ISO/ASTM 51900:2009

INTERNATIONAL ISO/ASTM
STANDARD 51900
Second edition
2009-06-15
Guide for dosimetry in radiation research
on food and agricultural products
Guide de la dosimétrie pour la recherche dans le domaine de
l’irradiation des produits alimentaires et agricoles
Reference number
© ISO/ASTM International 2009
ISO/ASTM51900:2009(E)
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ii © ISO/ASTM International 2009 – All rights reserved

ISO/ASTMFDIS 51900:2009(E)
Contents Page
1 Scope . 1
2 Referenced documents . 1
3 Terminology . 2
4 Significance and use . 3
5 Irradiation facilities and modes of operation . 3
6 Radiation source characteristics . 4
7 Dosimetry systems . 5
8 Performance qualification . 7
9 Experimental methodology and dose mapping . 7
10 Dosimetry during experimentation . 9
11 Documentation . 10
12 Measurement uncertainty . 10
13 Keywords . 11
ANNEX . 11
Bibliography . 11
Figure 1 Dosimeter placement for dose mapping a product container for photon irradiation . 8
Figure 2 Experimental set-up for the irradiation of ground meat . 9
Figure 3 Step width selection of target dose . 9
Table 1 Examples of routine dosimeters (see ISO/ASTM Guide 51261) . 5
© ISO/ASTM International 2009 – All rights reserved iii

ISO/ASTM51900:2009(E)
Foreword
ISO(theInternationalOrganizationforStandardization)isaworldwidefederationofnationalstandardsbodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
Draft International Standards adopted by the technical committees are circulated to the member bodies for
voting. Publication as an International Standard requires approval by at least 75% of the member bodies
casting a vote.
ASTM International is one of the world’s largest voluntary standards development organizations with global
participation from affected stakeholders. ASTM technical committees follow rigorous due process balloting
procedures.
A project between ISO and ASTM International has been formed to develop and maintain a group of
ISO/ASTM radiation processing dosimetry standards. Under this project, ASTM Subcommittee E10.01,
Radiation Processing: Dosimetry and Applications, is responsible for the development and maintenance of
these dosimetry standards with unrestricted participation and input from appropriate ISO member bodies.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. Neither ISO nor ASTM International shall be held responsible for identifying any or all such patent
rights.
International Standard ISO/ASTM 51900 was developed by ASTM Committee E10, Nuclear Technology and
Applications, through Subcommittee E10.01, and by Technical Committee ISO/TC 85, Nuclear energy.
Thissecondeditioncancelsandreplacesthefirstedition(ISO/ASTM51900:2002),whichhasbeentechnically
revised.
iv © ISO/ASTM International 2009 – All rights reserved

ISO/ASTM51900:2009(E)
Standard Guide for
Dosimetry in Radiation Research on Food and Agricultural
Products
This standard is issued under the fixed designation ISO/ASTM 51900; the number immediately following the designation indicates the
year of original adoption or, in the case of revision, the year of last revision.
1. Scope 1.6 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 Thisguidecoverstheminimumrequirementsfordosim-
responsibility of the user of this standard to establish appro-
etry needed to conduct research on the effect of radiation on
priate safety and health practices and determine the applica-
food and agricultural products. Such research includes estab-
bility of regulatory limitations prior to use.
lishment of the quantitative relationship between absorbed
dose and the relevant effects in these products. This guide also
2. Referenced documents
describes the overall need for dosimetry in such research, and
2.1 ASTM Standards:
in reporting of the results. Dosimetry must be considered as an
E 170 Terminology Relating to Radiation Measurements
integral part of the experiment.
and Dosimetry
NOTE 1—The Codex Alimentarius Commission has developed an
E 925 Practice for Monitoring the Calibration of
international General Standard and a Code of Practice that address the
Ultraviolet-Visible Spectrophotometers whose Spectral
applicationofionizingradiationtothetreatmentoffoodsandthatstrongly
Slit Width does not Exceed 2 nm
emphasize the role of dosimetry for ensuring that irradiation will be
2 E 1026 Practice for Using the Fricke Reference-Standard
properly performed (1).
Dosimetry System
NOTE 2—This guide includes tutorial information in the form of Notes.
Researchers should also refer to the references provided at the end of the E 2232 Guide for Selection and Use of Mathematical Meth-
standard, and other applicable scientific literature, to assist in the
odsforCalculatingAbsorbedDoseinRadiationProcessing
experimental methodology as applied to dosimetry (2-10).
Applications
1.2 This guide covers research conducted using the follow- E 2303 Guide for Absorbed-Dose Mapping in Radiation
ing types of ionizing radiation: gamma radiation, X-ray Processing Facilities
(bremsstrahlung), and electron beams. E 2304 Practice for Use of a LiF Photo-Fluorescent Film
1.3 This guide describes dosimetry requirements for estab- Dosimetry System
lishingtheexperimentalmethodandforroutineexperiments.It E 2381 Guide for Dosimetry In Radiation Processing of
does not include dosimetry requirements for installation quali- Fluidized Beds and Fluid Streams
fication or operational qualification of the irradiation facility. F 1355 Guide for Irradiation of Fresh Agricultural Produce
These subjects are treated in ISO/ASTM Practices 51204, as a Phytosanitary Treatment
51431, 51608, 51649, and 51702. F 1356 Practice for Irradiation of Fresh and Frozen Red
1.4 This guide is not intended to limit the flexibility of the Meat and Poultry to Control Pathogens and Other Micro-
experimenter in the determination of the experimental meth- organisms
odology.Thepurposeoftheguideistoensurethattheradiation F 1640 Guide for Selection and Use of Packaging Materials
source and experimental methodology are chosen such that the for Foods to Be Irradiated
results of the experiment will be useful and understandable to F 1736 Guide for Irradiation of Finfish and Aquatic Inver-
other scientists and regulatory agencies. tebrates Used as Food to Control Pathogens and Spoilage
1.5 The overall uncertainty in the absorbed-dose measure- Microorganisms
ment and the inherent absorbed-dose variation within the F 1885 Guide for Irradiation of Dried Spices, Herbs, and
irradiatedsampleshouldbetakenintoaccount(seeISO/ASTM Vegetable Seasonings to Control Pathogens and Other
Guide 51707). Microorganisms
2.2 ISO/ASTM Standards:
51204 Practice for Dosimetry in Gamma Irradiation Facili-
This guide is under the jurisdiction of ASTM Committee E10 on Nuclear
ties for Food Processing
Technology and Applications and is the direct responsibility of Subcommittee
51205 PracticeforUseofaCeric-CerousSulfateDosimetry
E10.01 on Radiation Processing: Dosimetry andApplications, and is also under the
System
jurisdiction of ISO/TC 85/WG 3.
Current edition approved June 18, 2008. Published June 2009. Originally
published as ASTM E 1900–97. Last previous ASTM edition E 1900–97. The
present International Standard ISO/ASTM 51900:2009(E) replaces E 1900–97 and For referenced ASTM and ISO/ASTM standards, visit the ASTM website,
is a major revision of the last previous edition ISO/ASTM 51900:2002(E). www.astm.org, or contact ASTM Customer Service at service@astm.org. For
The boldface numbers in parentheses refer to the bibliography at the end of this
Annual Book of ASTM Standards volume information, refer to the standard’s
guide.
Document Summary page on the ASTM website.
© ISO/ASTM International 2009 – All rights reserved
ISO/ASTM51900:2009(E)
D 5 d´¯/dm (1)
51261 Guide for Selection and Calibration of Dosimetry
Systems for Radiation Processing
3.1.1.1 Discussion—The discontinued unit for absorbed
51275 Practice for Use of a Radiochromic Film Dosimetry
dose is the rad (1 rad = 100 erg/g = 0.01 Gy).Absorbed dose is
System
sometimes referred to simply as dose.
51276 Practice for Use of a Polymethylmethacrylate Do-
3.1.2 absorbed-dose mapping—measurement of absorbed
simetry System
dose within an irradiated product to produce a one-, two- or
51310 Practice for Use of a Radiochromic Optical
three-dimensionaldistributionofabsorbeddose,thusrendering
Waveguide Dosimetry System
a map of absorbed-dose values.
51431 Practice for Dosimetry in Electron Beam and X-ray
˙
3.1.3 absorbed-dose rate D —absorbed dose in a material
(Bremsstrahlung) Irradiation Facilities for Food Process-
per incremental time interval, that is, the quotient of dD by dt
ing
(see ICRU 60).
51538 Practice for Use of the Ethanol-Chlorobenzene Do-
simetry System
˙
D 5 dD/dt (2)
51540 Practice for Use of a Radiochromic Liquid Dosim-
-1
Unit: Gy · s
etry System
51607 Practice for Use of the Alanine-EPR Dosimetry 3.1.4 accredited dosimetry calibration laboratory—
System
dosimetry laboratory with formal recognition by an accrediting
51608 Practice for Dosimetry in an X-ray (Bremsstrahlung) organization that the dosimetry laboratory is competent to
Facility for Radiation Processing
carry out specific activities which lead to the calibration or
51649 Practice for Dosimetry in Electron Beam Facility for calibration verification of dosimetry systems in accordance
Radiation Processing at Energies between 300 keVand 25
with documented requirements of the accrediting organization.
MeV
3.1.5 bremsstrahlung—broad-spectrum electromagnetic ra-
51650 Practice for Use of Cellulose Triacetate Dosimetry
diation emitted when an energetic charge particle is influenced
Systems
by a strong electric or magnetic field, such as that in the
51702 Practice for Dosimetry in a Gamma Irradiation Fa-
vicinity of an atomic nucleus.
cility for Radiation Processing
3.1.6 charged-particle equilibrium—condition in which the
51707 Guide for Estimating Uncertainties in Dosimetry for
kinetic energy of charged particles, excluding rest mass,
Radiation Processing
entering an infinitesimal volume of the irradiated material
51818 Guide for Dosimetry in an Electron Beam Facility
equalsthekineticenergyofchargedparticlesemergingfromit.
for Radiation Processing at Energies Between 80 and 300
3.1.7 dose uniformity ratio—ratio of the maximum to the
keV
minimum absorbed dose within the irradiated product.
51956 Practice for Use of Thermoluminescence Dosimetry
3.1.8 dosimeter—device that, when irradiated, exhibits a
(TLD) Systems for Radiation Processing
quantifiable change that can be related to absorbed dose in a
52116 Practice for Dosimetry for a Self-Contained Dry
given material using appropriate measurement instruments and
Storage Gamma Irradiator
procedures.
2.3 International Commission on Radiation Units and
Measurements (ICRU) Reports:
3.1.9 dosimeter response—reproducible, quantifiable radia-
ICRU 60 Fundamental Quantities and Units for Ionizing
tioneffectproducedinthedosimeterbyagivenabsorbeddose.
Radiation
3.1.10 dosimetry system—system used for determining ab-
2.4 NPL Report:
sorbed dose, consisting of dosimeters, measurement instru-
CIRM29 :GuidelinesforCalibrationofDosimetersforUse
ments and their associated reference standards, and procedures
in Radiation Processing, Sharpe, P., and Miller, A., Au-
for the system’s use.
gust, 1999
3.1.11 electron equilibrium—charged-particle equilibrium
when the charged particles are electrons set in motion by
3. Terminology
photons irradiating the material. See charged-particle equilib-
3.1 Definitions:
rium.
3.1.1 absorbed dose (D)—quantity of ionizing radiation
3.1.12 reference-standard dosimeter—dosimeter of high
energy imparted per unit mass of a specified material. The SI
metrological quality, used as a standard to provide measure-
unit of absorbed dose is the gray (Gy), where 1 gray is
ments traceable to measurements made using primary-standard
equivalent to the absorption of 1 joule per kilogram of the
dosimeters.
specified material (1 Gy = 1 J/kg). The mathematical relation-
– – 3.1.13 repeatability (of results of measurements)—
ship is the quotient of d´ by dm, where d´ is the mean
closeness of the agreement between the results of successive
incremental energy imparted by ionizing radiation to matter of
measurements of the same measurand carried out subject to all
incremental mass dm.
of the following conditions; the same measurement procedure,
the same observer, the same measuring instrument, used under
4 the same conditions, the same location, and repetition over a
Available from the International Commission on Radiation Units and Measure-
ments, 7910 Woodmont Ave., Suite 800, Bethesda, MD 20814 USA. short period of time.
© ISO/ASTM International 2009 – All rights reserved
ISO/ASTM51900:2009(E)
3.1.13.1 Discussion—These conditions are called “repeat- tiveness of irradiation of food and agricultural products to
ability conditions.” Repeatability may be expressed quantita- achieve a defined benefit involves very different absorbed-dose
tively in terms of the dispersion characteristics of the results. specifications from one study and one product to another. For
3.1.14 reproducibility (of results of measurements)— example, the absorbed dose required to sterilize fruit flies is
closenessofagreementbetweentheresultsofmeasurementsof muchlowerthanthedosesrequiredtoinactivatesomebacterial
the same measurand, where the measurements are carried out pathogens in meat, or to decontaminate spices.
under changed conditions such as differing: principle or
NOTE 4—Examples of the relevant effects of irradiation include reduc-
method of measurement, observer, measuring instrument, lo-
tion of viable food-borne bacteria, viruses and parasites and phytosanitary
cation, conditions of use, and time.
treatment (such as disinfestation of fruits and vegetables), prevention of
3.1.14.1 Discussion—A valid statement of reproducibility sprouting, delay of ripening, and changes in product chemistry and
quality. Further discussion of these effects is outside the scope of this
requires specification of the conditions that were changed for
guide. Refer to ASTM Guides F 1355, F 1356, F 1736 and F 1885.
the measurements. Reproducibility may be expressed quanti-
tatively in terms of the dispersion characteristics of the results.
4.2 Proper reporting of the irradiation aspect is important
In this context, results of measurement are understood to be
since the degree of biological effect may be a function of
corrected results.
various factors such as the radiation source, the absorbed-dose
3.1.15 routine dosimeter—dosimeter calibrated against a
rate, energy of the incident radiation, environmental effects
primary-, reference-, or transfer-standard dosimeter and used
during irradiation, and the type of incident radiation. This
for routine absorbed-dose measurement.
guide attempts to highlight the information, including the
3.1.16 simulated product—material with radiation attenua-
methodology and results of the absorbed-dose measurements,
tion and scattering properties similar to those of the product,
necessaryforanexperimenttoberepeatablebyotherresearch-
material or substance to be irradiated.
ers.
3.1.17 traceability—propertyoftheresultofameasurement
NOTE 5—Factors that may influence the response of agricultural prod-
or the value of a standard whereby it can be related to stated
ucts to ionizing radiation include genus, species, variety, vigor, life stage,
references, usually national or international standards, through
initial quality, state of ripeness, temperature, moisture content, pH,
an unbroken chain of comparisons all having stated uncertain-
packaging, shipping, and storage conditions. Although these factors are
ties. not discussed in this guide, they should be considered when planning
experiments (see ASTM Guides F 1355, F 1356, F 1640, F 1736 and
3.1.18 transfer-standard dosimeter—dosimeter, often a
F 1885.
reference-standard dosimeter, suitable for transport between
different locations, used to compare absorbed-dose measure- 4.3 Ideally, an experiment should be designed to irradiate
ments.
the sample as uniformly as possible. In practice, a certain
3.1.19 transit dose—absorbed dose delivered to a product variation in absorbed dose will exist throughout the sample.
(or a dosimeter) while it travels between the non-irradiation
Absorbed-dose mapping is used to determine the magnitude,
position and the irradiation position, or in the case of a location, and reproducibility of the maximum (D ) and
max
movable source while the source moves into and out of its
minimum absorbed dose (D ) for a given set of experimental
min
irradiation position. parameters. Dosimeters used for dose mapping must be ca-
3.1.20 uncertainty (of measurement)—parameter associated
pable of responding to doses and dose gradients likely to occur
with the result of a measurement, that characterizes the within irradiated samples.
dispersion of the values that reasonably could be attributed to
4.4 Theoretical calculations may provide useful information
the measurand or derived quantity (see ISO/ASTM Guide about absorbed-dose distribution in the irradiated sample,
51707).
especially near material interfaces (see ASTM Guide E 2232).
3.1.21 X-radiation—ionizing electromagnetic radiation,
5. Irradiation facilities and modes of operation
which includes both bremsstrahlung and the characteristic
5.1 Types of Facilities—This guide covers the use of
radiation emitted when atomic electrons make transitions to
more tightly bound states. gamma radiation, X-ray (bremsstrahlung), and accelerated
electrons used for studying the effects of ionizing radiation on
3.2 Definitions of Terms Specific to This Standard:
3.2.1 residual—difference between the observed value and food and agricultural products.
the value calculated by the regression model.
NOTE 6—Sections 5 and 6 give a brief overview of types of irradiation
3.2.2 target dose—absorbed dose intended for the volume
facilities and radiation source characteristics. Radiation source character-
of interest within the irradiated sample.
istics, the type of radiation produced, the energy of the photons or
electrons, and the sizes and densities of the samples to be irradiated, will
NOTE 3—Definitions of other terms used in this standard that pertain to
all be factors in determining how the incident radiation is absorbed in the
radiation measurement and dosimetry may be found in ASTM Terminol-
experimental samples. Researchers unfamiliar with radiation source char-
ogy E 170. Definitions in Terminology E 170 are compatible with ICRU
acteristics are strongly recommended to review appropriate reference
60; that document, therefore, may be used as an alternative reference.
materials before beginning experimentation (2-10).
4. Significance and use
5.2 Self-Contained Dry Storage Gamma and X-ray
4.1 This guide is intended to provide direction on dosimetry (bremsstrahlung) Irradiators—Much of the research currently
for experiments in food and agricultural research, and on the being conducted on food and agricultural products is accom-
137 60
reporting of dosimetry results. Research concerning the effec- plished by using gamma radiation from either Cs or Co
© ISO/ASTM International 2009 – All rights reserved
ISO/ASTM51900:2009(E)
self-contained irradiators or X-ray (bremsstrahlung) self- 5.5.1.1 Typically, accelerators produce a narrow beam of
contained irradiators. These devices are self-shielded using electrons that is diffused to cover the width of the conveyor,
lead (or other appropriate high atomic number material), and which is the location at which samples will be irradiated.
usually have a mechanism to move the sample container from Diffusion of the electron beam may be accomplished using a
the load to the irradiation position. magnetic scanner (to sweep the beam back and forth rapidly),
a magnetic defocusing lens, or scattering foils.
NOTE 7—Typically, self-contained dry storage gamma irradiators have
5.5.2 X-ray (Bremsstrahlung) Facility—An X-ray
a limited irradiation volume. This type of irradiator is classified as ANSI
(bremsstrahlung) generator emits short-wavelength electro-
Category I, Self-contained Dry Storage Gamma Irradiators (11).
magnetic radiation, which is analogous to gamma radiation
5.2.1 In self-contained gamma irradiators, a common ap-
from radioactive isotopic sources. Although their effects on
proach is to distribute the source in an annular array, such that
irradiated materials are generally similar, these kind of radia-
theabsorbeddoseisrelativelyuniformaroundthecenterwhere
tion differ in their energy spectra, angular distribution, and
the sample is irradiated.
dose rates.
5.2.2 For gamma and X-ray units, another method is to
5.5.2.1 Electrons are accelerated towards a metal target or
rotatethesamplecontaineronanirradiatorturntablewithinthe
“converter” of high atomic number (typically tungsten or
radiation field to achieve a more uniform dose within the
tantalum). The collision of the electrons with the target
sample.
generates X-ray (bremsstrahlung) with a broad continuous
5.3 Self-Contained Wet Storage Gamma Irradiators—
energy spectrum).
Irradiation of samples may also be carried out in a wet-storage
5.5.3 Sample Transport—Samples are typically carried on a
gamma irradiator. In these facilities, the source is contained in
conveyor through the radiation field. Because of the narrow
a storage pool (usually containing water), which is shielded at
angular distribution of the radiation, use of conveyors to
all times. The samples to be irradiated are enclosed in a
transport samples through the irradiation field, in contrast to
water-tight chamber and lowered into the water next to the
use of static irradiation systems or shuffle-dwell systems will
radiation source.
enhance the dose uniformity.
5.5.4 Refer to ISO/ASTM Practices 51431, 51608, and
NOTE 8—This type of irradiator is classified as ANSI Category III,
51649 for more detailed information or electron and X-ray
Self-Contained Wet Source Storage Gamma Irradiators (12).
(bremsstrahlung) facilities and modes of operation.
5.4 Large-Scale Gamma Irradiation Facilities—Gamma ir-
radiation of research samples is also carried out in large-scale
6. Radiation source characteristics
irradiators, either pool-type or dry-storage. In these facilities,
6.1 Gamma Irradiators:
the source typically consists of a series of rods that
6.1.1 The radiation source used in the gamma facilities
contain Co and can be raised or lowered into a large
considered in this guide consists of sealed elements of Co
irradiationroom.Whenretractedfromtheirradiationroom,the
or Cs that are typically linear rods arranged in one or more
source is shielded by water (pool-type), or an appropriate
planar or cylindrical arrays.
material of high atomic number (dry-storage), or both.
6.1.2 Cobalt-60 emits photons with discrete energies of
NOTE 9—These types of irradiators are classified asANSI Category IV, approximately 1.17 and 1.33 MeV in nearly equal proportions.
Wet Source Storage Gamma Irradiators orANSI Category II, Dry Source
Cesium-137emitsphotonswithenergyofapproximately0.662
Storage Gamma Irradiators (13).
MeV (14).
60 137
6.1.3 The radioactive decay half-lives for Co and Cs
5.4.1 Continuous Operation—A common method of use is
are regularly reviewed and updated. A recent publication gave
for the irradiation of sample containers to be carried on a
values of 1925.20 6 0.25 days for Co and 11018.3 6 9.5
conveyor in one or more revolutions around a central source in
days for Cs (15).
order to obtain a more uniform absorbed dose. The source is
6.1.4 For gamma-ray sources, the only variation in the
retracted from the irradiation room when the irradiator is not in
source output is the known reduction in the activity caused by
use.
radioactive decay. This reduction in the source activity, which
5.4.2 Batch Operation—An alternative approach is to place
necessitates an increase in the irradiation time to deliver the
the sample containers in the irradiation room while the source
same dose, may be calculated or obtained from tables provided
is shielded, and move the source into the irradiation position
by the irradiator manufacturer (refer to ISO/ASTM Practice
for the time required to achieve the desired absorbed dose.
51204).
5.5 Electron and X-ray (Bremsstrahlung) Facilities:
NOTE 10—Errors in the decay calculation may be introduced by the
5.5.1 Electron Facility—Radiation sources for electrons
existence of radioimpurities in the radiation source (for example, a small
(with energies greater than 300 keV) are either direct action
134 137
amount of Cs present as an impurity in Cs).
(potential-drop)orindirect-action(microwave-powered)accel-
erators. The radiation fields depend on the characteristics and 6.2 Electron Accelerator (Electron and X-ray (Bremsstrahl-
the design of the accelerators. Included among these charac- ung) Modes):
6.2.1 For an electron accelerator, the principal beam char-
teristics are the electron beam parameters, that is, the electron
energy spectrum, average electron beam current and beam acteristics are the electron energy spectrum, the beam current
current distribution on the product surface. and where applicable the instantaneous (per pulse) current
© ISO/ASTM International 2009 – All rights reserved
ISO/ASTM51900:2009(E)
together with pulse length and pulse repetition frequency (see routine dosimeters. Examples of reference-standard dosim-
ISO/ASTM Practices 51431, 51649 and 51818). eters, along with their useful dose ranges, are listed in
6.2.1.1 Direct-action electron accelerators employ direct ISO/ASTM Guide 51261.
current (dc) or pulsed high-voltage generators and typically 7.2.3 Transfer-Standard Dosimeters—Transfer-standarddo-
produce electron energies up to 5 MeV. simeters are specifically selected dosimeters used for transfer-
6.2.1.2 Indirect-action electron accelerators use microwave ring absorbed-dose information from an accredited or national
or very high frequency (VHF) alternating current (ac) to standards laboratory to an irradiation facility in order to
produce electron energies typically from 3 MeV to 15 MeV. establish traceability for that facility. These dosimeters should
6.2.2 For an X-ray (bremsstrahlung) facility, besides beam
be carefully used under conditions that are specified by the
characteristics noted in 6.2.1, X-ray target design is a critical issuing laboratory. Transfer-standard dosimeters may be se-
parameter. Although the X-ray (bremsstrahlung) is similar to
lected from either reference-standard dosimeters or routine
60 137
gamma radiation from the radionuclides Co or Cs and thus dosimeters taking into consideration the criteria listed in
their effects on materials are generally similar, these kinds of ISO/ASTM Guide 51261.
radiation differ in their energy spectra, angular distributions, 7.2.4 Routine Dosimeters—Routine dosimeters may be
and absorbed-dose rates. The continuous energy spectrum of
used for process control and dose mapping. Proper dosimetric
the X-ray (bremsstrahlung) extends up to the maximum energy techniques, including calibration, should be employed to en-
of the electrons incident on the X-ray target (see ISO/ASTM sure that measurements are reliable and accurate. Examples of
Practice 51608). In some cases, spectrum filtration is used to routine dosimeters, along with their useful dose ranges, are
reduce the low energy component of the radiation, so as to listed in Table 1 and ISO/ASTM Guide 51261.
improve dose uniformity. 7.3 Select a routine dosimetry system suitable for the
research taking into consideration those parameters associated
NOTE 11—In some countries, regulations may limit the maximum
with the radiation source and experimental set-up that may
energy for electrons or X-ray (bremsstrahlung) used to irradiate food for
influence dosimeter response (for example, absorbed-dose
human consumption.
range, radiation source, dose rate, energy, and environmental
7. Dosimetry systems
conditions, such as temperature, humidity and light) and the
uncertainty associated with it. More detailed selection criteria
7.1 Dosimetrysystemsareusedtodetermineabsorbeddose,
are listed in ISO/ASTM Guide 51261. For electron accelerator
usually in terms of absorbed dose to water. They consist of
dosimeters, measurement instruments and their associated applications, it is also essential to consider the influences of
absorbed-dose rate (average and peak dose rate for pulsed
reference standards, and procedures for the system’s use.
7.2 Dosimeters may be divided into four basic classes accelerators), pulse rate and pulse width (if applicable) when
selecting a dosimeter.
according to their relative quality and areas of application:
primary-standard, reference-standard, transfer-standard, and 7.3.1 For use, handling, storage, special precautions, cali-
bration, etc., for a specific routine dosimetry system, anASTM
routine dosimeters. ISO/ASTM Guide 51261 provides infor-
mation about the selection of dosimetry systems for different or ISO/ASTM standard and manufacturers recommendations
shall be used.
applications. Most research will be conducted using routine
dosimeters and transfer-standard dosimeters. 7.4 Prior to use, a dosimetry system shall be calibrated. The
calibration curve supplied by the dosimeter supplier should be
7.2.1 Primary-Standard Dosimeters—Primary-standard do-
simeters are established and maintained by national standards considered as general information and should not be used
without further verification of its applicability. The calibration
laboratories for calibration of radiation environments (fields)
and other classes of dosimeters. The two most commonly used of the existing lot of dosimeters should be checked at regular
intervals as appropriate. This check could take the form of a
primary-standard dosimeters are ionization chambers and calo-
rimeters. calibration verification exercise.
7.2.2 Reference-Standard Dosimeters—Reference-standard 7.4.1 Calibration verification can be performed by irradiat-
dosimeters are used to calibrate radiation environments and ingsetsofdosimetersateachofthreedosepoints(spanningthe
TABLE 1 Examples of routine dosimeters (see ISO/ASTM Guide 51261)
Dosimeter Measurement Instrument Useful Absorbed Dose Range (Gy) References
Alanine EPR spectrometer 1 to 10 ISO/ASTM 51607
2 5
Polymethylmethacrylate UV/Visible spectrophotometer 10 to 10 ISO/ASTM 51276
3 5
Cellulose triacetate Spectrophotometer 5310 to 3310 ISO/ASTM 51650
Thermoluminescence (TLD) Thermoluminescence reader 1 to 10 ISO/ASTM 51956
Lithium Fluoride Film Fluorimeter 50 to 3310 ASTM E 2304
Radiochromic dye films, solutions, Visible spectrophotometer 1 to 10 ISO/ASTM 51275
optical wave guide ISO/ASTM 51540
ISO/ASTM 51310
2 4
Ceric cerous sulfate solution Potentiometer or UV spectrophotometer 5310 to 5310 ISO/ASTM 51205
Fricke solution UV spectrophotometer 20 to 4310 ASTM E 1026
1 6
Ethanol chlorobenzene solution Spectrophotometer, color titration, 10 to 2310 ISO/ASTM 51538
high frequency conductivity
MOSFET Electronic Reader 1 to 2310 (16)
© ISO/ASTM International 2009 – All rights reserved
ISO/ASTM51900:2009(E)
calibration range) using the same dosimeter holder as used for 7.4.3.3 Irradiation at an Accredited Dosimetry Calibration
calibration irradiation and at the reference location where the Laboratory—This method involves irradiation of the routine
dose rate is known. These dose values are then compared with dosimeters in the reference radiation field of a calibration
the values calculated by using the response values of the laboratory. Although exactly matching the actual research
irradiated dosimeters and the current response function.Agree- conditions in a calibration laboratory is not generally possible,
ment at the three points within the uncertainty of the system an attempt should be made to irradiate dosimeters using dose
confirms the validity of the response function. rate and temperature conditions as closely as possible to those
7.4.2 Measurement Instruments—The measurement instru- that will be experienced during research experiments.
ment is an integral part of the dosimetry system, thus, the 7.4.3.4 Irradiation in a Self-contained Irradiator—This
calibration of a dosimetry system should be regarded as being method involves irradiating routine dosimeters at a static
specific to a particular instrument. Calibration that is estab- reference location in the radiation field where the dose rate is
lished with one instrument is not valid for another one. The accurately known (this location should be preferably where the
effect of any changes, or repairs, to the measurement instru- research samples would be irradiated). The dose rate shall be
ment should be assessed. A major repair may require either a knownatthisreferencelocationusingtransfer-standarddosim-
calibration check (for example, a calibration verification exer- eters from an accredited dosimetry calibration laboratory. This
cise), or a complete re-calibration of the dosimetry system. dose rate value is valid for an irradiation geometry and for the
Before use, the instrument shall be calibrated such that the specific dosimeter holder and its location in the radiation field.
measurements have traceability to a national or international If the routine and transfer-standard dosimeters are of signifi-
standard. Guidance on spectrophotometer calibration, a com- cantly different shape and size, the holder design needs special
mon measurement instrument for dosimeters, is given in considerations; for example, the attenuation characteristics
ASTM Practice E 925. should be similar for both. Various irradiation times can be
7.4.3 Calibration Procedure—Thecalibrationprocedurefor selected to give the specified dose to the routine dosimeters.
a dosimetry system mainly consists of the irradiation of Refer to ISO/ASTM Guide 52116.
dosimeters to a number of known absorbed doses spanning the
NOTE 13—The certified dose rate should be measured by a national or
required dose range, the reading of the irradiated dosimeters
accredited laboratory.
using a calibrated measurement instrument, and the generation
7.4.3.5 Irradiation at the Production Facility—Some pro-
of a response function (calibration curve). Refer to ISO/ASTM
duction facilities may be trying to expand their portfolio of
Practice 51261 for more details.
irradiation applications, and have irradiation time available for
7.4.3.1 Calibration Irradiation of Dosimeters—Dosimeters
radiation research. In this case, calibration irradiation of
should be irradiated over a dose range broader than that of the
routine dosimeters in a production irradiator using reference or
intended use.The non-linear nature of most response functions
transfer-standard dosimeters provides a calibration curve or
means that extrapolations are not acceptable. For dose ranges
response function valid for an actual production irradiation
oflessthanonedecade,useatleastfourdosepointsdistributed
condition existing during the calibration. This method takes
in an arithmetic progression (for example, 1, 3, 5, and 7 kGy).
combined environmental factors into account to the extent that
For dose ranges of greater than one decade use at least five
the reference or transfer dosimeter response can be corrected
dose points per decade and distribute the dose points in a
fordifferencesinenvironmentalfactorsbetweenthecalibration
geometric progression (for example, 0.1, 0.16, 0.25, 0.4, 0.63,
laboratory and production irradiator. Refer to ISO/ASTM
1.0, 1.6, 2.5, 4.0, 6.3, 10 kGy for two decades). Use a set of
Guide 51261.
dosimeters consisting of 3 to 5 dosimeters at each dose point.
7.4.3.6 Generation of Response Function—From the cali-
7.4.3.2 Environmental Conditions—For many dosimeters,
bration (experimental) data generate a function that will enable
the radiation-induced response is influenced by the environ-
dose to be determined from a measured dosimeter response
mental conditions, such as temperature during and after irra-
(see ISO/ASTM Guides 51261 and 51707). Although this
diation, humidity and dose rate. Because the dosimetry system
could be accomplished using a hand-drawn graph of response
calibration relationship is valid for the conditions present
versus dose, in practice a mathematical fitting procedure
during the calibration procedure, the calibration conditions
(regression analysis) is generally used to obtain an analytical
must be as similar as possible to those present during routine
relationship between the dosimeter response and the dose.
dose measurements in order to limit errors due to these effects.
Strictly speaking, dose should be used as the independent
Thus, calibration irradiations may be performed in one of two
variable(xvariable).However,thismayresultinanexpression
ways, by irradiating the dosimeters at an irradiator that
thatisdifficulttosolvefordose,whichisthequantityrequired.
provides an absorbed dose (or an absorbed-dose rate) having
In practice, letting dose be the dependent variable (y variable)
measurement traceability to nationally or internationally rec-
is more convenient. Provided that the dose range is not greater
ognized standards, or at the irradiator where the research
than one decade, this procedure will not result in an appre-
experiments are being conducted.
ciable error (see ISO/ASTM Guide 51707 and NPL Report
NOTE 12—Although not treated in detail in this guide, quantitative data
CIRM 29).
relating to environmental factors, such as temperature and moisture
NOTE 14—Commercially available software provides solutions for the
content of the irradiated food or agricultural products, should be reported
inversion of polynomials, making the application of non-linear regression
becausetheymayaffecttheresponseofdosimeters(seeISO/ASTMGuide
straightforward to manage. Mathematical functions that resemble the
51261).
© ISO/ASTM International 2009 – All rights reserved
ISO/ASTM51900:2009(E)
expectedbehaviorofthedosimetercanalsobeinvertedanalytically.Refer
can be accomplished by using reference standards such as
to Annex A1.
calibrated optical density filters, wavelength standards, or
NOTE 15—In general, there is no recommended type of mathematical
calibrated thickness gauges supplied by the manufacturer or
expression to represent the non-linear relationship between response and
national or accredited standards laboratories.
dose. In many cases, a polynomial function (for example, response = a +
2 8.2.2.2 Periodically, the performance of the equipment
b 3 dose + c 3 dose + .) will adequately describe the relationship.
should be checked and the equipment recalibrated.
Individual dosimeter response values should be used, that is, readings
from replicate dosimeters irradiated to the same dose should not be
averaged. This enables an estimation of the dosimeter-to-dosimeter 9. Experimental methodology and dose mapping
variability and allows outlying results to be identified. In selecting a
9.1 Objective—The purpose of dosimetry is to help estab-
polynomial function, the main consideration is to use the lowest order of
lish the most suitable irradiation geometry for samples and
polynomial that will adequately represent the data. One of the best
products including selection of all key process parameters, and
methodsofdeterminingtherequiredorderisbyexaminingthedistribution
to provide evidence of reproducibility of dose and dose
of residuals with dose for increasing orders of the polynomial (see CIRM
29). The polynomial order of choice is the lowest order that does not
distribution.
exhibit a systematic trend.
9.1.1 The absorbed dose received by any portion of a
NOTE 16—The residual (or error) represents unexplained (or residual)
sample or product depends on the irradiatior and experimental
variation after fitting a regression model. It is the difference (or left over)
parameters, such as the source type and geometry, irradiation
between the observed value of the variable and the value predicted by the
geometry, product composition and density, and product dis-
regression model. The ’relative residual’ is the residual divided by either
tribution.
the observed or the predicted value. Fitting software use residuals, not
9.2 Dose Mapping—Thisobjectiveisaccomplishedthrough
relative residuals. The sum of residuals (including squared sum of
residuals) is the q
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