NBS Measurement Services:

Dosimetry for

High Dose

Applications

U.S. Department of Commerce

National Bureau of Standards
Center for Radiation Research

The Center for Radiation Research is a major component of the National Measurement Laboratory in the National Bureau of Standards. The Center provides the Nation with standards and measurement services for ionizing

radiation and for ultraviolet, visible, and infrared radiation; coordinates and furnishes essential support

to the National Measurement Support Systemfor ionizing radiation; conducts research in radiation related

fields to develop improved radiation measurement methodology; and generates, compiles, and critically

evaluates data to meet major national needs. The Center consists of five Divisions and one Group.

Atomic and Plasma Radiation Division

Carries out basic theoretical and experimental research into the • Atomic Spectroscopy

spectroscopic and radiative properties of atoms and highly ionized • Atomic Radiation Data

species; develops well-defined atomic radiation sources as radiometric • Plasma Radiation

or wavelength standards; develops new measurement techniques and

methods for spectral analysis and plasma properties; and collects,

compiles, and critically evaluates spectroscopic data. The Division

consists of the following Groups:

Radiation Physics Division

Provides the central national basis for the measurement of far ultra- • Far UV Physics

violet, soft x-ray, and electron radiation; develops and disseminates • Electron Physics

radiation standards, measurement services, and data for for these radia- • Photon Physics

tions; conducts theoretical and experimental research with electron,

laser, ultraviolet, and soft x-ray radiation for measurement applications; determines fundamental mechanisms of electron and photon interactions with matter; and develops advanced electron- and photon-based

measurement techiques. The Division consists of the following Groups:

Radiometric Physics Division

Provides national measurement standards and support services for ultra- • Spectral Radiometry

violet, visible, and infrared radiation; provides standards dissemination • Spectrophotometry

and measurement quality assurance services; conducts research in optical • Radiometric Measurement Services

radiation, pyrometry, photometry, and quantum radiometry; and develops

spectroradiometric and spectrophotometric standards and calibration

procedures. The Division consists of the following Groups:

Radiation Source and Instrumentation Division

Develops, operates, and improves major NBS radiation facilities

including the electron Linac and race track microtron; develops,

designs, and builds electronic and mechanical instrumentation for

radiation programs and facilities; provides national leadership

in the standardization of nuclear instrumentation; and develops

new competence in radiation sources and instrumentation. The

Division consists of the following Groups:

• Accelerator Research

• Linac Operations

• Electronic Instrumentation

• Mechanical Instrumentation

Ionizing Radiation Division

Provides primary national standards, measurement services, and basic

data for applications of ionizing radiation; develops new methods of

chemical and physical dosimetry; conducts theoretical and experimental

research on the fundamental physical and chemical interactions of

ionizing radiation with matter; provides essential standards and measurement support services to the National Measurement Support

System for Ionizing Radiation; and develops and operates radiation

sources needed to provide primary radiation standards, fields, and

well-characterized beams of radiation for research on radiation

interactions and for development of measurement methods. The Division

consists of the following Office and Groups:

• Office of Radiation Measurement

• Radiation Theory

• Radiation Chemistry and Chemical

Dosimetry

• Neutron Measurements and Research

• Neutron Dosimetry

• Radioactivity

• X-Ray Physics

• Dosimetry

Nuclear Physics Group

Engages in forefront research in nuclear and elementary particle physics;

performs highly accurate measurements and theoretical analyses which

probe the structure of nuclear matter; and improves the quantitative

understanding of physical processes that underlie measurement science.
NBS MEASUREMENT SERVICES:

DOSIMETRY FOR HIGH DOSE

APPLICATIONS

Jimmy C. Humphreys

Dene Hocken

William L. McLaughlin

Center for Radiation Research

National Measurement Laboratory

National Bureau of Standards

Gaithersburg, MD 20899

U.S. DEPARTMENT OF COMMERCE, C. William Verity, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued March 1988
Library of Congress Catalog Card Number: 88-600506

National Bureau of Standards Special Publication 250-1

1

Natl. Bur. Stand. (U.S.), Spec. Publ. 250-11, 49 pages (Mar. 1988)

CODEN: XNBSAV

Certain commercial equipment, instruments, or materials are identified in this paper in order to adequately specify the experimental procedure. Such identification does not imply recommendation or endorsement by the National Bureau of Standards, nor does it imply that the materials or equipment

identified are necessarily the best available for the purpose.

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1988

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402-9325
PREFACE

The calibration and related measurement services of the National Bureau

of Standards are intended to assist the makers and users of precision

measuring instruments in achieving the highest possible levels of

accuracy, quality, and productivity. NBS offers over 300 different

calibration, special test, and measurement assurance services. These

services allow customers to directly link their measurement systems to

measurement systems and standards maintained by MBS. These services

are offered to the public and private organizations alike. They are described in NBS Special Publication (SP) 250, NBS Calibration Services

Users Guide .

The Users Guide is being supplemented by a number of special

publications (designated as the "SP 250 Series") that provide a detailed description of the important features of specific NBS

calibration services. These documents provide a description of the:

(1) specifications for the service; (2) design philosophy and theory;

(3) NBS measurement system; (4) NBS operational procedures; (5)

assessment of measurement uncertainty including random and systematic

errors and an error budget; and (6) internal quality control procedures

used by NBS. These documents will present more detail than can be

given in an NBS calibration report, or than is generally allowed in

articles in scientific journals. In the past NBS has published such

information in a variety of ways. This series will help make this type

of information more readily available to the user.

This document (SP 250-11), NBS Measurement Services: Dosimetry for

High-Dose Applications, by J. C. Humphreys, D. Hocken, and W. L. McLaughlin, is the eleventh to be published in this new series of

special publications. It covers the dosimetry services available to users of intense radiation fields, in particular large gamma-ray

sources and electron accelerators up to about 10 MeV. These are: dosimeter irradiation services (see test numbers 49010S, 49040S, and

49041S in the SP 250 Users Guide); dosimeter calibrations (49020S and

49030S); and measurements of dosimeter characteristics (49050S).

Inquiries concerning the technical content of this document or the

specifications for these services should be directed to the authors or one of the technical contacts cited in SP 250.

The Center for Radiation Research (CRR) is in the process of publishing

21 documents in this SP 250 series, covering all of the calibration

services offered by CRR. A complete listing of these documents can be

found inside the back cover.

NBS would welcome suggestions on how publications such as these might

be made more useful. Suggestions are also welcome concerning the need

for new calibration services, special tests, and measurement assurance

programs

.

Joe D. Simmons Chris E. Kuyatt

Acting Chief Director

Measurement Services Center for Radiation Research

iii
ABSTRACT

This document describes calibration services available at the National Bureau

of Standards for the standardization of high absorbed dose measurements of

ionizing radiation. The areas of application of such measurements include

medical product sterilization, electronic device radiation hardness testing an food processing. Detailed descriptions of the NBS dosimetry procedures and

uncertainty assessments are given. Measurement assurance program techniques

are discussed.

Key words: Dosimeter calibration, ionizing radiation, irradiation facilities,

measurement assurance program, uncertainties.

iv
TABLE OF CONTENTS

Page

1 . Description of Service 1

2. Design Philosophy and Theory 2

3. Description of System 3

3.1 60 Co Irradiation Facilities 3 3.2 Transfer Standard Dosimeters 9 3.3 Spectrophotometer 9 3.4 Thickness Gauge 9

4. Operating Procedures 9

4.1 Internal Dosimeter Calibration 9 4.2 Irradiation of Customer Dosimeters 14

4.3 Application of Transfer Dosimeters 18

4.4 Analysis of Dosimeters 20

5. Assessment of Uncertainties 20

6. Internal Quality Control 27

7. Safety 29

References 30

Appendix A: A Report of Calibration of Irradiation of Customer's Dosimeters

Appendix B: Instructions to Customer for Irradiation of Transfer Dosimeters

Appendix C: A Report of Calibration of Results of Transfer Dosmeter

Measurements

V
LIST OF TABLES

Page

Table 1 60 Co Decay Corrections Factors (Cd ) 13

Table 2 Various Dosimeters Types 17

Table 3 Uncertainties in Absorbed Dose Values for Irradiations with

Pool Source . 21

Table 4 Uncertainties in Absorbed Dose Values for Irradiations with

Gammacell 220 24

Table 5 Uncertainties in Absorbed Dose Values for Irradiations with

Vertical Beam Source 25

Table 6 Uncertainties in Absorbed Dose Values Employing Transfer

Standard Dosimeters 26

vi
LIST OF FIGURES

Page

Fig. 1. Photograph of model of NBS 60 Co Pool Source 4

Fig. 2. Schematic drawing of Gammacell 220 self -shielded 60 Co irradiator

in the chamber load position 6

Fig. 3. Schematic Drawing of Gammacell 220 irradiator in the irradiate

position 7

Fig. 4. Schematic drawing of teletherapy type shielded-head 60 Co

irradiator 8

Fig. 5. Examples of optical spectral scans of unirradiated radiochromic

dye film dosimeter 11

Fig. 6. Typical 605nm calibration curve for radiochromic dye film

dosimeters f$. 15

Fig. 7. Typical 510nm calibration curve for radiochromic dye film

dosimeters 16

Fig. 8. Dependence of response of radiochromic dye film dosimeters on temperature during irradiation 19

vi 1*

NATIONAL BUREAU OF STANDARDS

MEASUREMENT SERVICES:

DOSIMETRY FOR HIGH-DOSE APPLICATIONS

1 . Description of Service

1.1 The National Bureau of Standards, Ionizing Radiation Division, provides

dosimetry services for individual users of intense radiation fields, in

particular, large gamma-ray sources and electron accelerators up to

approximately 10 MeV. These services include the administering of known

absorbed doses of ionizing photons to customer- supplied dosimeters (such as solid radiochromic or liquid chemical types) or test samples that are sent to

NBS (schedule 49010S, previously 8 . 6A) , [1]* where they are packaged in

appropriate conditions of electron equilibrium and are then irradiated in the

NBS standard 6

0

Co calibration facility to specific agreed-upon absorbed dose

values in the nominal "high-dose" ranges of 10-106 grays (10 3 -10 8 rads). The

dosimeters may either be spectrophotometrically read and evaluated by NBS

(schedule 49040S and 49041S, previously 8 . 6D and 8.6E) or sent back to the

customer for analysis and evaluation.

1.2 Another service (schedules 49020S and 49030S, previously 8 . 6B and 8.6C)

consists of supplying to customers calibrated transfer dosimeters (radiochromic

dye type), packaged in appropriate equilibrium material, such as polystyrene or aluminum, for irradiation and subsequent readout and absorbed dose

interpretation. These dosimeters are provided in sealed packages and sent to

the customer for irradiation to nominal agreed-upon absorbed dose levels in a prescribed geometrical arrangement. The unopened packaged dosimeters are then

returned to NBS to be read and evaluated. The absorbed dose range that is

suitable for the radiochromic dosimeters is 1 to 50 kGy (0.1 to 5 Mrad) in

water, silicon, aluminum, graphite, or certain plastics.

1.3 Finally, NBS offers special measurement services (schedule 49050S

,

previously 8.6F) such as the determination of temperature dependence, absorbed

dose-rate dependence or reproducibility of dosimeter response, and measurement

of detailed absorbed dose distributions in specific irradiation geometries and

in selected absorbing materials. The absorbed dose distribution measurements

can include absorbed dose profiles in heterogeneous absorbers and at surfaces

and interfaces of different substances. Such information is important in

research leading to the commissioning of a radiation process, and in

measurement assurance that provides quality control of a given radiation

treatment

.

* Numbers in square brackets indicate references, to be found at the end of the

text

.

1
2 . Design Philosophy and Theory

2.1 There is a need for the standardization of high-absorbed-dose measurements

used in the radiation processing industry in order to provide measurement

assurance and traceability to national standards. Some areas of applications

of radiation processing include medical product sterilization, polymer

modification, hardness testing of electronic devices, and processing of food or food packaging materials.

2.2 The principal sources of radiation employed in processing are 60 Co gamma

rays and electron beams from accelerators . Other photon sources used to a much

more limited extent are 137 Cs gamma rays and high-energy bremsstrahlung x rays.

The absorbed-dose range of interest is from about 100 Gy (10 krad) to 50 kGy (5

Mrad) , depending on the application. The upper limit of electron beam energy

is assumed to be about 10 MeV to avoid the possibility of nuclear activation.

The lower practical energy limit for electron beams is determined by product

thickness and may be as low as 0.1 MeV for the curing of thin coatings.

2.3 The physical quantity of interest is absorbed dose in a material.

Absorbed dose is defined as energy absorbed per unit mass of a specific

material; the units are

1 gray (Gy) = 1 joule per kilogram (J kg" 1

) = 100 rad.

Generally, the materials of interest in radiation processing are made up of low

atomic -number elements such as carbon, hydrogen, oxygen, and nitrogen. Such

materials are quite well approximated by water. Thus, water is usually used as the reference material in which the absorbed dose measurement is specified. An

exception is for electronic device hardness testing in which the reference

material generally is silicon.

2.4 The primary standard employed in this service is a radiation-absorption

calorimeter. When a material is irradiated by a photon or electron source, the

energy absorbed results in a temperature increase. The absorbed dose, D, in

the material is given by

D = E/m = cAT

where E = energy absorbed in the material, m = mass of the material,

c = specific heat of the material,

AT = temperature increase of the material.

The absorbed dose rate from a radiation source may be determined in a similar

manner by measuring the rate of temperature increase in an irradiated material.

For a radionuclide source, the absorbed dose rate at some other time (different

from the actual measurement time) may be calculated by using the well-known

exponential decay rate (i.e., the half life).

2
2.5 The absorbed-dose rates encountered in radiation processing can cover an extremely wide range. For 6

0

Co sources, the rates may be as iow as a few grays

per minute; for electron beams, rates as high as 10 10 grays per second are not uncommon. Therefore, practical routine dosimeters must either be calibrated at

approximately the same absorbed-dose rate employed in processing or their

response must be known to be essentially absorbed dose-rate independent.

2.6 The principal dosimetry need in radiation processing is the provision for

calibration of the response of routine dosimeters (i.e., a physical change such

as optical absorbance) as a function of absorbed dose in water over the energy

and absorbed dose-rate range of interest. However, if for the specific

radiation type (i.e., photons or electron beams), the energy and absorbed dose

rate requirements cannot be met by the calibration facility, then the response

of the routine dosimeters must be shown to be independent of those qualities

over the range of interest.

2.7 An important requirement for performing proper calibration measurements is

that "electron equilibrium" conditions should exist during irradiation [2].

Such conditions exist when the number and energy of secondary electrons

(generated by the primary photons) entering the volume of interest are equal to

the number and energy of secondary electrons leaving the volume. Electron

equilibrium may be established by surrounding the dosimeter with an appropriate

thickness of material. For example, 5 mm of polystyrene is commonly used for

60 Co irradiations and the absorbed dose in polystyrene is usually converted to

absorbed dose in water. If the absorbed dose is to be specified in silicon,

then an appropriate material thickness for surrounding the dosimeter would be

2.2 mm of aluminum.

3 . Description of System

3.1 6

0

Co irradiation facilities . NBS employs three 60 Co gamma-ray irradiators

for its high-dose calibration service.

3.1.1 The pool-type source consists of a stationary annular array of twelve source rods of about 5 kiloCurie (kCi) total activity. It is situated at the

bottom of a twelve-foot deep tank filled with water for shielding and personnel

protection. The source array is shown in Figure 1. Irradiation of dosimeters

is done manually by inserting into the source array a watertight stainless

steel can with an inside diameter of 8 cm. The volume of uniform absorbed dose

rate is about 4 cm in diameter by 4 cm high, centered at 6.5 cm above the

inside bottom of the can on the central axis. The absorbed dose rate of this source has been previously determined by an adiabatic graphite spherical

calorimeter and a graphite ionization chamber of identical dimensions to an overall uncertainty estimated to be about +0.4% at a 99% confidence level [3].

Periodic verification checks of the absorbed dose rate is done annually by means of reference transfer dosimeters in collaboration with the National

Physical Laboratory (NPL) of the U.K. The absorbed dose rate in water in May

1986 was 0.076 kGymin" 1

. A complete discussion is given in reference [3] of

the sources of the uncertainties in the absorbed dose rate of this 60 Co

facility. The effect of these uncertainties on absorbed dose values assigned

to irradiations performed in this facility is discussed in Section 5.

3
4
3.1.2 The Gammacell 220 irradiator, illustrated in Figures 2 and 3 is a commercially supplied unit (manufactured by AECL of Canada), with 24 50 Co source rods of about 20 kCi total activity in a stationary annular array. The source rods are located inside a massive lead-steel shielding structure that

provides personnel protection. A motorized "drawer" assembly, consisting of an open irradiation chamber and shielding plugs above and below, can be moved up

and down through the cylindrical source array. Dosimeters are placed in the

irradiation chamber (with the drawer up) , then the drawer is lowered so that

the chamber is positioned reproducibly in the geometrical center of the source

array. Control of the drawer is by means of a preset timer so that

irradiations may be performed automatically. The irradiation chamber has

inside dimensions of 15 cm diameter by 20 cm high. The absorbed-dose rate in

water in May 1986 was 0.21 kGymin" 1. This rate was calibrated by means of

potassium dichromate reference transfer dosimeters from NPL in the U.K. and

verified by NBS radiochromic dye film transfer dosimeters on an annual basis.

The estimated overall uncertainty in this rate is about ±3% at a 95% confidence

level [4, 5]. Discussion of uncertainties associated with absorbed dose values

for dosimeters irradiated with this unit is given in Section 5.

Significant radiation heating of dosimeters can occur during irradiation in

this unit, so an active cooling system consisting of a flow of chilled dry

compressed air is provided to maintain the sample temperature at 24°C.

3.1.3 The vertical-beam 60 Co source consists of a single capsule containing

about 4 kCi, housed in a shielding head with a shutter and collimator assembly,

as shown in Figure 4. The dosimeters to be irradiated are placed at a measured

distance from the source, the shutter assembly is opened, and the gamma rays

emerge through the collimator unit into the shielded room. The irradiation

time is controlled by an automatic preset timer on the shutter assembly.

The absorbed dose rate available from this unit varies as the inverse square of

the distance from the source. At a distance of 1.5 meters, for May 1986, the

absorbed dose rate in water was 0.17 Gymin" 1

. This absorbed dose rate has

been determined with an NBS standard graphite ionization chamber and is

rechecked on an annual basis. The estimated overall uncertainty in this rate

is about ±1.3% at a 95% confidence level. See Section 5 for detailed

discussion of uncertainties in absorbed dose values for dosimeters irradiated

with this unit.

5
FRONT VIEW SHOWING DRAWER UP

Figure 2 - Schematic drawing of Gammacell 220 self-shielded Co

irradiator in the chamber load position

6
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CROSS ARM SUPPORTS

cavity ron lit t*ucx

t'hiGH X 32'wiOC

FRONT VIEW SHOWING DRAWER DOWN

Figure 3 - Schematic Drawing of Gammacell 220 irradiator in the

irradiate position

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3 . 2 Transfer Standard Dosimeters

These dosimeters are radiochromic dye films, purchased in large batches from

Far West Technology, that have been carefully and thoroughly characterized by

NBS as to their response reproducibility, stability, absorbed dose-rate

dependence, temperature and humidity dependence, and thickness. The dosimeters

are type FWT-60-00, consisting of a nylon matrix incorporating an organic dye

( leucocyanide of hexa- hydroxyethyl pararosaniline) in the form of a thin solid

film, 1.0 cm square and 50 /im thick [6]. A new batch is calibrated before

being utilized as transfer dosimeters as described in the Operating Procedures .

3 . 3 Spectrophotometer

The primary instrument employed for the analysis (reading) of the radiochromic

transfer dosimeters is a high-performance UV/VIS spectrophotometer. The

instrument presently used is a Varian/Cary 219. This instrument has very low

stray light characteristics so as to permit it to measure optical absorbance

values of 3 or less with an uncertainty of less than 1%. The absorbance scale

of the instrument is checked annually with a set of neutral density filters

(SRM 930D) . The wavelength scale is checked annually by means of emission

lines of well known wavelength from a mercury discharge lamp. The wavelength

scale must be within 0.2 ran of the specified value for the entire wavelength

range (200 to 800 ran)

.

3 . 4 Thickness Gauge

The radiochromic transfer dosimeters are normally 50 fj,m thick and are measured

with a thickness gauge to a resolution of 0 . 1 /im. The gauge is a Mitutoyo

electronic Model DGS-E with a linear displacement transducer that has a special

NBS developed digital display (not provided by the manufacturer) . The

calibration of the thickness scales is performed annually by use of a set of

Brown & Sharpe (Super-A Jo Blocks) metric gauge blocks.

4 . Operating Procedures

4 . 1 Internal Dosimeter Calibration

The radiochromic dye film dosimeters described under 3.2 are calibrated by

using the following procedures.

4.1.1 Upon receiving a new batch of dosimeters from the manufacturer, initial

visual inspection is performed to detect any obvious flaws (fingerprints, water

marks, etc.) that might make the batch unsuitable.

4.1.2 These dosimeters are sensitive to ultraviolet (UV) light and thus must

be protected at all times from sunlight (even through windows) , fluorescent

lamps, or other sources. One effective method to achieve this is to filter

laboratory fluorescent lamps with wrap-around filters made of a special UVabsorbing Mylar (trade named Llumar) . Even with such filters, the dosimeters

are only exposed to light during essential handling procedures, otherwise they

are stored in the dark.

9
4.1.3 Random dosimeter samples are taken from the batch to be calibrated.

These samples are irradiated to specific absorbed dose levels and their

responses are assumed to be indicative of the expected responses of the

unirradiated dosimeters in the rest of that batch. The validity of this

assumption has been verified experimentally for periods of 6 to 12 months.

After 12 months a new calibration of the batch should be performed.

4.1.4 Handling of the individual dosimeters is done only with fine- tipped

tweezers, touching only the outer 2 mm from the edges of the 1 cm square films,

and, thus, avoiding scratches, fingerprints, etc., in the center where the

analyzing light beam passes through. Small amounts of dust may be removed by

gently wiping with lens tissue; however, any films that show obvious flaws such

as fingerprints, dirt, optical imperfections, etc., are discarded.

4.1.5 The films are marked in a corner with a permanent ink pen so that

consistent orientation may be maintained in all subsequent analysis procedures.

The film is placed in a special black-anodized aluminum holder that masks the

analyzing spectrophotometer light beam to a 6-mm square while holding the film

perpendicular to the sample light beam in a reproducible position. A matching

empty holder is placed in the reference light beam. With no films in either

holder, the spectrophotometer may be properly balanced.

4.1.6 All films are irradiated to a low absorbed dose level of 1.0 kGy before

any optical analysis is performed. The slight coloration developed in the

films as a result of this uniform low absorbed dose is proportional to the dye

concentration in the films. Thus, optical absorbance readings of the films

after this initial "pre-calibration" irradiation are made in order to eliminate

the effects of variations in dye concentration and, therefore improve the

precision of the response of the system. These "pre-calibration" irradiations

are performed with the films packaged ten at a time under equilibrium

conditions as described in 4.1.8.

4.1.7 Initially, each film is analyzed by a wavelength scan of the

spectrophotometer from 5 ran above the primary absorption peak (at 605 ran) to 5

ran below on an expanded absorbance scale (0.1A full scale, where A represents

optical absorbance units) . This scan will sometimes show optical interference

fringes in the form of oscillations (see Fig. 5) . If the peak-to-peak

oscillations are greater than some specified value (0.001A), then the results

are considered to be unsatisfactory. The holder and film are removed from the

spectrophotometer and the film is rotated 90° and then read again. If the

oscillations are less than the specified value, then the film is considered

acceptable. If all possible orientations are tried and the oscillations are still greater than the specified limit, then that film is rejected and another

is selected to be tested in the same fashion. If the film reading is

acceptable, then it is marked with permanent ink in the lower left corner with

a unique code number. These initial readings are designated Ax

. All

subsequent readings of the film are done with this orientation. The

wavelengths of analysis are 605 ran and 510 ran, using a Varian/Cary 219

spectrophotometer with a spectral bandwidth of 3.5 ran.

10
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FIGURE 5 Examples of FWT A Q scans, from 610 nm down to 600 nm

,

showing various oscillations, for different orientations.

NOTE: Spectrophotometer settings:

RANGE: 0.1 ABS ; S.B.W.: 3.5 nm ; PERIOD (sec):

1.0; CHART DISPLAY: 5 nm/cm; SCAN RATE: 0.2 nm/sec.

A. First position: oscillations are too large and are not

acceptable; film rotated 90°.

B. First rotation f second position): oscillations are very

small and can be ignored; this is the most acceptable reading

of all

.

C. Second rotation (third position): oscillations, as in A, are

not acceptable.

D. Third rotation (fourth position): oscillations are within

specification; however, taking an average between the highest

and lowest readings around 606 nm would be required for an

accurate reading of low absorbance values of this film for

this orientation.

11
4.1.8 Before the calibration irradiations, the dosimeter films are stored at

room temperature (~ 24°C) in a controlled humidity environment (within the

range of 40 to 50% R.H.) for at least 24 hours [7]. After this period, the

dosimeters are packaged in appropriate equilibrium build-up material. For the

absorbed dose to be specified in water (or tissue) , the equilibrium material

used is polystyrene; for absorbed dose in silicon, the equilibrium material

used is aluminum. The equilibrium material is in the form of 25-mm square

blocks, which are 5 mm thick for polystyrene and 2.2 mm thick for aluminum.

There is a 12-mm square cavity, 1 mm deep, in one block of each pair of blocks.

A group of five dosimeters is stacked and placed in the cavity between the two

blocks of the appropriate material then heat sealed in two pouches of lOO^um

thick polyethylene; an inner black layer for light protection, then an outer

clear layer. After packaging, the dosimeters are ready for irradiation.

4.1.9 Most calibration irradiations are performed in the NBS 60 Co pool source. Each dosimeter package is placed in a polystyrene foam holder fitted into the

stainless steel can so as to locate it at the geometrical center of the source

array. Irradiations are done by manually lowering the water-tight irradiation can (attached to a long handling pole) into the source array, noting the clock

time, then removing the can (manually) at the end of the calculated Irradiation

time. The irradiation times for given absorbed doses are calculated before

irradiations are started, based on previous verifications of the source absorbed dose rate and corrected for the exponential radioactive decay for 60 Co

(based on a half-life of 5.27 years). Decay corrections are done every two

days to provide a current absorbed dose rate. The decay correction factor is

given by the equation:

D

p = DQ e" At

where D

p = absorbed dose rate on the desired date,

DQ = absorbed dose rate on December 31 of the previous year,

A =

6

0

Co decay constant, and

t = number of days from December 31 of the previous year to the desired

date

.

Now,

A=

0.693147

Tv (years) • 365.25 days/year

where T% = half life for 60 Co = 5.2714 years.

Thus A = 3.60006 x 10^/day.

The decay correction factor = Cd = e _At . Values for C d for various elapsed

times are given in Table 1

.

To use Table 1, determine the number of days since the previous December 31

(for which the absorbed dose rate was stated). Then multiply the correction

factors from Table 1 that correspond to the total number of elapsed days. For

example, if the absorbed dose rate on April 23 was desired, the number of

elapsed days (for a non-leap year) would be 113 days. To determine the decay

correction factor, look up the factor where the horizontal row for "100"

12
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13
intersects the vertical "10" column corresponding to 110 days. This factor is

0.9611. The factor for "3", the remaining number of days, in the first row is

0.9989. Multiply these two factors to give the correction for 113 days:

0.9600. Multiply this factor by the absorbed dose rate for the previous

December 31 to give the dose rate for April 23.

4.1.10 A typical calibration of a new batch would cover an absorbed-dose range

of 1 kGy to 50 kGy with absorbed dose values of 2, 5, 10, 15, 20, 30, 40 and

50 kGy.

4^1.11 After irradiation, the dosimeters are stored for approximately 24 hours

to allow for complete development of the dye [7]. After this period, the final

spectrophotometer readings (designated A2

) are made, taking care that the same orientation of each film is used as for the initial Ax readings.

4.1.12 Finally, the thickness of each dosimeter is read at three points across

the film corresponding to where the spectrophotometer light beam passes through

the dosimeter film. The mean value of these measurements is used as the film

thickness

.

4.1.13 All values of initial absorbance, Ax

, final absorbance after

irradiation, A2

, and thickness in mm, t, for each dosimeter are recorded in a data book. The response of the dosimeter is given by, R2

4.1.14 The mean R2 for each group of five dosimeters irradiated together is

plotted against the absorbed dose in the specified material. A curve is fitted

through the data by means of a least squares regression method such as a polynomial fit. In general, the curve will be nonlinear, at least over certain

portions of the absorbed dose range. Data for both wavelengths of analysis,

605 nm and 510 nm, are used to generate separate calibration curves. See

Figs. 6 and 7 for examples.

4.1.15 Dosimeters from the calibrated batch irradiated to some unknown

absorbed dose are read according to the procedures of this section and the

resulting absorbed dose is obtained from the calibration curves. The 605 nm calibration curve is used primarily to determine the absorbed dose value; the

510 nm results are used generally for redundancy to check on possible erroneous interpretation of the 605 nm results.

4 . 2 Irradiation of Customer Dosimeters

4.2.1 Various types of dosimeters may be submitted by customers for

irradiation to various absorbed dose levels. Table 2 gives a brief listing of some typical dosimeter types and the applicable absorbed dose range for which

they may be utilized; other types may also be processed.

4.2.2 The irradiation geometry used for these dosimeters depends on their size

and shape. In general, if the requested absorbed dose is in water, then a container made of polystyrene with a 5-mm wall thickness is used to hold the

dosimeters in the proper location (i.e., the center of the source array for the

14
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Table 2

VARIOUS DOSIMETER TYPES

Dosimeter Type Absorbed Dose Range

kGy in H2 0

FWT-60-00 dye film3 1-50

Harwell Red Perspexb 5-50

Harwell Amber Perspexb 1-20

Harwell HX Perspex and Radix

clear PMMAb 3-100

Ceric-cerous sulfate solutions 0.3-100

Potassium and silver dichromate

solutions 1-50

Fricke (ferrous sulfate) solution 0.01-0.4

Thermo luminescence dosimeters 0.01-1

(LiF, CaF2 , etc.)

FWT Opti-chromic 0.02-10

(liquid in optical waveguide)

a The material of this film is primarily "Elvamide"

nylon from DuPont . The radiochromic sensor is hexa-hydroxyethyl

pararosaniline cyanide.

b "Perspex" and "Radix" are trade names for polymethyl methacrylate

(PMMA)

.

17
pool source) during irradiation. This container may be in the form of square

blocks for FWT-60-00 thin dye films as used in the internal NBS calibration, or in the form of a cylindrical cup for Red Perspex or similar type dosimeters.

These containers supply the material needed to provide electron equilibrium

conditions during irradiation as previously discussed in 2.7. The Red Perspex

dosimeters, for example, are about 3-mm thick and a correction for self

attenuation (of about 3%) is necessary in order to specify the correct average

absorbed dose rate in the dosimeters during calibration.

4.2.3 Upon completion of the irradiations requested by the customer, the

dosimeters are returned promptly to him. In the case of fragile or unstable

dosimeters, it is sometimes necessary to specify special shipping conditions.

For example, because of instabilities following irradiation, Red Perspex

dosimeters should be sent by express overnight mail service and should be

protected from temperature extremes during that period. Aqueous chemical

liquid dosimeter ampoules also require such precautions, as well as protection

against breakage by careful packaging. After double checking the irradiation

times and calculations of the absorbed-dose rates for that day, a Report of

Calibration is prepared and sent to the customer specifying the absorbed doses

given to his dosimeters (see Appendix A) . The customer then formulates his own calibration curve based on the NBS absorbed-dose values and readout of the

dosimeters with his own instrumentation.

4 . 3 Application of Transfer Dosimeters

4.3.1 When a customer requests dosimeters to be supplied for irradiation in

his facility, the procedures of 4.1.4 to 4.1.8 are followed, using unirradiated

dosimeters from a calibrated batch, i.e., reading initial absorbances , humidity

conditioning, and then packaging the dosimeters.

4.3.2 The requested number of packaged unirradiated dosimeters (plus some controls) are sent to the customer, along with instructions on proper handling

(e.g., do not open the packages), the proper absorbed dose level to be given (1

to 50 kGy) , as well as reporting any special environmental conditions (e.g.,

elevated temperature during irradiation) (see Appendix B) . If the temperature

of the dosimeter package is expected to exceed 30°C during irradiation in the

customer's facility, then the customer is requested to measure that temperature

during the irradiation and provide NBS with those data (preferably as a function of time) in order that NBS can apply the proper correction factors to

the dosimeter response (see Fig. 8).

4.3.3 When the irradiations are completed by the customer, he sends the

dosimeter packages back to NBS. The packages are opened at NBS and the

dosimeters read as soon as possible following the procedures of 4.1.11 to

4.1.15. The results are corrected for elevated irradiation temperature, if

required, and the results are compared to the nominal absorbed dose the

customer reportedly gave the packages. Results are then supplied to the

customer in the form of a Report of Calibration (see Appendix C for an Example)

.

4 . 4 Analysis of Dosimeters

4.4.1 Reading of customers' dosimeters is done in a manner similar to that

used for the internal calibration procedures detailed in 4.1. For FWT-60-00

18
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19
dye film dosimeters, the procedures are identical to those discussed in 4.1.

For other types of dosimeters, the spectrophotometric analysis is tailored to

meet their particular requirements. For example, Red Perspex dosimeters are read at only one wavelength (640 ran) and require a different holder than the

FWT-type film.

5 . Assessment of Uncertainties

5.1 The estimates of uncertainties for the absorbed dose values assigned to a given group of dosimeters irradiated together in the 60 Co pool source are given

in Table 3. The designation of the types of uncertainties (A and B) follows

the recommendations of the BIPM Working Group on the Statement of Uncertainties

[8, 9] . Type A is the random component and is stated as an estimate of a sample standard deviation. These can be determined by standard (objective)

statistical methods. Type B uncertainties are determined by "other methods",

thus implying some element of subjective evaluation. Type B uncertainties may,

in some cases, correspond roughly to "systematic" contributions, but this may

not always be true. In line with the BIPM recommendations, the term

"systematic" is avoided. Those recommendations also treat both types of

uncertainties equally; that is, as being equivalent to "standard deviations".

Thus, each type is combined separately in quadrature (i.e., the square root of

the sum of the squares) . An overall combined uncertainty is obtained by

combining the two types once again in quadrature. Finally, a total uncertainty

is obtained by multiplying a "safety" factor (such as 2 or 3) ; in this case the

factor chosen was 3. For a normal population distribution this factor would

correspond approximately to the statistical "Student's t-factor" at a 99%

confidence level and a sample size of about 14 (13 degrees of freedom),

assuming that the combined uncertainties can actually be treated as a standard

deviation.

5.2 The values of the uncertainties given in Table 3 for irradiations done

with the pool source were determined from published literature or from

experimental estimates. The published values usually are given for a 95% or 99% confidence level, so the values given in Table 3 are obtained by dividing

the published values by two or three respectively so as to correspond to a "standard deviation" of one. The experimental estimates are usually the

"maximum" expected range which would correspond roughly to a 99% confidence

level. Thus, values for Table 3 were obtained by dividing these estimates by

three. The values of uncertainties listed are stated in terms of percentages

of the sample mean of the mesured quantity. This corresponds to a percentage

of an estimated coefficient of variation [10] given by:

100 a- 100. sx

x

where A estimated standard deviation of the sample mean,

x mean of the sample size n,

and computed sample standard deviation

20
Table 3

UNCERTAINTIES IN ABSORBED DOSE VALUES

FOR IRRADIATIONS WITH POOL SOURCE

Source of Uncertainty Type A (%) Type B (%)

( random) (other)

Graphite calorimeter/ion chamber 0.14

measurement of pool source dose rate

Source decay, half life 0.01

Timing of irradiations 0.23

Conversion of dose rate: graphite to 0.30

water, silicon, etc.

Attenuation corrections in equilibrium 0.03

material

Effect of dosimeter positioning in 0.25

irradiation can

Geometrical effects of equilibrium 1.00

material on dose rate

Source decay correction for given date 0.02

Type A, Type B combined (in quadrature), 0.34 1.05

separately

Combined (in quadrature) 1.11

TOTAL: 3X Combined 3.3

Zl
The sources of the uncertainties are as follows:

(1) The calorimeter/ion chamber measurements of the pool source absorbed

dose rate were analyzed in reference [3] for all possible sources of error contributions such as core mass, electrical power, attenuation, and heating

rate for the calorimeter, and air mass, current measurement, and collection

efficiency for the ion chamber. All factors were combined in quadrature

(square root of the sum of the squares) to give an overall value of 0.43% at

a 99% confidence level. The value for Table 3 would be 0.43% divided by 3 or 0.14%.

(2) The uncertainty in the half life of 60 Co was reported to be 5 parts out

of 52,714 or 0.01% [11]. The level of confidence was not reported, so it was assumed to correspond to one standard deviation.

(3) The uncertainty in the timing of the irradiations was estimated to be a maximum of 5s for the manual manipulation of the irradiation can into the source array. This would correspond roughly to a 99% confidence level, so dividing this time by 3 would give an uncertainty of 1.7s for one standard

deviation. For a 1 kGy absorbed dose at the current absorbed dose rate, the

irradiation time is about 750s: 1.7s is about 0.23% of this time.

(4) For the conversion of the absorbed dose rate of the source from one material (e.g., graphite) to another (e.g., water), the uncertainty in the

ratio of mass energy absorption coefficients for photon spectra with

significant scattered components down to about 100 keV is estimated to be

about 0.6% at a 95% confidence level [12]. Thus, the uncertainty value for one standard deviation would be 0.6% divided by 2 or 0.3%.

(5) For the correction for attenuation in the equilibrium buildup material

surrounding the dosimeters, the uncertainty in the mass attenuation

coefficients down to 5 keV is about 2% at a 95% confidence level [12], or 1%

corresponding to one standard deviation. The correction factor is about 3%, so the uncertainty in the factor would be about 0.03%.

(6) The effect of variation of the location of the dosimeter package

during irradiation can be estimated from isodose profiles that were determined previously. With a location imprecision of about 0.5 cm, the

uncertainty is estimated to be 0.5% at a 95% confidence level. The

uncertainty value corresponding to one standard deviation would be 0.25%.

(7) The effects of different geometrical configurations for the equilibrium

material (i.e., a cylinder compared to a slab) has been examined previously

[13] and are estimated to contribute about a 3% uncertainty at a 99%

confidence level. The uncertainty corresponding to one standard deviation

would be 1%.

(8) The uncertainty due to the calculation of the correction for source decay for a particular date can be estimated from the values in Table 1

.

Corrections are made every two days, so the maximum uncertainty would be

about 0.07% (the difference between day 0 and day 2 values) at a 99%

confidence level. The uncertainty corresponding to one standard deviation

would be 0.02%.

5.3 For irradiations done with the Gammacell 220 irradiator, the estimated

uncertainties for absorbed dose values are given in Table 4. Most of the

uncertainties are the same as for the pool source irradiations shown in Table 3 with some notable exceptions:

(1) The absorbed dose rate has been measured only with the NPL dichromate

reference transfer dosimeters [4, 5]. NPL gives an overall uncertainty of

2Z
3% at a 95% confidence level for use of these dosimeters. The uncertainty

corresponding to one standard deviation would be 1.5%. Other dosimetry

methods (such as calorimetry) are being developed to improve the accuracy of

the determination of this absorbed dose rate in the future.

(2) The other uncertainty factor that is different from the pool source is

the timing of irradiations. There is a significant transit time when the

dosimeters are entering and leaving the radiation field that is not

accounted for by the irradiation timer. This transit time has been

determined to effectively add 4.1 seconds to the irradiation time set on the

automatic timer. This transit time was determined with an estimated

uncertainty of one second at a 95% confidence level, or 0.5s corresponding

to one standard deviation. To minimize the effect of the transit time

uncertainty, irradiation times of at least 10 minutes are used. Thus, the

uncertainty in irradiation time caused by this transit time uncertainty

would be 0.08% for a 10 minute irradiation.

5.4 For irradiations done with the vertical beam source, the uncertainties in

absorbed dose values are given in Table 5. Some of the uncertainties have the same values as for the pool source discussed in 5.2. Those that are different

are

:

(1) Calibration of the exposure rate at a specific distance from the source by a standard graphite cavity ionization chamber to an estimated

uncertainty of ± 0.7% at a 95% confidence level [14]. Thus, the uncertainty

corresponding to one standard deviation would be 0.35%.

(2) Conversion of the exposure rate to absorbed dose rate in water

contributes an additional uncertainty of about 1.1% [15] due to factors such

as the uncertainties in the values for W (average energy required to produce

an ion pair in air), the displacement correction factor, the ratio of energy

transfer and energy absorption coefficients, and the ratio of absorbed dose

to kerma. The uncertainty value is for a 95% confidence level. The value

corresponding to one standard deviation would be 0.55%.

(3) The uncertainty value given in Section 3.1.3 (±1.3%) is obtained by

combining the uncertainties from (1) and (2) in quadrature.

(4) The accuracy of timing of irradiations is determined by the uncertainty

of the shutter transit time (~0.6s) and is estimated to be about 0.2s at a 95% confidence level. The value corresponding to one standard deviation

would be 0.1s. The minimum irradiation time that would generally be used

is about 1000s, so the uncertainty contribution would be about 0.01%.

(5) The error in positioning the dosimeters at a location different from

that of the calibrating ion chamber was estimated to be 1.0 mm at a 95%

confidence level for a source distance of 1000 mm. The value corresponding

to one standard deviation would be 0.5 mm and would contribute a random

uncertainty of about 0.05%.

5.5 The uncertainties in absorbed dose values assigned to the results when NBS

supplies transfer standard dosimeters to a customer for irradiation in the

customer's irradiation facility are given in Table 6. The transfer dosimeters

are calibrated only in the pool source, so the combined uncertainties

associated with irradiations with that source are listed in the first line of

Table 6. Additional uncertainties (corresponding to one standard deviation)

associated with the response characteristics of the transfer dosimeters are listed in the rest of Table 6. The total uncertainty is obtained in the same manner as that discussed in 5.1.

23
Table 4

UNCERTAINTIES IN ABSORBED DOSE VALUES

FOR IRRADIATIONS WITH GAMMACELL 220

Type A (%) Type B (%)

Source of Uncertainty (random) (other)

NPL dichromate reference 1 . 50

dosimeter measurement of dose rate

Source decay, half life 0.01

Timing of irradiations: 0.08

transit dose

Conversion of dose rate: 0.30

water to silicon, etc.

Attenuation corrections in 0.03

equilibrium material

Effect of dosimeter positioning 0.25

in irradiation chamber

Geometrical effects of equilibrium 1.00

material on dose rate

Source decay correction 0.02

for given date

Type A, Type B combined (in 0.26 1.83

quadrature) , separately

Combined (in quadrature) 1.85

TOTAL: 3X Combined 5.5
Table 5

UNCERTAINTIES IN ABSORBED DOSE VALUES

FOR IRRADIATIONS WITH VERTICAL BEAM SOURCE

Source of Uncertainty

Graphite ion chamber

measurement of exposure rate

Conversion of exposure rate

to absorbed dose rate in water

Type A (%)

(random)

Type B (%)

(other)

0.35

0.55

Source decay, half life

Timing of irradiations:

shutter transit time

0.01

0.01

Conversion of dose rate

water to silicon, etc.

0.30

Attenuation corrections in

equilibrium material

Effect of dosimeter positioning:

distance from source

0.05

0.03

Source decay correction

for given date

0.02

Type A, Type B combined

(in quadrature) , separately

Combined (in quadrature)

TOTAL: 3X combined

0.05

0.72

2.2

0.72

25
Table 6

UNCERTAINTIES IN ABSORBED DOSE VALUES

EMPLOYING TRANSFER STANDARD DOSIMETERS

Source of Uncertainty Type A (%) Type B (%)

(random') (other)

Combined (in quadrature) from

Table 3 0.34 1.05

Transfer standard dosimeter

response 1 . 00

Dosimeter response temperature

correction 0.50

Time dependence of dosimeter

response 0.50

Effects due to differences in photon

energy spectra of sources 0.50

Type A, Type B combined (in quadrature),

separately 1.06 1.36

Combined (in quadrature) 1.72

Total: 3X Combined 5.2

26
6. Internal Quality Control

6.1 Measurement assurance program (MAP) type techniques are used to ensure

that calibration irradiations are performed correctly and the process is in a state of statistical control [16].

6.2 A number, n, of check standards, in the form of calibrated radiochromic

dye film dosimeters, are placed immediately adjacent to the test dosimeters

during each irradiation. After irradiation, the check standard dosimeters are analyzed to produce a sequence of absorbed dose readings cx ,

. .

.

,cn.

Thus, for a given absorbed dose level, the accepted value of the check standard

is the mean of those values:

The estimated total standard deviation of the check standard dosimeter response

is

The number of degrees of freedom, u , required to estimate the initial value for

the actual standard deviation can be determined by choosing how close the

estimate should be to the true value at a given confidence level. For example,

if the estimate is to be within 20% of the true standard deviation at a 95%

confidence level, then the degrees of freedom, v = 46 = n-1, or n = 47

measurements [see sec. 2.4 of reference 14]. As the measurement assurance

program progresses, additional data are obtained on the variability of the

response of the check standard dosimeters, and a more reliable value for the

estimated standard deviation may be computed. This is done by "pooling" the

standard deviations obtained on separate occasions for the same process. If

individual standard deviations are s x

,

s

k with degrees of freedom

v x

,

,

f

k , respectively, then the pooled standard deviation is

n

i = l

n

r

S

P v x + . . .+i/k

The degrees of freedom associated with s

p is v = u x + . . . . +i/k

.

27
6.3 Control limits may be chosen for future check standard dosimeter

observations (where each observation is the mean of n = 5 readings) using the

following:

Upper control limit = Ac + —

7n

3sc

7n

Lower control limit = Ac

In this case, a safety factor of 3 was chosen; a factor of 2 is sometimes used, or for a near-normal response distribution, the appropriate percent point of

the Student's t distribution, ta

, 2 (v), may be used, where 1-a is the specified

confidence level.

6.4 The control procedure applied to each future calibration depends on a test

statistic, T, calculated from the value of the check standard, c f (the mean of n = 5 readings) by the following:

T =

S c 7n

If T < 3, then the process is in control. If T > 3, then the process is "out

of control" and remedial action is required.

6.5 Control charts are used to determine if the calibration irradiations are being performed in the proper way. Initial measurements are made to determine

the mean dosimeter response and variability for each absorbed dose level. Once

the dosimeter system response is adequately characterized, then control charts

are drawn up that provide a baseline value for each absorbed dose level and

appropriate control limits as discussed in 6.3. All subsequent readings are plotted as a function of time on these charts. All the readings should fall

within the control limits except for the few that would fall outside due to

pure chance (i.e. , about one in a hundred for a value of a = 0.01 or the 99%

confidence level) . If readings fall outside the control limits more often than

would be expected by pure chance, then the process is "out of control" and must

be investigated and corrected.

6.6 The radiation response of the check standard dosimeter batch may change

(drift) slowly with time. An "out of control" situation on the control chart

may indicate such a drift in response. In that case, it is necessary to

completely characterize the batch response again as was done initially in

setting up the control chart.

6.7 Quality control procedures are used in other areas such as data reduction

and report generation. All irradiation data, such as source decay corrections

and calculated irradiation times, are double -checked for accuracy. An

experienced, highly- trained technician performs all calibration irradiations

and analysis of dosimeters. Senior scientific staff review all results and

28
check all calibration reports. The condition of each group of test dosimeters

to be irradiated is evaluated when they are received to ensure they are of high

quality. Any unusual condition or appearance is checked by consulting with the

requesting customer before proceeding. Checks of the performance of the

various analytical instruments used are done on a periodic basis as described

in Section 3. Plans are underway to further automate the data handling, such

as automatic timing of the irradiation calibration.

7 . Safety

7.1 Operation of these calibration services involves use of high- intensity

ionizing radiation sources that have the potential to expose staff personnel to

hazardous levels of radiation. NBS health physics rules and Nuclear Regulatory

Commission regulations require that personnel using these sources have formal

training in the correct operation and safe use of them. In some cases, tests are given after the training to verify that the personnel have understood the

most important aspects of that training.

7.2 Access to all high- intensity source areas is limited to those staff with a need to use them. Doors to these areas are kept locked at all times with

control maintained over the minimum number of keys available to the areas.

29
References

1. Uriano, G . A. Garner, E.L. Kirby, R.K. , and Reed, W.P., Editors. NBS

Calibration Services Users Guide 1986-1988 Edition. NBS Special Publication 250

and Fee Schedule for SP 250, Office of Physical Measurement Services, National

Bureau of Standards, Gaithersburg , MD 20899 (1986)

2. Greening, J. R. , Fundamentals of Radiation Dosimetry . Chapters 5 and 6,

Medical Physics Handbook 6, Adams Hilger Ltd., Bristol, U.K. (1981).

3. Petree, B. , and Lamperti, P., "A Comparison of Absorbed Dose Determinations

in Graphite by Cavity Ionization Measurements and by Calorimetry" , J . Res

.

Natl. Bur. Stds., 71C, No . 1 , pp. 19-27 (1967).

4. Sharpe , P.H.G., "Dichromate Dosemeter Reference Service", National Physical

Laboratory, U.K. (1984).

5. Sharpe, P.H.G., Barrett, J.H., and Berkley, A.M., "Acidic Aqueous

Dichromate Solutions as Reference Dosimeters in the 10-40 kGy Range", Int. J.

Appl. Radiat. Isot., 36, pp. 647-652 (1985).

6. McLaughlin, W. L. , Jarrett, R. D., Sr., and Olejnik, T. A., "Dosimetry",

Chapter 8 in Preservation of Food by Ionizing Radiation . Vol. I,

Josephson, E. S., and Peterson, M. S., Eds., CRC Press, Boca Raton, FL, pp.

189-245 (1982) .

7. Levine , H. , McLaughlin, W. L. , and Miller, A., "Temperature and Humidity

Effects on the Gamma-Ray Response and Stability of Plastic and Dyed Plastic

Dosimeters", Radiat. Phys . Chem. , 14, pp. 551-574 (1979).

8. Kaarls, R. , "Report of the BIPM Working Group on the Statement of

Uncertainties", 1st meeting, 21-23 Oct. 1980.

9. Giacomo, P., "News From the BIPM", Metrologia, 17, pp. 66-74 (1981).

10. Ku, H.H. , "Notes on the Use of Propagation of Error Formulas", Precision

Measurement and Calibration . NBS Special Publication 300-Vol.l, pp. 331-341

(1969).

11. NCRP Report No. 58, 2nd Ed., "A Handbook of Radioactivity Measurements

Procedures", National Council on Radiation Protection and Measurements,

Bethesda, MD (1985).

12. Hubbell, J.H., "Photon Mass Attenuation and Energy-absorption Coefficients

from 1 keV to 20 MeV" , Int. J. Appl. Radiat. Isot., 33, pp. 1269-1290 (1982).

30
13. McLaughlin, W.L., "A National Standardization Programme for High-Dose

Measurements", High-Dose Measurements in Industrial Radiation Processing, IAEA

Tech. Report No. 205, IAEA, Vienna, pp. 17-32 (1981).

14. Loftus, T.P., and Weaver, J.T., "Standardization of 60 Co and 1 3

7

Cs GammaRay Beams in Terms of Exposure", J. Res. Natl. Bur. Stds., 78A, No . 4 , pp. 465-

476 (1974).

15. ICRU Report 14 "Radiation Dosimetry: X Rays and Gamma Rays with Maximum

Photon Energies Between 0.6 and 50 MeV" , Int. Com. on Radiat. Units and

Measurements, Bethesda, MD (1969).

16. Belanger, B. Measurement Assurance Programs Part I: General Introduction , and Croarkin, C. , Part II: Development and Implementation. National Bureau of

Standards Special Publication 6761 and 676II (1984).

17. Natrella, M.G., Experimental Statistics . NBS Handbook 91 (1963).

31

U.S. DEPARTMENT Of COMMERCE

KATKWAl IURIAU Of STANDARD*

OAiTMiRiiURO. marviano io«M Test 536/ 111111-86

NBS DB 100/100

XRG- 322

December 26, 1985

REPORT OF CALIBRATION

of

Far West Technology, Inc. Type 60-00 Rad1ochron1c Dosimeters

for

Kilorad Corporation

89 Irradiator Avenue

Moline, IL 60609

Attention: Jeffrey Doe

Chemistry Lab Supervisor

Ref. P.O. No.: Ill

Far West Technology radlochromlc dosimeters, type 60-00, supplied by Kilorad

Corporation, were irradiated, ten at each dose, under controlled conditions using

gamma radiation from a standard 60 Co source. During Irradiation the dosimeters

were held between 5.0-mm thick blocks of polystyrene, which were sealed inside

polyethylene packets. The relative humidity at the time of sealing was 56%. The

temperature during Irradiation was 24°C. The dates of Irradiation and values of

absorbed dose were as follows:

Dosimeter No. Date of Irradiation Absorbed Dose in Water

CkGy)* (Mrad)

101-110 19 Dec. 1985 10.0 1.00

111-120 20 Dec. 1985 15.0 1.50

121-130 20 Dec. 1985 20.0 2.00

131-140 19 Dec. 1985 25.0 2.50

141-150 23 Dec. 1985 30.0 3.00

*1 kGy = 0.1 Mrad

APPENDIX A

A-l
Test 536/ HHU-86

NBS DB 100/100

XRG-322

December 26, 1985

Page 2 of 2 pages

The attached page describes uncertainties and related factors In high-dose

calibrations, such as the one covered by this Report of Calibration. Any questions

regarding environmental conditions, different types of materials used, and

systematic uncertainties associated with these calibrations can be answered by this

attachment. If there are further questions, they should be directed to the first

individual named below.

Measurements were made by

D. G. Hocken, Calibrations Technician

(301)921-2201

Approved by

J. W. Moiz, Leader

X-Ray Physics Group

For the Director

A. S. Caswell, Chief

Ionizing Radiation Division

Center for Radiation Research

APPENDIX A

A-2
UNCERTAINTIES AND RELATED FACTORS IN HIGH- DOSE CALIBRATIONS

Standard High-Dose Gamma-Ray Irradiations at NBS

(Estimated uncertainty: ± 3.3% at a 99% confidence level)

The high-dose calibrations at NBS (schedule 49010S) involve the

administration of 60 Co gamma radiation absorbed doses in certain materials

(e.g., water, carbon, aluminum, silicon, polystyrene, etc.), under

environmentally controlled conditions. The dose values are based on standard graphite calorimetry measurements, which are corrected by certain

modifying factors (the estimated photon spectrum, tabulated weighing

factors, such as radiation energy absorption and attenuation factors, and source decay factors) . The irradiations are usually carried out using the

NBS calibrated 60 Co water-well type irradiator. The uncertainties cited

above are pertinent to absorbed values specified in a given material, with

the dosimeters irradiated under approximate equilibrium conditions, in the

absorbed dose region of 1 KGy and upward.

Absorbed Dose Evaluations Based on Traceability through

Mailed Chemical Transfer Dosimeters

(Estimated uncertainty: ± 5.2% at a 99% confidence level)

It must be recognized by calibration users that routinely applied chemical

dosimeters consisting of liquid solutions, solid films, ceramics,

crystalline materials, plastics, etc., are subject to imprecision and

systematic error due to environmental effects during field use, production,

irradiation, and readout. Therefore, if these factors are not sufficiently

known and understood, absorbed dose interpretations using such systems have

reproducibility and accuracy values that are difficult to establish.

Although, as indicated above, NBS in its high-dose calibrations (e.g.

schedule 49010S) administers to within prescribed uncertainty limits

standard absorbed doses of gamma radiation under controlled environmental

conditions, the routine dosimeters for field use are subject to uneven

quality control of manufacture and are occasionally susceptible to

anomalous batch-to-batch or intrabatch sensitivity differences, poor

reproducibility of readout results, and adverse environmental effects.

In the case of absorbed dose evaluation based on mailed transfer NBScontrolled radiochromic film dosimeters (nominal dose range 1 x 103 to

5 x 104 Gy) that are traceable to 60 Co gamma-ray calibrations at NBS, the

uncertainty values cited above (± 5.2%) may be assumed as long as suitable

care against environmental and other sources of systematic error is

exercised.

A detailed list of the various sources of uncertainty that make up the

overall uncertainties given above may be obtained by requesting such

information from NBS

.

Appendix A

A-3

UNITED STATES DEPARTMENT OF COMMERCE

National Bureau of Standards

Gaithersburg. Maryland 2QB99

June 27, 1986

FEDERAL EXPRESS PRIORITY 1

Mr. John Doe

Senior Engineer

Gamma Radiations, Inc.

123 University Avenue

Chicago, IL 60606

Dear Mr. Doe:

Reference: Your P.O. No. 12345

Enclosed are the packaged dosimeters which you requested for irradiation in

your facility. There are fourteen packages: thirteen for irradiation plus one control package which should not be irradiated. Please do not open the

packages at any time; they provide a controlled environment for the dosimeters. If the temperature of the packaged dosimeters is expected to

increase more than 10°C above room temperature during irradiation, please

provide information on the temperature as a function of time for the longest

irradiation period. Other irradiation data, such as date and time of irradiation, length of the irradiation period, and any other pertinent information

should be included with the returned dosimeters. The nominal absorbed doses

received by these dosimeters should be within the range of 1 kGy (0.1 Mrad)

and 30 kGy (3.0 Mrad). Please return the dosimeters to us as soon as the

irradiations are completed so that we may get the results back to you promptly.

If you have any questions, please call me or Jim Humphreys at (301)921-2201.

Dene G. Hocken

Calibrations Technician

X-Ray Physics Group

Center for Radiation Research

Enclosures

Sincerely,

APPENDIX B B-l

U.S. DEPARTMENT OF COMMERCE

NATIONAL BURCAU Of STANDARD!

QAITHERSBURQ. MARYLAND 20SSS

REPORT OF CALIBRATION

of

Gammacell 220 Irradiator

for

Gammaray, Inc.

999 Cobalt Street

Miami, FL 32111

Attention: James Doe

Ref. P.O. No.: 32123

Transfer dosimetry packets, consisting of five calibrated FWT-60-00 radlochromic

dosimeters (NBS Batch 144), held between 5.0-mm thick blocks of polystyrene and

sealed Inside two thin polyethylene pouches (R.H. 43% at time of sealing), were

supplied to Gammaray for Irradiation in their Gammacell 220 irradiator facility.

Upon their return to NBS,. the dosimeters were analyzed on 9 September 1985, at two

wavelengths (605 nm and 510 nm) using a Cary Model 219 spectrophotometer (3.5 nm

S.B.W.). Absorbed dose Interpretations were made from a calibration of this batch

of radlochromic dosimeters performed 1n April 1985. The results are summarized 1n

the following table:

NBS Absorbed

Dosimeter Dose 1n H

2 0. kGy*

No. (605 nm)

696-700 (Controls) 0

701-705 18.55

706-710 9.00

711-715 16.25

716-720 U.40

721-725 19.70

726-730 18.90

731-735 7.50

736-740 23.20

741-745 18.30

746-750 19.60

Test 536/222222-86

NBS DB 100/001

XRG-321

October 10, 198b

*1 kGy - 0.1 Mrad APPENDIX C

C-l
Test. 536/222222-86

NBS DB 100/001

XRG-321

October 10, 1985

Page 2 of 5 pages

The dosimeters were read 1n terms of optical absorbance before (A0

) and after (A*)

Irradiation, using a Cary Model 219 spectrophotometer (3.5 nm S.B.W.), at two

optical wavelength settings/ 605 nm and 510 nm. Dosimeter film thicknesses were

read using a Mltutoyo Model DGS-E thickness gage. Values of Increase 1n optical

absorbance per unit thickness (AA/mm, where aA Aj - A

Q

) are also Included.

Date,

Dosimeter Time

No. ; (605 nm) (510 nm

of A

1

) Reading (605 nm)

4

(510 nm)

Thickness

(mm)

AA/mm

(605 nm)(510 nm

Ov . 1S16 1J1U 0 0591 9/9/85 0.1516 0.0591 0.050

fiQ7 n i R7n 0 0787 11*15 0 1563 0.0781 vi v/ Ul 0 050

0 id?7 O 0597 M 0 1435 0 0596 0 049 —Controls--

699 0.1496 0.0605 N 0.1487 0.0599 0.051

700 0.1504 0.0599 M 0.1507 0.0604 0.051

7m U. iHtJ 0 0591 9/9/85 1 4947 0 2256 0 050 27.04 3.330

7n? U. I3UU n ofioi 1111 •iL?SJ 11 t

(JLJ( i?37 0 0^0 27.47 3.360

7m n i tqq M 0 ??dfi O OR1 26.07 3.167

70d O OfiO"? II 1 635? 0 2380 0 053 28.01 3.353

705 0.1514 0.0627 N 1.6253 0.2392 0.052 28.34 3.394

706 0.1498 0.0600 9/9/85 0.8804 0.1483 0.051 14.33 1.731

707 0.1526 0.0712 14:35 0.8906 0.1587 0.052 14.19 1.683

708 0.1472 0.0598 N 0.8893 0.1476 0.050 14.84 1.756

709 0.1551 0.0628 N 0.9297 0.1537 0.051 15.19 1.782

710 0.1487 0.0638 M 0.9136 0.1549 0.051 15.00 1.786

711 0.1625 0.0800 9/9/85 1.4276 0.2314 0.052 24.33 2.912

712 0.1650 0.0742 14:45 1.4719 0.2291 0.053 24.66 2.923

713 0.1563 0.0722 N 1.3659 0.2209 0.052 23.26 2.860

714 0.1489 0.0598 N 1.4138 0.2149 0.051 24.80 3.041

715 0.1555 0.0604 N 1.4299 0.2168 0.052 24.51 3.008

716 0.1547 0.0640 9/9/85 1.0597 0.1742 0.052 17.40 2.119

717 0.1419 0.0586 15:00 1.0341 0.1673 0.051 17.49 2.131

718 0.1494 0.0600 N 1.0486 0.1675 0.050 17.98 2.150

719 0.1570 0.0646 N 1.0935 0.1753 0.051 18.36 2.171

720 0.1550 0.0643 N 1.0759 0.1732 0.050 18.42 2.178

APPENDIX C

C-2
Test 536/222222-86

NBS DB 100/001

XRG- 321

October 10, 1985

Page 3 of 5 pages

Date,

Dosimeter Time

No. Aq of Aj Aj Thickness aA/mm

(605 nm)(510 nmj Reading (605 nm)(510 nmj (mm) (605 nm)(510 nm)

t CI U. 10** 3 n 07fift 7/7/ OJ 1 6103 0 ?5?*i 0 05? ?7C 1 .ouRO J.3 J37Q/ 7 777 1 CC U. 10c7 n 07R7 15*10 1A • 5869 JOU7 0V • ?474 C*t # *t 0 0^0 ?ft CO • 4ft HO 3J. J374/ H 723 0.1506 0.0599 1.6251 0.2367 0.051 28.91 3.467

724 0.1449 0.0596 « 1.6124 0.2376 0.050 29.35 3.560

/ nv. 1901 irm 0 0603 N

1 6466 0 2411 0 051 ?QC7 . c*t ?4 J.3 >t4H Of 0

7?fi / CO U. lOOU 0 0640 9/9/85 7/ 7/ W«J 1.5462 0 2343 0 05? 26 73 3O.C/?7*iJ 7?7 1 CI U. 134

1

0 0660 15*15 1.5674 0 2401 0 OH? ?7 ?? 3 34ft

728 0.1456 0.0628 M 1.5400 0.2312 0.050 27.89 3.368

729 0.1487 0.0619 N 1.6037 0.2309 0.051 28.53 3.314

730 U. 1HOO O 0613 M1 5786 0 2339 0 0«il ?RCO. 101U J3 3ft4 . JOH

731 nU. 1H31 10Jl 0 0603 9/9/85 7/ 7/ O.J 0 7674 0 1338 o om 1?AC .U*T 04 1A • 441 **? 1 73? 1 Jc U. 1 OJO O 0fi?7 15*?0 0 8066 0 140 1* 0 0*>? 1?AC *»fi . OO 1 4Qfi

733 0.1467 0.0622 M 0.7493 0.1348 0.050 12.05 1.452

734 0.1533 0.0626 M 0.7802 0.1384 0.051 12.29 1.486

73R / JO U. locO U.UOU/ M 0V/ . 7fiQ0 / U7U 0U .

1A 344 Oft o n^n 11c9 37 • J J

1A . A7A *T / H

73fi / JO U. lolc o ofi?o Q/q/pr; 7/ 7/ OJ 1A .08718 1 AO 0 ?74ft oU .UOl nm JJ. 33 7A/H a*• i it. 1/

J

737 /J/ n i qi a U. 1 010 U.U/ n 07?ft CO AO • JU 1A . 74HQ / H07 U • COOO U.UOl Jl31 • 39Jc 3 RA.7 J.Of J

73ft / JO nU. 1 A77/ A .OUO/ 0UiLO?fi3*» JO oU.UOl n<>i J33J .07AO. * .uuo 739 0.1508 0.0671 M 1.8354 0.2701 0.050 33.69 4.060

740 0.1469 0.0599 it 1.7632 0.2608 O.049 32.99 4.100

741 0.1614 0.0790 9/9/85 1.4965 0.2416 0.052 25.68 3.127

742 0.1516 0.0666 15:40 1.5044 0.2305 0.052 26.02 3.152

743 0.1581 0.0620 M 1.5585 0.2317 0.051 27.46 3.327

744 0.1471 0.0608 It 1.5296 0.2278 0.050 27.65 3.340

745 0.1464 0.0602 n 1.5344 0.2273 0.051 27.22 3.276

746 0.1501 0.0629 9/9/85 1.6048 0.2418 0.051 28.52 3.508

747 0.1518 0.0604 15:45 1.6099 0.2355 0.050 29.16 3.502

748 0.1538 0.0644 M 1.6830 0.2481 0.052 29.41 3.533

749 0.1488 0.0680 tt 1.5938 0.2435 0.052 27.79 3.375

750 0.1467 0.0642 M 1.6026 0.2380 0.051 28.55 3.408

APPENDIX C

C-3
Test 536/222222-86

NBS DB 100/001

XR6- 321

October 10, 1985

Page 4 of 5 pages

Analysis of the dosimeter response consists of determining the mean a A/mm for each

group of five dosimeters irradiated together and the standard deviation of each

group as shown below.

Dosimeter Mean AA/mm X Std. Dev., a , n-i

No. (605 nm) (510 nm) (605 nm) (510 nm)

696-700 —Controls—

701-705 27.39 3.321 3.24X 2.70X

706-710 14.71 1.748 2.94X 2.42X

711-715 24.31 2.949 2.52X 2.51X

716-720 17.93 2.150 2.65X 1.17%

721-725 28.76 3.465 2.20X 2.54X

726-730 27.69 3.338 2.59X 1.31%

731-735 12.25 1.470 1.73X 1.56X

736-740 33.09 4.036 3.13X 3.07X

741-745 26.81 3.244 3.33X 3.05X

746-750 28.69 3.465 2.20X 2.00X

APPENDIX C C-4
Test 536/222222-86

NBS DB 100/001

XRG- 321

October 10, 1985

Page 5 of 5 pages

The attached page describes uncertainties and related factors In high-dose

calibrations, such as the one covered by this Report of Calibration. Any questions

regarding environmental conditions, different types- of materials used, and

systematic uncertainties associated with these calibrations can be answered by this

attachment. If there are further questions, they should be directed to the first

Individual named below.

Measurements were made by

D. G. Hocken, Calibrations Technician

(30i)921-2201

Approved by

J. W. Motz, Leader

X-Ray Physics Group

For the 01 rector

R. S. Caswell, Chief

Ionizing Radiation Division

Center for Radiation Research

APPENDIX C

C-5
UNCERTAINTIES AND RELATED FACTORS IN HIGH-DOSE CALIBRATIONS

Standard High-Dose Gamma-Ray Irradiations at NBS

(Estimated uncertainty: ± 3.3% at a 99% confidence level)

The high-dose calibrations at NBS (schedule 49010S) involve the administration

of 60 Co gamma radiation absorbed doses in certain materials (e.g., water,

carbon, aluminum, silicon, polystyrene, etc.), under environmentally controlled

conditions. The dose values are based on standard graphite calorimetry

measurements, which are corrected by certain modifying factors (the estimated

photon spectrum, tabulated weighing factors, such as radiation energy

absorption and attenuation factors, and source decay factors). The

irradiations are usually carried out using the NBS 60 Co gamma-ray pool source. The uncertainty values cited above are for the absorbed doses given typical

thin dosimeters (5 or less irradiated at a time) held under layers

approximating electron equilibrium in a given material, in the absorbed dose

region of 1 KGy and upward.

Absorbed Dose Evaluations Based on Traceability through

Mailed Chemical Transfer Dosimeters

(Estimated uncertainty: ± 5.2% at a 99% confidence level)

It must be recognized by calibration users that routinely applied chemical

dosimeters consisting of liquid solutions, solid films, ceramics, crystalline

materials, plastics, etc., are subject to imprecision and systematic error due

to environmental effects during field use, production, irradiation, and

readout. Therefore, if these factors are not sufficiently known and

understood, absorbed dose interpretations using such systems have

reproducibility and accuracy values that are difficult to establish. Although,

as indicated above, NBS in its high-dose calibrations (e.g. schedule 49010S)

administers to within prescribed uncertainty limits standard absorbed doses of

gamma radiation under controlled environmental conditions, the routine

dosimeters for field use are subject to uneven quality control of manufacture

and are occasionally susceptible to anomalous batch-to-batch or intrabatch

sensitivity differences, poor reproducibility of readout results, and adverse

environmental effects.

In the case of absorbed dose evaluation based on mailed transfer NBScontrolled radiochromic film dosimeters (nominal dose range 1 x 10 3 to 5 x 10 A Gy) that are traceable to 60 Co gamma-ray calibrations at NBS, the uncertainty

values cited above (± 5.2%) may be assumed as long as suitable care against

environmental and other sources of systematic error is exercised.

A detailed list of the various sources of uncertainty that make up the overall

uncertainties given above may be obtained by requesting such information from

NBS.

Appendix C

C-6
NBS-114A (REV. 2-80) U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NBS/SP-250/11

2. Performing Organ. Report No. 3. Publication Date March 1988

4. TITLE AND SUBTITLE

NBS Measurement Services:

National Bureau of Standards High Dose Calibration Services

5. AUTHOR(S)

J.C. Humphreys, Dene Hocken, and William L. McLaughlin

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions)

NATIONAL BUREAU OF STANDARDS

U.S. DEPARTMENT OF COMMERCE

GAITHERSBURG, MD 20899

7. Contract/Grant No.

8. Type of Report & Period Covered

Final

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City, State, ZIP)

Same as item 6

.

10. SUPPLEMENTARY NOTES

Library of Congrss Catalog Card Number 88-600506

| | Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a si gnificant

bibliography or literature survey, mention it here)

This document describes calibration services available at the National Bureau of

Standards for the standardization of high absorbed dose measurements of ionizing

radiation. The areas of application of such measurements include medical product

sterilization, electronic device radiation hardness testing and food processing.

Detailed descriptions of the NBS dosimetry procedures and uncertainty assessments

are given. Measurement assurance program techniques are discussed.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by s-emicolon s) dosimeter calibration; ionizing radiation; irradiation facilities;

measurement assurance program; uncertainties

13. AVAILABILITY

Unlimited

| | For Official Distribution. Do Not 'Release to NTiS

{q3 Order From Superintendent of Documents, U.S. Government (Printing Off ice, Washington, D.C.

20402.

Qjj Order From National Technical limffonnation Service (iNTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

49

15. Price

tf-U.S. Government Printing Office : 1988 - 201-597/82534 USCOMM-DC 4M3-P80



THE SP 250 SERIES ON NBS MEASUREMENT SERVICES*

SP 250-1 Spectral Radiance Calibrations 003-003-02792 $3.50

SP 250-2 Far Ultraviolet Detector Standards 003-003-02810-0 $4.25

SP 250-3 Radiometric Standards In the Vacuum

Ultraviolet 003-003-02806-1 $6.50

SP 250-4 Frlcke Dosimetry in High-Energy Electron Beams

003-003-0281 6-9 $2.75

SP 250-5 Alpha-Particle Calibrations SN003-003-0283-1 $2.00

SP 250-6 Regular Spectral Transmlttance 003-003-02805-3 $3.25

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003-003-02817-7 $2.00

SP 250-10 Radioactivity Calibrations with the "4ir" Gamma Ionization Chamber, and Other

Radioactivity Calibration Capabilities

003-003-02824-0 $2.25

SP 250-1 1 Dosimetry for High-Dose Applications

SP 250-12 Neutron Personnel Dosimetry

003-003-O2811-8 $2.50

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Fission Sources

SP 250-14 Activation Foil Irradiation by Reactor Cavity

Fission Sources

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Measuring Instruments

SP 250-17 The NBS Photodetector Spectral Response

Calibration Transfer Program

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Brachytherapy Sources

SP 250-20 Spectral Irradlance Calibrations 003-003-02829-1 $5.50

SP 250-21 Calibration of Beta-Particle Radiation Instrumentation

SP 250-22 Platinum Resistance Thermometer

Calibrations 003-003-02831-2 $17.00

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Calibration Service

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SP 250-28 Solid-State DC Voltage Standard Calibrations SN003--003-02842-8 $2.00

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SP 250-30 GOES Satellite Time Code Dissemination:

Description and Operation

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* Those entries containing a stock number (003-003—) and price can be purchased from the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402. GPO will accept checks, money orders, VISA, and Mastercharge. For more information, or to place an order, call (202)783-3238. Be sure to use the stock number In all orders. Titles without stock numbers are In preparation.
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