1、Designation: E 1894 97 (Reapproved 2002)Standard Guide forSelecting Dosimetry Systems for Application in PulsedX-Ray Sources1This standard is issued under the fixed designation E 1894; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision
2、, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide provides assistance in selecting and usingdosimetry systems in flash x-ray experiments. Both
3、 dose anddoserate techniques are described.1.2 Operating characteristics of flash xray sources aregiven, with emphasis on the spectrum of the photon output.1.3 Assistance is provided to relate the measured dose to theresponse of a device under test (DUT). The device is assumedto be a semiconductor e
4、lectronic part or system.2. Contents2.1 Section 1: Scope of guide.2.2 Section 2: Outline.2.3 Section 3: Related ASTM and ICRU documents.2.4 Section 4: Definition of terms.2.5 Section 5: Significance and use of this document for theselection of dosimetry systems for use in pulsed xray sources.2.6 Sec
5、tion 6: Description of large flash xray sources andtheir characteristics.2.7 Section 7: Measurement principles with an emphasis onobtaining absorbed dose measurements for different spectralconditions in the dosimeter, the DUT, and the relationshipbetween them.2.8 Section 8: The primary information i
6、n this guide. Theexperimenter will find details on each dosimetry system. Listedare details such as: 1) how the dosimeters works, i.e., physicalprinciples, 2) typical applications or instrumentation configu-rations, 3) advantages, 4) limitations, 5) sensitivity 6) proce-dures for calibration and pro
7、per use and finally reproducibilityand accuracy.2.9 Section 9: Suggested documentation requirements.2.10 Section 10: Description of how the experimenter de-termines uncertainty in the dosimetry measurements.2.11 Section 11: References.3. Referenced Documents3.1 ASTM Standards:E 170 Terminology Relat
8、ing to Radiation Measurementsand Dosimetry2E 665 Practice for Determining Absorbed Dose VersusDepth in Materials Exposed to the Xray Output of FlashXray Machines2E 666 Practice for Calculating Absorbed Dose from Gammaor X Radiation2E 668 Practice for the Application of Thermoluminescence-Dosimetry (
9、TLD) Systems for Determining AbsorbedDose in RadiationHardness Testing of Electronic De-vices2E 1249 Practice for Minimizing Dosimetry Errors in Radia-tion Hardness Testing of Silicon Electronic Devices UsingCo60 Sources2E 1261 Guide for Selection and Calibration of DosimetrySystems for Radiation Pr
10、ocessing2E 1275 Practice for Use of a Radiochromic Film DosimetrySystem2E 1310 Practice for Use of a Radiochromic OpticalWaveguide Dosimetry System23.2 International Commission on Radiation Units (ICRU)and Measurements Reports:3ICRU Report 14Radiation Dosimetry: X rays and GammaRays with Maximum Pho
11、ton Energies Between 0.6 and 50MeVICRU Report 17Radiation Dosimetry: X rays Generated atPotentials of 5 to 150 kVICRU Report 33Radiation Quantities and UnitsICRU Report 34The Dosimetry of Pulsed Radiation4. Terminology4.1 Absorbed Dosequotient of de/dm, where de is themean energy imparted by ionizin
12、g radiation to matter of massdm:D 5ddme . (1)The special name for the unit for absorbed dose is the gray(Gy).1Gy5 1J/kg. (2)1This practice is under the jurisdiction of ASTM Committee E10 on NuclearTechnology and Applications and is the direct responsibility of Subcommittee94E 10.07 on Radiation Dosi
13、metry for Radiation Effects on Materials and Devices.Current edition approved June 10, 1997. Published July 1998.2Annual Book of ASTM Standards, Vol 12.02.3Available from the International Commission on Radiation Units and Measure-ments, 7910 Woodmont Ave., Suite 800, Bethesda, MD 20814, U.S.A.1Copy
14、right ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Formerly, the special unit for absorbed dose was the rad,where 1 rad = 100 erg/g.1 rad 5 0.01 Gy. (3)Because the magnitude of the absorbed dose is materialdependent, it is important to inclu
15、de the material compositionfor which the dose is being reported, e.g., 15.3 Gy(LiF).4.2 Absorbed Dose Enhancementincrease (or decrease) inthe absorbed dose (as compared to the equilibrium absorbeddose) at a point in a material of interest. This can be expectedto occur near an interface with a materi
16、al of higher or loweratomic number.4.3 Convertera target for electron beams, generally of ahigh atomic number material, in which bremsstrahlung x raysare produced by radiative energy losses of the incident elec-trons.4.4 DosimeterA device that, when irradiated, exhibits aquantifiable change in some
17、property of the device which canbe related to absorbed dose in a given material using appro-priate analytical instrumentation and techniques.4.5 Dosimetry SystemA system used for determiningabsorbed dose, consisting of dosimeters, measurement instru-ments, and their associated reference standards, a
18、nd proceduresfor the systems use.4.6 DUTDevice under test. This is the electronic compo-nent or system tested to determine its performance during orafter irradiation.4.7 Endpoint EnergyEndpoint energy refers to the peakenergy of the electron beam, usually in MeV, generated in aflash xray source and
19、is numerically equal to the endpointvoltage in MV. The word endpoint refers to the highest photonenergy of the bremsstrahlung spectra, and this endpoint isequal to the maximum or peak in the electron energy. Forexample, if the most energetic electron that strikes the con-verter is 10 MeV, this elect
20、ron produces a range of bremsstrahl-ung photon energies but the maximum energy of any photon isequal to 10 MeV, the endpoint energy. Most photons haveenergies one-tenth to one-third of the maximum electronenergy for typical flash x-ray sources in the 10 MV to 1 MVendpoint voltage region, respectivel
21、y.4.8 Endpoint VoltageEndpoint voltage refers to the peakvoltage across a bremsstrahlung diode in a flash x-ray source.For example, a 10-MV flash x-ray source is designed to reacha peak voltage of 10-MV across the anode-cathode gap whichgenerates the electron beam for striking a converter to produce
22、bremsstrahlung.4.9 Equilibrium Absorbed Doseabsorbed dose at someincremental volume within the material in which the conditionof electron equilibrium (the energies, number, and direction ofcharged particles induced by the radiation are constantthroughout the volume) exists. For lower energies whereb
23、remsstrahlung production is negligible the equilibrium ab-sorbed dose is equal to the kerma.NOTE 1For practical purposes, assuming the spatial gradient in thex-ray field is small over the range of the maximum energy secondaryelectrons generated by the incident photons, the equilibrium absorbeddose i
24、s the absorbed dose value that exists in a material at a distance fromany interface with another material greater than this range.5. Significance and Use5.1 Flash x-ray facilities provide intense bremsstrahlungradiation environments, usually in a single sub-microsecondpulse, which unfortunately, oft
25、en fluctuates in amplitude,shape, and spectrum from shot to shot. Therefore, appropriatedosimetry must be fielded on every exposure to characterizethe environment. These intense bremsstrahlung sources have avariety of applications which include the following:5.1.1 Generation of xray and gammaray env
26、ironmentssimilar to that from a nuclear weapon burst.5.1.2 Studies of the effects of xrays and gamma rays onmaterials.5.1.3 Studies of the effects of radiation on electronic devicessuch as transistors, diodes, and capacitors.5.1.4 Vulnerability and survivability testing of militarysystems and compon
27、ents.5.1.5 Computer code validation studies.5.2 This guide is written to assist the experimenter inselecting the needed dosimetry systems (often in an experimentnot all radiation parameters must be measured) for use atpulsed xray facilities. This guide also provides a briefsummary of the information
28、 on how to use each of thedosimetry systems. Other guides (see Section 3) provide moredetailed information on selected dosimetry systems in radiationenvironments and should be consulted after an initial decisionis made on the appropriate dosimetry system to use. There aremany key parameters which de
29、scribe a flash x-ray source, suchas dose, dose rate, spectrum, pulse width, etc., such thattypically no single dosimetry system can measure all theparameters simultaneously.6. General Characteristics of Flash X-ray Sources6.1 Flash X-ray Facility ConsiderationsFlash xray sources operate like a denta
30、l xray source but atmuch higher voltages and intensities and usually in a single,very short burst. A high voltage is developed across ananode-cathode gap (the diode) and field emission creates apulsed electron beam traveling from the cathode to the anode.A high atomicnumber element such as tantalum
31、is placed onthe anode to maximize the production of bremsstrahlungcreated when the electrons strike the anode. Graphite is usuallyplaced downstream of the converter to stop the electron beamcompletely but let the x radiation pass through. Finally, a debrisshield is sometimes necessary to stop explod
32、ing convertermaterial from leaving the source. All of these componentstaken together form what is commonly called a bremsstrahlungdiode.6.2 Relationship Between Flash X-ray Diode Voltage andX-ray Energy of BremsstrahlungFlash x-ray sources produce bremsstrahlung by generating anintense electron beam
33、 which then strikes a high atomic number(Z) converter such as tantalum. The electron-solid interactionsproduce “braking” radiation or, in German, bremsstrahlung.Fig. 1 shows the typical range of photon energies produced bythree different sources. If the average radiation produced is inthe 20100 keV
34、region, the source is said to be a mediumhardxray simulator. If the average photon energy is in the100300keV region, the term used is “hard xray simulator.”E 18942At the high end of the flash xray range are sources whichproduce an average photon energy of around 2 MeV. Becausethis photon energy is i
35、n the typical gamma-ray spectral range,the source is called a gammaray simulator.The average energy of the bremsstrahlung spectrum, Ephoton,through an optimized converter (1) in the mediumhard xrayregion (50 keV 500 keV) is given empirically by,Ephoton 5 e1/2(4)where Ephotonis the average energy of
36、the bremsstrahlungphotons in keV and e is the average energy of the electrons inthe electron beam incident on the converter in keV. Thisequation and Fig. 1 indicate that most of the photons haveenergies much less than the endpoint electron energy, or involtage units, the flash xray voltage.7. Measur
37、ement Principles7.1 Typically in flash xray irradiations, one is interested insome physical change in a critical region of a device under test(DUT). The dosimetry associated with the study of such aphysical change may be broken into three parts:7.1.1 Determine the absorbed dose in a dosimeter.7.1.2
38、Using the dosimeter measurement, estimate the ab-sorbed dose in the region and material of interest in the DUT.7.1.3 If required, relate the estimated absorbed dose in theDUT to the physical change of interest (holes trapped, interfacestates generated, photocurrent produced, etc.)7.2 This section wi
39、ll be concerned with the first two of theabove listed parts of dosimetry: (1) what is necessary todetermine a meaningful absorbed dose for the dosimeter and(2) what is necessary to extrapolate this measured dose to theestimated dose in the region of interest. The final step indosimetry, associating
40、the absorbed dose with a physicalchange of interest, is outside the scope of this guide.7.3 Energy Deposition7.3.1 Secondary ElectronsBoth in the case of absorbeddose in the DUT and absorbed dose in the dosimeter, theenergy is deposited largely by secondary electrons. That is, theincident photons in
41、teract with the material of, or surrounding,the DUT or the dosimeter and lose energy to Comptonelectrons, photoelectrons, and Auger electrons. The energywhich is finally deposited in the material is deposited by thesesecondary particles.7.3.2 Transport of PhotonsIn some cases, it is necessaryto cons
42、ider the transport and loss of photons as they move tothe region whose absorbed dose is being determined. Acorrection for the attenuation of an incident photon beam is anexample of such a consideration.7.3.3 Transport of ElectronsElectron transport may causeenergy originally imparted to electrons in
43、 one region to becarried to a second region depending on the range of theelectrons. As a result, it is necessary to consider the transportand loss of electrons as they move into and out of the regionswhose absorbed dose is being determined. In particular, it isnecessary to distinguish between equili
44、brium and non-equilibrium conditions for electron transport.7.3.3.1 Charged Particle EquilibriumIn some cases, thenumbers, energies, and angles of particles transported into aregion of interest are approximately balanced by those trans-ported out of that region. Such cases form an important class of
45、limiting cases which are particularly easy to interpret. (See“Equilibrium Absorbed Dose” in Section 4.6.)7.3.3.2 Dose EnhancementBecause photoelectron pro-duction per atom is roughly proportional to the atomic numberraised to the fourth power for energies less than 100 keV (2),one expects more photo
46、electrons to be produced in high atomicnumber layers than in low atomic number layers for the samephoton fluence and spectrum. Thus, there may be a net flow ofenergetic electrons from the high atomic number layers into thelow atomic number layers. This nonequilibrium flow ofelectrons may result in a
47、n enhancement of the dose in the lowatomic number layer. Dose enhancement problems are oftencaused by high atomic number bonding layers (e.g., gold), andFIG. 1 Range of Available Bremsstrahlung Spectra from Flash X-ray SourcesE 18943metallization layers (e.g., WSi or TaSi).7.4 Absorbed Dose in Dosim
48、eter7.4.1 Equilibrium Absorbed Dose in Dosimeter7.4.1.1 It is frequently possible to use dosimeters underapproximately equilibrium conditions. The interpretation of theoutput of the dosimeter is straightforward only when theenergy deposition processes within the dosimeter are approxi-mately in equil
49、ibrium. That is, when the absorbed dose withinthe dosimeter is an equilibrium absorbed dose.7.4.1.2 It is possible to treat nonequilibrium energy depo-sition within a dosimeter, but such an analysis requires electronand photon transport calculations, often in the form of com-puter codes.7.4.2 Limiting Cases7.4.2.1 There are two limiting cases for which the dosimeterdata can be analyzed in a straightforward manner.7.4.2.2 Limiting Case One: Short Electron Range7.4.2.2.1 For this case, secondary electron ranges are smallin compariso
