a) astatement of the scope of the calibration services to be performed by the laboratory,
including the radiation types, energies, and dose rates;

b) documentation of the model and serial numbers of each critical piece of equipment used
in a particular calibration;

c) a fully documented generic (or representative specific) procedure for each type of
calibration performed (for example, passive radiochromic dosimeters calibrated with gamma
radiation). The procedure shall provide the appropriate operational steps to permit a
knowledgeable person to reproduce a particular calibration technique with a precision
consistent with the specified uncertainty of the laboratory. Each calibration procedure shall
give the following information where relevant:

© concise but complete account of the procedure;

e range and limitations of the procedure;

© equipment and standards to be used;

@ environmental constraints to be met in addition to those in 6.6;

@ sequence of the procedure, drawing attention to special precautions;

@ an example of a completed data sheet; and

@ an cxamplec of a calibration report or certificate.
d) a tabulated assessment of the various components of uncertainty and their associated
confidence levels, the method used in combining the components, and the calculated overall
uncertainty associated with determination of the reference field for each generic calibration;
and
e) the procedure or reference for auditing calibration data and approving reports.

6.4.5 Each page of the quality manual shall indicate its date of initiation or revision.

6.4.6 A copy of the latest revision of the laboratory's quality manual shall be kept on file and be
readily available to the staff.

6.5 Personnel

6.5.1 The technical manager (however named) shall understand the quality system and
calibration procedures, and ensure that they are being followed.

16


handling these during calibration is to fold the pouch tightly around the slab of each dosimeter
and place it into the hole of the five-hole cup normally occupied by an ampoule. To determine
the effects of this geometry, Red Perspex slabs were removed from their pouches, 5 mm holes
were drilled in each in three places, and alanine pellets were inserted in these holes. The slabs

were reinserted in the pouches, the pouches are refolded and inserted into the holes of the five-
hole cup.

inmm

Figure 10 - Five-Hole Cup
for Ampoule Irradiation

33


invalidate their performance as reference standards.

5.8.5 Reference standards of measurement shall be traceable to a national or international
standard of measurement. There shall be a program of calibration and verification for reference
standards.

5.8.6 Where relevant, reference standards and measuring equipment shall be subjected to in-
service checks (constancy checks) between calibrations and verifications.

5.9 Calibration Methods

5.9.1 The laboratory shall have documented instructions for using and operating all relevant
equipment, for handling and preparing dosimeters, and for performing calibrations, where the
absence of such instructions could jeopardize the calibrations. All instructions, standards,
manuals, and reference data relevant to the work of the laboratory shall be maintained up-to-date
and be readily available to the staff.

5.9.2. The laboratory shall use appropriate methods and procedures for all calibrations and
related activities within its responsibility (including handling, transport, storage, and preparation
of dosimeters, estimation of uncertainty of measurement, and analysis of calibration data (4,5)).
The methods and procedures shall be consistent with the accuracy required, and with any
standard specifications relevant to the calibrations concerned.

5.9.3 Where methods and procedures are not specified, the laboratory shall, wherever possible,
use those that have been published as international or national standards, published by reputable
technical organizations, or published in relevant scientific texts or journals.

5.9.4 Where it is necessary to employ methods and procedures that have not been established as
standard, these shall be subject to agreement with the client, be fully validated and documented,
and be available to the client and other recipients of the relevant reports.

5.9.5 Calculations and data transfers shall be subject to appropriate checks.

5.9.6 Where computers or automated equipment are used to capture, process, manipulate,
record, report, store, or retrieve calibration data, the laboratory shall ensure that:

a) computer software is validated and documented where the software provides operational
control or contributes to a quality management decision process;

b) procedures are established and implemented for protecting the integrity of data; such

procedures shall include, but not be limited to, integrity of data entry or capture, data storage,
data transmission, and data processing;

10


associated equipment involved with the calibration services.
NOTE 3 - A complaint is not that an estimated completion date does not meet the customer’s
schedule. The Division will make every effort to help a customer, but the Division’s service
schedule can not be dictated by a customer’s needs. Also, complaints are not that the
calibration fees are too costly, that the type of calibration services offered do not meet the
customer’s requirements, or that the reported uncertainties are too large.

6.15.3 A discrepancy is a customer expression of disagreement or divergence (an
inconsistency) in measurement results from a calibration service. This is different than a
complaint but should be handled in essentially the same manner, since this could indicate a
problem with the calibration service’s data handling or quality control.
NOTE 4 - Many times discrepancies are the result of the customer’s inappropriate use of the
calibrated dosimeters or misunderstanding how to apply the calibration data. Division
personnel should determine if the calibration service is operating properly or if the customer
is having a problem at their end. The latter situation is often impossible to determine
definitively, but a reasonable effort should be made as resources allow (i.e., Division
personnel can not do the measurements for the customer unless they are willing to pay for it).

6.15.4 Complaint Process Procedures

6.15.4.1 Any Division personnel receiving a complaint about calibration services shall follow
the procedures detailed in this section.

6.15.4.2 The complaint (whether received by phone, fax, mail, or in person) shall be entered in
a Complaint Log. This Log shall contain the customer’s (company) name and address, name of
the point-of-contact person, and telephone number, date received, date closed and the Group
Leader for that service. The complaints shall be numbered in chronological order.

6.15.4.3 A Complaint Response Form shall be filled out for each complaint showing the
person receiving the complaint, date received, calibration service complaint number (from the
Complaint Log), the Group Leader for that service, the customer information from the Complaint
Log, a description of the complaint or a copy of a written complaint attached to the Response
Form, a description of the action taken to resolve the complaint, and the date of closure. Upon
closure, the Response Form shall be initialed by the Group Leader, the Technical Manager, and
the Quality Manager.

6.15.4.4 Any and all immediate and reasonable action shall be taken to resolve the complaint.
Each action shall be recorded and dated in the Response From.

6.15.4.5 If the complaint is received by a person other than the Group Leader, then the
complaint shall be forwarded to the Group Leader who is responsible for resolving the complain.

6.15.4.6 Copies of the Complaint Response Form shall be distributed to Technical Manager,

20


1. Scope

1.1. This document contains descriptions of the characteristics of the high-dose radiation
dosimetry calibration services at the National Institute of Standards and Technology (NIST).

2. Referenced Documents
2.1. ASTM Standards:

E170 Terminology Relating to Radiation Measurements and Dosimetry

E1249 Practice for Minimizing Dosimetry Errors in Radiation Hardness Testing of Silicon
Electronic Devices using Co-60 Sources

E1250 Method for Application of Ionization Chambers to Assess the Low Energy Gamma
Component of Cobalt-60 Irradiators Used in Radiation-Hardness Testing of Silicon Electronic
Devices

E1261 Guide for Selection and Calibration of Dosimetry Systems for Radiation Processing
E1607 Practice for Use of the Alanine-EPR Dosimetry System

E1707 Guide for Estimating Uncertainties in Dosimetry for Radiation Processing

2.2 International Organization for Standards:

ISO/IEC Guide 25 (1990) General requirements for the competence of calibration and testing
laboratories

2.3. American National Standards Institute:

ANSI/NCSL Z540-1-1994 Calibration Laboratories and Measuring and Test Equipment -
General Requirements

2.4 National Institute of Standards and Technology:

NIST Special Publication 250-45 High-Dose Radiation Dosimetry Calibration Services: Manual
of Calibration Procedures

3. Terminology

3.1 Descriptions of Terms Specific to This Document:

3.1.1 calibration - the process whereby the response of a dosimeter or measuring instrument is
characterized through comparison with an appropriate standard that is traceable to, and consistent

with, a national standard.

3.1.2 dosimetry system - a system used for determining absorhed dose, consisting of


Dpoot Dec 45, Dec '-232
Dyp Dyp Dyp
26.85 75.18 248.6
PRIMARY STANDARD VERTICAL BEAM]
(Domen water calorimeter) ‘SOURCE
ALANINE TRANSFER
DOSIMETRY
HIGH-DOSE Co
IRRADIATORS (POO) 232
coteRPostION | Proot Bocas Doosse
FILM | Of, Bees DiS
PERSPEX | OS Oma [set
mveour| op etme ae

Figure 8 - Traceability Chain for Vertical Beam
Source to High-Dose Rate Irradiators

Calculation of the dose rate for a given geometrical configuration, e.g., radiochromic film

dosimeters in the Pool source, is given by:

POOL, > POOL
Ram _ Daum

POOL 4 POOL
RO By

and,

R POOL

. L .

dD POOL _ Dore ‘FILM
RPO

FILM

31

2)

13)



6.5.2 The technical manager shall have a minimum of a bachelor's degree and should have at
least three (3) years of experience in radiological physics or a closely related scientific field.

6.5.3 The supervisor of the calibration laboratory shall have at least three (3) years of
experience in radiological physics or a closely related scientific field.

6.5.4 NIST oversight staff may consider an alternative organizational structure utilizing
existing expertise, provided a clear line of responsibility exists and the organization clearly
provides for continuing control.

6.6 Facilities and Environment

6.6.1 Suitable storage facilities shall be provided for reference standards, equipment,
documented instructions, manuals, and calibration certificates and reports.

6.6.2 Environmental monitoring equipment shall be provided for recording temperature and
relative humidity within the laboratory.

6.6.3 Although strict temperature control is not essential, it is desirable that the laboratory be
kept at a reasonably uniform temperature so that the accuracy of equipment is not adversely
affected, and so that an adequate stability is achieved before the start of calibration
measurements. It is recommended that the laboratory temperature be maintained within the
range of 20°C to 24°C.

6.6.4 It is recommended that the relative humidity should be maintained within the range of 15
to 65 percent for laboratory operation unless the calibration of specific dosimeter types require a
different range.

6.6.7 A closely controlled environment is not normally necessary in a storage area, but wide
temperature and humidity fluctuations should be avoided so as to protect instruments and
standards temporarily held there, and to minimize the time required for an instrument to reach
equilibrium when brought to the calibration laboratory from the storage area.

6.6.8 The electrical power shall be appropriate to the equipment used, suitably stable, and free
of switching surges and significant line noise. When necessary, local auxiliary voltage stabilizers
and filters shall be provided. For critical control and data acquisition equipment, battery backup
uninterruptable power supplies may be required.

6.6.9 The laboratory shall be provided with an adequate grounding system. Where there is a
possibility of interference arising from equipment connected to a single grounding system,
separate grounding systems shall be provided and adequate precautions taken against any
possible interconnection between systems.

17


71.73

Descriptions of NIST Irradiation Facilities

7.1.3.1 Vertical Beam Co Source - This source consists of a single capsule containing about 7

wen CaP

ruwcsten Aor

TOME HAMEPLATE, ;

ore

ruestex autor

|
'

|___——-tea»

|_—— source onawen

SMICLOWNG SHUTTER BLOCK

FULLY OPEN swurreR PostTtow

—_
1

Figure 2 - Vertical Beam “Co Source

kilocuries (kCi), housed in a
shielding head with a shutter
and collimator assembly, as
shown in Figure 2. 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.

Ata distance of 146 cm (105 cm scale distance), for December 1995, the absorbed dose rate in
water was 0:43 Gy/min. This absorbed dose rate has been determined with an NIST water
calorimeter (6). The estimated overall uncertainty in this rate is about + 0.8% at a 95%
confidence level. See the companion document SP250-45 Manual of Calibration Procedures for
detailed discussion of uncertainties in absorbed dose values for dosimeters irradiated with this
unit. This source is located in Room B036 of Building 245. There is a similar source with a much
lower dose rate located in Room B034; it is generally used only for low dose applications and has
not been calibrated-with the NIST water calorimeter.

23


c) the results of all interlaboratory comparisons.
6.12 Certificates and Reports

6.12.1 Calibration certificates or reports shall include an appropriate statement clearly specifying
the conditions under which the calibrations or measurements were performed. These conditions
could include the type of radiation (gamma ray, x ray, or electron beam), the dose rate(s),
temperature, and for electron beams, the electron energy, pulse width, dose rate within the pulse,
and repetition rate.

6.12.2 Certificates or reports should state that application of the calibration results to an
individual measurement is the responsibility of the user, and that care must be exercised in
interpolation of the calibration results.

6.12.3 The laboratory shall indicate whether the calibration was performed using either an
accredited or non-accredited procedure. The use of non-accredited procedures shall be justified
and those procedures completely explained and documented.

6.12.4 If the calibration laboratory discovers a mistake in a calibration report, the person or
institution that received the report shall be immediately notified. The mistake shall be corrected
as soon as possible, either by sending a corrected report to the client or by recalibrating a new
group of dosimeters, as applicable. The laboratory shall determine the reason for the mistake and
take action necessary to prevent recurrences.

6.13 Sub-contracting of Calibration - There are no additional requirements beyond the general
requirements set forth in Section 5.

6.14 Outside Support Services and Supplies - There are no additional requirements beyond the
general requirements set forth in Section 5.

6.15 Complaints
6.15.1 The policy of the Ionizing Radiation Division on complaints is:

All complaints received from customers or other parties on calibration services are
important and every effort shall be made to resolve the complaints in a prompt and
professional manner. A record shall be maintained of all complaints and of all
actions taken by the Division to resolve them.

6.15.2 A customer complaint is an expression of dissatisfaction with a requested calibration
service. Complaints can be broken, damaged, or missing dosimeters or equipment, excessive
delay from the estimated completion date without a reasonable explanation, or missing data in
the report. A complaint can be caused by the action (or inaction) of Division personnel or

19


Now, using equation (11), gives:

POOL POOL
. . R,
pp POOL _ yy VB Ro FILM

HLM = 0 * Ve” * oon (14)
RY” Ry
and,
R POOL
» POOL _ 7 VB, RriLM
Derm = Do * RS? a5)

Equivalent equations have been developed for other configurations and dosimeter types; these are
discussed in detail in the next section.

7.8.8 The alanine ratio measurements
of the various sources described thus far

a ee Single-hole cup were for a single geometrical
t i for alanine pellets, arrangement, namely, a polystyrene
Hy 1H 5.1 mm hole dia., _ single-hole cylindrical cup with a hole

3.7 mm wall diameter slightly larger than the alanine
pellets (5 mm) and a wall thickness of
3.7 mm. This cup was mounted on a
Support polystyrene rod which was, in turn,
Rod mounted to a 6 mm thick polycarbonate
base disk to locate the alanine pellets in
the geometrical center of the radiation
field of each irradiator (see Fig. 9).

SES

Se

Polycarbonate base,

80 & 152 mm dia.
6 mm thick

\

Figure 9 - Single-Hole Geometry for Alanine
Pellets in High-Dose Rate Irradiators

SEITE
ORS SS

RSLS

=
ROSS

7.8.9 The Pool source and
Gammacells are used to calibrate a
variety of types of dosimeters including
liquid solutions sealed in glass
ampoules such as ceric cerous sulfate
and dichromate, thin radiochromic solid films, and thick solid slabs such as Red Perspex. Each
type of dosimeter requires a unique holder and geometry during irradiation. For the liquid in
ampoules type, a polystyrene holder was used as shown in Fig. 10. This holder is referred to as
the “five-hole cup” since the five circumferential holes are normally used to hold the dosimeters
being calibrated and the center hole is used for quality control dosimetry. The hole size was
chosen so that a 2-mL ampoule would fit snugly. To determine the effects of scattering and
attenuation of the holder, alanine pellets were placed in polystyrene cylinders that fit snugly in
the holes in place of the ampoules. Red Perspex dosimeters are normally sealed in aluminum
pouches by the manufacturer and are not opened until after irradiation. The usual method for

32


5.14 Outside Support Services and Supplies

5.14.1 Where the laboratory procures outside services and supplies other than those referred to
in this section, in support of calibrations, the laboratory shall use only those outside support
services and supplies that are of adequate quality to sustain confidence in the laboratory's
calibrations.

5.14.2 Where no independent assurance of the quality of outside support services or supplies is
available, the laboratory shall have procedures to ensure that purchased equipment, materials,
and services comply with specified requirements. The laboratory should, wherever possible,
ensure that purchased equipment and consumable materials are not used until they have been
inspected, calibrated, or otherwise verified as complying with any standard specifications
relevant to the calibrations concerned.

5.14.3 The laboratory shall maintain records of all suppliers from whom it obtains support
services or supplies required for calibrations.

5.15 Complaints

5.15.1 The laboratory shall have documented policy and procedures for the resolution of
complaints received from clients or other parties about the laboratory's activities. A record shall
be maintained of all complaints and of the actions taken by the laboratory.

5.15.2 When a complaint, or any other circumstance, raises doubt concerning the laboratory's
compliance with the laboratory's policies or procedures, or with the requirements of this section
or otherwise concerning the quality of the laboratory's calibrations, the laboratory shall ensure
that those areas of activity and responsibility involved are promptly reviewed in accordance with
5.4.3.

6. Specific Criteria for Ionizing Radiation

6.1 This section sets specific requirements to which a laboratory shall adhere if it is to perform
calibrations using ionizing radiation. This section amplifies and interprets the general
requirements set forth in Section 5 (see 4.4 and 4.5).

6.2 This section may also be used as a guide by ionizing radiation calibration laboratories in the
development and implementation of their quality systems.

6.3 Organization and Management: The relationship among the various technical groups, the
quality manager, deputy quality manager, and the calibration services of the Ionizing Radiation
Division are shown in Fig. 1. This chart includes all calibration activities within the Division, not

just those relating to high-dose level dosimetry. However, only those subjects relating to high-
dose calibration activities are specifically addressed in this document.

14


system;

d) procedures for control and maintenance of documentation;

e) job descriptions of key staff and reference to the job descriptions of other staff;
f) identification of the laboratory's approved signatories;

g) the laboratory's procedures for achieving traceability of measurements;

h) the laboratory's scope of calibrations;

i) arrangements for ensuring that the laboratory reviews all new work to ensure that it has
the appropriate facilities and resources before commencing such work;

j) _ reference to the calibration and verification procedures used;

k) _ procedures for handling calibration and test items;

1) _ reference to the major equipment and reference measurement standards used;

m) reference to procedures for calibration, verification, and maintenance of equipment;

n) reference to verification practices including interlaboratory comparisons, use of reference
materials, and internal quality control schemes;

0) procedures to be followed for consultation and corrective action whenever discrepancies
in interlaboratory comparisons are detected, or departures from documented policies and
procedures occur;

p) the laboratory management arrangements for exceptionally permitted departures from
documented policies and procedures or from standard specifications;

q) procedures for dealing with complaints;
1) procedures for protecting confidentiality and proprietary rights;
s) procedures for review of calibration program and measurements; and

t) statements of uncertainties of all offered services, including detailed breakdown of all
components contributing to each uncertainty.

5.4.3. The laboratory shall arrange for review of ils activities al appropriate intervals to verify


Monte Carlo calculations were performed to verify the
validity of the scaling theorem. The measured incident
fluence rate spectra from the Co source, averaged
over corresponding field sizes, were calculated for the
corresponding detector planes, i.e., at depths of 5 cm in
water, and 4.87 cm in polystyrene. Both fluence rate
spectra were integrated over the mass energy-
absorption coefficient for water to obtain the dose rate
for a point water detector. For a point source, the
square of the scaling factor corresponds exactly to the

SOURCE

COLLIMATOR

/) A 1/R? correction factor. Comparisons of the dose rates
oEresron 7) 75 from the two methods indicate agreement within 0.1%.

Independent experimental test measurements (10)
indicate agreement with the scaling theorem within

Vi YG

0.5% or better.
Figure 7 - Vertical “Co Beam Geometry
for Polystyrene Phantom
Table 1
Medium p (g/cm?) <Z/A> e/Ny x (cm) z(cm)
water 1.00 0.555087 0.555087 5.00 100.00
polystyrene 1.06 0.537680 0.569941 4.87 97.39

7.8.7 Take the normalized EPR signal, S,.;, from 7.8.4, and divide by the irradiation time, tre,
to get a response proportional to dose rate:

R=— ©

29



7.8 Measurement Traceability and Calibration

7.8.1 The Vertical Beam “Co source described in 7.7.3.1 is the reference source to which all
the other source
facilities are compared.
The comparisons are

RADICAL nomeasurable performed using
nny ionizing CATION paramagnetic species reference transfer
| ragetion standard dosimeters, in
He" | Pree * NH this case, NIST
" RADICAL + electron paramagnetic
ALANINE ANION wt resonance (EPR)
me 4 “ee dosimetry with alanine
fong-lived as the sensor. Alanine,
Paes an amino acid of
composition
CH,CH(NH,)CO,H,
has been identified (8)

Figure 5 - Production Mechanism of Paramagnetic Species as an excellent material

for use as a radiation
dosimeter. Upon absorption of ionizing radiation by dry crystalline alanine, deamination of the
radical anion (Fig. 5) produces a free-radical center that is exceptionally stable (9). The attributes
of the alanine system have been summarized elsewhere (see ASTM Practice E 1607).

7.8.2 The alanine dosimeters used in this work were 90 percent L-c-alanine (Aldrich, 99.9 %)
by weight and prepared as described below. The alanine was ground in a centrifugal mill
(Brinkmann) fixed with a 0.5 mm ring sieve. The ground crystals of alanine were transferred to a
vibrating siever (Brinkmann) from which a particle size distribution in the range 53 xm to

125 ym was selected. Appropriate weights of sieved alanine and polyethylene (Polysciences,
mw = 700, 60 jum) were blended in a powder mixer (Paterson-Kelly). The mixture was loaded
into a Manesty hand-tableting press to produce alanine dosimeters 4.9 mm in diameter and
approximately 2.7 mm thick. The dosimeters were then placed in a 130 °C oven for 30 min,
followed by 5 min in an 85 °C oven. They were then stored in the dark at ambient temperature
under controlled humidity conditions (45 + 5 % r.h.).

7.8.3 The NIST EPR dosimetry facility consists of a Bruker ESP 300E and an ECS 106
electron paramagnetic resonance spectrometers. The alanine dosimeters were measured in a
Bruker ‘MH microwave resonator. A specially designed clear-fused quartz holder (Wilmad
Glass) held the dosimeter in the center of the resonator reproducibly. The spectrometer settings
were: microwave frequency, 9.8 GHz; center magnetic field strength, 0.3485 T; magnetic field
sweep width, 8.0 mT; microwave power, 10 mW; modulation frequency, 100 kHz; modulation
amplitude, 1.0 mT; conversion time, 41 ms; sweep-time, 41 s; time constant, 655 ms. The EPR
spectrum for an alanine dosimeter irradiated with gamma radiation to 100 Gy is shown in Fig. 6.

26


for transport between different locations, used to compare absorbed dose measurements.

3.1.14 verification - confirmation by examination of objective evidence that specified
requirements have been met.
NOTE 2 - In the case of measuring equipment, the result of verification leads to a
decision either to restore to service or to perform adjustments, or to repair, or to
downgrade, or to declare obsolete. In all cases it is required that a written trace of the
verification performed be kept on the instrument's individual record.

3.1.15 working standard - a standard, usually calibrated against a reference standard, used
routinely to calibrate or check measuring instruments or devices.

3.2 Also see Terminology E 170.
4. Significance and Use

4.1 The radiation industry needs a source of reliable, prompt, dosimeter calibration services to
support accurate measurements of absorbed dose during radiation processing. Those
measurements, made routinely in industrial facilities, should be consistent with and traceable to
the physical measurement standards maintained by an appropriate national or international
standards laboratory.

4.2 To ensure the provision of adequate services, a calibration laboratory should be operating
with a full measurement assurance program (MAP). The fundamental requirements for such a
program include: (1) compliance with operational requirements of this document; (2)
documented procedures and in-house quality assurance (QA) program specific to the calibration
services provided; and (3) periodic performance evaluations, such as internal review by NIST
staff and measurement intercomparisons between NIST and other national laboratories (1,2)'.

4.3 In addition to standard calibration services such as irradiation of dosimeters and supplying
transfer dosimeters for client in-house source calibration, the NIST calibration laboratory MAP
can provide technical information, troubleshooting (at the client's facility if necessary), and serve
as an independent group for resolution of disputes. NIST can also conduct long term studies of
dosimetry system characteristics, such as environmental effects, and evaluate new, emerging
dosimetry systems to assist in technology transfer to industry.

4.4 Section 5 sets forth general criteria that shall be satisfied by the NIST calibration laboratory.
These general criteria are completely consistent with ISO/IEC Guide 25 and its U.S. equivalent
ANSI/NCSL Z540-1. Laboratories that meet these general requirements comply, for calibration
activities, with Guide 25/Z540 and the relevant requirements of the ISO 9000 series of standards,
including those of the model described in ISO 9002 when they are acting as suppliers producing

'The bold numbers in parenthesis indicate references at the end of the text.

3


dosimeters, measurement instruments and their associated reference standards, and procedures
for the system's use.
NOTE 1 - The types of dosimeters include reference standard dosimeters, transfer
standard dosimeters, and routine dosimeters. See Guide E 1261 for guidance on the
selection and calibration of the various dosimetry systems.

3.1.3 measurement assurance program - a documented program for the measurement process
that quantifies on a continuing basis the overall uncertainty of the measurements. This program
requires traceability to and consistency with national or international standards, and shall ensure
that the overall uncertainty meets the requirements of the specific application.

3.1.4 measurement traceability - the ability to demonstrate and document periodically that the
measurement results from a particular measurement system are in agreement with comparable
measurement results obtained with a national standard (or some identifiable and accepted
standard) to a specified uncertainty.

3.1.5 primary standard dosimeter - dosimeter, of the highest metrological quality, established
and maintained as an absorbed dose standard by a national or international standards
organization.

3.1.6 quality assurance - all systematic actions necessary to provide adequate confidence that a
calibration or measurement is performed to a predefined level of quality.

3.1.7 quality control - the operational techniques and procedures that are employed routinely to
achieve and sustain a predefined level of quality.

3.1.8 quality manual - document stating the quality policy, quality system, and quality practices
of an organization.

3.1.9 quality system - organizational structure, responsibilities, procedures, processes, and
resources for implementing quality management.

3.1.10 radiation processing - the intentional irradiation of products or materials to preserve,
modify, or improve their characteristics.

3.1.11 reference standard dosimeter - a dosimeter, of high metrological quality, used as a
standard to provide measurements traceable to, and consistent with, measurements made using
primary standard dosimeters.

3.1.12 routine dosimeter - dosimeter calibrated against a primary-, reference-, or transfer-
standard dosimeter and used for routine absorbed dose measurement.

3.1.13 transfer standard dosimeter - a dosimeter, often a reference standard dosimeter, suitable


Ionizing
Radiation
Divison Chief

Radiation
Interactions &
Dosimetry

Neutron
Interactions &
Dosimetry

Quality
‘Manager

Deputy Quality
Manager

Radioactivity

Xray &
Gamma-ray
Instruments

Standard
Reference
Materials

High-Dose
Dosimetry

Beta-particle
Dosimetry

Neutron
Instruments

Neutron
Sources

Radioactivity
Sources

Figure 1 - Organizational Chart for lonizing Radiation Division Calibration Services

6.4 Quality System and Review of Activities

6.4.1 The laboratory shall perform interlaboratory comparisons at least annually for those
types of services offered. If the test results indicate that corrective action is required, the
laboratory shall take action to achieve the overall uncertainty stated in the appropriate section of
this document.

6.4.2 The interlaboratory comparisons shall be performed with a nationally or internationally
recognized standards laboratory.

6.4.3 If necessary, the interval between interlaboratory comparisons may be increased. Under
no circumstances shall more than 15 months pass between such comparisons.

6.4.4 The quality manual and related quality documentation shall contain:

15


d) specify and document the responsibility, authority, and interrelation of all personnel who
manage, perform, or verify work affecting the quality of calibrations;

©) provide adequate supervision by persons familiar with the calibration methods and
procedures, the objective of the calibration and the assessment of the results;

f) have a technical manager (however named) who has overall responsibility for the
technical operations;

g) have a quality manager (however named) who has responsibility for the quality system
and its implementation. The quality manager shall have direct access to the technical
manager and to the highest level of management at which decisions are made on calibration
laboratory policy or resources. In some laboratories, the quality manager may also be the
technical manager or deputy technical manager of the calibration laboratory;

h) nominate deputies in case of absence of the technical or quality manager;

i) where relevant, have documented policy and procedures to ensure the protection of
clients' confidential information and proprietary rights;

j)_ where appropriate, participate in interlaboratory comparisons.
5.4 Quality System and Review of Activities

5.4.1 The laboratory shall establish and maintain a quality system appropriate to the type, range,
and volume of calibration activities it undertakes. The elements of this system shall be
documented. The quality documentation shall be available for use by the laboratory personnel.
The laboratory shall define and document its policies and objectives for, and its commitment to,
good laboratory practice and quality of calibration services. The laboratory management shall
ensure that these policies and objectives are documented in a quality manual and communicated
to, understood, and implemented by all laboratory personnel concerned. The quality manual shall
be maintained current under the responsibility of the quality manager.

5.4.2 The quality manual, and related quality documentation, shall state the laboratory's policies
and operational procedures established in order to meet the requirements of this section. The
quality manual and related quality documentation shall also contain:

a) a quality policy statement, including objectives and commitments, by top management;

b) the organization and management structure of the laboratory, its place in any parent
organization and relevant organizational charts;

c) the relations between management, technical operations, support services, and the quality


the Quality Manager, and all Division personnel involved.

6.15.4.7 In most cases the complaint probably can not be resolved by the person receiving the
complaint. In those cases the Group Leader shall be responsible for resolving the complaint. If
necessary, the Group Leader and all Division personnel involved shall meet to decide on a plan
of action to resolve the complaint. That plan and the date shall be noted on the Complaint
Response Form and a copy of the plan attached.

6.15.4.8 The Quality Manager or Deputy shall follow up on all complaints to see that they are
resolved in a timely manner. When the complaint is resolved, the date shall be entered on the
Complaint Response Form and the Group Leader, Technical Manager, and Quality Manager shall
initial the Form. The date shall also be entered in the Compliant Log. A copy of the closed
(resolved) Complaint Response From shall be filed with the Complaint Log.

7. Specific Criteria for Calibrations using Photons and Electrons

7.1 This section sets specific requirements to which the laboratory shall adhere if it is to
provide calibrations using gamma rays, electron beams, or x-ray (bremsstrahlung) beams. This
section amplifies and interprets the general requirements set forth in Section 5, and expands upon

the specific requirements contained in Section 6 (see 4.4 and 4.5).

7.2 The criteria contained in this section apply to calibration of dosimeters at absorbed-dose
levels appropriate for radiation processing.

7.3. Organization and Management - There are no additional requirements beyond those set
forth in Sections 5 and 6.

7.4 Quality System and Review of Activities - There are no additional requirements beyond
those set forth in Sections 5 and 6.

7.5 Personnel - There are no additional requirements beyond those set forth in Sections 5 and 6.
7.6 Facilities and Environment

7.6.1 If interpretation of the response of a particular type of dosimeter requires a history of the
environmental conditions, the temperature and humidity shall be recorded.

7.6.2 Fluorescence lamps, sunlight, and other sources of ultraviolet light shall be filtered if the
dosimeters are adversely affected by ultraviolet radiation.

7.6.3. Any area used for storage of dosimeters shall have its temperature and relative humidity
controlled as required for the specific dosimetry system employed.

21


NIST Special Publication 250-44

NIST MEASUREMENT SERVICES:

Radiation Processing Dosimetry Calibration
Services and Measurement Assurance Program

Jimmy CG. Humphreys, James M. Puhl, Stephen M. Seltzer,
William L. McLaughlin, Marc F. Desrosiers, Debra L. Bensen,
and Marlon L. Walker

lonizing Radiation Division

Physics Laboratory

National Institute of Standards and Technology
Gaithersburg, MD 20899-0001

March 1998

ent OF

he

ty,

aot * dep

"
neg,

*tares of TM

US, Department of Commerce
William M. Daley, Secretary

Technology Administration
Gary R. Bachula, Acting Under Secretary for Technology

National Institute of Standards and Technology
Raymond G. Kammer, Director


5.6 Facilities and Environment

5.6.1 Laboratory facilities including calibration areas, electrical power sources, lighting, heating,
and ventilation shall be adequate to facilitate proper performance of calibrations.

5.6.2. The environment in which calibrations and related activities are undertaken shall not
invalidate the results or compromise the specified uncertainty of measurement.

5.6.3 The laboratory shall provide facilities for the effective monitoring, control, and recording
of environmental conditions as appropriate. Due attention shall be paid, for example, to dust,
electromagnetic interference, humidity, electrical power stability, temperature, and sound and
vibration levels, as appropriate to the calibrations performed.

5.6.4 The laboratory design shall provide adequate protection between areas where the activities
are incompatible.

5.6.5 Access to and use of all areas affecting the quality of calibration and related activities shall
be defined and controlled.

5.6.6 Adequate procedures shall be taken to ensure good housekeeping.
5.6.7 The laboratory shall comply with all relevant health and safety requirements.
5.7 Equipment

5.7.1 The laboratory shall be furnished with all items of equipment required for the correct
performance of calibrations. In those cases where the laboratory needs to use equipment outside
its permanent control it shall ensure that the relevant requirements of this section are met.

5.7.2, All equipment relevant to calibration processes shall be properly maintained. Maintenance
procedures shall be documented. Any item of equipment which has been subjected to
overloading or mishandling, or which gives suspect results, or has been shown by verification or
during calibration or use to be defective, shall be taken out of service, clearly identified, and
wherever possible stored at a specified place until it has been repaired and shown by calibration,
verification, or test to perform satisfactorily. The laboratory shall examine the effect of this
defect on previous calibrations.

5.7.3. Each item of equipment shall, when appropriate, be labeled, marked, or otherwise
identified to indicate its calibration status.

5.7.4 Records shall be maintained for each item of equipment significant to the calibrations

performed. The records shall include:


that its operations continue to comply with the requirements of the quality system. Such reviews
shall be carried out by trained and qualified NIST staff. Where the review findings cast doubt on
the correctness or validity of the laboratory's calibration results, the laboratory shall take
corrective action and shall notify, in writing, as soon as practically possible, any client whose
work may have been affected.

5.4.4 The quality system adopted to satisfy the requirements of this section shall be reviewed
at least once a year by the management to ensure its continuing suitability and effectiveness and
to introduce any necessary changes or improvements. Any changes in the quality system shall be
approved by NIST oversight staff prior to implementation.
5.4.5 All review findings and any corrective actions that arise from them shall be documented.
The person responsible for quality shall ensure that these actions are discharged within the agreed
time scale.
5.4.6 In addition to periodic reviews, the laboratory shall ensure the quality of results provided
to clients by implementing and documenting checks. These checks shall be reviewed by
management and shall include, as appropriate, but not be limited to:

a) internal quality control schemes using, whenever practical, statistical techniques;

b) _ participation in interlaboratory comparisons;

¢) replicate calibrations using the same or different methods; and

d) _re-calibration of retained instruments and dosimeters.

5.5. Personnel

5.5.1 The laboratory shall have sufficient personnel with the necessary education, training,
technical knowledge, and experience to carry out their assigned functions.

5.5.2 The laboratory shall ensure that the training of its personnel is kept up-to-date (see Section
6).

5.5.3 Records on the relevant qualifications, training, skills, and experience of the technical
personnel shall be maintained by the laboratory.


e Two configurations, each consisting of regions of medium surrounded by vacuum:

System 1, medium has electron density of:
€, = pysZ/A>Nq @
System 2, medium has electron density of:

€ = ,<Z/A>,N, @)

where p = medium density;
<Z/A> = ratio of the number of electrons in a compound to the molecular weight;
and
N, = Avogadro constant.

e All distances and dimensions are scaled according to

&
X= TX @)

&

where the quantity €,/e, is the scaling factor.

As a result of using the scaling theorem, the fluence at points P, and P, at appropriately scaled
positions has identical energy and angular distributions, differing only by a constant given by the
square of the scaling factor, i-e.,

2
, = B >, (c)

&

The relationship of the various elements of the vertical beam irradiation geometry is shown in
Fig. 7. The calculation of x and z distances are shown in Table 1.With the collimator opening s
held constant, the field size f scales automatically.

28


7.8.4 The EPR signal intensity of each alanine pellet was measured in two orientations, one at
an initial orientation (0°) and then
with the pellet rotated 90°. As can be
seen from Fig. 6, the signal is the
vertical distance between the
minimum and maximum of the trace.
A normalized signal, Sy, is obtained
by taking the average of the signals at
the two orientations and dividing by
the mass of the pellet. The mass of
each pellet is measured with a

3340 339.0 Err) 490 so Denver Instrument Company model
Magnetic Field (mT) 160 electronic balance to the nearest
0.1 mg before measuring its EPR
Figure 6 - Electron Paramagnetic Resonance signal. The masses of the pellets
Spectrum of Alanine average about 55 mg. The EPR

system sensitivity is checked at the
beginning and end of each measurement session by means of a stable paramagnetic species (a
pitch sample). The response of alanine has a small temperature dependence during irradiation of
about 0.18%/°C. The mass normalized signal, Sy, from above is normalized to a reference
irradiation temperature by means of the following equation:

Syr = Sy + [Sy (0.0018 (Tpep - Tigp))] (9)

where Sy; = signal normalized for mass and irradiation temperature;
Trp = reference temperature (usually 23°C); and
Tiger = irradiation temperature.

7.8.5 Alanine dosimeters were used to measure ratios of the dose rates of each Co facility,
i.e., the Pool source and the two Gammacells, in comparison to the vertical beam source. This
was accomplished by irradiating several alanine pellets in a polystyrene holder to the same
absorbed dose in each facility and calculating the ratios of responses.

7.8.6 The dose rate of the reference vertical beam source was measured with an NIST water
calorimeter at a source-to-detector distance of 100 cm at a depth of 5 cm in a water phantom (6).
To transfer those measurements to alanine dosimeters, it was decided that a polystyrene phantom
was more practical than one of water. In order to determine the equivalent distance and thickness
in polystyrene that corresponds to those for the water phantom, a scaling theorem was employed
(10). This theorem has the following assumptions:

e Radiation interacts with the media only by pure Compton scattering;

27


calibration results,

4.5 For laboratories engaged in specific fields of calibration, the general requirements of
ISO/IEC Guide 25/ANSI Z540 need amplification and interpretation. Section 6 of this document
contains specific criteria which provide that amplification and interpretation for ionizing
radiation. Section 7 contain specific criteria for particular types of ionizing radiation, that is,
gamma rays, electron beams and x-ray (bremsstrahlung) beams. It contains the theoretical basis
for the traceability of dosimetry measurements used in the calibration services. The detailed
procedures used in the handling of customer’s calibration requests, for the generation of
calibration reports, and in the determination of the uncertainties for the various calibration
services are contained in the companion document NIST Special Publication 250-45 Manual of
Calibration Procedures.

4.6 For ease of use, all sections of this document after Section 5 employ the format established
in Section 5. It is therefore readily apparent how the subsequent Sections amplify and interpret
the general requirements contained in Section 5.

5. General Criteria

5.1 This section sets forth the general requirements that shall be satisfied by a laboratory. In
addition to satisfying the general criteria of this section, a laboratory shall also satisfy the specific
criteria contained in Section 6 and in those parts of Section 7 relevant to each calibration service
offered (see 4.4 and 4.5).

5.2 This section may also be used by calibration laboratories in the development and
implementation of their quality systems, and by others concerned with evaluating the competence
of laboratories.

5.3. Organization and Management

5.3.1 The laboratory shall be organized and shall operate in such a way that its facilities meet
the requirements of this section.

5.3.2. The laboratory shall:
a) have managerial staff with the authority and resources needed to discharge their duties;

b) have arrangements to ensure that its personnel are free from any commercial, financial,
and other conflicts which might adversely affect the quality of their work;

c) be organized in such a way that confidence in its independence of judgement and integrity
is maintained at all times;


6.6.10 The radiation room shall be of sufficient size and design such that scattered radiation at
the positions where dosimeters or instruments are normally placed for calibration does not
compromise the specified accuracy goals. If necessary, appropriate scatter corrections shall be
applied. In uncollimated free-air calibration facilities, the radiation room should be used
exclusively for calibrations to avoid variable scatter conditions. The contribution to absorbed
dose by scattered radiation should be known.

6.6.11 If compressed air is used, a pressure regulator and means for removing moisture, dust,
and oil from the compressed air shall be provided.

6.7 Equipment - The laboratory shall have reference standards and transfer standards that
cover the range of calibrations performed.

6.8 | Measurement Traceability and Calibration

6.8.1 The reference standards used by the laboratory shall be traceable to national or
international standards.

6.8.2 The use of a working standard instead of a reference standard is acceptable for
calibrations.

6.8.3 The standards or equipment originally calibrated by comparison with a higher-level
standard shall be recalibrated when the need is demonstrated by the results of interlaboratory
comparisons or routine quality control.

6.9 Calibration Methods - All new or amended calibration procedures that could have
significant impact on the accuracy of a calibration shall receive approval from the NIST
oversight staff before being adopted for routine use.

6.10 Handling of Dosimeters and Associated Equipment - All handling, unpacking, and
packing of dosimeters, instruments, and reference standards, shall be done by trained staff who
are familiar with the equipment.
6.11 Records
6.11.1 The laboratory's permanent records shall include:
a) the date, client, description of the dosimeters calibrated, the batch number or serial
number, details of the service provided, calibration report or certificate number, and invoice

or other accounting number;

b) documentation of routine quality control actions and any resultant control charts;


Table 3
Dose Rates for “Co Sources for December 31, 1996
filename = B140 P5-90 c:\qpw\DR97c.WB1
Effective 3/1/97
Co-60 half-life value is adjusted from 1925.34 days to 1925.12 days

‘Domen Water Calorimeter Transfer Calibration
Source in B036 under 5 cm water at 100 cm source
for 14.5 cm by 14.5 cm field size
For 1/11/90 Dose rate = 1.8144 Gy/min
For 12/31/96 Elapsed time = 2546 days
Co-60 daily decay constant ( In2 / 1925.12 ) = 3.60054e-04
Decay correction factor = 0.399837
Dose rate = 0.72546 Gy/min
or 0.012091 Gy/s

Absorbed Dose Rate in Water

GC232 Ratio Gy/s Gy/min kGy/h
3.5 mm Single-hole vial geometry 248.6 3.005 180.3 10.82
5.0 mm Polystyrene Film Block Geometry 0.9870 2.966 178.0 10.68
4.2 mm polystyrene 5-hole cup Perspex Geometry 0.9710 2.918 175.1 10.51
4.2 mm polystyrene 5-hole cup Ampoule Geometry 0.9560 2.873 172.4 10.34
GC232 in Stainless Steel Dewar
3.5 mm Single-hole vial geometry 239.9 2.901 174.0 10.44
5.0 mm Polystyrene Film Block Geometry 0.9913 2.875 172.5 10.35
4.2 mm polystyrene 5-hole cup Perspex Geometry 0.9692 2.811 168.7 10.12
4.2 mm polystyrene S-hole cup Ampoule Geometry 0.9599 2.784 167.1 10.02
GC45
3.5 mm Single-hole vial geometry 75.18 0.9090 54.54 3.272
5.0 mm Polystyrene Film Block Geometry 0.9889 0.8989 53.93 3.236
4.2 mm polystyrene 5-hole cup Perspex Geometry 0.9730 0.8844 53.07 3.184
4.2 mm polystyrene S-hole cup Ampoule Geometry 0.9595 0.8722 52.33 3.140
F101 Pool Source
3.5 mm Single-hole vial geometry 26.85 0.3246 19.48 1.169
5.0 mm Polystyrene Film Block Geometry 0.9941 0.3227 19.36 1.162
4.2 mm polystyrene 5-hole cup Perspex Geometry 0.9883 0.3208 19.25 1.155
4.2 mm polystyrene 5-hole cup Ampoule Geometry 0.9749 0.3164 18.99 1.139

for Gammacell and Pool, Combined Relative Expanded Uncertainty = 1.8%; dose rate (Silicon) = dose rate (Water) * 0.913

elapsed time = 366 days, decay correction factor = 0.876534

B036 Co-60 Vertical Beam Geometry Gy/s Gy/min Gy/h
B036 s.d.=30.0 cm, coll=20 x 20 6 mm ps plate 2.676¢e-02 1.605e+00 96.32
B036 s.d.=41.6 cm, coll=20 x 20 6 mm ps plate 1.944e-02 1.167e+00 70.00
BO036 s.d.=105 cm, coll=20 x 20 6 mm ps plate 6.227e-03 3.736e-01 22.42

B034 Co-60 Vertical Beam

BO034 s.d.=15.0 cm, coll.= 25 x 25 6 mm ps plate 5.306e-03 3.184e-01 19.10

5x 25 6 mm ps plate 9.476¢-04 5.685e-02 3.411
B034 s.d.=130 cm, coll.= 25 x 25 6 mm ps plate 6.568e-04 3.941e-02 2.364

for vertical beams, Combined Relative Expanded Uncertainty = 2.2%; dose rate (Silicon) = dose rate (Water) * 0.896

35


8. Keywords - Absorbed dose; calibration laboratory; dosimeter; dosimetry system; electron beam; gamma ray;
ionizing radiation; radiation processing; reference standard dosimeter.

9 References

i. Inn, K.G.W., Coursey, B.M., Eisenhower, E.H., Walker, M.D., Humphreys, J.C., Heaton, H.T., Duvall, K.C.,
“The role of the Office of Radiation Measurement in quality assurance,” The Science of the Total Environment,
130/131, Elsevier Science Publishers B.V., Amsterdam, 1993, pp. 497-507.

2. McLaughlin, W.L., “Reference dosimetry and measurement quality assurance,” Rad. Phys. Chem. 40, 1989, pp.
945-951.

3. Humphreys, J.C., Hocken, D., and McLaughlin, W.L., “Dosimetry for High Dose Applications,” NBS Special
Publication 250-11, Natl. Bur. Stand., Gaithersburg, MD, 1988.

4. McLaughlin, W.L., “Standardization of high-dose measurement of electron and gamma-ray absorbed doses and
dose rates,” High-Dose Dosimetry, Proceedings of International Symposium, Vienna, 1984, IAEA STI/PUB/671,
International Atomic Energy Agency, Vienna, 1985, pp. 357-371.

5. McLaughlin, W.L., Boyd, A.W., Chadwick, K.H., McDonald, J.C., and Miller, A., Dosimetry for Radiation
Processing, Taylor and Francis, London, 1989.

6. Domen, S.R., “A Sealed Water Calorimeter for Measuring Absorbed Dose,” J. Res. Natl. Inst. Stand. Tech., 99,
1994, pp. 121-141.

7. Petree, B. and Lamperti, P., “A Comparison of Absorbed Dose Determinations in Graphite by Cavity Ionization
Measurements and by Calorimetry,” J. Res. Natl. Bur. Stand., 71C, 1967, pp. 19-27.

8. Bradshaw, W.W., Cadena, C.G., Crawford, E.W., and Spetzler, H.A.W., “The Use of Alanine as a Solid
Dosimeter,” Radiat. Res. 17, 1962, pp. 11-21.

9. Sinclair, J.W. and Hanna, W., “Electron Paramagnetic Resonance Study of L-Alanine Irradiated at Low
Temperatures,” J. Phys. Chem., 71(1), 1967. pp. 84-88.

10. Pruitt, J. S. and Loevinger, R., “The photon-fluence scaling theorem for Compton-scattered radiation,” Med.
Phys., 9(2), 1982, pp. 176-179.

36


Figure 3 - Pool Co Source

7.7.3.2 Pool °Co Source - The pool-type source consists of a stationary annular array of twelve
source rods of about 1 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 3. 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 (7).
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 December 1995 was 22 Gy/min. A complete discussion is given in
reference (7) of the sources of the uncertainties in the absorbed dose rate of this Co facility. The
effect of these uncertainties on absorbed dose values assigned to irradiations performed in this
facility is discussed in the SP250-45 Manual of Calibration Procedures.

7.1.3.3. Gammacell 220 Co Irradiators - Two Gammacell 220 irradiators * are employed in the
irradiation of dosimeters and other materials.

?The mention of commercial products throughout this document does not imply
recommendation or endorsement by the National Institute of Standards and Technology, nor
does it imply that the products identified are necessarily the best available for the purpose.

24


PREFACE

The basis for this document was developed within the American Society for Testing and
Materials (ASTM) subcommittee E10.01 on Dosimetry for Radiation Processing. The version
that is published as an ASTM standard is designated as E1400 entitled “Standard Practice for
Characterization and Performance of a High-Dose Radiation Dosimetry Calibration Laboratory,”
with the latest revision dated 1995. This document differs substantially from the ASTM standard
in that it addresses calibration services operated under the direction of NIST staff, whereas the
ASTM standard deals with the accreditation of secondary calibration laboratories.

iti


c) computer and automated equipment is maintained to ensure proper functioning and is
provided with the environmental and operating conditions necessary to maintain the integrity
of calibration data; and

d) appropriate procedures for the maintenance of security of data including the prevention
of unauthorized access to, and the unauthorized amendment of, computer records are
established and implemented.

5.9.7 Documented procedures shall exist for the purchase, receipt, and storage of consumable
materials used for the technical operations of the laboratory.

5.10.. Handling of Client's Dosimeters

5.10.1 The laboratory shall have a documented system for uniquely identifying the dosimeters, to
ensure that there can be no confusion regarding the identity of such dosimeters at any time.

5.10.2 Upon receipt, the condition of the dosimeters, including any abnormalities or departures
from standard condition as prescribed in the relevant calibration method, shall be recorded.
Where there is any doubt as to the dosimeter's suitability for calibration, where the dosimeter
does not conform to the description provided, or where the calibration required is not fully
specified, the laboratory shall consult the client for further instruction before proceeding. The
laboratory shall establish whether the dosimeter has received all necessary preparation, or
whether the client requires the laboratory to perform or arrange for such preparations.

5.10.3 The laboratory shall have documented procedures and appropriate facilities to avoid
deterioration or damage to the dosimeters during storage, handling, preparation, and calibration;
any relevant instructions provided with the dosimeter shall be followed. Where dosimeters have
to be stored or conditioned under specific environmental conditions, these conditions shall be
maintained, monitored, and recorded where necessary. Where dosimeters are to be held secure
(for example, for reasons of record, safety, or value, or to enable check calibrations to be
performed later), the laboratory shall have storage and security arrangements that protect the
condition and integrity of the secured dosimeters.

5.10.4 The laboratory shall have documented procedures for the receipt, retention, or safe
disposal of dosimeters, including all provisions necessary to protect the integrity of the
laboratory.

5.11 Records
5.11.1 The laboratory shall maintain a record system to suit its particular circumstances and
comply with any applicable regulations. It shall retain on record all original observations,

calculations and derived data, calibration records, and a copy of the calibration certificate or
report, for an appropriate period. The records for each calibration shall contain sufficient

1


1) asignature and title, or an equivalent identification of the person(s) accepting
responsibility for the content of the certificate or report (however produced), and date of
issue;

m) where relevant, a statement to the effect that the results relate only to the dosimeters
calibrated; and

n) astatement that the certificate or report shall not be reproduced except in full, without the
written approval of the laboratory.

5.12.3 Where the certificate or report contains results of calibrations performed by sub-
contractors, these results shall be clearly identified.

5.12.4 Particular care and attention shall be paid to the arrangement of the certificate or report,
especially with regard to presentation of the calibration data and ease of assimilation by the
reader. The format shall be carefully and specifically designed for each type of calibration. carried
out, but the headings shall be standardized as far as possible.

5.12.5 Material amendments to a calibration certificate or report after issue shall be made only in
the form of a further document, or data transfer including the statement "Supplement to
Calibration Certificate (or Calibration Report), serial number... (or as otherwise identified)", or
equivalent form of wording. Such amendments shall meet all the relevant requirements of 5.12.

5.12.6 The laboratory shall notify clients immediately, orally and in writing, of any event such as
the identification of defective measuring equipment that casts doubt on the validity of results
given in any calibration certificate or report, or amendment to a report or certificate.

5.12.7 The laboratory shall ensure that, where clients require transmission of calibration results
by telephone, telex, facsimile, or other electronic or electromagnetic means, staff will follow
documented procedures that ensure the requirements of this Section are met and that
confidentiality is preserved.

5.13 Sub-contracting of Calibration

5.13.1 Where a laboratory sub-contracts any part of the calibration, this work shall be placed
with a laboratory complying with these requirements. The laboratory shall ensure and be able to
demonstrate that its sub-contractor is competent to perform the activities in question and
complies with the same criteria of competence as the laboratory in respect to the work being
subcontracted. The laboratory shall advise the client in writing of its intention to sub-contract any
portion of the calibration to another party.

5.13.2 The laboratory shall record and retain details of its investigation of the competence and
compliance of its subcontractors and maintain a register of all sub-contracting.

13


TABLE OF CONTENTS

TERMINOLOGY... 2.6... eee cece eee etree ener nent e tere nen ee eene 1
SIGNIFICANCE AND USE ....... 00. c ccc e eect e ete e ene n ene e nen e ence en eneee 3
GENERAL CRITERIA .... 6... ccc c ccc cece ener nen nent ete n een nen n ee 4
SPECIFIC CRITERIA FOR IONIZING RADIATION. .......0. 00s essence erence eee 14

SPECIFIC CRITERIA FOR CALIBRATIONS
USING PHOTONS AND ELECTRONS

KEYWORDS ... 1... occ ccc ccc ee neeer ene ent enn een e eee e nance 36

REFERENCES 2.0.2.6 cece cece cence nen nen e nee eee n ence nnn eee 36

ii


The radiochromic thin film dosimeters are normally irradiated in polystyrene two-piece square
slab holders as shown in Fig. 11. The slab assembly, with several radiochromic films sealed in
the interior cavity, is held vertically during irradiation. To simulate this geometry with alanine
dosimeters, a 3 mm thick polystyrene slab was drilled through in five places as shown in Fig. 12.
After alanine pellets were placed in the five holes, slabs of 3 mm thick polystyrene were
sandwiched on each side of the alanine-loaded slab. The effects of the three main irradiation
configurations on the dose rates in the three calibration sources were determined by the alanine
measurements and compared to the single-hole cup alanine measurements and appropriate
correction factors calculated. The dose rates for all sources and configurations are given in Table
3. The conversion of absorbed dose values in water to dose in silicon was done with the use of
ratios of mass energy absorption coefficients.

Dimensions in mm

es
a) 8 —
| K 3
SEED Cavity for
no | films
{|
—— 254

Figure 11 - Holder for Radiochromic Thin Film Irradiation

Dimensions inmm Cavities for alanine pellets

6
one

25.4

jm 25.4 —-}

Figure 12 - Holder for Alanine Pellets to Simulate Thin Film
Holder Geometry

34


7.7 Equipment
7.1.1 Radiation Source(s)

7.7.1.1 The laboratory shall have access to a source of gamma radiation, either “Co or '°’Cs,
with a fluence rate sufficient to deliver an absorbed dose within the range of 10 to 10° Gy (10° to
10” rad) within a reasonable time.

7.7.1.2 In addition, the laboratory may have an electron beam or x-ray beam (bremsstrahlung)
radiation source, or both, that can provide dose rates appropriate to radiation processing
conditions.

7.71.2 Characterization of the Radiation Field

7.7.2.1 Determine the absorbed-dose rate in each location in which dosimeters are irradiated
using reference standard dosimetry systems. Ensure that dosimeters are irradiated in the locations
where the dose rate is determined. At the time a given radiation facility is first calibrated and at
intervals not to exceed three years thereafter, demonstrate that the dose rates are traceable to
appropriate national standards by direct measurement intercomparisons.

7.7.2.2. Ensure that the absorbed-dose rate over the volume in which dosimeters are irradiated
does not vary more than + 1% at a 95% confidence level from its average value.

7.7.2.3 Ifthe dosimeters are irradiated in open air (for example, with a beam-port or panoramic
irradiator), ensure that the room is of sufficient size and design such that scattered radiation at
each position where dosimeters are placed for irradiation does not compromise the specified
overall accuracy goals.

7.7.2.4 Monitor and control the temperature of the irradiation volume during irradiation to the
degree required by the characteristics of the dosimeter. Measure this temperature during a
simulated irradiation of dosimeters or in a manner that will not perturb the radiation field during
the irradiation of dosimeters.

7.7.2.5, Maintain information related to the photon or electron energy spectrum at each dosimeter
irradiation location.

7.7.2.6 Minimize low-energy components of the photon source spectrum through the use of a

filter box when dosimeters used for radiation hardness testing are irradiated. (For additional
information see Practice E 1249 and Method E 1250.)

22


National Institute of Standards and Technology Special Publication 250-44
Natl. Inst. Stand. Technol. Spec. Publ. 250-44, 40 pages (Mar. 1998)
CODEN: NSPUE2

U.S. GOVERNMENT PRINTING OFFICE
WASHINGTON: 1998

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


For an irradiation in the Vertical Beam source in a polystyrene phantom, the scaling theorem
gives:

= pA
=RYEV
Ry = Roop fo)

For the Gammacells or Pool sources, the alanine is located inside a polystyrene cylinder with a
wall thickness of 3.7 mm. It has been experimentally determined that this wall thickness causes
an attenuation of 0.980 to the incident gamma radiation, requiring a correction to the dose rate
given by:

Ry = Sos ®

The ratio of the response, R, for a particular gamma source to another is equal to the ratio of the
dose rates for those gamma sources:

FP

-2 ©)
Db,

For example, the ratio of responses of the Pool source, R,’°°, to that of the Vertical Beam

source, Ry”, is given by:

POOL , POOL
Ro Do

= (10)
VB 5 VB
Ry Dy
Thus,
POOL
4 POOL _ 4 vB, Ro
Do = Do's RA? (iJ)

Experimentally determined ratios of dose rates for the Pool source and Gammacells, with serial
numbers GC-45 and GC-232, relative to the Vertical Beam source are shown in Table 2. The
chain of traceability is shown in Fig. 8.

30


These units, illustrated in Figure 4, are manufactured by Nordion, Intl. of Canada. Each unit
contains 24 “Co source rods in a stationary annular array, one with a total activity of about 18
kCi (serial number GC-232) and the other with about 5 kCi (serial number GC-45). The source
rods are located inside a massive lead-steel shielding structure that provides personnel protection.

Access Tust
2S em 1.398 in Oa

‘COLLAR ASANPLE CHAMAER INTERLOCKS
a microswircHes:

‘SAMPLE CHAMBER DOOR \

‘SAMPLE CHAMGER

DRAWER, UP
(toed Postion!

‘Brower Down

wenoswircH
{Top Shing Pas)

‘TOP SHELOWNG PLUG
SAFETY COLUMN

LEAD SHiELOING COLLAR

{Opened fortosding)
icnoswrtcn
{Door eroek)

BACK-UP McROSWITCHES
{For Drwerap & Drawer sown)

Figure 4 - Gammacell 220 Co Irradiator

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 December 1995
was 199 Gy/min for GC-232

and 62 Gy/min for GC-45. These rates were determined by means of alanine reference transfer
dosimeters referenced to the dose rate of the Vertical Beam source described in 7.7.3.1. These
rates, in turn, are verified on an annual basis by means of interlaboratory comparisons using
transfer dosimeters from the National Physical Laboratory (NPL) in the U.K. and with NIST
transfer dosimeters. The estimated overall uncertainty in this rate is about + 2% at a 95%
confidence level. Discussion of uncertainties associated with absorbed dose values for
dosimeters irradiated with these units is given in the SP250-45 Manual of Calibration
Procedures. Significant radiation heating of dosimeters can occur during irradiation in GC-232,
so an active cooling system consisting of a flow of chilled dry compressed air is provided to

maintain the sample temperature at 23°C.

25


a) the name of the item of equipment;

b) the manufacturer's name, type identification, and serial number or other unique
identification;

c) the date received and the date placed in service;

d) the current location, where appropriate;

e) the condition when received (for example, new, used, reconditioned);
f) acopy of the manufacturer's instructions, where available;

g) the dates and results of calibrations or verifications, or both, and the date of the next
calibration or verification or both;

h) the name and signature of the person who performed the calibrations or verifications, or
both;

I) the details of maintenance carried out to date and planned for the future; and
j) the history of any damage, malfunction, modification, or repair.
5.8 | Measurement Traceability and Calibration

5.8.1 All measuring equipment having an effect on the accuracy or validity of calibrations shall
be calibrated or verified, or both, before being put into service. The laboratory shall have an
established program for the calibration and verification of its measuring equipment (3).

5.8.2 The overall program of calibration or verification, or both, and validation of equipment
shall be designed and operated so as to ensure that, wherever applicable, measurements made by
the laboratory are traceable to national or international standards of measurement where
available. Calibration certificates shall, wherever applicable, indicate the traceability to national
standards of measurement, and shall provide the measurement results and associated uncertainty
of measurement or a statement of compliance, or both, with an identified metrological
specification.

5.8.3 Where traceability to national or international standards of measurement is either not
available or not applicable, the laboratory shall provide satisfactory evidence of correlation of
results, for example by participation in a suitable program of interlaboratory comparisons.

5.8.4 Reference standards of measurement held by the laboratory shall be used for calibration
only and for no other purpose, unless it can be demonstrated that use for other purposes will not


information to permit their repetition. The records shall include the identity of personnel
involved in calibration.

5.11.2 All records (including those listed in 5.7.4 pertaining to calibration equipment),
certificates, and reports shall be safely stored, held secure, and in confidence to the client.

5.12 Certificates and Reports
5.12.1 The results of each calibration or series of calibrations carried out by the laboratory shall
be reported accurately, clearly, unambiguously, and objectively in accordance with any
instructions in the calibration methods or procedures. The results should normally be reported in
a calibration certificate or report, and should include all the information necessary for the
interpretation of the calibration results and all information required by the method used.
5.12.2 Each certificate or report shall include at least the following information:

a) atitle, for example, "Calibration Certificate", or "Calibration Report";

b) name and address of the laboratory, and location where the calibration was carried out if
different from the address of the laboratory;

c) unique identification of the certificate or report (such as serial number) and of each page,
and the total number of pages;

d) name and address of client, where appropriate;

e) description and unambiguous identification of the dosimeters calibrated (supplier, type,
and batch number);

f) characterization and condition of the dosimeters;
g) date of receipt of dosimeters and date(s) of performance of calibration, where appropriate;

h) identification of the calibration method used, or unambiguous description of any non-
standard method used;

i) any deviations from, additions to, or exclusions from the calibration method, and any
other information relevant to a specific calibration, such as environmental conditions;

j) measurements, examinations, and derived results, supported by tables, graphs, sketches,
and photographs as appropriate, and any failures identified;

k) astatement of the estimated overall uncertainty of the calibration result (where relevant);

12