation orotection measurements for NRC regulatory programs, then these aspects of Minogue's

goals [38] for the cooperative "Regulatory-Industry"

development of standards for safety will have been accompl ished

IV. Some Basic Problems and Considerations

Requiring Attention in Implementing

Performance Testing Programs

It should be obvious to this audience that one cannot deal in a single article with all the con- siderations of testing performance of the various

radiation measurements made for protection pur- poses. Many books could be written on this

subject. The standards and guides already referenced could fill many volumes, and those that

will be written in the next few years would

probably fill many more volumes. The publication

of this Conference itself will fill a large

volume, and this Conference has only begun to approach many of the problems that need to be solved. The IAEA handbook [76] describing a laboratory for testing and calibrating radiation

survey instruments is a good example of the kind of detail that must be specified just to begin

setting up a calibration laboratory. Thus, only a

As implied by the foregoing discussion, the NRC's interest in "traceabil i ty" may be broadly translated into an interest in establishing all of the procedures licensees, and those firms who carry

out calibrations or measurements for them, should follow to ensure the sufficient accuracy and reliability of radiation measurements made for purposes of protecting employees and the public from radiation exposure, as required by the regu- lations in Title 10 [32]. These "things that licensees and/or their subcontractors should do" may be outlined as follows:

(1) Procedures carried out by the licensee's

own staff for instrument selection,

maintenance, calibration, qual ity control

and usage, in order to optimize accuracy

and reliability of the licensee's

surveys for purposes of radiation protection of employees [1 9, 21 , 22, 68] and

the public [100-103], as required in general terms by the regulations 10 CFR Part 20 [32].

(2) Procedures for quality control, calibration, and/or repair carried out in house

by commercial companies or independent

154
few questions will be discussed to stimulate

thought on some matters that require further study.

A. Rational Definition of Accuracy Requirements,

Limits of Detection

Statements of the accuracy requirements for radiation survey measurements , as made in current guides

and standards, appear to have been arbitrarily

derived based on the judgments of the authors of

these reports regarding practical feasibility and

the state of the art. A more substantial effort

to arrive at a rational basis for stating required

accuracies and documenting this basis is needed,

both for guiding further development of performance requirements, and for explaining the reasons

for acceptability of errors or uncertainties to administrators and beneficiaries of radiation

protection programs. Stating an "acceptable" level of accuracy implies the acceptance of a certain

range of error.

This need for rational derivation of acceptable

errors can perhaps be illustrated by posing some cogent questions:

1. What accuracy is needed and justified by the accuracy in assessing biological risks

when the exposure is known?

Recently, Warren Sinclair [118] reviewed

the estimated ranges of uncertainty in assessing carcinogenic effects of radiation

alone, placing "error bars" on the estimated risk (or an estimated confidence level)

of a factor of 2 to 10 just for the effects

of lowering dose or dose rate in reducing

the estimated (average) risk factors

obtained from the "linear hypothesis"

(which themselves contain uncertainties

often given as a factor of 2-3 when based

on linear interpolations from high dose

rate [119]). Thus, let us say for purposes of illustration that the 95 percent confidence interval for our best estimate of a risk factor, R, for a particular radiation

category in the range of doses to be measured (which also needs rational definition) is R 1 10 (R times or divided by 10; i.e., R x 10 or R/10). This would imply

that radiation protection standards (exposure limits) should be derived with at least a factor of 10 safety included when

based on "best" risk estimates, and that

protection measures to maintain exposures

within limits as well as ALARA should perhaps generally strive for additional

factors of safety of 10-100 below the exposure limits. (This author believes that effective radiation protection practice has sometimes deliberately (and sometimes

inadvertently) already converged to this

degree of conservatism (purposeful over- estimation of risk) over the past eight

decades [120].)

Then, a factor of 2 uncertainty in monitoring radiation exposure would seem small on

a logarithmic scale compared to the order

of magnitude uncertainties of risk estimates

and safety factors. Indeed, although NCRP

Report 57 [78] calls for an "accuracy" of + 30%

at doses approaching maximum permissible

levels (MPD) and + 20% at higher doses, it mentions a factor of 2 uncertainty (+ 100%, -50%)

as acceptable in the lower range (below 1/4

MPD) (see pp 63-64, Ref. 78). (This factor

of 2 statement implies a recognition that monitoring error distributions tend to be lognormal, as indicated below.) However, NCRP

Report 57 calls for a precision of + 10% in personnel monitoring to improve comparisons

of trends between persons and time periods.

Even if risk estimates were known with

certainty, "biological variations" in responses

of different animals from a single strain may

vary within a factor of 2 or more even for so- called "non-stochastic" effects. For example,

the standard geometric deviation of the 30-day

mortality curve for gamma irradiation of mice

in Fig. 17, Ref. 90, can be seen to be about

Sg = * 1.2. The 95 percent range of variability would be Sg = f 1.44; i.e., 95 percent of

animals would die at doses between 725 * 1.44 rad, or 503 to 1044 rads. This is about a factor of 2 variation to cover the 95 percent

range.

The stochastic (probabilistic) effects of

radiation at high and low dose levels also show

a variability of response between animals which may be partly due to inherent biological variations. However, much of the range over which

individual animals may respond -- as characterized by the dose-response curve for given

experimental conditions -- may in fact be attributable to the stochastic (chance) nature

of the cancer induction process [91, 92]. As with chemical agents such as cigarette tars, some individuals may be more resistant (or

luckier) and absorb larger. doses over longer

time periods before succumbing to cancer. Some may die in old age of other causes without

contracting cancer at all — even at the largest doses. The 95% ranges of radiation

dose for lethality for mammals by cancers of

various types generally include doses varying

by more than a factor of 2 [91, 92]. Carcinogenesis by internal emitters generally exhibits

dose-response curves covering a broader range. However, the majority of scientific opinion

embraces the belief that the probability of

inducing cancer decreases but remains finite

down to the lowest doses, without threshold

[118, 119]. At whole-body doses of 1 rem to younger individuals, probabilities of about

2 x 10" 1* per rem have been estimated by linear

extrapolation throuqh the origin from data at

high doses and dose rates; for low LET radiation, and for doses below 5 rem/year [118, 119],

this probability is believed to be reduced

another factor of 2 to 10.

Thus, the dose at which any given individual

will respond to "non-stochastic" effects can vary by a factor of 2 or more 95% of the time. The same is true for "stochastic effects," but the probabil ity of an effect is of interest

down to the lowest dose levels because of the non-threshold nature of the effect. Yet, this

probability can be estimated only to within

155
about an order of magnitude.

Thus, a dilemma is created in rationally

specifying "acceptable" accuracy. Obviously,

uncertainties by as much as a factor of 2 in measuring a dose will not influence very much

the order of magnitude of risk estimates. This

is particularly true if the dose measurements

are made, interpreted and recorded in unbiased

fashion, so that the random errors of imprecision (or uncontrolled variation) are partly

cancelled according to the statistical laws of

large numbers in estimating a cumulative (e.g.,

annual) dose from many measurements [87], Yet, our intuitive ideas of "good practice" would

often cause us to reject a factor of 2 uncer- tainty as "unacceptable." We do not consciously realize that in the fields of radiation measurement and protection we are usually

operating on a logarithmic scale [121 ,122, 130], and a factor of two does not represent a large

numerical uncertainty range.

Perhaps, looking toward the future for more

precise definition of dose-response and measurement phenomena, we should in the meantime

satisfy our taste for precision by starting

with measurements in the radiation dose range where "non-stochastic" effects are likely,

setting the acceptable 95% confidence band of

a measurement at one-tenth the relative ranqe of variation of the 30-day gamma lethality

curve for pure-bred mice (Figure 17, Reference

90). This would establish an accuracy goal for measurements in the "non-stochastic" range of ? 1.05, which is just about equivalent to

+ 5% since such a narrow distribution may be approximated by either the log-normal or normal shape over the 95% range [121, 122]. This accuracy goal is consistent with that for calibration of radiation beams used in radiation therapy [123].

It would be difficult to establish the limits

of accuracy of measurements for protection

against stochastic effects on a more rational

basis before the ranges of uncertainty of risk

estimates are more firmly established and understood

The ICRP (Publication 12, 1968) (see Reference

76, p 54) states "The uncertainties acceptable

in routine individual monitoring should be somewhat less than the investigation level and

can best be expressed in relation to the

annual dose. The uncertainty in assessing the upper limits to the annual dose equivalent to the whole body or to the organs of the body

should not exceed 50%. Wherever these doses are less than 2 rem, an uncertainty of 1 rem

is acceptable." However, these errors will include variations in field measurements due

to variations in spectral energy, direction

sensitivity, environmental conditions, instru- ment stability, dose interpretations, and many

other factors [76, 78]. For the moment at least, this author will defer to the judgments

in the more recent NCPP Report 57 [78]. Perhaps a more rational approach will be discovered during the development and implementation of the performance testing programs described above.

2. What are the legal requirements ^or accuracy?

There was considerable discussion about the

legal requirements for radiation measurements and record keeping at the Medical

Radiation Information for Litigation

Conference [90], and some recognition by the lawyers present of the difficulties of

providing exact numbers to "prove" or "disprove" the causation of diseases by radiation. The proof of causation "beyond

reasonable doubt" becomes impossible when

the same diseases may also be caused by

other agents, when the causation by radiation can only be expressed as a probability

that depends upon dose and many other

conditions, and when even down to the lowest dose levels there is reason to believe

the probability remains small by finite

[91, 92]. I do not believe that a complete legal basis has yet been devised

for selecting "acceptable" accuracies of

radiation measurements or assessments. The

NRC regulations [32] do not allow for uncertainties of measurement, and any

recorded exposures that exceed limits

allowed under 10 CFR Part 20 are deemed to be evidence of the violation of regulations.

Perhaps the definition of acceptable accur- acy is a fertile topic for discussion

between scientists and lawyers concerned

with radiation protection.

3. How should accuracy (precision and bias) be expressed in rigorous statistical terms?

A brief summary o-f the considerations in defining detection limits, sometimes better

called "minimum detectable amounts or quantities," is given in section 7 of NCPP

Report No. 58 [79]. Further reference to the literature cited in this report will show that there are many ways of defining

detection limits, and lack of standard

practice in many areas o* radiation measurement has often led to confusion in understanding the limitations of given

types of measurement. In the field of

radioactivity and environmental measurements,

however, the practice has been increasing

of utilizing formulations of minimum

detectable activity, or lower limit of

detection, such as given by the following

formula [102, 125]:

l= E - V- 2.22 Y • exp(-XAt)

where

LLD is the smallest concentration of radioactive material in a sample that will yield a net count (above system background)

that will be detected with 95% probability

with only 5% probability of falsely con- cluding that a blank observation represents a "real " signal

156
s is the observed standard deviation of the background counting rate or of the counting

rate of a blank sample, as appropriate (as counts per minute)

E is the counting efficiency (as counts per disintegration)

V is the sample size (in units of mass or

volume)

2.22 is the number of disintegrations per minute per picocurie

Y is the fractional radiochemical yeild

(when applicable)

X is the radioactive decay constant for the particular

At is the elapsed time between sample coir

lection, or end of the sample collection

period, and time of counting

This formulation is somewhat different from that

adapted in the NRC Report No. 58 [79] from the work of Currie [128]. Currie defines several levels of

detection: the decision limit, Lq, above which

the higher count would produce the decision that it was more probable than not that activity above

background had been detected; the detection limit,

Lq, at or above which level a true signal is likely

to be detected with 95% probability (i.e., the probability of non-detection at level Ln is approximately 5%); and a higher level above which

a measurement may be made with a given degree of

precision. These definitions take into account

statistics only and are formulated by the following

equations

L

c

= 2.327T (2)

L D

= 2.71 + 4.65/F (3)

As pointed out in NCRP Report No. 58 (pp 276-277),

the probability of false detection at the chosen

level of L c is approximately 5% and the probability

of non-detection at a level L n is approximately 5%. These formulas are derived under the assumption

that the counts of background and total counts are

paired observations and no allowance is made for experimental variations due to such factors as variations in back scatter or absorption of some background radiation by the sample. As pointed

out in the Report, the procedure calls for a decision of no detection if the net number of counts is less than L

c

, and asks "should the signal level corresponding to Lg be called the 'minimum detectable activity'?" As pointed out, at this level the flipping of a coin would give the same results in the long run as the measurements. This condition

is unsatisfactory because by minimum detectable

activity is meant the activity level that could be detected most of the time, not just occasionally.

Yet, one will often find laboratories quoting

values calculated by equations similar to that of

(2) to be their minimum detectable activity while

other more conservative laboratories will use a formula similar to that of (3) or (1).

Thus it is important that definitions of minimum

detectable activity or other quantities be defined

in standardized ways and be Drooerly understood

before requirements are made for detection capabilities. There is also a relationship between

these definitions and accuracy requirements,

because it must be realized that in most radiation measurements one must usually be well above the minimum detectable amounts (MDA) before confidence

intervals on the measurements become relatively

stabl e.

In Equation (1), the constant 4.66 is derived under

the assumption that when you have an MDA quantity

the overlap of the frequency distributions in total counts and backqround counts will be such that there will be exactly a probabil ity 6 = 0.05 that you will not detect that MDA quantity and have what

is called a "Type ?" error. This is also dependent

on the previous acceptance of a probability of ct = 0.05 that this fluctuation of a background count

will not be called a positive measurement. Thus, one can see that any definition of MDA has arbitrary assumptions, and there is no sharp dividing

line below which probability of making an erroneous decision is zero. This must be emphasized because

the word "minimum" in the term MDA, or "limit" in the term LLD, makes the term sound rather absolute.

Any definition of MDA or LLD is an arbitrary state- ment of detection capability under given conditions

and counting times (or observation times in the case of the fluctuating needle on a survey meter).

However, the adoption of uniform definitions of

statistical terms will be very important to the implementation of performance testing programs.

B. Probabilities in Evaluating Measurement Error Distributions

Another area that deserves attention is the study

of the characteristic distributions of error in measurements, where they are made in the same manner that they will need to be made for participation in performance testing programs. This will

be necessary in order to properly establish the probabilities of any given set of measurements

falling outside of defined ranges. Often, error analysis has been carried out under the assumption

that errors follow a Normal distribution. Perhaps

statisticians should adopt the term "Gaussian"

distribution as used by physicists since the elementary statistics courses give the impression

that the Gaussian distribution of error, when called "Normal," is the one to assume for most measurements. This has not been found to be the case in radiation measurements; when distributions

have been wide enough they have most often shown themselves to be more closely approximated by the log-normal function [121, 122].

Figure 1 shows a plot [90] on log-probability

paper of the cumulative distributions of ratios

Y-j/Xj, of reported divided by delivered doses,

for those film badges of each radiation category

that were next to farthest away from perfect

performance, for each of 26 companies tested by the National Sanitation Foundation (NSF) in 1965

[83]. These distributions were plotted in order

to study the nature of the overall errors in film

157
dosimetry. When these same points were plotted on

a linear-probability paper, they lay on a curve

rather than a straight line, showing that a lognormal frequency distribution would be a better

description of the data. Figure 1 shows the fre- quency distribution of error factors for the data pooled for all categories in order to obtain a sufficient sample size for a gross picture of the distribution of errors, without considering any particular weighting of different radiation categories. This approximate fit to a log-normal

distribution of errors lends a posteriori support

to the fact that NSF selected error bands that were

equal distances on a logarithmic scale above and below the 45-degree line of perfect accuracy (i.e., error limits obtained by multiplying and dividing

the median (true) dose value by the same error

factor). When error data follow the log-normal

distribution, another advantage of this kind of

plot is the easy observation of trends in performance. As the performance of the companies or participants improves, the slope of the line in Figure 1 should increase while the median moves closer to 1

In Figure 1, the median is 0.88 (half the reported

categories included Y-j/X-j values above 88% of the true dose and half reported below). The geometric

standard deviation (

1-/Xi at 50% divided by Y1 /X 1

- at 16%) is s Q

= 1.72, meaning that 68 percent of

the Y.-/X,- values lie between (88 x 1.72)% and (88/1.72)% of the true dose; and about 95% of the deviations lie between 88x(1.72) 2 % and 88/(1. 72) 2 % of the true dose; i.e., within a "factor of 3" of

the true dose. It was interesting to note in this

Conference that Dr. Plato's data [124] on error distributions in personnel dosimetry performance

tests as it appeared on a linear plot also generally

seemed to be skewed in the manner of log-normal

distributions and the overall results seem to have

a margin of error about the same magnitude as that

in the more limited studies of the National Sanitation Foundation [83], It would be interesting

to examine the more recent data to determine the nature of the error distributions in each test category as well as a pooled overview of the per- formance in general

It is also interesting that urinary output of a patient [129] under chelation therapy for several years varied daily according to a log-normal

distribution with an S q

= 1.4, similar in width to the distribution of personnel dosimetry test errors of Figure 1. Thus, the fundamental single

sample measurements of both internal and external dosimetry may have similar inherent error distributions .

C. Practical Limits to Accuracy of Field Measurements

References 34-37, 76, 78, 79, 83, 84, 94, and 95 review many of the sources of error in calibrations

and field measurements of external radiation with

various types of instruments. References 104-107

provide some further insight on sources of error

in interpreting bioassay measurements in terms of

internal dose. However, in performance testing programs with specific instruments, specific

standardized radiation fields or sources, and specific experimental procedures, the quantitative

contribution and frequency distribution of each

source of error will need to be determined for each type of instrument and radiation category.

This is necessary before the results of perform- ance tests can be completely interpreted, and measures to improve quality control and accuracy

can be taken.

D. Effects of Environmental Conditions on Error Distributions

The need to test instrument operations and the accuracy of their calibrations under environmental

conditions of use has been adequately discussed

in a general way in current international and national guides [76, 78, 79]. However, the effects of environmental variables such as temper- ature pressure, humidity, and ambient radiofrequency electromagnetic radiation under test conditions, must be understood so that conditions

can be specified for implementing performance

tests for the desired instruments.

In some cases, the time interval of use of dosimeters may influence the degree to which environmental conditions influence the accuracy of exposure determinations. For example, consider the studies of Ron Kathren et. al designed to separate

out the effects of the variables temperature,

humidity, dose level and wearing interval on the accuracy of film determinations of radiation exposure [87-89]. As it turned out (even for unprotected film packets under high humidity

conditions, when they were readable) for weekly

exchange intervals, cumulative 12-week exposures

in the range of most personnel monitoring results were found to be reliable under all environmental

conditions studied. However, for exchange intervals greater than 6 weeks, film fogginq under

high humidity conditions exceeded latent image

fading and produced high erratic dose interpretations .

The effects of temperature and humidity on individual interpretations was examined for badges

exposed weekly to 10 mr from a radium-gamma

source, for environmental conditions including

some of the more extreme environments encountered

in the field. The powerful effect of the statistical law of large numbers was experimentally

evidenced, showing that when even small and variable measurements are recorded as obtained to within appropriate significant digits, the random

variations will tend to cancel over a 12-week

period, for each of the environmental conditions,

to give a total dose within 10% of the true total 120 mr dose. Similar results were obtained at other dose levels. Studies with optical density

amplification [88] showed that the sensitivity

and precision of films may be limited primarily

by fluctuations of only a few percent in film

emulsion thickness or composition, if the effects

of changing environmental conditions can be removed or accounted for. However, when exposure

intervals increased beyond 4-6 weeks, high

humidities and temperatures tended to produce a large fogging effect that overcompensated the fading of the latent images with time, resulting

in large overestimates of exposure [89].

Similar studies that orthogonal ize and separate

the influence of important environmental variables

on other dosimeters and instruments used for 158
occupational health protection will probably need

to be incorporated in pilot studies of performance

testing programs.

(4)

E. Problems in Shipping "Standard" or "Unknown"

Samples, Sources, Transfer Chambers or Instruments

Problems and recommendations for preparing radiochemical test samples for shipment for analysis

have been addressed in previous analytical perform- ance testing programs [96-99]. Recommendations

for shipping and handling sensitive instruments

and detectors have been provided by the MCRP [78,

79]. However, studies and tests to validate the conditions for shipping appropriate tests or simulated samples or instruments will need to be an integral part of any specific pilot performance

testing program.

F. Selection of Categories of Radiation and

Radioactivity Measurements for Testing

As in the case of the personnel dosimetry testing

program, types of measurements or assays to be tested will need to be grouped into categories

taking into consideration that some laboratories may specialize in services for particular sectors

of radiation users. Also, types of instruments,

types of assays, various qualities and energies

of radiation,, and other factors may naturally fall into convenient groups for purposes of operating

performance testing programs. The selection of

categories for testing thus involves the consideration of a complex of many factors -- scientific,

statistical, and operational. Thus, the categories

to be selected will need to be subjected to pilot

testing to optimize the effectiveness of any

testing program.

G. Development of Standard Procedures for Statistical Evaluation and Presentation of

Program Results and Criteria for Certification

When all other details of performance testing programs are worked out, a standard design for evaluation and presentation of program results,

incorporating certification decisions, must be worked out. This is not a trivial consideration,

and requires careful and rigorous evaluation of

the probabilities of all outcomes, as well as the degree of assurance desired that accuracy

goals have been met before certification for a category is made for the appropriate period of

time. A simple example may suffice to indicate

the importance of these considerations.

Suppose that it has been decided that a +10%

error, at a 95% confidence interval, represents

good practice and is quite acceptable for radiobioassay samples of a given nuclide. Since each analysis is conducted separately in the laboratory,

and since the error may be considered a random

variable composed of the sum of a random bias,

plus a random uncontrolled variation over time

(such as chemical yield), the probability Pjq that none out of 10 assays of unknowns provided by the testing laboratory will be outside of the +

10% range even for a laboratory that meets the accuracy criteria would be:

which for all P. = .95 becomes

i

P = (.95) 10

= 0.5987 (5)

Thus, unless the random nature of errors is con- sidered in establishing certification criteria,

a 10-sample testing in a given category would

produce a 40% chance that even an excellent

laboratory would fail the tests for the given

radionuclide. Now, consider that 10 different

radionuclide categories are being tested, and we assume for simplicity that all P^ = .95. The chance that no sample would be outside the + 10% range would become

P]00

= (0.95) 100= 0.00592 (6)

In other words, there would be only a .6% chance

that an excellent laboratory would receive certification if perfect adherence to the 95% error range were required, and the true random nature

of errors were not considered in certification

criteria. Since the determination of reasonable accuracy requirements is much more complex and depends upon the type of radiation measurement,

the level of radiation or radioactivity and many

other factors in any given category, one can see that even experienced judgment will not suffice

to arrive at a suitable set of test criteria

without actually subjecting a performance testing

program to complete pilot testing, includinq mock

runs of certification criteria, and cooperative

examinations with the laboratory tested of final

results in order to eliminate those sources of

error that are correctable.

V. Summary

The author hopes that this summary of considerations in providing programs to improve occupational radiation exposure measurements will be supportive of further efforts toward this end. The progress already made in the personnel dosimetry testing program [124] and in the British

performance testing and calibration programs [116] lends hope for future progress toward the establishment of complete performance testing of

all of the important types o f measurements made

for radiation protection purposes in the United

States.

As pointed out earlier in this Conference, in order to define "traceabil ity" to the National Bureau of Standards, one must first state: "traceabil ity to what degree of accuracy?" In order to ascertain accuracy, ultimately the independent performance testing proqrams are required.

Thus, the links between "traceabil ity" and "performance testing" are inseparable.

159
Appendix A*

Illustrative Examples of "Acceptability of Radiation Survey Instrument Cal i brations" (4th Draft)

Special Definition for Purposes of NRC Regulations

and Guides (DraftT

"Acceptable Calibration" - the calibration of a survey instrument used for surveys to comply with

the requirements of 10 CFR Part 20, section 20.201

(b), 1s defined for purposes of these regulations

to be an acceptable calibration 1f one (or more)

of the following conditions 1s met:

(a) The survey Instrument is calibrated by exposure

to a standard radiation field under the following conditions:

(1) Exposure is made in a radiation field

emitted by a source of radioactive material

that has been certified by the supplier

to have: a specified radiation exposure

rate at unit distance (e.q., one meter)

under specified scattering conditions (for

calculation of exposure rates over a range

of distances); or specified exoosure rates at various distances under specified

scattering and exposure conditions. The

certified exposure rates in either case

shall be evidenced by a certificate 1 from

the supplier including all appropriate

information needed for converting Instru- ment readings to the particular exposure

or dose units to be used for demonstrating

compliance with exposure limits of 10 CFR

Part 20;

(11) The supplier's certificate states that the

specified exposure rates are within + 15%

(or some smaller uncertainty) of the true

values;

(11i) The source supplier has determined the

value(s) of the licensee's calibration

source by comparing it with a standard source of radiation maintained in the supplier's laboratory. At least three

replicate comparisons with identical

equipment-geometry setups of the radiation measurement system shall be made,

in order to avoid errors that might result

'Certificates shall contain any pertinent data on source purity that may over time affect calibration values, as specified in ICRU Report No. 12,

"Certification of Standardized Radioactive

Sources," International Commission on Radiation

Units and Measurements," September 15, 1968.

*This appendix is under further revision for possible use In regulations or regulatory guidance. It is presented here only to provide a more concrete illustration of the details

required to specify how "traceable" or acceptable

calibrations might be performed for radiation

survey instruments.

r *In all calibration procedures, the radiation

field 1n which the survey instrument 1s to be calibrated shall be of a type and energy appro- priate for the instrument and its intended use.

from operator mistakes, instrument drift,

or instrument malfunction. The value of

the supplier's standard source shall have

been certified by the National Bureau of

Standards for exposure rate at a fixed

distance (e.g., one meter) according to one of its standard calibration services. The changes in value or intensity of the supplier's radiation measurement system are

checked on at least a monthly frequency

and verified to remain within + 3% of the value calculated by correcting the initial

National Bureau of Standards certified

value for radioactive decay. Records of

all source certificates, calibration

methods, measured values, and all calculations used by the supplier to certify his sources shall be maintained permanently in the supplier's records and be available for Inspection by the NRC.

(1v) The instrument has been calibrated on each ranqe that will be used to comply with

requirements of 10 CFR 20 or license conditions. These ranges shall be calibrated

by exposure to a field of the appropriate

type and energy of radiation, in field

intensities that will produce at least two instrument readings on each scale, one within 20-30% of the scale range and the other within 70-80% of the ranqe (in linear

distance along the scale, for log or linear

scales). Other scales of the instrument

shall be checked for oneration, but marked

"not of Verified Accuracy" for purposes of

compliance with NRC requirements.

(v) Source intensities or values certified by the supplier have been corrected by the licensee for radioactive decay as necessary

to maintain calibrations within an accuracy of + 20%, which includes the maximum allow- able + 15% uncertainty in the specified exposure rates for the source (in paragraph

(ii) above; and

(vi) The licensee has maintained records available for inspection on source certifications,

calibration methods, calibration measurements, and calculations including decay

corrections as necessary to compare instru- ment readings versus administered calibration exposures in units as specified in 10 CFR 20 for the particular type of

radiation involved.

(b) The survey instrument is calibrated by exposure

to a standard source of radioactivity under the following conditions:

(1) Exposure is made to a source that is certified by the supplier to have a given amount

of radioactivity, known radionucl idic purity, and a sufficiently known radioactive

decay scheme and half-life, so that the necessary field intensities as specified

in (a)(i) above may be calculated by the licensee from established scientific

information. In this case, all calculations

of exposure or dose rates from radioactivity

units and references used in these calculations shall be maintained for inspection
with other calibration records.

(ii) The supplier's certificate 1 states that the specified radioactivity of the source used

for calibration is within + 15% (or some smaller uncertainty) of the true values;

and

(iii) Conditions (a)(iii) through (a)(vi) above

are also applicable, except that in (a) (iii) the supplier's standard source shall have been certified for radioactivity,

rather than the exposure rate at fixed

distance, by the National Bureau of

Standards

.

(c) The survey instrument is calibrated in a radiation field standardized with a secondary

standard instrument under the following conditions:

(i) The source used for survey meter calibrations has been provided with an associated

set of exposure or dose rates at specified

distances, and these values have been provided and certified by a qualified

person using a secondary standard instru- ment that has been calibrated directly by exposure to standard sources at the

National Bureau of Standards, or at one of the Regional Calibration Laboratories

accredited by the American Association of

Physicists in Medicine with the cooperation of the National Bureau of Standards.

(ii) Conditions (a)(iv) through (a)(vi) also

are appl icable.

(d) The survey instrument is calibrated by comparison with a secondary standard instrument under

the following conditions:

(i) The radiation field used for survey meter calibrations is of appropriate type, energy, geometry, and intensity, and

remains stable during the period when calibrations are performed. The survey meter is calibrated by comparison with

a secondary standard instrument at a fixed point within the radiation field. At each selected point, a technique

involving simultaneous exposure or sub- stitution is used to compare values

indicated by the secondary standard instru- ment and the instrument under calibration.

The secondary standard instrument shall have been calibrated by the National Bureau of Standards, or by one of the

Regional Calibration Laboratories accredited by the American Association of Physicists in Medicine with the cooperation

of the National Bureau of Standards.

(ii) The secondary standard instrument is certified to have been calibrated so that

its indicated values (after application of

any necessary calibration factors) are within + 103! (or some smaller uncertainty)

of the true values.

(iii) Conditions (a)(iv) and (a)(v1) also are

appl Icable.

(iv) Calibrations of ttie survey instrument shall

be made to within a maximum uncertainty of

+ 20% (or less) of the true value. This

uncertainty includes the maximum allowable

+10% uncertainty in the values Indicated

by the secondary standard instrument,

which shall be taken into account in deter- mining survey instrument accuracy.

*Qualified persons include persons offering radiation dosimetry and calibration services who are certified by either: The American College of

Radiology in one of the areas of radiological

physics; the American Board of Health Physics; or

the American Board of Industrial Hygiene in radiological aspects.

161
Table 1

SENSITIVITIES OF UNIVERSITY OF PITTSBURGH PROCEDURES

FOR SEVERAL NUCLIDES (1968)*

Radionucl ide Lower (97. 5% CL)

Limit of Detection in Lung for 40 Minutes with

Standard Chair

Technique

Maximum Per- missible Body

Burden ('

)

Fraction

of MPBB

Detectable

Fission products:

Cs-137

Zr-95-Nb-95

1-131 Ba- 140- La- 140 Ce-144-Pr-144

C0-6O /,» Uranium- 238 u;

Uranium-235 . Thorium- Natural

(

z ' Plutonium-239(3)

Americium-241 (3) Natural Potassium

Total Gamma Activit

2x1

_1

* nCi

9x10-5

3x1 0"7 |iCi

9xI0_I

* uCl 2x10-3 u,Ci

4x1 0"{* uCi 4x1 0~2 UCi

lxl0"£ uXi

6x10 uCi

0. 03 uCi 4xl0_i

* |iCi

Measurable within +

.y (Equivalent) 6x10

30 uCi 20 uCI

0. 7uCl 4 uCI

5 UCi

10 uCI 5x10-3 uCI 0.03 uCI

0. 04 uCi

0.04 |iCi

0.05 uCi

3% for adult male: J* (Cs-137 equival<

6.6x10~*

4. 5xl0-5

4. 3x1 0"{*

2. 2x10"^

4.0x10-**

4.0x10-5

0. 08

0. 003

0.015

0. 75

0. 008*

jnt)

(1) As given in ICRP Committee II Report, Health Physics 3_» I960, for the total body burden when the most critical organ is receiving the maximum permissible occupational exposure rate.

(2) Evaluated by a procedure similar to that given by L M. Scott,

Health Physics ]Z, 101-102, January, 1966.

(3) Counted with a thin-window, 1 mm thick x 2"D Na| crystal against

chest for 40 minutes, to detect low energy photons, as in Reference 84.

0.0033 uCi for 10 minute count on 8x4 behind back, assuming +25%

fluctuation for uncertainty of K-40 background.

*From A. Brodsky, Reference 90, with permission.

162
_95 — 90

MEDIAN = 0.88 (8858 OF TRUE DOSE)

s g

- 1-72

tegory, 7b"% were r

Log Normall Fit of Er-or Distribution (Y;/X;) for NSF

Film Badge Tests. Trie plot shows that the median reportei

Yj is aboi t 88% of the true delivered dose (hal f of the —

reported \alues are lower, and half higher than this)

For the next - to-worst ratios, Yj/Xj, in each radiation

caof the trde

reported

category)

graph would indicate

ported less than 52% (or 88%* 1.72)

dose. Note that the distribution of al

ijeadings (rather than the next-to-worst in each

would be narrower (more precise) than this

Median = 0.88

50%

30

20

10

0.5 1 2 3

Y,/Xj - DOSE REPORTED/DOSE GIVEN (FOR NEXT-TO-WORST READING)

Figure 1

163
References

[1] USNRC Regulatory Guide 8.1, "Radiation Symbol,"

2/2/73.

[2] USNRC Regulatory Guide 8.2, "Guide for Administrative Practices in Radiation Monitoring,"

2/2/73.

[3] USNRC Regulatory Guide 8.3, "Film Badge

Performance Criteria," 2/2/73.

[4] USNRC Regulatory Guide 8.4, "Direct-Reading

and Indirect-Reading Pocket Dosimeters,"

2/26/73.

[5] USNRC Regulatory Guide 8.5, "Immediate Evacua- tion Signal ," 2/16/73.

[6] USNRC Regulatory Guide 8.6, "Standard Test Procedure for Geiger-Mliller Counters," 5/73.

[7] USNRC Regulatory Guide 8.7, "Occupational Radiation Exposure Records Systems," 5/73.

[8] USNRC Regulatory Guide 8.8, "Information Rele- vant to Ensuring that Occupational Radiation

Exposures at Nuclear Power Stations Will Be As Low As Is Reasonably Achievable," Revision 3, 6/78.

[9] USNRC Regulatory Guide 8.9, "Acceptable Con- cepts, Models, Equations, and Assumptions for

A Bioassay Program," 9/73.

[10] USNRC Regulatory Guide 8.10, "Operating

Philosophy for Maintaining Occupational Radiation Exposures As Low As Is Reasonably Achievable," Revision 1-R, 9/75.

[11] USNRC Regulatory Guide 8.11, "Applications of

Bioassay for Uranium," 6/74.

[12] USNRC Regulatory Guide 8.12, "Criticality Accident Alarm Systems," 12/74.

[13] USNRC Regulatory Guide 8.13, "Instruction

Concerning Prenatal Radiation Exposure,"

Revision 1 , 11/75.

[14] USNRC Regulatory Guide 8.14, "Personnel Neutron Dosimeters," Revision 1, 8/77.

[15] USNRC Regulatory Guide 8.15, "Acceptable Pro- grams for Respiratory Protection," 10/76.

[16] USNRC Regulatory Guide 8.18, "Information

Relevant to Ensuring that Occupational Radiation Exposures at Medical Institutions Will Pe As Low As Reasonably Achievable," 12/77.

[17] USNRC Regulatory Guide 8.19, "Occupational

Radiation Dose Assessment in Light-Water

Reactor Power Plants Design Stage Man-Rem

Estimates," Revision 1, 6/79.

[18] USNRC Regulatory Guide 8.20, "Applications of

Bioassay for 1-125 and 1-131," Revision 1, 9/79.

[19] USNRC Regulatory Guide 8.21, "Health Physics

Surveys for Byproduct Material at NRC-Licensed

Processing and Manufacturing Plants," Revision

1, 10/79.

[20] USNRC Regulatory Guide 8.22, "Bioassay at Uranium Mills," 7/78.

[21] USNRC Regulatory Guide 8.23, "Radiation Safety

Surveys at Medical Institutions," 2/79.

[22] USNRC Regulatory Guide 8.24, "Health Physics

Surveys During Enriched Uranium-235 Processing

and Fuel Fabrication," Revision 1, 10/79.

USNRC Regulatory Guide 10.1, "Compilation of

Reporting Requirements for Persons Subject to NRC Regulations," Revision 3, 5/77.

[24] USNRC Regulatory Guide 10.2, "Guidance to Academic Institutions Applying for Specific

Byproduct Material Licenses of Limited

Scope," Revision 1, 12/76.

[25] USNRC Regulatory Guide 10.3, "Guide for the Preparation of Applications for Special

Nuclear Material Licenses of Less Than Critical Mass Ouantities," Revision 1, 4/77.

[26] USNRC Regulatory Guide 10.4, "Guide for the Preparation of Applications for Licenses to Process Source Material," Revision 1, 3/77.

[27] USNRC Regulatory Guide 10.5, "Guide for the Preparation of Applications for Type A Licenses of Broad Scope for Byproduct Material,"

9/76.

[28] USNRC Regulatory Guide 10.6, "Guide for the Preparation of Applications for Use of Sealed

Sources and Devices for the Performance of

Industrial Radiography," 9/76.

164
[29] USNRC Regulatory Guide 10.7, "Guide for the

Preparation of Applications for Licenses for Laboratory and Industrial Use of Small Quantities of Byproduct Material," Revision 1, 8/79.

[30] USNRC Regulatory Guide 10.8, "Guide for the

Preparation of Applications for Medical

Programs," 1/79.

[31] USNRC Regulatory Guide 10.9, "Guide for the

Preparation of Applications for Licenses for

the Use of Gamma Irradiators," 4/80.

[32]

Title 10, Code of Federal Regulations, Part

20, "Standards for Protection Against Radiation," U.S. Government Printing Office,

Washington, D.C., 1980.

[33]

Notice to Licensees, Personnel Dosimetry

Processors and Other Interested Persons,

U.S. Nuclear Regulatory Commission,

Washington, D.C. 20555, April 17, 1980.

[34]

Phillip Plato and Glenn Hudson, Performance

Testing of Personnel Dosimetry Services:

Procedures Manual , NUREG/CR-1063, prepared

for U.S. Nuclear Regulatory Commission by

University of Michigan, January 1980.

[35]

P. Plato and G. Hudson, Performance Testing

of Personnel Dosimetry Services, Final Report

of a Two-Year Pilot Study October 1977- September 1979 , NUREG/CR-1064, prepared for

U.S. Nuclear Regulatory Commission by University of Michigan, January 1980.

[36]

P. Plato and G. Hudson, Performance Testing

of Personnel Dosimetry Services, Supplementary

Report of a Two-Year Pilot Study October

1977-December 1979 , NUREG/CR-1 304, prepared

for U.S. Nuclear Regulatory Commission by

University of Michigan, April 1980.

[37]

"Draft American National Standard Criteria

for Testing Personnel Dosimetry Performance,"

N13.ll, American National Standards Institute, Inc., 1430 Broadway, New York, N.Y. 10018, July 1978.

[38]

Robert B. Minogue, "The Regulatory- Industry

Interface in Standards Development,"

presented at the Atomic Industrial Forum Workshop on Reactor Licensing and Safety,

San Diego, California, December 11, 1974.

[39]

Allen Brodsky, R. E. Alexander, and R. J. Mattson, "NRC's Radiation Protection Regulations," published in the proceedings of the Health Physics Society Midyear Topical

Symposium, Occupational Health Physics , edited by P. L. Carson, W. R. Hendee, and

D. C. Hunt, Feb. 9-12, 1976 (available from

Central Rocky Mountain Chapter, Health Physics

Society, P. 0. Box 3229, Boulder, CO 80303).

[40]

Calculation of Absorbed Dose from Gamma Radiation, Practice For, ANSI/ASTM D2568-70.

[41]

Dosimetry, Definitions of Terms Relating to, ANSI/ASTM El 70-76.

[42] Gamma or X Radiation, Test for Calculation

of Absorbed Dose from, ANSI/ASTM E666-78.

[43] Internal Dosimetry for Mixed Fission and Activation Products, ANSI N343-1978.

[44] Neutron and Gamma-Ray Flux-to-Dose-Rate

Factors, AMSI/ANS 6.1.1-1977.

[45]

Performance, Testing, and Procedural

Specifications for Thermoluminescence

Dosimetry: Environmental Applications,

ANSI N545-1975.

[46] Fast-Neutron Flux Measurements by Track-Etch

Technique, Method for, ANSI/ASTM E418-73.

[47]

Cobalt-60 and Cesium-137 Teletherapy

Equipment, Guidelines for Maintaining, ANSI N449-1974.

[48]

Integrity and Test Specifications for Selected Brachytherapy Sources, ANSI N44.1-

1973.

[49] Leak Testing Radioactive Brachytherapy

Sources, ANSI N44.2-1979.

[50]

Teletherapy Equipment, Procedures for Periodic Inspection of Cobalt-60 and Cesium137, ANSI N449. 1-1978.

[51]

Thyroid Rad1oiod1ne Uptake Measurements Using

a Neck Phantom, ANSI N44. 3-1973.

[52] "Dose Calibrator" Ionization Chambers for

the Assay of Radionuclides, Calibration and Usage of, ANSI N42. 13-1978.

165
[53]

Calibration of Germanium Detectors for Measure- ment of Gamma-Ray Emission Rates of Radionuclides, Method of, ANSI/ASTM E522-78.

[54]

Direct Reading and Indirect Reading Pocket

Dosimeters for X- and Gamma Radiation, Per- formance, Specifications for, ANSI N1 3. 5-1972.

[55]

Geiger-Muller Counters, Test Procedure for,

ANSI/IEEE 309-1970.

[56]

Germanium Detectors for Measurement of Gamma

Ray Emission of Radionuclides, Calibration

and Usage of, ANSI N42. 14-1978.

[57]

Germanium Gamma-Ray Detectors, Test Proce- dures for, ANSI/IEEE 325-1971.

[58]

Germanium Semiconductor Detector Gamma Ray

Efficiency Determination Using a Standard

Marinelli (Reentrant) Beaker Geometry, ANSI/

TEEE 680-1978.

[59]

Portable X- or Gamma Radiation Survey

Instruments, Specification of, ANSI N13.4-

1971 (Rl 977)

[60]

Radiation Protection Instrumentation Test and Calibration, ANSI N323-1978.

[61]

Semiconductor Radiation Detectors, Test Pro- cedures for, ANSI/IEEE 300-1969.

[62]

Administrative Practices in Radiation Monitoring (A Guide for Management), ANSI N13.2-

1969.

[63]

Dosimetry for Critical ity Accidents, ANSI

N13. 3-1969.

[64]

Film Badge Performance, Criteria for, ANSI

Nl 3.7-1 972

[65]

Glossary of Terms Used in Radiation Shielding and Dosimetry, Draft Standard, ANSI/ANS

6.5

[66]

Immediate Evacuation Signal for Use in Industrial Installations Where Radiation

Exposure May Occur, ANSI N2. 3-1 967.

[67]

Occupational Radiation Exposure Records

Systems, Practice for, ANSI Nl 3.6-1 966

(R1 972).

[68]

Sampling Airborne Radioactive Materials in Nuclear Facilities, Guide to, ANSI Nl 3.1 -1969.

[69]

Installations Using Non-Medical X-Ray and Sealed Gamma-Ray Sources, Energies Up To 10 MeV, General Safety Standard for, ANSI/NRS

114.

[70]

Packages for Shipment of Radioactive Materials, Leakage Tests On, ANSI N14. 5-1977.

[71]

Evaluating Films for Monitoring X-Rays and Gamma Rays Having Energies Up To 3 Million

Electron Volts, Method for, ANSI PH2.10-

1965 (R1979).

[72]

Sensitometry of Industrial X-Ray Films for Energies Up to 3 Million Electron Volts,

Method for, ANSI PH2.8-1975.

[73]

Sensitometry of Medical and Dental X-Ray

Films, Methods for the, ANSI PH2.9-1974.

[74] NRCP Report No. 10, "Radiological Monitoring

Methods and Instruments," April 7, 1952.*

[75]

International Atomic Energy Agency (IAEA)

Technical Report Series No. 120, "Monitoring

of Radioactive Contamination on Surfaces,"

1970.*

[76] IAEA Technical Report Series No. 133, "Hand- book on Calibration of Radiation Protection

Monitoring Instruments," 1971.*

[77]

International Commission on Radiation Units

and Measurements (ICRU) Report No. 12,

"Certification of Standardized Radioactive

Sources," September 15, 1968.*

[78] NCRP Report No. 57, "Instrumentation and Monitoring Methods for Radiation Protection,"

1978.*

[79] NCRP Report No. 58, "A Handbook of Radioactivity Measurement Procedures," 1978.*

*IAEA reports may be obtained from UNIPUB, Inc.,

P.O. Box 433, New York, N.Y. 10016.

ICRP reports may be obtained from Pergamon Press, Maxwell House, Fairview Park, Elmsford, N.Y. 10523.

ICRU reports may be obtained from the International Commission on Radiation Units and Measurements, P.O. Box 30165, Washington, D.C. 20014.

NCRP reports may be obtained from NCRP Publications, P. 0. Box 30175, Washington, D.C. 20014.

166
[80]

International Atomic Energy Commission

"Advances in Radiation Protection Monitoring"

(ISP494), 1979, 788 pp.

[81]

Office of Management and Budget, Office of

Federal Procurement Policy, "Federal Participation in the Development and Use of Voluntary

Standards; Final Issuance," 0MB Circular No. A-119, Federal Register, Vol. 45, No. 14,

Monday, January 21, 1980.

[82]

"Notice Regarding Need for Establishment of

Film Dosimetry Calibration Laboratory," U.S. Atomic Energy Commission, Federal Register, Document 63-9411, September 4, 1963.

[83]

D. E. Barber, "Report on the National Sanitation Foundation Film Radge Performance Test

Program," The National Sanitation Foundation, Ann Arbor, Michigan, June 30, 1965; also,

Radiological Health Data and Reports, pp 623-

626, Nov. 1966.

[84]

C. M. Unruh, H. V. Larson, T. M. Beetle, and

A. R. Keene, "The Establishment and Utilization of Film Dosimeter Performance Criteria,"

BNWL-542, Battelle-Northwest, Richland, WA, 1967.

[85]

First Topical Symposium on Personnel Radiation Dosimetry , Health Physics Society,

Chicago, Illinois, Jan. 30, 31, Feb. 1, 1967 (reported in Health Physics, 1968).

[86]

"Employee Radiation Hazards and Workmen's

Compensation," Hearings before the Joint

Committee on Atomic Energy, U.S. Government

Printing Office, Washington, D.C., 1959.

[87]

A. Brodsky, "Accuracy and Sensitivity of

Film Measurements of Gamma-Radiation, Part

II, Limits of Sensitivity and Precision,"

Health Physics 9, 463-471, 1963.

[88]

A. Brodsky, "An Optical Device for Extending

the Range of Film Measurements of Gamma Radiation," Health Physics 9, 656-663, 1963.

[89]

R. L. Kathren and A. Brodsky, Health

Physics 9, 769, 1963.

[90]

"Characteristics of Radiation Monitoring

Instrumentation and Methods," by Allen

Brodsky, in Medical Radiation Information

for Litigation , edited by S. C. Bushong,

J. S. Cox, V. P. Collins, J. B. Neibel,

and G. B. Murphy, pp 5-59, U.S. Department

Health, Education, and Welfare, Document

No. DMRE 69-3, July 1969.

1

[91]

Allen Brodsky, "A Stochastic Model of

Carcinogenesis Incorporating Certain Observations from Chemical and Radiation Dose- Response Data," Health Physics 35, 421-428,

1978.

[92]

Allen Brodsky, "Time and Dose Factors in Carcinogenesis," Letter to the Editor,

Health Physics 36, 468-471, 1979.

[93]

Allen Brodsky, "ALARA -- Radiation Risks and

the Need to Keep Exposures 'As Low As Reasonably Achievable'," presented at the Eleventh National Conference on Radiation

Control, Sheraton Century Center, Oklahoma

City, Oklahoma, May 7, 1979, sponsored by the Conference of Radiation Control Program

Directors, to be published by the Bureau of

Radiological Health, DHEW, Washington, D.C.

[941

R. L. Kathren, "Instruments in the Field Use, Abuse, and Misuse," Health Physics Operational

Monitoring , Vol. 2, C. A. Willis and J. S. Handloser, Eds., Gordon and Breach, New York,

1972, p. 811.

[951

W. P. Howell and R. L. Kathren, "Calibration

and Field Use of Ionization Chamber Survey

Instruments," Health Physics Operational

Monitoring , Vol. 2, C. A. Willis and J. S. Handloser, Eds., Gordon and Breach, New York,

1972, p. 925.

[96]

Herbert L. Volchok and Melvin Feiner, "A Radioanalytical Laboratory Intercompari son Exercise," EML-366, Environmental Measurements Laboratory, Department of Energy, New

York, New York, October 2, 1979.

[97]

"Environmental Radioactivity Laboratory

Intercomparison Studies Program 1978-1979,

EPA-600/4-78-032, Ouality Assurance Branch,

Monitoring Systems Research and Development

Division, Environmental Monitoring and Support Laboratory, U.S. Environmental Pro- tection Agency, Las Vegas, NV 89114, June

1978.

[98] Lee H. Ziegler, "Radioactivity Standards

Distribution Program 1978-1979," EPA-600/4-

78-033, Monitoring Systems Research and Development Division, Environmental

Monitoring and Support Laboratory, U.S. Environmental Protection Agency, Las Vegas,

NV 89114, June 1978.

[99] "Manual for the Interim Certification of

Laboratories Involved in Analyzing Public

Drinking Water Supplies, Criteria and Pro- cedures," prepared by the Water Supply

Ouality Assurance Work Group, U.S. Environmental Protection Agency, Wash, D.C. 20460,

Sept. 1977.
[TOO] USNRC Regulatory Guide 4.13, "Performance,

Testing, and Procedural Specifications for

Thermol uminescence Dosimetry: Environmental

Applications," Revision 1, 7/77.

[101] USNRC Regulatory Guide 4.14, "Measuring,

Evaluating, and Reporting Radioactivity in Releases of Radioactive Materials in Liquid

and Airborne Effluents from Uranium Mills

(For Comment)," 6/77.

[102] USNRC Regulatory Guide 4.15, "Quality Assurance for Radiological Monitoring Programs

(Normal Operations)--Effl uent Streams and

the Environment," Revision 1, 2/79.

[103] USNRC Regulatory Guide 4.16, "Measuring,

Evaluating, and Reporting Radioactivity in Releases of Radioactive Materials in Liquid and Airborne Effluents from Nuclear

Fuel Processing and Fabrication Plants (For

Comment)," 3/78.

[104]

M. R. Ford, S. R. Bernard, L. T. Dillman,

and S. B. Watson, Internal Dosimetry and Methods of ICRP - Part I , ORNL/NUREG/TM315, Oak Ridge National Laboratory, Oak

Ridge, Tennessee 37830, June 1979.

[105]

K. W. Skrable, "Internal Dosimetry and Action Levels Applicable to In Vivo Counting and Other Bioassay Procedures,"

unpublished, October 1979 (available from

Dr. Kenneth W. Skrable, University of

Lowell, One University Avenue, Lowell,

Massachusetts 01854).

[106]

L. T. Dillman, "EDISTR -- A Computer

Program to Obtain a Nuclear Decay Data Base for Radiation Dosimetry," ORNL/TM6689, Oak Ridge National Laboratory,

Oak Ridge, Tennessee 37830, January 1980 (available from the National Technical

Information Service, Springfield, VA 22161).

[107] The ICRP 10 series of reports describing

methods of calculating internal dose from

bioassay data is under revision and

updating. Information on published ICRP reports may be obtained from Pergamon

Press, Inc., Maxwell House, Elms ford, N.Y. 10523.

[108] USNRC Regulatory Guide 5.58, "Considerations for Establishing Traceability of

Special Nuclear Material Accounting Measure- ments," Revision 1, 2/80.

[1091

R. J. Brouns, F. P. Roberts, and J. A. Merrill, "Monitoring the Random Errors of

Nuclear Material Measurements," NUREG/CR0830, Pacific Northwest Laboratory, Richland,

Washington 99352, April 1979.

[110]

R. J. Brouns, F. P. Roberts, J. A. Merrill,

and W. B. Brown, "A Measurement Control Pro- gram for Nuclear Material Accounting,"

NUREG/CR-0829, Pacific Northwest Laboratory

and Office of Standards Development, U.S. Nuclear Regulatory Commission, Wash. D.C. 20555, September 1979.

[Ill]

E. H. Eisenhower, "Traceability - A View from

the CRR," National Bureau of Standards, this

conference, 1980.

[112]

R. L. Kathren, "Traceability - A User's View,"

Battelle-Morthwest, Richland, Washington,

this conference, 1980.

[113]

K. R. Heid, Chairman, Working Group 2.5,

Health Physics Society Standards Committee,"

"Criteria for Testing Performance of Radiobioassay Services" (draft), Rattelle North- west Laboratory, P. 0. Pox 999, Richland,

Washington 99352, 1980.

[114]

A. N. Jarvis, "The EPA National Quality Assurance Program," this conference, 1980.

[115]

Ron Colle, informal remarks, first session,

this conference, 1980.

[116]

W. A. Jennings, "Radiation Measurement Traceability in the U.K.," National Physical

Laboratory, England, this conference, 1980.

[117]

L. K. Cohen, "NRC Traceability Concerns in its Inspection and Enforcement Proqram,"

this conference, 1980.

[118] Warren K. Sinclair, "The Scientific Basis

for Risk Quantification," to be published in the Proceedings of the Annual Meeting of the National Council on Radiation Protection

and Measurements, April 2-3, 1980.

[119] NCRP Report No. 64, "The Influence of Dose and Its Distribution in Time on Dose Effect Relationships for Low LET Radiation,"

National Council on Radiation Protection and Measurements, 1980.

168
[120]

A. Brodsky, "Radiation Risks: An Historical

Perspective," invited talk presented at the Radiation and Health Conference, Hershey,

PA, September 1979, available from author.

[121]

J. Shubert, A. Brodsky, and S. Tyler, "The Log-Normal Function As A Stochastic Model of the Distribution of Sr-90 and Other

Fission Products in Humans," Health Phys.

13, 1187-1204, 1967.

[122]

A. Brodsky, R. P. Specht, P. Brooks, and

W. S. Cool, "Log Normal Distributions of

Occupational Exposure in Medicine and Industry," in the proceedings of the Health

Physics Society Midyear Topical Symposium,

Occupational Health Physics (available from

Central Rocky Mountain Chapter, P.O. Box 3229, Boulder, CO 80303, 1976.

[123]

R. Loevinger, NBS Standards for Radiation

Dosimetry," this conference, 1980.

[124]

P. Plato, "Performance Testing of Personnel Dosimetry Services," this conference, 1980.

[125]

E. Conti , J. S. Bland, J. D. Buchanan, P. J. Magno, W. L. Britz, L. K. Cohen, B. H. Weiss, and E. G. Wright, "Radiological Environmental Monitoring by NRC Licensees for Routine Operations of Nuclear Facilities,"

NUREG-0475, 1978.

[126]

R. E. Alexander, "Applications of Rioassay

for Uranium," WASH-1251, Superintendent of

Documents, U.S. Government Printing Office,

Washington, D.C. 20402, 1974.

[127]

The British Calibration Service, Documents:

0021, November 1977; Document 0802, Jan. 1977

(General Criteria for Laboratory Approval,

Provision of Personal Dosimetry Services); Document 0811, Jan. 1977 (Supplementary

Criteria for Laboratory Approval, Calibration of Radiological Protection Level Instruments: X-, Gamma- and Beta-Rays); Document 0812, Jan. 1977 (Supplementary

Criteria for Laboratory Approval, Calibration of Radiological Therapy Level Instru- ments; X- and Gamma Rays); Document 0813,

Sept. 1977 (Supplementary Criteria for Lab- oratory Approval, Calibration of Radiological

Protection Level Instruments: Neutrons); Document 0821, Oct. 1977 (Supplementary

Criteria for Laboratory Approval, Provision

of Personal Dosimetry Services Using Film Dosimeters for Beta, Gamma, X- and Thermal Neutron Radiations); Document 0822, Oct. 1977 (Supplementary Criteria for Laboratory

Approval, Provision of Personal Dosimetry

Services Using Nuclear Emulsion, Film Dosim- eters for Neutron Radiations); Document

0823, Oct. 1977 (Supplementary Criteria for

Laboratory Approval, Provision of Personal Dosimetry Services Using Thermoluminescent

Dosimeters for Beta, Gamma, X- and Neutron Radiations); Document 6601, Jan. 1977 (Calibration of Radiological Instruments at Protection and Therapy Levels), British

Calibration Service National Physical

Laboratory, Teddington, Middlesex TW 11 0LW,

England.

[128]

L. A. Currie, "Limits for Oualitative Detection and Ouantitative Determination

Application to Radiochemi stry , " Anal. Chem.

40, 586-93 (1968).

[129]

A. Brodsky and I. F. Horm, "Removal of 21,1 Am

from Humans with DTPA," Progress Report, Bureau of Radioloqical Health Grant 2801

EC 00122-03, University of Pittsburgh, 1971.

[1301

A. Brodsky, "Determining Industrial Hygiene

Requirements for Installations Using Radioactive Materials, Am. Ind. Hyg. Assn. J. 26,

294-310, 1965.

169

DOSIMETRY FOR INDUSTRIAL RADIATION PROCESSING

William L. McLaughlin, Jimmy C. Humphreys, and Arne Miller*

Center for Radiation Research

National Bureau of Standards

Washington, D.C. 20234

ABSTRACT

In the dosimetry related to sterilization of goods by ionizing photons and electrons, and in other industrial radiation applications, i.e., modification of plastic and other materials, food preservation, and treatment of waste products, it

is important to have traceability to standard absorbed dose measurements. The preferred primary methods of dosimetry for large radiation doses (>10 Gy) are:

(1 ) Calorimetry, which is suitable for both electron and photon radiations; (2) Standard chemical dosimetry, in particular, ferrous sulfate dosimetry, which,

because of its relatively narrow response range (40 - 400 Gy) and rate dependence

at dose rates >10 7 Gys , is mainly suited to x- and gamma radiation. Using

these techniques as primary reference methods, it is possible to calibrate the response characteristics of routine dosimeters, such as plastics, dyed plastics,

and solid-state sensors in terms of a reproducible signal versus known values of absorbed dose. Dose levels and dose gradients within a sizable irradiated

volume, e.g., product packages, are determined within specified values of un- certainty, which may be set in terms of statistical error and precision in making

practical interpretation of dose and dose limits.

(Calorimetry; dosimeter calibration; dosimetry; electron beams; gamma radiation; quality control raidation measurement; radiation processing; radiation sterilization; traceability.)

I. Introduction

The radiation processing of industrial goods and

the use of radiation in food preservation, waste

treatment, and energy research involve large-scale

product handling in intense fields of electrons

and photons having energies ranging mainly from a few hundred keV to MO MeV D,3J. Examples of

commercially successful or potentially viable ra- diation processes are listed in Table I.

TABLE 1

COMMERCIAL RADIATION PROCESSES

Sterilization of medical supplies

Recycling of municipal and industrial wastes Treatment of gaseous effluents and smoke Water purification

Production of electrical, thermal, and sound in- sulation

Production of shrinkable films, tape, and tubing

Production of dry lubricants and pressure-sensitive

adhesi ves Food shelf-life extension

Tire and elastomer manufacture

Curing of inks and paints, plastics, and coil coatings

Manufacture of electronics components and battery

separators

Production of improved textiles

Fusion research

Non-destructive testing

Radiation effects studies

Insect population control

Radiation absorbed doses in such applications are generally large, exceeding 10 Gy; and in some cases

reach values of 10 6 Gy. Standardization of dosimetry for such applications, on both national and

international levels, has generally been lacking.

In radiation processing that affects public health

and safety, it is especially important to standardize the measurement of radiation quantities.

Applications in this category include the following: The sterilization of medical supplies,

pharmaceuticals, cosmetics; disinfestation and preservation of food supplies; treatment of

gaseous, liquid and solid wastes; quality assurance

and safety of many commodities. In limiting the costs of radiation processing, the improvement of measurement assurance increases quality control, energy saving, and waste and pollution abatement.

This paper is intended to outline means of stan- dardizing large dose radiation measurement,

techniques for reducing error and increasing pre- cision in routine dosimetry, and ways of applying

certain special dosimetry methods for the mapping

of absorbed dose profiles in typical irradiated

products and in dosimeter probes and their containers .

II. Primary Methods of Dose Measurement

A. Calorimetry

In radiation processing by intense radiation

fields, calorimetry is one of the best primary

standard means of measuring absorbed dose [4,6]

.

At verv large dose rates, ionization methods are

not satisfactory because of saturation effects

I 7 , 8J . The first question that arises in calorimetric dosimetry is how complicated one must be in measuring thermal energy imparted to an irradiated

*Visiting scientist from Accelerator Department,

Rispr National Laboratory, Roskilde, Denmark.
substance, that is, whether or not the calorimeter

must be adiabatic and contain reference calorimetric bodies with calibration heat sources.

III. Establishing Traceability for Absorbed Dose

A. Calibration Services

Relatively simple heat sensors that lose heat to their surroundings exponentially with time can

be used successfully, if the decay factors are determined accurately and are extrapolated to zero

time, that is, the time of the beginning of the irradiation [5,9]. In the case of pulsed or continuous electron beams, useful designs for calibrating dosimeter response factors include thin

foil calorimeters, in which other dosimeter systems

are positioned at the location of the displaced

calorimetric body [9-11]. Liquid calorimetry is also a useful approach, in which water or organic

solvents or solutions can be placed in an insulated Petri dish or larger container with thermocouples or thermistors for measurement of energy

deposited locally in the irradiated volume [5,6,

12,13].

Most cal ibrations of dosimeters at NBS for radiation processing users involve 60 Co gamma radiation in a cylindrical^ isotropic source of some tens of kilocuries in activity [14]. For traceability to absorbed dose in graphite, all measurements or calibrations with this source are

based on calorimetry with a spherical graphite

calorimetric body surrounded by spherical graphite

shells thick enough to approximate electron equilibrum conditions [15]. The dose rate can also be checked using' a graphite ionization chamber of the

same dimensions or with ferrous sulfate solution

dosimeters (in terms of absorbed dose in water)

of similar dimensions [16]. Knowing the approximate

photon spectrum in the gamma-ray field, it is pos- sible to estimate within approximately ± 2 percent

absorbed dose in other dosimeters, by applying

ratios of mass energy absorption coefficients of different dosimetry materials, weighted over the approximate spectrum [17-19].

B. Aqueous Chemical Dosimetry

For absorbed doses in the range 40-400 Gy, a convenient standard method of dosimetry involves

acidic aqueous solutions of ferrous sulfate or ferrous ammonium sulfate, the so-called "Fricke

dosimeter" [19-22]. This may be considered a pri- mary method, since values of chemical yield of

ferric ion (G-value) and molar extinction coefficient (cr 3+) at 305 nm optical wavelength are

well documented, and measureable with high pre- cision (within ± 1 percent) using quality ultraviolet spectrophotometers. The main limitations

are the requirements of ultra pure ingredients,

triply distilled water devoid of organic impurities, and extremely clear glass containers.

It is possible to measure larger doses than 400 Gy using other types of aqueous chemical

solutions, such as ferrous-cupric sulfate [20,23], or ceric-cerous sulfate [20,24], or "super Fricke"

solutions, involving oxygen-saturation and greater concentrations of ferrous ions and NaCl [22].

In such systems, although G-values and molar ex- tinction coefficients are known, impurities may cause even greater problems than with the ferrous

sulfate dosimeter.

1

Calibration services were instituted at NBS in 1977 for compliance with needs of radiation

processing and radiation testing users of high- power electron accelerators and large radionuclide

sources of gamma radiation [25]. The aim of these

services, as specified in NBS Special Publication

250, is to allow routine dosimetry practitioners

in industrial plants and national laboratories to establish traceability to primary standard methods

of dose determination based on calorimetry. The

following services are featured.

1. Administer to the user's dosimeters known

known absorbed doses (range: 0.1-600 kGy) of

electrons or photons of energy range (0.1 MeV).

2. Make dose interpretations in the user's irradiatior (e.g. during processing), by means

of transfer radiochromic dye films calibrated

at NBS.

3. Intercompare routine dosimeter performance be- tween laboratories.

4. Make spectrophotometry analysis of various

high-dose chemical and plastic dosimeters in the ultraviolet and visible spectral region.

5. Determine dose-rate dependence, temperature

dependence, and humidity dependence of response

of routine dosimeters.

6. Carry out special measurement at the user's facility (e.g. dose mapping or process commissioning)

Results of these services are supplied to the user

in the form of an NBS calibration test report.

Statistical evaluation of the ability of the user to meet product specifications may also be included, as illustrated in Figure 1 [25].

BO, min

Figure 1 Frequency distribution of absorbed

dose in typical product assortment

treated in a radiation process, showing variations in minimum and maximum

dose due mainly to differences in pro- duct bulk density (BD), as measured

at positions where minimum and maxi- mum dose have been determined to occur.
Here are illustrated typical Gaussian-shaped

frequency distributions of absorbed dose readings at the minimum dose (Dm-j n

) and maximum dose

CWx) Positions in irradiated product of given average bulk density (BD). Such dose interpretations are made by placing in a large sampling of

product boxes pairs of calibrated dosimeters of

known limits of uncertainty considerably smaller

than the values of two standard deviations of dose

due to variation in bulk density. C2apn m^ n and 2o

BD raax^' Practical dose limits may thin De set according to specifications of one-sided tolerance

factors, k - and k , which determine the factor

6 of product boxes irradiated below or above the limits at a specified probability level P, as based on an adequate number of measurement samples, N. The tolerance factor can be calculated

from Student's t- value tables of N versus 6 for specified values of P. Thus, traceable dosimetry

data in an industrial production application can

be used to determine whether or not a given radiation process meets specifications of the uniformity ratio U = Dmax/ Dmin> say> in terms of a certain value of limiting uniformity ratio U^:

U < u s °max

+ kmax °BD,max

*~ ^min " ^min CT BD,min

The determination of detailed absorbed dose

distribution in the 60 Co irradiated chamber at NBS was necessary in order to assure that dose

gradients over the volume of dosimeters being

calibrated did not exceed ±2 percent. The

chamber is generally a cylindrical air-filled

cavity 30 cm long and 9 cm in inner diameter,

consisting of a water-tight stainless steel can- ister lowered manually to a 3 meter depth in water, so that it is surrounded by a cylindrical array of twelve 14 cm long 60 Co rods (see elevation view in Figure 2). Nitrogen flow to the dosimeter is also possible, as indicated. In most

calibrations the dosimeter is held between layers

of polystyrene, aluminum, silicon, etc. (depending on the material of interest) having thick- nesses sufficient to approximate conditions

of electron equilibrium. The absorbed dose rate

is known at this position within approximate un- certainly limits of ±1 percent £15J.

Measurements were made using longer strips of

radiochromic dye film dosimeters held in polystyrene layers, in order to map absorbed dose

distributions and isodose contours within the irradiation volume of the cannister 1273 - Figures

3 and 4 show the results of this mapping study,

and reveal that within approximately 2 cm of the calibration position, namely 6.5 cm above the inner bottom surface along the cylindrical axis,

the absorbed dose rate is uniform to within ±2 percent.

B. Means of Achieving Traceability

The routes to traceability through the NBS high-dose calibration service for intense fields

of electrons and photons are illustrated in Figure 5. The approximate uncertainty of each measurement level is given in the left. At NBS primary standardization is provided by calorimetry,

and in the case of gamma ray fields, the absorbed

Figure 2 Elevation view of cylindrical stainless steel cannister positioned for dosimeter calibration in cylindrical array of twelve 60 Co source rods at bottom of 3-meter deep pool of water. Then thin dosimeters are calibrated

either in air or in nitrogen, while

held between layers of a medium

(plastic, metal, etc.) simulating con- ditions of electron equilibrium.

dose rate, Dc

, is checked periodically with

standard graphite ionization chambers matching the dimensions of the graphite calorimeter [15]. In the case of electron beams, the absorbed dose, D,

in either graphite or metal is measured by means

of a thin calorimetric body. Multiplication by

ratios of photon energy absorption coefficients

over the approximate radiation spectrum makes it possible to determine dose, D . , or dose rate, D-j

,

in other materials of interest, such as water,

plastic, silicon, biological substances, etc. Industrial users generally characterize radiation

of standard chemical dosimetry over the absorbed

dose ranges indicated. Electron beam users may

depend on calorimetry intercompared with that of a national standards laboratory, or they may use transfer dosimeters calibrated against primary

standards. The latter is made possible by the calibration service described earlier.

IV. Routine Methods of Dose Determination

In radiation processing dosimetry, routine pro- cedures require large numbers of commercially

173
Figure 3 Isodose curves in a vertical plane bisecting the bottom portion of the volume inside the cannister

shown in figure 2, according to measurements by means of strips of calibrated radiochromic dye

films.

available measurement systems that must have the following characteristics [28]:

1. Be similar to products cf interest in terms of radiation ebsorption properties.

2. Have linear response in terms of radiation

effect yields, or give reproducible characteristics response curves when calibrated in terms Of effect-vs.-dose.

3. Be easy to prepare or available in large

reproducible commercial batches.

4. Have sufficient response range and precision

at dose levels of interest.

5. Show sufficiently small systematic error due

to effects of extremes of dose rate and environmental factors during irradiation.

6. Be rugged for production-line use.

7. Be easy to calibrate and analyze for radiation effects of interest.

8. Be readily mailed and have long shelf life.

9. Be stable over time of irradiation and storage before analysis for dose interpretation.

10. Be inexpensive for routine use.

The most widely used and successful methods in industrial applications, for doses in the kilogray

and tens of kilogray dose regions are plastic

dosimeters, such as red acrylic cylinders (a), red or amber Perspex (b), Perspex HX (c), radiochromic dye film (d), or cellulose triacetate film

(e), [18,25,19]. Of these, radiochromic dye films were selected by NBS as a transfer measurement

system capable of supplying traceability to the primary standard of absorbed dose in water, gra- phite, etc. The film consists of a colorless

leucocyanide dye derivative dissolved in a clear

plastic matrix, and may be supplied in thickness

ranging from 8 urn to 700 urn, in order to cover

a wide range of absorbed doses ( 1 0-1

6 Gy). Be- sides this advantage, these films have the fol- lowing favorable properties:

1 . Long shelf life. *

2. Dose rate independence [32].

af) Supplied by AECL, Ottawa, Canada

b) Supplied by AERE, Harwell, UK

(c) Supplied by UK Panel on Electron and Gamma Ray

Irradiation, UK

(d) Supplied by Far West Technology, Inc., Goleta,

CA, USA

(e) Supplied by CAPRI-Saclay, France

(f) A psuedo low-intensity rate dependence occurs with some types of radiochromic dye films,

when irradiated to doses exceeding ^ 1 kGy at rates < 5 Gys" 1 and relative humidities <50%

[30,31].

174
LATERAL DISTANCE FROM VERTICAL AXIS (cm)

Figure 4 Horizontal dose distribution at a level of the calibration position 6.5 cm above the bottom surface of the cannister shown in figure 2 [27].

3. Low average atomic number; small energy dependence [31].

4. Essentially same response to photons, electrons, protons; low LET dependence [33].

5. Essentially same response in air, vacuum, N 2 , etc. [33].

6. Relatively small and well -defined temperature

dependence of response [35].

7. Relatively stable radiation-induced integral

signal, i.e., optical density increase that

is nearly linear with dose and does not change

appreciably between irradiation and readout

(good archival properties) [35].

8. Available in large, reproducible batches of

relatively uniform thickness [36].

9. Inexpensive end not very sensitive to the presence of impurities.

10. Relatively simple readout procedures using

optical photometers at specified visible light

wavelengths.

There are also certain pitfalls that must be

guarded against.

1. Sensitivity to ultraviolet light, so that a clear plastic film containing a UV blocking

agent must be used over windows and fluor- escent light fixtures.

2. Sensitivity to wide changes in relative

humidity, in particular relative humidities

below 20% and above 80% [35]. Best results occur when the films are hermetically packaged in individual polyethylene or foil en- velopes.

3. The films need to be protected against

scratches, fingerprints, and other blemishes.

4. The accuracy and precision of film response

between different batches depends on periodic

calibration, in order to make dose interpretations traceable to primary standards.

V. Cone! usion

Although a successful calibration service has been instituted at NBS to partially satisfy the needs of industrial and national radiation users

for traceability at high doses, the program

is still incomplete. This is indicated by the list of needs in Table II. Not only are international standards and intercomparison studies

important, but also improved portable calorimeters

175
Approx.

Uncertainty

± I %

±3

± 5 %

± 10% I

Figure 5 Traceabil ity chart, according to high-dose calibration

services at NBS designed for users of intense radiation

sources.

based on water vs. tissue-equivalent plastics,

better energy dependence data, dosimeter quality

control, and continued development of improved measurement systems.

TABLE II

NEEDS FOR SP'-VING PROBLEMS OF TRACEABILITY

1. International standards

2. Systematic international intercomparisons

3. Transfer calorimeters to reduce number of

levels

4. Development of improved water calorimeter

5. Knowledge of radiation spectra in both calibration and application

6. Better quality control of transfer dosimeters

7. Development of improved routine dosimeters.

176
REFERENCES

[1]

[2]

[3]

[4]

[5]

[6]

[7]

Radiation Processing , Vols. 1 and 2, Silverman, J. and van Dyken, A.R., eds.,

Pergamon Press, Ltd., Oxford; Radiat.

Phys. Chem. 9 (1977)

Advances in Radiation Processing , Vols. 1 and

2, Silverman, J., ed., Pergemon Press, Ltd.,

Oxford; Radiat. Phys. Chem. 14 (1979)

Advances in Radiation Processing, Vols. 3 and

4, ed., Silverman, J., Pergamon Press, Ltd.,

Oxford; Radiat. Phys. Chem. (1981) (in press)

Laughlin, J. S., Genna, S., Calorimetry,

Chapt. 16 in Radiation Dosimetry , Vol. 2, 2nd Ed., Attix, F. H., Roesch, W.C., eds.,

Academic Press, New York (1966)

Radak, B.B., Markovic, V.M., Calorimetry,

Chapt. 3 in Manual on Radiation Dosimetry , Holm, N.W., Berry, R.J., eds., Marcel Dekker,

New York (1970)

Domen, S.R., Absorbed Dose Water Calorimeter,

Med. Phys. 7 , 157 (1980)

Boag, J.W., Ionization Chambers, Chapt. 1 in Radiation Dosimeter , Vol. 2, 2nd ed.,

Attix. F.H., Roesch, W.C. eds. Press, New York (1966)Academic

[8]

[9]

Loevinger, R., Ionization chamber recombination

loss in high intensity radiation fields

" Selected Topics in Radiation Dosimetry" , Proc. Int. Sympos., Vienna, 1960, International

Atomic Energy Agency, Vienna 173 (1961)

Chappell , S.C., Humphreys, J.C., The dose

rate response of a dye- polycnlorostyrene film

dosimeter, IEEE Trans, on Nucl . Sci. NS-19 , 175 (1972)

Proc. Int. Sympos., Vienna, 1975, International

Atomic Energy Agency, Vienna, 663 (1975)

[14] Rabin, H., Price, W.E., Mapping radiation

fields with silver activated phosphate glass,

Nucleonics 13 (3) 33 (1955)

[15] Petree, B., Lamperti, P., A comparison of

absorbed dose determinations in graphite by

cavity ionization chamber and by calorimetry,

NBS J. Res. 71C, 19 (1967)

[16] McLaughlin, W.L., A National Standardization

programme for high-dose measurement, High- Dose Measurements in Industrial Radiation

Processing , IAEA Technical Reports Series,

International Atomic Energy Agency (1980)

(in press)

[17]

t 10 ^0swald, R.B., Jr., Eisen, H.A., Conrad, E.E.,

Pulsed electron beam dosimetry, IEEE Trans, on Nuclear Science., NS-13 , 229 (1966]

[^Miller, G.H., Lockwood, G.J., Halbleib, J. A.,

Improved Calorimeter method for energy deposition

measurement, IEEE Trans, on N ucl. Sci., NS-21 , 359, (1974)

[12] Holm, N.W., Jarrett, R.D., An evaluation of

dosimetry procedures for use in food irradiation, Nat. Acad. Sci., - Nat. Res. Council Publ. 1273 , NAS-NRC, Washington, D.C.,

(1965)

[13]

Radak, B.B., Kosanic, M.M., Sesic, M.B.,

McLaughlin, W.L., A calorimetric approach to the calibration of liquid dose meters in highintensity electron beams, Biomedical Dosimetry

Hubbell, J.H., Photon mass attenuation and energy absorption coefficients for 1 keV to 20 MeV , Trends in Radiation Dosimetry,

McLaughlin, W.L., ed., Pergamon Press, Oxford,

(1981) (in press)

[18] McLaughlin, W.L., Solid-phase chemical

dosimeters, Sterilization by Ionizing Radiation , Gaughran, E.R.L., Goudie, A.J., eds.,

Multiscience, Montreal, 219 (1974)

[19] Chadwick, K.A. , Ehlermann, D.A.E.,

McLaughlin, W.L., Manual on Food Irradiation

Dosimetry , IAEA Technical Reports Series No. 178, International Atomic Energy Agency,

Vienna (1977)

[20] Fricke, H. Hart, E. J., Chemical dosimetry,

Chapt. 12 in Radiation Dosimetry , Vol. 2, 2nd ed., Attix, F.H., Roesch, W.C, eds.,

Academic Press, New York (1966)

[21] Ehrlich, M. Soares, C.G., Measurement assurance studies of high-energy electron and photon dosimetry in radiation theraphy

applications; Intercomparison Procedures in the Dosimetry of High-Energy Electrons and X-rays , IAEA Technical Reports Series,

International Atomic Energy Agency, Vienna

(1980) (in press)

[22] Sehested, K. , The Fricke dosimeter, Manual on Radiation Dosimetry , Holm, N.W., Berry, R.J.,

eds., Marcel Dekker, New York, 313 (1970)

[23] Bjergbakke, E., Sehested, K., Lang Rassmussen,

0., The reaction mechanism

+and rate constants in the radiolysis of Fe2+-Cu 2 Solutions, Radiat.

Res., 66, 433 (1976)

[24] Bjergbakke, E., Ceric-cerous sulfate dosimetry,

Trends in Radiation Dosimetry , McLaughlin, W.L.,

ed., Pergamon Press, Oxford (1981 ) (in press)

177
[25] McLaughlin, W.L., Dosimetry standards for industrial radiation processing, National and International Standardization of Radiation

Dosimetry , Vol. T, Prcc. Int. Sympos.,

Atlanta, 1977, International Atomic Energy

Agency, Vienna, 89 (1978)

ed., Pergamon Press, Ltd., Oxford; Radiat . Phys. Chem. 14 , 551 (1980)

[36]

[26] Vas, K., Beck, E.R.A., McLaughlin, W.L.,

Ehlermann, Chadwick, K.H., Dose limits versus dose range, Acta Alimentaria 7 (2) 343 (1978)

Kantz, A.D., Humpherys, K.C., Quality assurance for radiation processing, Advances

in Radiation Processing , Vol. 2, Silverman, J., ed., Pergamon Press, Ltd.,

Oxford; Radiat. Phys. Chem. 14 , 575 (1980)

[27] Humphreys, J.C., McLaughlin, W.L., Dye film

dosimetry for radiation processing,

Application of Accelerators in Research and Industry , Proc. of 6th Conf . , North Texas

State University, 1980, U.S. Department of

Energy (1981) (in press)

[28] McLaughlin, W.L., Radiation measurement and quality control, Radiat. Phys. Chem. 9 , 147

(1977)

[29] Barrett, J.H., Sharpe, P.H.G., Stuart, I. P., Dosimetry with dyed and indyed acrylic plastic,

Trends in Radiation Dosimetry , McLaughlin,

W.L., ed., Pergamon Press, Ltd.,

Oxford (1981) (in press)

[30] Gehringer, P., Eschweiler, H., Proksch, E., Dose-rate and humidity effects upon the gamma- radiation response of nylon-based radiochromic

film dosimeters, Int . J. Appl . Radiat.

Isotopes 31_ 595 (1980]

[31] McLaughlin, W.L., Humphreys, J.C., Levine,

H., Miller, A., Radak, B.B., Rativanich, N.

,

The gamma-ray response of radiochromic dyes at different absorbed dose rates, Advances in Radiation Processing , Vol Pergamon Press, Ltd

(1981) (in press)

4, Silverman, J. , ed.

,

Oxford; Radiat. Phys. Chem .

[32] McLaughlin, W.L., Humphreys, J.C., Radak,

B.B., Miller, A., Oleinik, J. A., The response

of plastic dosimeters to gamma rays and electrons at high absorbed dose rates, Advances

in Radiation Dosimetry , Vol. 2, Silverman, J., ed., Pergamon Press Ltd., Oxford, Radiat. Phys. Chem. 14, 535 (1980)

[33] McLaughlin, W.L., Rosenstein, M., Levine, H., Bone-and muscle-equivalent, solid chemical dose meters for photon and electron doses above one

kilorad, Biomedical Dosimetry , Proc. Int. Sympos., Vienna, 1975, International Atomic

Energy Agency, Vienna, 267 (1975)

[34] Hansen, J., Ris# National Laboratory, Roskilde,

Denmark, private communicotion, (1980)

[35] Levine, H., McLaughlin, W.L., Miller, A.,

Temperature and humidity effects on the gamma-ray response and stability of plastic

and dyed plastic dosimeters, Advances in Radiation Processing , Vol. ?., Silverman, J., 178
SEMINAR ON TRACEABILITY FOR IONIZING RADIATION MEASUREMENTS

National Bureau of Standards

Gaithersburg, MD May 8-9, 1980

List of Attendees

John Arras

Armed Forces Radiobiology Research Institute

Bethesda, MD 20014

Allen Brodsky

U.S. Nuclear Regulatory Commission

Office of Standards Development

Washington, DC 20555

Doris Brunner

Penn. Dept. of Environmental Resources

Bureau of Radiation Protection

P.O. Box 1467 Harrisburg, PA 17120

Lily Buja-Bijunas

National Research Council of Canada

Bldg M-35

Montreal Road

Ottawa, Ont. K1A 0R6 CANADA

George Campbell Lawrence Livermore National Laboratory

Hazards Control Department

Livermore, CA 94550

Arthur Carlson

Illinois Department of Public Health

Division of Radiation Protection

535 West Jefferson St. Springfield, IL 62761

Randall S. Caswell National Bureau of Standards Center for Radiation Research

Washington, DC 20234

Lucy Cavallo

National Bureau of Standards Center for Radiation Research

Washington, DC 20234

Lawrence K. Cohen

U.S. Nuclear Regulatory Commission

Office of Inspection & Enforcement

Washington, DC 20555

R. Colle

National Bureau of Standards Center for Radiation Research

Washington, DC 20234

Dave Dieter

Eastman Kodak Co. Kodak Part B6 MC5

Rochester, NY 1465Q

Dave Dieterly

New England Nuclear

Medical Diagnostic Division

601 Treble Cove Rd North Bill erica, MA 01862

Margarete Ehrlich

National Bureau of Standards Center for Radiation Research

Washington,

Elmer H. Eisenhower

National Bureau of Standards Center for Radiation Research

Washington, DC 20234

Robert R. Eng

Armed Forces Radiobiology Research Institute

Bldg 42 NNMC Bethesda, MD 20014

Roger W. Ferris

Amersham Corporation

2636 Clearbrook Dr. Arlington Heights, IL 60005

Leo Fitzpatrick

Biomedics Corp. (Mail Stop TBC) CIF Bldg Rm 398 Kennedy Space Center, FL 32899

D.M. Fleming

Battel le, Pacific Northwest Labs. Battel le Blvd Richland, WA 99352

Ralph D. Flint

Battel le Memorial Institute

505 King Ave. Columbus, OH 43201

Claude Florg

Armed Forces Radiobiology Research Institute

Bethesda, MD, 20014

Andreas George

U.S. Department of Energy

Environmental Measurement Laboratory

376 Hudson St. New York, NY 10014

Thomas F. Gesell University of Texas School of Public Health

P.O. Box 20106 Houston, TX 77025

Robert Golden

Walter Reed Army Medical Center

Diagnostic Radiology Services

Department of Radiology

Washington, DC 20012

179
Michael Grisson

Armed Forces Radiobiology Research Institute

Bldg 42, NNMC Bethesda, MD 20014

Ken Groves

Navy Nuclear Power Unit

Code 40

Port Hueneme, CA 93043

James A. Grundl

National Bureau of Standards Center for Radiation Research

Washington, DC 20234

H.T. Heaton, II National Bureau of Standards

Center for Radiation Research

Washington, DC 20234

Gene Hendrix

Naval Facilities Engineering Command

Attn: 111N 200 Stovall St. Alexandria, VA 22332

Phil Hesse

Naval Surface Weapons Center

Silver Spring, MD 20910

J.M.R. Hutchinson

National Bureau of Standards Center for Radiation Research

Washington, DC 20234

Jeffrey N. Iadisernia

Keithley Instruments

31300 Bainbridge Rd. Solon, OH 44129

Kenneth Inn National Bureau of Standards Center for Radiation Research

Washington, DC 20234

Richard Jaquish

Battel le, Pacific Northwest Labs. Box 999 Richland, WA 99352

Arthur N. Jarvis

U.S. Environmental Protection Agency

Office of Quality Assurance-Radiation

National Environmental Research Center

P.O. Box 15027

Las Vegas, NV 89114

W.A. Jennings

National Physical Laboratory

Division of Radiation Science and Acoustics

Teddington, Middlesex, TW 11 0LW

UK

M. Jimenez

Duke Power Co. Steam Production Dept.

P.O. Box 33189 Charlotte, NC

Don Jordan

USAF

0E HL/RZE

Brooks Air Force Base, TX 78235

Ronald L. Kathren

Battel le, Pacific Northwest Labs. Battelle Blvd Richland, WA 99352

Bergene Kawin

Food and Drug Administration

5600 Fishers Lane, HFX-150

Rockville, MD 20857

Frank Kearly

Bureau of Radiological Health, HFX-70

5600 Fishers Lane Rockville, MD 20857

Kirk J. King

Naval Research Labs, Code 6073 Washington, DC 20375

George Komada Bureau of Radiological Health, HFX-260

5600 Fishers Lane Rockville, MD 20857

Chris E. Kuyatt

National Bureau of Standards Center for Radiation Research

Washington, DC 20234

George T. Lalos

Naval Surface Weapons Center

Silver Spring, MD 20910

John J. Lanza

Naval Surface Weapons Center

Silver Spring, MD 20910

Robert Loevinger

National Bureau of Standards Center for Radiation Research

Washington, DC 20234

Ronald B. Luersen

Naval Research Labs, Code 6073 Washington, DC 20375

William McLaughlin

National Bureau of Standards Center for Radiation Research

Washington, DC 20234

Robert Mills

Brookhaven National Laboratory

Bldg 535 A Upton, NY 11973

Robert Morton

Bureau of Radiological Health, HFX-70

5600 Fishers Lane Rockville, MD 20857

Robert J. Murray

PA Power & Light

2 North Ninth St Allentown, PA 18101

Harold W. Nass Union Carbide

Box 324 Tuxedo, NY 10987
Richard E. Need ham

Dept. Health and Human Services

Food and Drug Authority

Engineering & Analytical Center

109 Hoi ton St. Winchester, MA 01890

Maury Neuweg

Illinois Dept. of Public Health

Division of Radiation Protection

535 West Jefferson St. Springfield, IL 62761

Thomas R. Ohlhaber

Bureau of Radiological Health

5600 Fishers Lane Rockville, MD 20857

Dale Olson

U.S. Dept. of Energy

550 2nd St. Idaho Falls, ID 83401

Phillip Plato

Univ. of Michigan

School of Public Health

Ann Arbor, MI 48109

Adelbert Potter

New York State Dept. of Health

Bureau of Radiological Health

Rm 359 Tower Bldg

E.S.P. Albany, NY 12237

Federick Prevo Bureau of Radiological Health, HFX-260

5600 Fishers Lane Rockville, MD 20857

Lawrence A. Proud

The Boeing Co. P.O. Box 3707 M/S 2T-04

Seattle, WA 98124

Nongnooch Ratinavich

Office of Atomic Energy for Peace Bancock, THAILAND

Dennis Riley

Dosimeter Corp. of America

P.O. Box 42377

Cincinnati, OH 45242

Genevieve Roessler

Univ. of Florida

237 Nuclear Science Center

Gainesville, FL 32611

Daniel Sam

Naval Surface Weapons Center

Silver Spring, MD 20910

Robert J. Shalek

M.D. Anderson Hospital

Physics Dept.

Houston, TX 77030

Donovan Smith

U.S. Nuclear Regulatory Commission

Washington, DC 20555

C. Soares

National Bureau of Standards Center for Radiation Research

Washington, DC 20234

Paul B. Sundy RADCAL Corp. 426 W. Duarte Rd. Monrovia, CA 91016

Kathy Teasdale

Reynolds Electrical & Engineering Co

P.O. Box 14400

Las Vegas, NV 89114

Bruce Thomadsen

Univ. of Wisconsin

K4/B100 Clinical Science Center

600 Highland Avenue

Madison, WI 53792

Anthony Tse

U.S. Nuclear Regulatory Commission

Washington, DC 20555

Paul Tyree

New England Nuclear

NS Division

601 Treble Cove Rd North Billercia, MA 01862

Ivan Vajcovec

Atomic Energy of Canada, Limited

Commercial Products

Box 6300, Station J Ottawa K2A 3W3 CANADA

Lorraine Vekens

New England Nuclear Corp.

601 Treble Cove Rd. North Bill erica, MA 01862

Stephen S. Voris

Bell Laboratories

600 Mountain Ave. Murray Hill, NJ 07974

Graham V. Walford

Technology for Energy Corp.

975 West Outer Drive

Oak Ridge, TN 37830

R.C. Yoder

Battele, Pacific Northwest Labs.

P.O. Box 999 Richland, WA 99352

Robert Zapp

Battelle Memorial Institute

505 King Ave. Columbus, OH 43201

Joseph Zelenski

E.R. Squibb and Sons, Inc. Rt. 1, Box 89 Stockton, NJ 08559

Garry Zeman

National Naval Medical Center

Bethesda, MD 20014

181
NBS-114A (REV, 2-8C) U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO. MBS SP 609

2. Performing Organ. Report N04 3. Publication Date

FEBRUARY 198?

4. TITLE AND SUBTITLE

Proceedings of a Meeting on Traceability for Ionizing Radiation Measurements

held at the National Bureau of Standards, Gaithersburg , MD, on May 8-9, 1980.

EDITOR:

H. Thompson Heaton, II

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D C 20234

7. Contract/Grant No.

8. Type of Report <L Period Covered

Final

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State, ZIP)

Same as no. 6

10. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number: 81-600197

I | Document describes a computer program; SF-185, FlPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here)

These proceedings are the compilation of 21 papers presented at a seminar on Traceability for Ionizing Radiation Measurements held at the National Bureau

of Standards, Gaithersburg, MD, on May 8-9, 1980. General concepts of traceability were presented from several perspectives. The national standards for

radiation dosimetry, radioactivity measurements, and neutron measurements were

described. Specific programs for achieving traceability to the national standards for radiation measurements in medical, occupational, and environmental

applications were summarized.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

Calibrations, ionizing radiation, measurements, national standards, quality

assurance, secondary standard laboratory, traceability.

13. AVAILABILITY

[yi Unlimited

| | For Official Distribution. Do Not Release to NTIS

|"~~| Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D C

20402.

Order From National Technical Information Service (NTIS), Springfield, VA 22161

14. NO. OF

PRINTED PAGES

175

15. Price

!^U.S. GOVERNMENT PRINTING OFF

USCOMM-DC eOO-PBO

CE: 1982-360-997/2012




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the authority of the National Standard Data Act (Public Law

90-396).

NOTE: The principal publication outlet for the foregoing data is the Journal of Physical and Chemical Reference Data (JPCRD)

published quarterly for NBS by the American Chemical Society

(ACS) and the American Institute of Physics (AIP). Subscriptions,

reprints, and supplements available from ACS, 1 155 Sixteenth St., NW, Washington, DC 20056.

Building Science Series—Disseminates technical information developed at the Bureau on building materials, components,

systems, and whole structures. The series presents research results,

test methods, and performance criteria related to the structural and

environmental functions and the durability and safety characteristics of building elements and systems.

Technical Notes—Studies or reports which are complete in themselves but restrictive in their treatment of a subject. Analogous to monographs but not so comprehensive in scope or definitive in treatment of the subject area. Often serve as a vehicle for final reports of work performed at NBS under the sponsorship of other government agencies.

Voluntary Product Standards—Developed under procedures

published by the Department of Commerce in Part 10, Title 15, of

the Code of Federal Regulations. The standards establish nationally recognized requirements for products, and provide all concerned interests with a basis for common understanding of the

characteristics of the products. NBS administers this program as a supplement to the activities of the private sector standardizing

organizations. Consumer Information Series—Practical information, based on NBS research and experience, covering areas of interest to the con- sumer. Easily understandable language and illustrations provide

useful background knowledge for shopping in today's technological marketplace. Order the above NBS publications from: Superintendent of Documents. Government Printing Office, Washington, DC 20402. Order the following NBS publications—FIPS and NBSIR's—from

the National Technical Information Services. Springfield, VA 22161

.

Federal Information Processing Standards Publications (FIPS

PUB)—Publications in this series collectively constitute the Federal Information Processing Standards Register. The Register

serves as the official source of information in the Federal Govern- ment regarding standards issued by NBS pursuant to the Federal Property and Administrative Services Act of 1949 as amended.

Public Law 89-306 (79 Stat. 1127), and as implemented by Executive Order 11717 (38 FR 12315. dated May 11, 1973) and Part 6 of Title 15 CFR (Code of Federal Regulations).

NBS Interagency Reports (NBSIR)—A special series of interim or

final reports on work performed by NBS for outside sponsors

(both government and non-government). In general, initial dis- tribution is handled by the sponsor; public distribution is by the National Technical Information Services. Springfield, VA 22161,

in paper copy or microfiche form.
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