1、ISO/ASTM 51431:2005(E)Standard Practice forDosimetry in Electron Beam and X-Ray (Bremsstrahlung)Irradiation Facilities for Food Processing1This standard is issued under the fixed designation ISO/ASTM 51431; the number immediately following the designation indicates theyear of original adoption or, i
2、n the case of revision, the year of last revision.1. Scope1.1 This practice outlines the installation qualification pro-gram for an irradiator and the dosimetric procedures to befollowed during operational qualification, performance quali-fication and routine processing in facilities that process fo
3、odwith high-energy electrons and X-rays (bremsstrahlung) toensure that product has been treated within a predeterminedrange of absorbed dose. Other procedures related to operationalqualification, performance qualification and routine processingthat may influence absorbed dose in the product are also
4、discussed. Information about effective or regulatory dose limitsfor food products, and appropriate energy limits for electronbeams used directly or to generate X-rays is not within thescope of this practice (see ASTM Guides F1355, F1356,F1736, and F1885).NOTE 1Dosimetry is only one component of a to
5、tal quality assuranceprogram for adherence to good manufacturing practices used in theproduction of safe and wholesome food.NOTE 2ISO/ASTM Practice 51204 describes dosimetric proceduresfor gamma irradiation facilities for food processing.1.2 For guidance in the selection and calibration of dosim-etr
6、y systems, and interpretation of measured absorbed dose inthe product, see ISO/ASTM Guide 51261 and ASTM PracticeE666. For the use of specific dosimetry systems, see ASTMPractices E1026 and E2304, and ISO/ASTM Practices 51205,51275, 51276, 51310, 51401, 51538, 51540, 51607, 51650 and51956 For discus
7、sion of radiation dosimetry for electrons andX-rays also see ICRU Reports 35 and 14. For discussion ofradiation dosimetry for pulsed radiation, see ICRU Report 34.1.3 While gamma radiation from radioactive nuclides hasdiscrete energies, X-rays (bremsstrahlung) from machinesources cover a wide range
8、of energies, from low values (about35 keV) to the energy of the incident electron beam. Forinformation concerning electron beam irradiation technologyand dosimetry, see ISO/ASTM Practice 51649. For informationconcerning X-ray irradiation technology and dosimetry, seeISO/ASTM Practice 51608.1.4 This
9、standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced documents2
10、.1 ASTM Standards:2E170 Terminology Relating to Radiation Measurements andDosimetryE666 Practice for Calculating Absorbed Dose From Gammaor X RadiationE1026 Practice for Using the Fricke Dosimetry SystemE2232 Guide for Selection and Use of Mathematical Meth-ods for Calculating Absorbed Dose in Radia
11、tion Process-ing ApplicationsE2303 Guide for Absorbed-Dose Mapping in RadiationProcessing FacilitiesE2304 Practice for Use of a LiF Photo-Fluorescent FilmDosimetry SystemF1355 Guide for Irradiation of FreshAgricultural Produce asa Phytosanitary TreatmentF1356 Guide for Irradiation of Fresh, Frozen o
12、r ProcessedMeat and Poultry to Control Pathogens and Other Micro-organismsF1736 Guide for Irradiation of Finfish and Aquatic Inverte-brates Used as Food to Control Pathogens and SpoilageMicroorganismsF1885 Guide for Irradiation of Dried Spices, Herbs, andVegetable Seasonings to Control Pathogens and
13、 OtherMicroorganisms2.2 ISO/ASTM Standards:251204 Practice for Dosimetry in Gamma Irradiation Facili-ties for Food Processing51205 Practice for Use of a Ceric-Cerous Sulfate DosimetrySystem1This practice is under the jurisdiction of ASTM Committee E61 on RadiationProcessingand is the direct responsi
14、bility of Subcommittee E61.04 on SpecialtyApplication, and is also under the jurisdiction of ISO/TC 85/WG 3.Current edition approved by ASTM Oct. 1, 2004. Published May 15, 2005.Originally published as E 143191. Last previous ASTM edition E 1431981.ASTM E 143191 was adopted by ISO in 1998 with the i
15、ntermediate designationISO 15562:1998(E). The present International Standard ISO/ASTM 51431:2005(E)is a major revision of the last previous edition ISO/ASTM 51431:2002(E), whichreplaced ISO 15562.2For referenced ASTM and ISO/ASTM standards, visit the ASTM website,www.astm.org, or contact ASTM Custom
16、er Service at serviceastm.org. ForAnnual Book of ASTM Standards volume information, refer to the standardsDocument Summary page on the ASTM website. ISO/ASTM International 2017 All rights reservedThis international standard was developed in accordance with internationally recognized principles on st
17、andardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.151261 Guide for Selection and Calibration of DosimetrySystems for Radiation Processing
18、51275 Practice for Use of a Radiochromic Film DosimetrySystem51276 Practice for Use of a Polymethylmethacrylate Dosim-etry System51310 Practice for Use of a Radiochromic Optical Wave-guide Dosimetry System51400 Practice for Characterization and Performance of aHigh-Dose Radiation Dosimetry Calibrati
19、on Laboratory51401 Practice for Use of a Dichromate Dosimetry System51538 Practice for Use of the Ethanol-Chlorobenzene Do-simetry System51539 Guide for Use of Radiation-Sensitive Indicators51540 Practice for Use of a Radiochromic Liquid DosimetrySystem51607 Practice for Use of the Alanine-EPR Dosim
20、etry Sys-tem51608 Practice for Dosimetry in an X-ray (Bremsstrahlung)Facility for Radiation Processing51631 Practice for Use of Calorimetric Dosimetry Systemsfor Electron Beam Dose Measurements and DosimeterCalibrations51649 Practice for Dosimetry in an Electron Beam Facilityfor Radiation Processing
21、 at Energies Between 300 keVand 25 MeV51650 Practice for Use of a Cellulose Triacetate DosimetrySystem51707 Guide for Estimating Uncertainties in Dosimetry forRadiation Processing51956 Practice for Thermoluminescence Dosimetry (TLD)Systems for Radiation Processing2.3 International Commission on Radi
22、ation Units and Mea-surements (ICRU) Reports:3ICRU Report 14 Radiation Dosimetry: X Rays and GammaRays with Maximum Photon Energies Between 0.6 and 50MeVICRU Report 34 The Dosimetry of Pulsed RadiationICRU Report 35 Radiation Dosimetry: Electron Beamswith Energies Between 1 and 50 MeVICRU Report 37
23、Stopping Powers for Electrons and Posi-tronsICRU Report 60 Fundamental Quantities and Units forIonizing Radiation3. Terminology3.1 Definitions:3.1.1 absorbed dose, Dquantity of ionizing radiation en-ergy imparted per unit mass of a specified material. The SI unitof absorbed dose is the gray (Gy), wh
24、ere 1 gray is equivalentto the absorption of 1 joule per kilogram of the specifiedmaterial (1 Gy = 1 J/kg). The mathematical relationship is thequotient of d by dm, where d is the mean incremental energyimparted by ionizing radiation to matter of incremental massdm (see ICRU 60).D 5 ddm (1)3.1.1.1 D
25、iscussionThe discontinued unit for absorbeddose is the rad (1 rad = 100 erg/g = 0.01 Gy).Absorbed dose issometimes referred to simply as dose. Water is frequentlyselected as the specified material for defining absorbed dose. Inpractice, dosimeters are most often calibrated in terms of doseto water.
26、That is, the dosimeter measures the dose that waterwould absorb if it were placed at the location of the dosimeter.Water is a convenient medium to use because it is universallyavailable and understood, and its radiation absorption andscattering properties are close to those of tissue. The require-me
27、nt of tissue-equivalency historically originates fromradiation-therapy applications. However, to determine the tem-perature increase in an irradiated material, it is necessary toknow the absorbed dose in that material. This may be deter-mined by applying conversion factors in accordance withISO/ASTM
28、 Guide 51261.3.1.2 absorbed-dose mapping (for a process load)measurement of absorbed dose within a process load usingdosimeters placed at specified locations to produce a one-, two-or three-dimensional distribution of absorbed dose, thus ren-dering a map of absorbed-dose values.3.1.3 average beam cu
29、rrenttime-averaged electron beamcurrent.3.1.3.1 DiscussionFor a pulsed machine, the averagingshall be done over a large number of pulses.3.1.4 beam lengthdimension of the irradiation zone alongthe direction of product movement, at a specified distance fromthe accelerator window (see Fig. 1).3.1.4.1
30、Discussion(1) This term usually applies to elec-tron irradiation. (2) Beam length is therefore perpendicular tobeam width and to the electron beam axis. (3) In case of alow-energy, single-gap electron accelerator, beam length isequal to the active length of the cathode assembly in vacuum.(4) In case
31、 of product that is stationary during irradiation,beam length and beam width may be interchangeable.3Available from the International Commission on Radiation Units andMeasurements, 7910 Woodmont Ave., Suite 800, Bethesda, MD 20814, U.S.A.FIG. 1 Diagram showing beam length and width for a scannedbeam
32、 using a conveyor systemISO/ASTM 51431:2005(E)2 ISO/ASTM International 2017 All rights reserved 3.1.5 beam widthdimension of the irradiation zone per-pendicular to the direction of product movement, at a specifieddistance from the accelerator window (see Fig. 1).3.1.5.1 Discussion(1) This term usual
33、ly applies to elec-tron irradiation. (2) Beam width is therefore perpendicular tobeam length and to the electron beam axis. (3) In case ofproduct that is stationary during irradiation, beam width andbeam lengthmay be interchangeable. (4) Beam width may bequantified as the distance between two points
34、 along the doseprofile, which are at a defined fraction of the maximum dosevalue in the profile (see Fig. 2). (5) Various techniques may beemployed to produce an electron beam width adequate to coverthe processing zone, for example, use of electromagneticscanning of pencil beam (in which case beam w
35、idth is alsoreferred to as scan width), defocusing elements, and scatteringfoils.3.1.6 bremsstrahlungbroad-spectrum electromagnetic ra-diation emitted when an energetic charged particle is influ-enced by a strong electric or magnetic field, such as that in thevicinity of an atomic nucleus.3.1.6.1 Di
36、scussionIn radiation processing, bremsstrahl-ung photons with sufficient energy to cause ionization aregenerated by the deceleration or deflection of energetic elec-trons in a target material. When an electron passes close to anatomic nucleus, the strong coulomb field causes the electron todeviate f
37、rom its original motion. This interaction results in aloss of kinetic energy by the emission of electromagneticradiation. Since such encounters are uncontrolled, they producea continuous photon energy distribution that extends up to themaximum kinetic energy of the incident electron. Thebremsstrahlu
38、ng spectrum depends on the electron energy, thecomposition and thickness of the target, and the angle ofemission with respect to the incident electron. Even thoughbremsstrahlung has broad energy spectrum, the energy of theincident electron beam is referred to as the nominalbremsstrahlung energy.3.1.
39、7 compensating dummySee simulated product(3.1.35).3.1.8 continuous-slowing-down-approximation range(CSDA range), r0average path length traveled by a chargedparticle as it slows down to rest, calculated under thecontinuous-slowing-down approximation (see ICRU Report35).3.1.8.1 DiscussionValues of r0f
40、or a wide range of elec-tron energies and for several materials are tabulated in ICRUReport 37.3.1.9 depth-dose distributionvariation of absorbed dosewith depth from the incident surface of a material exposed toa given radiation (see Fig. 3 for a typical distribution).3.1.9.1 DiscussionDepth-dose di
41、stributions for severalhomogeneous materials produced by electron beams of differ-ent energies are shown in ISO/ASTM Practice 51649.3.1.10 dose uniformity ratio (for a process load)ratio ofthe maximum to the minimum absorbed dose within theprocess load. The concept is also referred to as the max/min
42、dose ratio.3.1.11 dosimeter setone or more dosimeters used to mea-sure absorbed dose at a location and whose average response isused to determine absorbed dose at that location.3.1.12 dosimetry systemsystem used for determining ab-sorbed dose, consisting of dosimeters, measurement instru-ments and t
43、heir associated reference standards, and proceduresfor the systems use.3.1.13 electron beam energyaverage kinetic energy of theaccelerated electrons in the beam. Unit: J3.1.13.1 DiscussionElectron volt (eV) or its multiples isoften used as the unit for electron (beam) energy, where 1 eV= 1.602 10-19
44、J (approximately).3.1.14 electron beam rangepenetration distance of anelectron beam along its axis in a specific, totally absorbingmaterial.FIG. 2 Example of measured electron-beam dose distributionalong the beam width, where the beam width is noted at somedefined fractional level f of the average m
45、aximum dose DmaxNOTE 1The peak-to-surface dose ratio depends on the energy of theincident electron beam (ICRU Report 35). The distribution shown here istypically for about 10 MeV electrons. For this case, Rp= Rex, since X-raybackground is negligible. For the case where Rpis not equal to Rex, seeISO/
46、ASTM Practice 51649, Annex A1.FIG. 3 Typical (idealised) depth-dose distribution for an electronbeam in a homogeneous material composed of elements of lowatomic numberISO/ASTM 51431:2005(E)3 ISO/ASTM International 2017 All rights reserved 3.1.14.1 DiscussionThis quantity may be defined andevaluated
47、in several ways. For example, extrapolated electronbeam range, Rex (see 3.1.16), practical electron beam range,Rp (see 3.1.23), and continuous-slowing-down-approximation range, r0 (see 3.1.8). Rpand Rexcan bedetermined from measured depth-dose distributions in a refer-ence material (see Fig. 3). Ele
48、ctron range is usually expressedin terms of mass per unit area (kgm-2), but sometimes in termsof thickness (m) of a specific material.3.1.15 electron energy spectrumparticle fluence distribu-tion of electrons as a function of energy.3.1.16 extrapolated electron beam range, Rexdepth fromthe incident
49、surface of a reference material where the electronbeam enters to the point where the tangent at the steepest point(the inflection point) on the almost straight descending portionof the depth-dose distribution curve meets the depth axis.3.1.16.1 DiscussionUnder certain conditions, Rex= Rp,which is shown in Fig. 3. These conditions generally apply tofoodstuff irradiated at
