1、Designation: E1894 13E1894 13aStandard Guide forSelecting Dosimetry Systems for Application in PulsedX-Ray Sources1This standard is issued under the fixed designation E1894; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year
2、of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide provides assistance in selecting and using dosimetry systems in flash X-ray experiments. Both dose and d
3、ose-ratetechniques are described.1.2 Operating characteristics of flash X-ray sources are given, with emphasis on the spectrum of the photon output.1.3 Assistance is provided to relate the measured dose to the response of a device under test (DUT). The device is assumed tobe a semiconductor electron
4、ic part or system.2. Referenced Documents2.1 ASTM Standards:2E170 Terminology Relating to Radiation Measurements and DosimetryE666 Practice for Calculating Absorbed Dose From Gamma or X RadiationE668 Practice for Application of Thermoluminescence-Dosimetry (TLD) Systems for Determining Absorbed Dose
5、 inRadiation-Hardness Testing of Electronic DevicesE1249 Practice for Minimizing Dosimetry Errors in Radiation Hardness Testing of Silicon Electronic Devices Using Co-60SourcesISO/ASTM 51261 Guide for Selection and Calibration of Dosimetry Systems for Radiation ProcessingISO/ASTM 51275 Practice for
6、Use of a Radiochromic Film Dosimetry systemISO/ASTM 51310 Practice for Use of a Radiochromic Optical Waveguide Dosimetry system2.2 ISO/ASTM Standards:3ISO/ASTM 51261 Practice for Calibration of Routine Dosimetry Systems for Radiation ProcessingISO/ASTM 51275 Practice for Use of a Radiochromic Film D
7、osimetry SystemISO/ASTM 51310 Practice for Use of a Radiochromic Optical Waveguide Dosimetry System2.3 International Commission on Radiation Units (ICRU) and Measurements Reports:4ICRU Report 14 Radiation Dosimetry: X rays and Gamma Rays with Maximum Photon Energies Between 0.6 and 50 MeVICRU Report
8、 17 Radiation Dosimetry: X rays Generated at Potentials of 5 to 150 kVICRU Report 3334 Radiation Quantities and UnitsThe Dosimetry of Pulsed RadiationICRU Report 51 Quantities and Units in Radiation Protection DosimetryICRU Report 3460 The Dosimetry of Pulsed Fundamental Quantities and Units for Ion
9、izing RadiationICRU Report 76 Measurement Quality Assurance for Ionizing Radiation DosimetryICRU Report 77 Elastic Scattering of Electrons and PositronsICRU Report 80 Dosimetry Systems for Use in Radiation ProcessingICRU Report 85a Fundamental Quantities and Units for Ionizing Radiation1 This practi
10、ce is under the jurisdiction of ASTM Committee E10 on Nuclear Technology and Applications and is the direct responsibility of Subcommittee E10.07 onRadiation Dosimetry for Radiation Effects on Materials and Devices.Current edition approved June 1, 2013Aug. 1, 2013. Published July 2013September 2013.
11、 Originally approved in 1997. Last previous edition approved in 20082013 asE1894 08.E1894 13. DOI: 10.1520/E1894-13.10.1520/E1894-13A.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume infor
12、mation, refer to the standards Document Summary page on the ASTM website.3 For referenced ISO/ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page o
13、n the ASTM website.4 Available from the International Commission on Radiation Units and Measurements, 7910 Woodmont Ave., Suite 800, Bethesda, MD 20814, U.S.A.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 ma
14、de to the previous version. Becauseit may not be technically possible to adequately 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.Cop
15、yright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13. Terminology3.1 absorbed dosequotient of dd/dm,e/dm, where dde is the mean energy imparted by ionizing radiation to matter ofmass dm:D 5 ddme (1)D 5 ddm (1)See ICRU Report 33.85a. The spe
16、cial name for the unit for absorbed dose is the gray (Gy).1Gy51J/kg (2)Formerly, the special unit for absorbed dose was the rad, where 1 rad = 100 erg/g.1rad50.01 Gy (3)Since the absorbed dose due to a given radiation field is material dependent, it is important to include the material compositionfo
17、r which the dose is being reported, e.g., 15.3 Gy(LiF).3.2 absorbed dose enhancementincrease (or decrease) in the absorbed dose (as compared to the equilibrium absorbed dose)at a point in a material of interest. This can be expected to occur near an interface with a material of higher or lower atomi
18、c number.3.3 convertera target for electron beams, generally of a high atomic number material, in which bremsstrahlung X-rays areproduced by radiative energy losses of the incident electrons.3.4 dosimetera device that, when irradiated, exhibits a quantifiable change in some property of the device wh
19、ich can be relatedto absorbed dose in a given material using appropriate analytical instrumentation and techniques.3.5 dosimetry systema system used for determining absorbed dose, consisting of dosimeters, measurement instruments, andtheir associated reference standards, and procedures for the syste
20、ms use.3.6 DUTdevice under test. This is the electronic component or system tested to determine its performance during or afterirradiation.3.7 endpoint energyendpoint energy refers to the peak energy of the electron beam, usually in MeV, generated in a flash X-raysource and is numerically equal to t
21、he maximum voltage in MV. The word endpoint refers to the highest photon energy of thebremsstrahlung spectra, and this endpoint is equal to the maximum or peak in the electron energy. For example, if the mostenergetic electron that strikes the converter is 10 MeV, this electron produces a range of b
22、remsstrahlung photon energies but themaximum energy of any photon is equal to 10 MeV, the endpoint energy. Most photons have energies one-tenth to one-third ofthe maximum electron energy for typical flash X-ray sources in the 10 MV to 1 MV endpoint voltage region, respectively.3.8 endpoint voltageEn
23、dpoint voltage refers to the peak voltage across a bremsstrahlung diode in a flash X-ray source. Forexample, a 10-MV flash X-ray source is designed to reach a peak voltage of 10-MV across the anode-cathode gap which generatesthe electron beam for striking a converter to produce bremsstrahlung.3.9 eq
24、uilibrium absorbed doseabsorbed dose at some incremental volume within the material in which the condition ofelectron equilibrium (the energies, number, and direction of charged particles induced by the radiation are constant throughout thevolume) exists. For lower energies where bremsstrahlung prod
25、uction is negligible the equilibrium absorbed dose is equal to thekerma.NOTE 1For practical purposes, assuming the spatial gradient in the X-ray field is small over the range of the maximum energy secondary electronsgenerated by the incident photons, the equilibrium absorbed dose is the absorbed dos
26、e value that exists in a material at a distance from any interface withanother material greater than this range.4. Significance and Use4.1 Flash X-ray facilities provide intense bremsstrahlung radiation environments, usually in a single sub-microsecond pulse,which often fluctuates in amplitude, shap
27、e, and spectrum from shot to shot. Therefore, appropriate dosimetry must be fielded onevery exposure to characterize the environment, see ICRU Report 34. These intense bremsstrahlung sources have a variety ofapplications which include the following:4.1.1 Generation of X-ray and gamma-ray environment
28、s similar to that from a nuclear weapon burst.4.1.2 Studies of the effects of X-rays and gamma rays on materials.4.1.3 Studies of the effects of radiation on electronic devices such as transistors, diodes, and capacitors.4.1.4 Vulnerability and survivability testing of military systems and component
29、s.4.1.5 Computer code validation studies.4.2 This guide is written to assist the experimenter in selecting the needed dosimetry systems (not all radiation parameters mustbe measured in a given experiment) for use at pulsed X-ray facilities. This guide also provides a brief summary of the information
30、E1894 13a2on how to use each of the dosimetry systems. Other guides (see Section 2) provide more detailed information on selected dosimetrysystems in radiation environments and should be consulted after an initial decision is made on the appropriate dosimetry systemto use. There are many key paramet
31、ers which describe a flash X-ray source, such as dose, dose rate, spectrum, pulse width, etc.,such that typically no single dosimetry system can measure all the parameters simultaneously.5. General Characteristics of Flash X-ray Sources5.1 Flash X-ray Facility ConsiderationsFlash X-ray sources opera
32、te like a dental X-ray source but at much higher voltagesand intensities and usually in a single, very short burst, see ICRU Report 17.Ahigh voltage is developed across an anode-cathodegap (the diode) and field emission creates a pulsed electron beam traveling from the cathode to the anode. A high a
33、tomicnumberelement such as tantalum is placed on the anode to maximize the production of bremsstrahlung created when the electrons strikethe anode. Graphite or aluminum is usually placed downstream of the converter to stop the electron beam completely but let theX-radiation pass through. Finally, a
34、debris shield made of Kevlar or low-density polyethylene is sometimes necessary to stopexploding converter material from leaving the source. All of these components taken together form what is commonly called abremsstrahlung diode.5.2 Relationship Between Flash X-ray Diode Voltage and X-ray Energy o
35、f BremsstrahlungFlash X-ray sources producebremsstrahlung by generating an intense electron beam which then strikes a high atomic number (Z) converter such as tantalum.The electron-solid interactions produce “braking” radiation or, in German, bremsstrahlung. Fig. 1 shows the typical range ofphoton e
36、nergies produced by three different sources. If the average radiation produced is in the 20100 keV region, the source issaid to be a mediumhard X-ray simulator. If the average photon energy is in the 100300keVregion, the term used is “hard X-raysimulator.”At the high end of the flash X-ray range are
37、 sources which produce an average photon energy of around 2 MeV. Becausethis photon energy is in the typical gamma-ray spectral range, the source is called a gamma-ray simulator.5.2.1 The average energy of the bremsstrahlung spectrum, Ephoton, through an optimized converter (1)5 in the medium-hardX-
38、ray region (50 keV 500 keV) is given empirically by,Ephoton 51/2 (4)where Ephoton is the average energy of the bremsstrahlung photons in keV and is the average energy of the electrons in theelectron beam incident on the converter in keV. This equation and Fig. 1 indicate that most of the photons hav
39、e energies muchless than the endpoint electron energy, or in voltage units, the flash X-ray voltage.6. Measurement Principles6.1 Typically in flash X-ray irradiations, one is interested in some physical change in a critical region of a device under test(DUT). The dosimetry associated with the study
40、of such a physical change may be broken into three parts:6.1.1 Determine the absorbed dose in a dosimeter.6.1.2 Using the dosimeter measurement, estimate the absorbed dose in the region and material of interest in the DUT.5 The boldface numbers in parentheses refer to the list of references at the e
41、nd of this standard.FIG. 1 Range of Available Bremsstrahlung Spectra from Flash X-ray SourcesE1894 13a36.1.3 If required, relate the estimated absorbed dose in the DUT to the physical change of interest (holes trapped, interface statesgenerated, photocurrent produced, etc.)6.2 This section will be c
42、oncerned with the first two of the above listed parts of dosimetry: (1) what is necessary to determinea meaningful absorbed dose for the dosimeter and (2) what is necessary to extrapolate this measured dose to the estimated dosein the region of interest. The final step in dosimetry, associating the
43、absorbed dose with a physical change of interest, is outsidethe scope of this guide.6.3 Energy Deposition:6.3.1 Secondary ElectronsBoth in the case of absorbed dose in the DUT and absorbed dose in the dosimeter, the energy isdeposited largely by secondary electrons. That is, the incident photons int
44、eract with the material of, or surrounding, the DUT orthe dosimeter and lose energy to Compton electrons, photoelectrons, and Auger electrons. The energy which is finally depositedin the material is deposited by these secondary particles.6.3.2 Transport of PhotonsIn some cases, it is necessary to co
45、nsider the transport and loss of photons as they move to theregion whose absorbed dose is being determined.Acorrection for the attenuation of an incident photon beam is an example of sucha consideration.6.3.3 Transport of ElectronsElectron transport may cause energy originally imparted to electrons
46、in one region to be carriedto a second region depending on the range of the electrons.As a result, it is necessary to consider the transport and loss of electronsas they move into and out of the regions whose absorbed dose is being determined. In particular, it is necessary to distinguishbetween equ
47、ilibrium and non-equilibrium conditions for electron transport.6.3.3.1 Charged Particle EquilibriumIn some cases, the numbers, energies, and angles of particles transported into a regionof interest are approximately balanced by those transported out of that region. Such cases form an important class
48、 of limiting caseswhich are particularly easy to interpret. (See “Equilibrium Absorbed Dose” in 3.9.)6.3.3.2 Dose EnhancementBecause photoelectron production per atom is roughly proportional to the atomic number raisedto the fourth power for energies less than 100 keV (2), one expects more photoelec
49、trons to be produced in high atomic numberlayers than in low atomic number layers for the same photon fluence and spectrum. Thus, there may be a net flow of energeticelectrons from the high atomic number layers into the low atomic number layers.This nonequilibrium flow of electrons may resultin an enhancement of the dose in the low atomic number layer. Dose enhancement problems are often caused by high atomicnumber bonding layers (for example, gold), and metallization layers (for example, WSi or TaSi).6.4 Absorbed Dose in Dosimeter:6
