ISO/ASTM 51431:2005

INTERNATIONAL ISO/ASTM
STANDARD 51431
Second edition
2005-05-15
Practice for dosimetry in electron beam
and X-ray (bremsstrahlung) irradiation
facilities for food processing
Pratique de la dosimétrie dans les installations de traitement des
produits alimentaires irradiés par faisceau d’électrons et de
rayons X (bremsstrahlung)
Reference number
© ISO/ASTM International 2005
PDF disclaimer
ThisPDFfilemaycontainembeddedtypefaces.InaccordancewithAdobe’slicensingpolicy,thisfilemaybeprintedorviewedbutshall
not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe’s licensing policy. Neither the ISO Central
Secretariat nor ASTM International accepts any liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies
and ASTM members. In the unlikely event that a problem relating to it is found, please inform the ISO Central Secretariat or ASTM
International at the addresses given below.
© ISO/ASTM International 2005
Allrightsreserved.Unlessotherwisespecified,nopartofthispublicationmaybereproducedorutilizedinanyformorbyanymeans,electronicormechanical,
including photocopying and microfilm, without permission in writing from either ISO at the address below or ISO’s member body in the country of the
requester. In the United States, such requests should be sent to ASTM International.
ISO copyright office ASTM International, 100 Barr Harbor Drive, PO Box C700,
Case postale 56 • CH-1211 Geneva 20 West Conshohocken, PA 19428-2959, USA
Tel. +41 22 749 01 11 Tel. +610 832 9634
Fax +41 22 749 09 47 Fax +610 832 9635
E-mail copyright@iso.org E-mail khooper@astm.org
Web www.iso.org Web www.astm.org
Published in the United States
ii © ISO/ASTM International 2005 – All rights reserved

Contents Page
1 Scope . 1
2 Referenced documents . 1
3 Terminology . 2
4 Significance and use . 5
5 Radiation source characteristics . 5
6 Irradiation facilities . 5
7 Dosimetry systems . 6
8 Process parameters . 7
9 Installation qualification . 7
10 Operational qualification . 7
11 Performance qualification . 9
12 Routine product processing . 11
13 Measurement uncertainty . 12
14 Certification . 12
15 Keywords . 13
Bibliography . 13
Figure 1 Diagram showing beam length and width for a scanned beam using a conveyor
system . 2
Figure 2 Example of measured electron-beam dose distribution along the beam width, where the
beam width is noted at some defined fractional level f of the average maximum dose D . 3
max
Figure 3 Typical (idealised) depth-dose distribution for an electron beam in a homogeneous
material composed of elements of low atomic number . 3
Figure 4 Regions of D and D (indicated by hatching) for a rectangular process load after
max min
one-sided irradiation using an electron beam . 10
Figure 5 Regions of D and D (indicated by hatching) for a rectangular process load after
max min
two-sided irradiation using an electron beam . 11
© ISO/ASTM International 2005 – All rights reserved iii

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,
Dosimetry for Radiation Processing, 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 51431 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/ASTM51431:2002),whichhasbeentechnically
revised.
iv © ISO/ASTM International 2005 – All rights reserved

Standard Practice for
Dosimetry in Electron Beam and X-Ray (Bremsstrahlung)
Irradiation Facilities for Food Processing
This standard is issued under the fixed designation ISO/ASTM 51431; 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 1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This practice outlines the installation qualification pro-
responsibility of the user of this standard to establish appro-
gram for an irradiator and the dosimetric procedures to be
priate safety and health practices and determine the applica-
followed during operational qualification, performance quali-
bility of regulatory limitations prior to use.
fication and routine processing in facilities that process food
with high-energy electrons and X-rays (bremsstrahlung) to
2. Referenced documents
ensure that product has been treated within a predetermined
2.1 ASTM Standards:
rangeofabsorbeddose.Otherproceduresrelatedtooperational
E 170 Terminology Relating to Radiation Measurements
qualification, performance qualification and routine processing
and Dosimetry
that may influence absorbed dose in the product are also
E 666 PracticeforCalculatingAbsorbedDosefromGamma
discussed.Informationabouteffectiveorregulatorydoselimits
or X Radiation
for food products, and appropriate energy limits for electron
E 1026 Practice for Using the Fricke Reference Standard
beams used directly or to generate X-rays is not within the
Dosimetry System
scope of this practice (see ASTM Guides F 1355, F 1356,
E 2232 Guide for Selection and Use of Mathematical Mod-
F 1736, and F 1885).
els for CalculatingAbsorbed Dose in Radiation Processing
NOTE 1—Dosimetry is only one component of a total quality assurance
Applications
program for adherence to good manufacturing practices used in the
E 2303 Guide for Absorbed-dose Mapping in Radiation
production of safe and wholesome food.
Processing Facilities
NOTE 2—ISO/ASTM Practice 51204 describes dosimetric procedures
E 2304 Practice for Use of a LiF Photo-Fluorescent Film
for gamma irradiation facilities for food processing.
Dosimetry System
1.2 For guidance in the selection and calibration of dosim-
F 1355 Guide for Irradiation of Fresh Fruits as a Phytosani-
etry systems, and interpretation of measured absorbed dose in
tary Treatment
the product, see ISO/ASTM Guide 51261 and ASTM Practice
F 1356 Guide for Irradiation of Fresh and Frozen Red Meat
E 666. For the use of specific dosimetry systems, see ASTM
and Poultry to Control Pathogens and Other Microorgan-
Practices E 1026 and E 2304, and ISO/ASTM Practices 51205,
isms
51275, 51276, 51310, 51401, 51538, 51540, 51607, 51650 and
F 1736 Guide for Irradiation of Finfish and Shellfish to
51956. For discussion of radiation dosimetry for electrons and
Control Pathogens and Spoilage Microorganisms
X-rays also see ICRU Reports 35 and 14. For discussion of
F 1885 Guide for Irradiation of Dried Spices, Herbs, and
radiation dosimetry for pulsed radiation, see ICRU Report 34.
Vegetable Seasonings to Control Pathogens and Other
1.3 While gamma radiation from radioactive nuclides has
Microorganisms
discrete energies, X-rays (bremsstrahlung) from machine
2.2 ISO/ASTM Standards:
sources cover a wide range of energies, from low values (about
51204 Practice for Dosimetry in Gamma Irradiation Facili-
35 keV) to the energy of the incident electron beam. For
ties for Food Processing
information concerning electron beam irradiation technology
51205 PracticeforUseofaCeric-CerousSulfateDosimetry
anddosimetry,seeISO/ASTMPractice51649.Forinformation
System
concerning X-ray irradiation technology and dosimetry, see
51261 Guide for Selection and Calibration of Dosimetry
ISO/ASTM Practice 51608.
Systems for Radiation Processing
51275 Practice for Use of a Radiochromic Film Dosimetry
System
This practice is under the jurisdiction of ASTM Committee E10 on Nuclear 51276 Practice for Use of a Polymethylmethacrylate Do-
Technology and Applications and is the direct responsibility of Subcommittee
simetry System
E10.01 on Dosimetry for Radiation Processing, and is also under the jurisdiction of
ISO/TC 85/WG 3.
Current edition approved by ASTM Oct. 1, 2004. Published May 15, 2005.
e1
Originally published as E 1431–91. Last previous ASTM edition E 1431–98 .
ASTM E 1431–91 was adopted by ISO in 1998 with the intermediate designation For referenced ASTM and ISO/ASTM standards, visit the ASTM website,
ISO 15562:1998(E). The present International Standard ISO/ASTM 51431:2005(E) www.astm.org, or contact ASTM Customer Service at service@astm.org. For
is a major revision of the last previous edition ISO/ASTM 51431:2002(E), which Annual Book of ASTM Standards volume information, refer to the standard’s
replaced ISO 15562. Document Summary page on the ASTM website.
© ISO/ASTM International 2005 – All rights reserved
51310 Practice for Use of a Radiochromic Optical selectedasthespecifiedmaterialfordefiningabsorbeddose.In
Waveguide Dosimetry System practice, dosimeters are most often calibrated in terms of dose
51400 Practice for Characterization and Performance of a to water. That is, the dosimeter measures the dose that water
High-Dose Radiation Dosimetry Calibration Laboratory would absorb if it were placed at the location of the dosimeter.
51401 Practice for Use of a Dichromate Dosimetry System Water is a convenient medium to use because it is universally
51538 Practice for Use of the Ethanol-Chlorobenzene Do- available and understood, and its radiation absorption and
simetry System scattering properties are close to those of tissue. The require-
51539 Guide for Use of Radiation-Sensitive Indicators ment of tissue-equivalency historically originates from
51540 Practice for Use of a Radiochromic Liquid Dosim- radiation-therapy applications. However, to determine the tem-
etry System perature increase in an irradiated material, it is necessary to
51607 Practice for Use of the Alanine-EPR Dosimetry know the absorbed dose in that material. This may be deter-
System mined by applying conversion factors in accordance with
51608 Practice for Dosimetry in an X-ray (Bremsstrahlung) ISO/ASTM Guide 51261.
Facility for Radiation Processing 3.1.2 absorbed-dose mapping (for a process load)—
51631 Practice for Use of Calorimetric Dosimetry Systems measurement of absorbed dose within a process load using
for Electron Beam Dose Measurements and Dosimeter dosimetersplacedatspecifiedlocationstoproduceaone-,two-
Calibrations or three-dimensional distribution of absorbed dose, thus ren-
51649 Practice for Dosimetry in an Electron Beam Facility dering a map of absorbed-dose values.
for Radiation Processing at Energies Between 300 keV 3.1.3 average beam current—time-averaged electron beam
and 25 MeV current.
51650 Practice for Use of a Cellulose Triacetate Dosimetry 3.1.3.1 Discussion—For a pulsed machine, the averaging
System shall be done over a large number of pulses.
51707 Guide for Estimating Uncertainties in Dosimetry for 3.1.4 beam length—dimension of the irradiation zone along
Radiation Processing thedirectionofproductmovement,ataspecifieddistancefrom
51956 Practice for Thermoluminescence Dosimetry (TLD) the accelerator window (see Fig. 1).
Systems for Radiation Processing 3.1.4.1 Discussion—(1) This term usually applies to elec-
2.3 International Commission on Radiation Units and tron irradiation. (2) Beam length is therefore perpendicular to
beam width and to the electron beam axis. (3) In case of a
Measurements (ICRU) Reports:
ICRUReport14 RadiationDosimetry:XRaysandGamma low-energy, single-gap electron accelerator, beam length is
RayswithMaximumPhotonEnergiesBetween0.6and50 equal to the active length of the cathode assembly in vacuum.
MeV (4) In case of product that is stationary during irradiation,
ICRU Report 34 The Dosimetry of Pulsed Radiation ‘beam length’ and ‘beam width’ may be interchangeable.
ICRU Report 35 Radiation Dosimetry: Electron Beams 3.1.5 beam width—dimension of the irradiation zone per-
with Energies Between 1 and 50 MeV pendicular to the direction of product movement, at a specified
ICRU Report 37 Stopping Powers for Electrons and distance from the accelerator window (see Fig. 1).
Positrons 3.1.5.1 Discussion—(1) This term usually applies to elec-
ICRU Report 60 Fundamental Quantities and Units for tron irradiation. (2) Beam width is therefore perpendicular to
Ionizing Radiation
3. Terminology
3.1 Definitions:
3.1.1 absorbed dose, D—quantity of ionizing radiation
energy imparted per unit mass of a specified material. The SI
unit of absorbed dose is the gray (Gy), where 1 gray is
equivalent to the absorption of 1 joule per kilogram of the
specified material (1 Gy = 1 J/kg). The mathematical relation-
ship is the quotient of de¯ by dm, where de¯ is the mean
incremental energy imparted by ionizing radiation to matter of
incremental mass dm (see ICRU 60).
D 5 de¯/dm (1)
3.1.1.1 Discussion—The discontinued unit for absorbed
dose is the rad (1 rad = 100 erg/g = 0.01 Gy).Absorbed dose is
sometimes referred to simply as dose. Water is frequently
FIG. 1 Diagram showing beam length and width for a scanned
Available from the International Commission on Radiation Units and Measure-
ments, 7910 Woodmont Ave., Suite 800, Bethesda, MD 20814, U.S.A. beam using a conveyor system
© ISO/ASTM International 2005 – All rights reserved
beam length and to the electron beam axis. (3) In case of 3.1.8.1 Discussion—Values of r for a wide range of elec-
product that is stationary during irradiation, ‘beam width’ and tron energies and for several materials are tabulated in ICRU
‘beam length’may be interchangeable. (4) Beam width may be Report 37.
quantified as the distance between two points along the dose
3.1.9 depth-dose distribution—variation of absorbed dose
profile, which are at a defined fraction of the maximum dose with depth from the incident surface of a material exposed to
value in the profile (see Fig. 2). (5) Various techniques may be
a given radiation (see Fig. 3 for a typical distribution).
employedtoproduceanelectronbeamwidthadequatetocover
3.1.9.1 Discussion—Depth-dose distributions for several
the processing zone, for example, use of electromagnetic
homogeneous materials produced by electron beams of differ-
scanning of pencil beam (in which case beam width is also
ent energies are shown in ISO/ASTM Practice 51649.
referred to as scan width), defocusing elements, and scattering
3.1.10 dose uniformity ratio (for a process load)—ratio of
foils.
the maximum to the minimum absorbed dose within the
3.1.6 bremsstrahlung—broad-spectrum electromagnetic ra-
process load. The concept is also referred to as the max/min
diation emitted when an energetic charged particle is influ-
dose ratio.
enced by a strong electric or magnetic field, such as that in the
3.1.11 dosimeter set—one or more dosimeters used to
vicinity of an atomic nucleus.
measure absorbed dose at a location and whose average
3.1.6.1 Discussion—In radiation processing, bremsstrahl-
response is used to determine absorbed dose at that location.
ung photons with sufficient energy to cause ionization are
3.1.12 dosimetry system—system used for determining ab-
generated by the deceleration or deflection of energetic elec-
sorbed dose, consisting of dosimeters, measurement instru-
trons in a target material. When an electron passes close to an
ments and their associated reference standards, and procedures
atomic nucleus, the strong coulomb field causes the electron to
for the system’s use.
deviate from its original motion. This interaction results in a
3.1.13 electron beam energy—average kinetic energy of the
loss of kinetic energy by the emission of electromagnetic
accelerated electrons in the beam. Unit: J
radiation.Sincesuchencountersareuncontrolled,theyproduce
3.1.13.1 Discussion—Electron volt (eV) or its multiples is
a continuous photon energy distribution that extends up to the
often used as the unit for electron (beam) energy, where 1 eV
maximum kinetic energy of the incident electron. The -19
= 1.602 3 10 J (approximately).
bremsstrahlung spectrum depends on the electron energy, the
3.1.14 electron beam range—penetration distance of an
composition and thickness of the target, and the angle of
electron beam along its axis in a specific, totally absorbing
emission with respect to the incident electron. Even though
material.
bremsstrahlung has broad energy spectrum, the energy of the
3.1.14.1 Discussion—This quantity may be defined and
incident electron beam is referred to as the nominal
evaluated in several ways. For example, ‘extrapolated electron
bremsstrahlung energy.
beam range, R ’ (see 3.1.16), ‘practical electron beam range,
ex
3.1.7 compensating dummy—See simulated product
(3.1.35).
3.1.8 continuous-slowing-down-approximation range
(CSDA range), r —average path length traveled by a charged
particle as it slows down to rest, calculated under the
continuous-slowing-down approximation (see ICRU Report
35).
NOTE—The peak-to-surface dose ratio depends on the energy of the
incident electron beam (ICRU Report 35). The distribution shown here is
typically for about 10 MeV electrons. For this case, R = R , since X-ray
p ex
background is negligible. For the case where R is not equal to R , see
p ex
ISO/ASTM Practice 51649, Annex A1.
FIG. 2 Example of measured electron-beam dose distribution FIG. 3 Typical (idealised) depth-dose distribution for an electron
along the beam width, where the beam width is noted at some beam in a homogeneous material composed of elements of low
defined fractional level f of the average maximum dose D atomic number
max
© ISO/ASTM International 2005 – All rights reserved
R ’ (see 3.1.23), and ‘continuous-slowing-down- 3.1.26 production run (for continuous-flow and shuffle-
p
approximation range, r ’ (see 3.1.8). R and R can be dwell irradiations)—series of process loads consisting of
0 p ex
determined from measured depth-dose distributions in a refer- materials or products having similar radiation-absorption char-
ence material (see Fig. 3). Electron range is usually expressed acteristics, that are irradiated sequentially to a specified range
-2
in terms of mass per unit area (kg·m ), but sometimes in terms of absorbed dose.
of thickness (m) of a specific material.
3.1.27 pulse rate—pulse repetition frequency in hertz (Hz).
3.1.15 electron energy spectrum—particle fluence distribu-
3.1.27.1 Discussion—(1) This is relevant to a pulsed accel-
tion of electrons as a function of energy. erator. (2) It is also referred to as pulses per second or
repetition (rep) rate.
3.1.16 extrapolated electron beam range, R —depth from
ex
the incident surface of a reference material where the electron 3.1.28 pulse width—timeintervalbetweentwopointsonthe
beam enters to the point where the tangent at the steepest point leading and trailing edges of the pulse beam current waveform
(the inflection point) on the almost straight descending portion where the current is 50 % of its peak value.
of the depth-dose distribution curve meets the depth axis. 3.1.28.1 Discussion—This is relevant to a pulsed accelera-
3.1.16.1 Discussion—Under certain conditions, R = R , tor.
ex p
which is shown in Fig. 3. These conditions generally apply to
3.1.29 reference material—material with one or more prop-
foodstuff irradiated at electron energy equal to or less than 10 erties, which are sufficiently well established to be used for
MeV. Also see 3.1.23.
calibration of an apparatus, the assessment of a measurement
method, or for assigning values to materials.
3.1.17 half-entrance depth, (R )—depth in homogeneous
50e
material at which the absorbed dose has decreased to 50 % of
3.1.30 reference plane—selected plane in the radiation zone
the absorbed dose at the entrance surface of the material (see
that is perpendicular to the electron beam axis.
Fig. 3).
3.1.31 reference-standard dosimeter—dosimeter of high
3.1.18 half-value depth (R )—depth in homogeneous ma-
metrological quality used as a standard to provide measure-
terial at which the absorbed dose has decreased 50 % of its ments traceable to measurements made using primary-standard
maximum value (see Fig. 3). dosimeters (see ISO/ASTM Guide 51261).
3.1.19 installation qualification (IQ)—obtaining and docu-
3.1.32 routine dosimeter—dosimeter calibrated against a
menting evidence that the irradiator, with all its associated primary-, reference-, or transfer-standard dosimeter and used
equipment and instrumentation, has been provided and in- for routine absorbed-dose measurements (see ISO/ASTM
stalled in accordance with specification. Guide 51261).
3.1.20 operational qualification (OQ)—obtaininganddocu- 3.1.33 scanned beam—electronbeamthatissweptbackand
menting evidence that installed equipment and instrumentation
forth with a varying magnetic field.
operate within predetermined limits when used in accordance
3.1.33.1 Discussion—This is most commonly done along
with operational procedures.
one dimension (beam width); although two-dimensional scan-
3.1.21 optimum thickness (R )—depth in homogeneous
ning (beam width and length) may be used with high-current
opt
material at which the absorbed dose equals the absorbed dose electron beams to avoid overheating the beam exit window, or
at the surface where the electron beam enters (see Fig. 3). the X-ray target.
3.1.22 performance qualification (PQ)—obtaining and 3.1.34 scan frequency—number of complete scanning
documenting evidence that the equipment and instrumentation, cycles per second expressed in Hz.
as installed and operated in accordance with operational
3.1.35 simulated product—material with radiation attenua-
procedures, consistently perform according to predetermined
tion and scattering properties similar to those of the product,
criteria and thereby yield product that meets specifications.
material, or substance to be irradiated.
3.1.23 practical electron beam range (R )—depth from the 3.1.35.1 Discussion—Simulated product is used during ir-
p
incident surface of a reference material where the electron
radiator characterization as a substitute for the actual product,
beam enters to the point where the tangent at the steepest point material or substance to be irradiated. When used in routine
(the inflection point) on the almost straight descending portion
production runs in order to compensate for the absence of
of the depth-dose distribution curve meets the extrapolated product, simulated product is sometimes referred to as com-
X-raybackground(seeFig.3).SeeISO/ASTM51649formore pensating dummy. When used for absorbed-dose mapping,
details.
simulated product is sometimes referred to as phantom mate-
rial.
3.1.23.1 Discussion—Forenergiesbelowabout10MeV,the
X-ray background created by the incident electrons is insig-
3.1.36 transfer-standard dosimeter—dosimeter, often a
nificant for materials composed of elements with low atomic reference-standard dosimeter, suitable for transport between
numbers (such as foodstuff). For this case, R = R (see 3.1.16). different locations, used to compare absorbed-dose measure-
p ex
3.1.24 primary-standard dosimeter—dosimeter of the high- ments (see ISO/ASTM Guide 51261).
est metrological quality, established and maintained as an 3.1.37 X-radiation—ionizing electromagnetic radiation,
absorbed-dose standard by a national or international standards which includes both bremsstrahlung and the characteristic
organization (see ISO/ASTM Guide 51261). radiation emitted when atomic electrons make transitions to
more tightly bound states. See 3.1.6.
3.1.25 process load—volume of material with a specified
product loading configuration irradiated as a single entity. 3.1.38 X-ray—see X-radiation.
© ISO/ASTM International 2005 – All rights reserved
3.1.38.1 Discussion—In radiation processing applications, products during irradiation, monitoring of critical operating
the principal X-radiation source is bremsstrahlung. The term parameters, and documentation of all relevant activities and
X-radiation may be used to refer to X-ray. functions.
3.1.39 X-ray converter—device for generating X-rays
5. Radiation source characteristics
(bremsstrahlung) from an electron beam, consisting of a target,
5.1 Electron Facilities—Radiation sources for electrons
means for cooling the target, and a supporting structure.
with energies greater than 300 keV considered in this practice
3.1.40 X-ray target—that component of the X-ray converter
are either direct-action (potential-drop) or indirect-action
that is struck by the electron beam.
(microwave-powered or radiofrequency-powered) accelera-
3.1.40.1 Discussion—It is usually made of metal with high
tors. The radiation fields depend on the characteristics and the
atomic number, high melting temperature, and high thermal
design of the accelerators. Beam characteristics include the
conductivity.
electron beam parameters, such as, electron energy spectrum,
3.2 Definitions of other terms used in this standard that
average electron beam current, pulse duration, beam cross
pertain to radiation measurement and dosimetry may be found
section, and beam current distribution on the product surface.
in ASTM Terminology E 170. Definitions in E 170 are com-
For a more complete discussion refer to ISO/ASTM Practice
patible with ICRU 60; therefore, ICRU 60 may be used as an
51649.
alternative reference.
5.2 X-ray Facilities:
4. Significance and use
5.2.1 A high-energy X-ray generator emits short-
wavelength electromagnetic radiation (photons), whose effects
4.1 Food products may be treated with accelerator-
on irradiated materials are generally similar to those of gamma
generated radiation (electrons and X-rays) for numerous pur-
radiation from radioactive nuclides. However, these kinds of
poses, including control of parasites and pathogenic microor-
radiation differ in their energy spectra, angular distribution and
ganisms, insect disinfestation, growth and maturation
dose rates.
inhibition, and shelf-life extension. Food irradiation specifica-
5.2.2 The characteristics of the X-rays depend on the design
tions almost always include a minimum or a maximum limit of
of the X-ray converter and the parameters of the electron beam
absorbeddose,sometimesboth:aminimumlimitmaybesetto
striking the target, that is, electron energy spectrum, average
ensure that the intended beneficial effect is achieved and a
beam current, and beam current distribution on the target.
maximum limit may be set for the purpose of avoiding product
5.2.3 The physical characteristics of an X-ray source and its
or packaging degradation. For a given application, one or both
suitability for radiation processing are further discussed in
of these values may be prescribed by government regulations
ISO/ASTM Practice 51608.
that have been established on the basis of scientific data.
5.3 Codex Alimentarius Commission (1) as well as regula-
Therefore, prior to the irradiation of the food product, it is
tions in some countries currently limit the maximum electron
necessary to determine the capability of an irradiation facility
energy and X-ray energy for the purpose of food irradiation.
to consistently deliver the absorbed dose within any prescribed
limits. Also, it is necessary to monitor and document the
6. Irradiation facilities
absorbeddoseduringeachproductionruntoverifycompliance
6.1 The design of an irradiation facility affects the delivery
with the process specifications at a predetermined level of
of absorbed dose to a product. Therefore, the facility design
confidence.
should be considered when performing the absorbed-dose
NOTE 3—The Codex Alimentarius Commission has developed an
measurements required in Sections 10-12.
international General Standard and a Code of Practice that address the
6.2 Facility Components—Electron and X-ray irradiation
applicationofionizingradiationtothetreatmentoffoodsandthatstrongly
facilities include the electron beam accelerator system; product
emphasize the role of dosimetry for ensuring that irradiation will be
handling system; a radiation shield with personnel safety
properly performed (1).
system; product loading, unloading and storage areas as
4.2 For more detailed discussions of radiation processing of
required by regulations; auxiliary equipment for power, cool-
various foods, see Guides F 1355, F 1356, F 1736, and F 1885
ing, ventilation, etc.; equipment control room; a laboratory for
and Refs (2-15).
dosimetry; and personnel offices. An X-ray facility also in-
4.3 Accelerator-generated radiation can be in the form of
cludes an X-ray converter (see ISO/ASTM Practice 51608).
electrons or X-rays produced by the electrons. Penetration of
6.3 Electron Accelerator—The electron beam accelerator
radiation into the product required to accomplish the intended
system consists of the radiation source, equipment to disperse
effect is one of the factors affecting the decision to use
the beam on product, and associated equipment. These aspects
electrons or X-rays.
are further discussed in ISO/ASTM Practice 51649.
4.4 To ensure that products are irradiated within a specified
6.4 Product Handling System:
dose range, routine process control requires routine product
6.4.1 The absorbed-dose distribution within the food prod-
dosimetry, documented product handling procedures (before,
uct being irradiated may be affected by the configuration of the
during and after the irradiation), consistent orientation of the
product handling system.
6.4.2 X-ray Facilities—The penetrating quality of high-
energy photons permits the treatment of large containers or full
TheboldfacenumbersinparenthesesrefertotheBibliographyattheendofthis
standard.
pallet loads of food products. For optimum photon power
© ISO/ASTM International 2005 – All rights reserved
utilization and dose uniformity, the container size depends on dosimeters, taking into consideration the criteria listed in
the maximum energy and product density. The narrow angular ISO/ASTM Guide 51261.
distribution of the radiation favors the use of continuously 7.2.4 Routine Dosimeters—Routine dosimeters may be
movingconveyorsratherthanshuffle-dwellsystemstoenhance usedforradiationprocessqualitycontrol,absorbed-dosemoni-
dose uniformity. toring, and absorbed-dose mapping. Proper dosimetric tech-
niques, including calibration, shall be employed to ensure that
6.4.3 Electron Facilities—For optimum beam power utili-
measurements are reliable and accurate. Examples of routine
zation and dose uniformity, the process load size depends on
dosimeters, along with their useful absorbed-dose ranges, are
the beam energy and product density. Two different configu-
given in ISO/ASTM Guide 51261.
rations are commonly used.
7.3 Selection of Dosimetry Systems—Select dosimetry sys-
6.4.3.1 Conveyors or Carriers—Process loads containing
temssuitablefortheexpectedradiationprocessingapplications
food products are placed upon carriers or conveyors for
at the facility using the selection criteria listed in ISO/ASTM
passage through the electron beam. The speed of the conveyor
Guide 51261. During the selection process, for each dosimetry
or carriers is controlled so that the required dose is delivered.
system, take into consideration its performance behavior with
Also see Note 13.
respect to relevant influence quantities and the uncertainty
6.4.3.2 Bulk-flow System—For irradiation of liquids or par-
associated with it. For accelerator applications, it is also
ticulate foodstuff like grain, bulk-flow transport through the
essential to consider the influences of absorbed-dose rate
irradiation zone may be used.
(average and peak dose rate for pulsed accelerators), pulse rate
and pulse width (if applicable) on dosimeter performance.
7. Dosimetry systems
Some of the dosimetry systems that are suitable for gamma
7.1 Dosimetry systems are used to measure absorbed dose.
radiation from radioactive nuclides (such as those from Co)
Theyconsistofdosimeters,measurementinstrumentsandtheir
may also be suitable for X-rays (17).
associatedreferencestandards,andproceduresforthesystem’s
NOTE 5—Dosimeters consisting mainly of water or hydrocarbon mate-
use (see ASTM Practices E 1026 and E 2304, ISO/ASTM
rials are generally suitable for both gamma radiation from radioactive
Practices 51205, 51275, 51276, 51310, 51401, 51538, 51540,
nuclides and X-rays. Some exceptions are dosimeters containing substan-
51607, 51650, 51956 and ISO/ASTM Guide 51261).
tial amounts of material with elements of high atomic numbers which are
highly sensitive to the low-energy photons in the X-ray spectrum. Also,
NOTE 4—For a comprehensive discussion of various dosimetry meth-
the X-ray dose rate may be higher than that for an isotopic gamma-ray
ods applicable to the radiation types and energies discussed in this
source used for radiation processing, especially in products passing near
practice, see ICRU Reports 14, 34 and 35, and Ref (16).
the converter. The dose-rate dependence of the dosimeters should be
considered in their calibration procedure (18,19).
7.2 Description of Dosimeter Classes—Dosimeters may be
divided into four basic classes according to their relative
7.4 Calibration of Dosimetry Systems:
quality and areas of application: primary-standard, reference-
7.4.1 Adosimetrysystemshallbecalibratedpriortouseand
standard, transfer-standard, and routine dosimeters. ISO/
at intervals thereafter, in accordance with the user’s docu-
ASTM Guide 51261 provides information about the selection
mented procedure that specifies details of the calibration
of dosimetry systems for different applications. All classes of
process and quality assurance requirements. Calibration re-
dosimeters, except the primary standards, require calibration
quirements are given in ISO/ASTM Guide 51261.
before their use.
7.4.2 Calibration Irradiation—Irradiation is a critical com-
7.2.1 Primary-Standard Dosimeters—Primary-standard do-
ponent of the calibration of the dosimetry system. Acceptable
simeters are established and maintained by national standards
ways of performing the calibration irradiation depend on
laboratories for calibration of radiation environments (fields)
whether the dosimeter is used as a reference-standard, transfer-
and other classes of dosimeters. The two most commonly used
standard or routine dosimeter.
primary-standard dosimeters are ionization chambers and calo-
7.4.2.1 Reference- or Transfer-Standard Dosimeters—
rimeters.
Calibration irradiations shall be performed at a national or
7.2.2 Reference-Standard Dosimeters—Reference-standard
accredited laboratory using criteria specified in ISO/ASTM
dosimeters are used to calibrate radiation environments and
Practice 51400.
routinedosimeters.Reference-standarddosimetersmayalsobe
7.4.2.2 Routine Dosimeters—The calibration irradiation
used as routine dosimeters. Examples of reference-standard
may be performed by irradiating the dosimeters at (a) a
dosimeters, along with their useful absorbed-dose ranges, are
national or accredited laboratory using criteria specified in
given in ISO/ASTM Guide 51261.
ISO/ASTM Practice 51400, (b) an in-house calibration facility
7.2.3 Transfer-Standard Dosimeters—Transfer-standarddo- that provides an absorbed dose (or an absorbed-dose rate)
simeters are specially selected dosimeters used for transferring having measurement traceability to nationally or internation-
absorbed-dose information from an accredited or national ally recognized standards, or (c) a production irradiator under
standards laboratory to an irradiation facility in order to actual production irradiation conditions, together with
establish traceability for that facility. These dosimeters should reference- or transfer-standard dosimeters that have measure-
ment traceability to nationally or internationally recognized
be carefully used under conditions that are specified by the
issuing laboratory. Transfer-standard dosimeters may be se- standards. In case of option (a) or (b), the resulting calibration
lected from either reference-standard dosimeters or routine curve shall be verified for the actual conditions of use.
© ISO/ASTM International 2005 – All rights reserved
7.4.3 Measurement Instrument Calibration and Perfor- 9.2.2 Accelerator specifications and characteristics,
mance Verification—Forthecalibrationoftheinstruments,and 9.2.3 Description of the operating procedure of the irradia-
for the verification of instrument performance between calibra- tor,
tions, see ISO/ASTM Guide 51261, the corresponding ISO/ 9.2.4 Description of the construction and operation of the
ASTM or ASTM standard for the dosimetry system, and/or product handling equipment,
instrument-specific operating manuals. 9.2.5 Description of the materials and construction of any
containers used to hold food products during irradiation,
8. Process parameters
9.2.6 Description of the process control system, and
9.2.7 Description of any modifications made during and
8.1 Parameters characterizing the components of the irra-
after the irradiator installation.
diation facility, the process load and the irradiation conditions
9.3 Testing, Operation and Calibration Procedures—
are referred to as process parameters. The establishment and
Establish and implement standard operating procedures for the
control of these parameters will determine the absorbed dose
testing, operation and calibration (if necessary) of the installed
received by a product.
irradiator and its associated processing equipment and mea-
8.2 For irradiation facilities with accelerator-generated ra-
surement instruments.
diation (electrons and X-rays) process parameters include:
9.3.1 Testing Procedures—These procedures describe the
8.2.1 Beam characteristics (for example, electron beam
testing methods used to ensure that the installed irradiator and
energy, beam current, pulse frequency, pulse duration, beam
its associated processing equipment and measurement instru-
cross section, X-ray converter design),
ments operate according to specification.
8.2.2 Beam dispersion (for example, scan width, scan fre-
9.3.2 Operation Procedures—These procedures describe
quency, collimator aperture),
how to operate the irradiator and its associated processing
8.2.3 Product handling characteristics (for example, con-
equipment and measurement instruments during routine opera-
veyor speed),
tion.
8.2.4 Product loading characteristics (for example, size of
9.3.3 Calibration Procedures—These procedures describe
the process load, bulk density, orientation of product), and
periodic calibration and verification methods that ensure that
8.2.5 Irradiation geometry (for example, 1- or 2-sided irra-
the installed processing equipment and measurement instru-
diation, multiple passes, reflectors).
ments continue to operate within specifications. The frequency
8.3 The first three sets of parameters (8.2.1, 8.2.2 and 8.2.3)
of calibration for some equipment and instruments might be
are used to characterize the irradiation facility without refer-
specified by a regulatory authority. Calibration of some equip-
ence to the product or the process. These parameters are
ment and instruments might be required to be traceable to a
referred to as operating parameters.
national or other accredited standards laboratory.
NOTE 6—Procedures during operational qualification (OQ) deal with
9.4 Testing of Processing Equipment and Measurement
operating parameters. The objective of performance qualification (PQ) is
Instruments—Verify that the installed processing equipment
to establish the values of all process parameters (including operating
and measurement instruments operate within their design
parameter) for the radiation process under consideration. During routine
product processing, operating parameters are continuously controlled and specifications by following the testing procedures noted in
monitored for process control.
9.3.1. If necessary, ensure that the equipment and instruments
have been calibrated according to the calibration procedures
9. Installation qualification
noted in 9.3.3.
9.1 Objective—The purpose of an installation qualification
9.4.1 Test all processing equipment to verify satisfactory
program is to demonstrate that the irradiator and its associated
operation of the irradiator within the design specifications.
processing equipment and measurement instruments have been
Document all testing results.
delivered and installed in accordance with their specifications.
9.4.2 Test the performance of the measurement instruments
Installationqualificationincludesdocumentationoftheirradia-
to ensure that they are functioning according to performance
tor and the
...