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Significance and Use
4.1 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 per unit mass, whereas exposure is related to the amount of charge produced in air per unit mass. Absorbed dose, as referred to here, implies that the measurement is made under conditions of charged particle (electron) equilibrium (see Appendix X1). In practice, such conditions are not rigorously achievable but, under some circumstances, can be approximated closely.
4.2 Different materials, when exposed to the same radiation field, absorb different amounts of energy. Using the techniques of this standard, charged particle equilibrium must exist in order to relate the absorbed dose in one material to the absorbed dose in another. Also, if the radiation is attenuated by a significant thickness of an absorber, the energy spectrum of the radiation will be changed, and it will be necessary to correct for this.
1.1 This practice presents a technique for calculating the absorbed dose in a material from knowledge of the radiation field, the composition of the material, (1-5)2,3 and a related measurement. The procedure is applicable for X and gamma radiation provided the energy of the photons fall within the range from 0.01 to 20 MeV.
1.2 A method is given for calculating the absorbed dose in a material from the knowledge of the absorbed dose in another material exposed to the same radiation field. The procedure is restricted to homogeneous materials composed of the elements for which absorption coefficients have been tabulated. All 92 natural elements are tabulated in (2). It also requires some knowledge of the energy spectrum of the radiation field produced by the source under consideration. Generally, the accuracy of this method is limited by the accuracy to which the energy spectrum of the radiation field is known.
1.3 The results of this 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 of widely differing atomic numbers. For more information on this topic, see Practice E1249.
1.4 Energy transport computer codes4 exist that are formulated to calculate absorbed dose in materials more precisely than this method. To use these codes, more effort, time, and expense are required. If the situation warrants, such calculations should be used rather than the method 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 responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
E170 Terminology Relating to Radiation Measurements and Dosimetry
E668 Practice for Application of Thermoluminescence-Dosimetry (TLD) Systems for Determining Absorbed Dose in Radiation-Hardness Testing of Electronic Devices
E1249 Practice for Minimizing Dosimetry Errors in Radiation Hardness Testing of Silicon Electronic Devices Using Co-60 Sources
ICS Number Code 17.240 (Radiation measurements)
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ASTM E666-14, Standard Practice for Calculating Absorbed Dose From Gamma or X Radiation, ASTM International, West Conshohocken, PA, 2014, www.astm.orgBack to Top