ISO/ASTM 51431:2005
(Main)Practice for dosimetry in electron beam and X-ray (bremsstrahlung) irradiation facilities for food processing
Practice for dosimetry in electron beam and X-ray (bremsstrahlung) irradiation facilities for food processing
ISO/ASTM 51431:2005 outlines the installation qualification program for an irradiator and the dosimetric procedures to be followed during operational qualification, performance qualification and routine processing in facilities that process food with high-energy electrons and X-rays (bremsstrahlung) to ensure that the product has been treated within a predetermined range of absorbed dose. Other procedures related to operational qualification, performance qualification and routine processing that may influence absorbed dose in the product are also discussed. Information about effective or regulatory dose limits for food products, and appropriate energy limits for electron beams used directly or to generate X-rays is not within the scope of this practice (see ASTM Guides F 1355, F 1356, F 1736, and F 1885).
Pratique de la dosimétrie dans les installations de traitement des produits alimentaires irradiés par faisceau d'électrons et rayons X (Bremsstrahlung)
General Information
Relations
Standards Content (Sample)
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 51431:2005(E)
© ISO/ASTM International 2005
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ISO/ASTM 51431:2005(E)
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ISO/ASTM 51431:2005(E)
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
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ISO/ASTM 51431:2005(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,
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.
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ISO/ASTM 51431:2005(E)
Standard Practice for
Dosimetry in Electron Beam and X-Ray (Bremsstrahlung)
1
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
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
2.2 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
1
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 .
2
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
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ISO/ASTM 51431:2005(E)
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
3
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
3
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
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ISO/ASTM 51431:2005(E)
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-
0
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
0
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
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ISO/ASTM 51431:2005(E)
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-
50
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.
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ISO/ASTM 51431:2005(E)
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,
...
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