1、Designation: E666 09E666 14Standard Practice forCalculating Absorbed Dose From Gamma or X Radiation1This standard is issued under the fixed designation E666; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision
2、. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope1.1 This practice presents a technique for calcul
3、ating the absorbed dose in a material from knowledge of the radiation field, thecomposition of the material, (1-5)2,3 and a related measurement. The procedure is applicable for X and gamma radiation providedthe energy of the photons fall within the range from 0.01 to 20 MeV.1.2 A method is given for
4、 calculating the absorbed dose in a material from the knowledge of the absorbed dose in anothermaterial exposed to the same radiation field. The procedure is restricted to homogeneous materials composed of the elements forwhich absorption coefficients have been tabulated tabulated. All 92 natural el
5、ements are tabulated in (2). It also requires someknowledge of the energy spectrum of the radiation field produced by the source under consideration. Generally, the accuracy ofthis method is limited by the accuracy to which the energy spectrum of the radiation field is known.1.3 The results of this
6、practice are only valid if charged particle equilibrium exists in the material and at the depth of interest.Thus, this practice is not applicable for determining absorbed dose in the immediate vicinity of boundaries between materials ofwidely differing atomic numbers. For more information on this to
7、pic, see Practice E1249.1.4 Energy transport computer codes4 exist that are formulated to calculate absorbed dose in materials more precisely than thismethod. To use these codes, more effort, time, and expense are required. If the situation warrants, such calculations should be usedrather than the m
8、ethod described here.1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to
9、use.2. Referenced Documents2.1 ASTM Standards:5E170 Terminology Relating to Radiation Measurements and DosimetryE380 Practice for Use of the International System of Units (SI) (the Modernized Metric System) (Withdrawn 1997)6E668 Practice for Application of Thermoluminescence-Dosimetry (TLD) Systems
10、for Determining Absorbed Dose inRadiation-Hardness Testing of Electronic DevicesE1249 Practice for Minimizing Dosimetry Errors in Radiation Hardness Testing of Silicon Electronic Devices Using Co-60Sources1 This practice is under the jurisdiction of ASTM Committee E10 on Nuclear Technology and Appli
11、cationsand is the direct responsibility of Subcommittee E10.07 onRadiation Dosimetry for Radiation Effects on Materials and Devices.Current edition approved June 1, 2009Jan. 1, 2014. Published June 2009February 2014. Originally approved in 1997. Last previous edition approved in 20082009 asE666-08.-
12、09. DOI: 10.1520/E0666-09.10.1520/E0666-14.2 The boldface numbers in parentheses refer to the list of references appended to this practice.3 See also ICRU Report 80. For calculation of absorbed dose in biological materials such as tissue or bone, etc., ICRU Report 14 provides more information and pr
13、oceduresfor a more accurate calculation than this practice.dosimetry systems and materials used in radiation processing, mass attenuation coefficients and mass-energy absorptioncoefficients for key elements, compounds and materials used in radiation processing dosimetry over the photon range from 10
14、0 keV to 20 MeV are given in Appendix 1 ofthat report.4 Information on and packages of computer codes can be obtained from The Radiation Safety Information Computational Center, Oak Ridge National Laboratory, P.O.Box 2008, Oak Ridge, TN 37831-6362. This information center collects, organizes, evalua
15、tes, and disseminates shielding information related to radiation from reactors,weapons, and accelerators and to radiation occurring in space.5 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolum
16、e information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequa
17、tely depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocke
18、n, PA 19428-2959. United States12.2 International Commission on Radiation Units and Measurements (ICRU) Reports:ICRU Report 14Radiation Dosimetry: X Rays and Gamma Rays with Maximum Photon Energies Between 0.6 and 60 MeV76ICRU Report 18Specification18 Specification of High Activity Gamma-Ray Sources
19、ICRU Report 21Radiation21 Radiation Dosimetry: Electrons with Initial Energies Between 1 and 50 MeVICRU Report 33Radiation51 Radiation Quantities and Units in Radiation Protection DosimetryICRU Report 60 Radiation Fundamental Quantities and Units for Ionizing RadiationICRU Report 34The34 The Dosimet
20、ry of Pulsed RadiationICRU Report 80 Dosimetry Systems for Use in Radiation Processing3. Terminology3.1 energy fluence spectrum(E)spectrum, (E)the product of the particle fluence spectrum (see Terminology E170) andthe particle energy. In this standard, the particles referred to are photons. The ener
21、gy fluences spectrum is the same as the energyfluence per unit energy.3.2 energy fluence, the integral of the energy fluence spectrum over the complete range of particle energies that are present.3.3 mass-depth and mass-thickness, tthe product of a length traversed in a material and the mass density
22、 of the material. Themass-depth and the mass-thickness have dimensions of mass per unit area.4. Significance and Use4.1 The absorbed dose is a more meaningful parameter than exposure for use in relating the effects of radiation on materials.It expresses the energy absorbed by the irradiated material
23、 per unit mass, whereas exposure is related to the amount of chargeproduced in air per unit mass.Absorbed dose, as referred to here, implies that the measurement is made under conditions of chargedparticle (electron) equilibrium (see Appendix X1). In practice, such conditions are not rigorously achi
24、evable but, under somecircumstances, can be approximated closely.4.2 Different materials, when exposed to the same radiation field, absorb different amounts of energy. Using the techniques ofthis standard, charged particle equilibrium must exist in order to relate the absorbed dose in one material t
25、o the absorbed dose inanother. Also, if the radiation is attenuated by a significant thickness of an absorber, the energy spectrum of the radiation will bechanged, and it will be necessary to correct for this.NOTE 1For comprehensive discussions of various dosimetry methods applicable to the radiatio
26、n types and energies and absorbed dose rate rangesdiscussed in this method, see ICRU Reports 14, 21, 34 and 34.80.5. Calculation of Absorbed Dose5.1 The absorbed dose, D, at a point may be expressed as:D 5I *0 E!enE!/#dE (1)where (E) is the energy fluence per unit energy at the point of interest; en
27、 (E)/ is the mass energy absorption coefficient (2);and I is a normalizing factor. If all of the variables in Eq 1 are expressed in SI units, I = 1. In this case the units for D are Gy (Jkgkg1), of (E), are m2 , of en/ are m2kgkg1, and of E are J. For an alternative use of the normalizing factor I,
28、see AppendixX2. For further information on the use of energy absorption coefficients to calculate absorbed dose see the discussion in Attix (1).The energy fluence spectrum, (E), is that which is incident at the point where the dose is to be determined. In practice, the limitsof integration are the l
29、imits of energy over which (E) is of a significant magnitude. If material intervenes between the source andthe point of dose determination, then the spectrum used in the calculation must be the output spectrum of the source modified bythe absorbing effects of the intervening material. The values of
30、en(E)/ are found in the tables of Ref 2.NOTE 2For units and terminology in reports of data, E170 and ICRU Report 33 Reports 51 and 60 may be used as guides.5.2 If the material in which the absorbed dose is to be calculated is a homogeneous combination of materials not listed in thetables of Ref 2, e
31、n(E)/ is determined as follows:5.2.1 From Ref 2, obtain values of eni E!/ for each component, i.5.2.2 Determine the atomicmass fraction, fwi, for each component.5.2.3 Calculate en(E)/ from the following equation:enE!/5(ifieni E!/# (2)enE!/5(iwieni E!/# (2)6 Available from International Commission on
32、 Radiation Units and Measurements (ICRU), 7910 Woodmont Ave., Suite 800,400, Bethesda, MD 20814.20841.E666 1425.2.4 Values of en(E)/ must be determined for each value of E for which (E) is significant, where E is the photon energy.5.3 The integral contained in Eq 1 is evaluated numerically. The valu
33、es of en(E)/ in Ref 2 are tabulated for specific energies.In evaluation of the integral referred to in actual practice, it is often desirable to choose energy intervals that would not correspondto the tabulated values in Ref 2. In such cases, the appropriate value of en(E)/ for the chosen energies s
34、hould be determined byan acceptable interpolation procedure. The range of energy over the total photon spectrum is divided into energy intervals or bins.The width of these bins is somewhat flexible but should be chosen small enough so as not to distort the shape of the spectrum.For the purpose of se
35、lecting appropriate values of en(E)/, the energy value selected for each energy interval can be taken eitheras that energy at the beginning or midpoint of each energy interval over the entire spectrum.5.4 The energy fluence spectrum, (E), is commonly given in arbitrary units and may be normalized to
36、 some source parameter.If a standard or calibrated dosimeter is used, then the integral in Eq 1 must be calculated for the material from which this dosimeteris constructed.The value of I is then given by the observed dose, D, measured by the dosimeter, divided by the value of the integral.6. Estimat
37、ing the Absorbed Dose in One Material from That Measured in Another Material6.1 If the absorbed dose is known in one material, A, then the absorbed dose can be estimated in another material, B, using themethod described in this section.6.1.1 The absorbed dose observed in A occurs at some depth in th
38、e region of material A; similarly, it is desired to know theabsorbed dose in material B at some depth in the region of material B. If it is presumed that we know the surface energy fluencespectrum o(E) (the energy fluence spectrum incident on the surface of materials A and B) then the energy fluence
39、 spectrum (E)to be used in Eq 1 must be related to the known surface energy fluence spectrum o(E). A good approximation to the attenuatedenergy fluence spectrum at mass-depth t is given bytE! 5oE!exp2enE!/#t! (3)where t is the mass-depth (in kgm2) of material between the surface and the depth of int
40、erest, E is a particular energyrepresented in the spectrum, and t(E) is the energy fluence per unit energy at mass-depth t. For a derivation of Eq 3 see AppendixX4. See also the qualifications of 6.1.3 and 6.1.4. For a demonstration of the experimental plausibility of Eq 3, see Appendix X5.6.1.2 Usi
41、ng Eq 1 and 3, the relationship between the known dose DA and the desired dose DB can be expressed asDADB 5*0 oE!exp2enA E!/A#tA!#enA E!/A#dE*0 o E! exp 2enB E!/B# tB#! enB E!/B# dE (4)DADB 5*0 oE!exp2enA E!/A#tA!#enA E!/A#dE*0 oE!exp2enB E!/B#tB!#enB E!/B#dE (4)where enA , A, and tA are the energy
42、absorption coefficient, the density and the relevant mass-depth for material A, and wheresimilar notation is used for material B. For further details on the derivation of Eq 4, see Appendix X6. All the variables in Eq 4are presumed to be known except the desired value for DB. The integrals in Eq 4 m
43、ust be performed numerically.6.1.3 The use of Eq 3 is based on the existence of charged particle equilibrium (for further discussion see 1.3). This conditionmay be reasonably well met when the region of interest is at a sufficient distance from boundaries representing changes in atomicnumber or mate
44、rial density (see Appendix X1).6.1.4 Wide Beam vs. Narrow Beam Approximation.6.1.4.1 The use of the energy coefficient, en , in Eq 3 is based on the assumption that the irradiation approaches the “wide beam”as opposed to “narrow beam” condition. The wide beam and narrow beam conditions represent lim
45、iting cases which are onlyapproximately realized for real experiments. In the narrow beam case, photons which are scattered out of the narrow beam areassumed to be lost from the beam, and are assumed to have no further importance to the experiment. In the broad beam case,photons which are scattered
46、out of a given small region of the broad beam are presumed to be replaced by photons scattering infrom adjacent regions of the beam. For the narrow beam limiting case, Eq 3 should be replaced bytE! 5oE!exp2E!/#t! (5)where is the photon attenuation coefficient. Values of (E)/ are found in the tables
47、of Ref 2. For most practical problems theresults of photon attenuation lie between the results of Eq 3 and Eq 5.6.1.4.2 It is possible to determine the magnitude of the change which would have resulted had Eq 1 and Eq 5 been used ratherthan using Eq 1 and Eq 3 in order to develop Eq 4. The resulting
48、 change in the ratio DA/DB calculated by Eq 4 is related to thefactorFE! 5 exp2enB E!/B#t!exp2BE!/B#t!exp2AE!/A#t!exp2enA E!/A#t! (6)FE! 5 exp2enB E!/B#t!exp2BE!/B#t!exp2AE!/A#t!exp2enA E!/A#t! (6)E666 143If, over the energy range of interest, F(E) differs from unity by a percentage which is greater
49、 than the acceptable dosimetry error,then the application of this practice may be inappropriate. In that case an appropriate transport calculation is recommended (see1.5).6.1.4.3 Depending on the scattering geometry, it is possible for the absorbed dose to be different from that calculated usingeither or en. The use of en in Eq 3 is an expedient device that is used as a means for yielding
