1、Designation: E 2450 06Standard Practice forApplication of CaF2(Mn) Thermoluminescence Dosimeters inMixed Neutron-Photon Environments1This standard is issued under the fixed designation E 2450; the number immediately following the designation indicates the year oforiginal adoption or, in the case of
2、revision, 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 practice describes a procedure for measuringgamma-ray absorbed dose in CaF2(Mn) thermolumi
3、nescencedosimeters (TLDs) exposed to mixed neutron-photon environ-ments during irradiation of materials and devices. The practicehas broad application, but is primarily intended for use in theradiation-hardness testing of electronics. The practice is appli-cable to the measurement of absorbed dose f
4、rom gammaradiation present in fields used for neutron testing.1.2 This practice describes a procedure for correcting for theneutron response of a CaF2(Mn) TLD. The neutron responsemay be subtracted from the total response to give the gamma-ray response. In fields with a large neutron contribution to
5、 thetotal response, this procedure may result in large uncertainties.1.3 More precise experimental techniques may be applied ifthe uncertainty derived from this practice is larger than the usercan accept. These techniques are not discussed here. Thereferences in Section 8 describe some of these tech
6、niques.1.4 This practice does not discuss effects on the TLDreading of neutron interactions with material surrounding theTLD to ensure charged particle equilibrium. These effectsdepend on the surrounding material and its thickness, and onthe neutron spectrum (1).22. Referenced Documents2.1 ASTM Stan
7、dards:3E 170 Terminology Relating to Radiation Measurementsand DosimetryE 666 Practice for CalculatingAbsorbed Dose from Gammaor X RadiationE 668 Practice for Application of Thermoluminescence Do-simetry (TLD) Systems for Determining Absorbed Dose inRadiation-Hardness Testing of ElectronicsE 720 Gui
8、de for Selection and Use of Neutron-ActivationFoils for Determining Neutron Spectra Employed inRadiation-Hardness Testing of ElectronicsE 721 Guide for Determining Neutron Energy Spectra fromNeutron Sensors for Radiation-Hardness Testing of Elec-tronicsE 722 Practice for Characterizing Neutron Energ
9、y FluenceSpectra in Terms of an Equivalent Monoenergetic NeutronFluence for Radiation-Hardness Testing of ElectronicsE 1854 Practice for Assuring Test Consistency in Neutron-Induced Displacement Damage of Electronic PartsF 1190 Guide for Neutron Irradiation of Unbiased Elec-tronic Components3. Termi
10、nology3.1 Definitions:3.1.1 absorbed dosesee Terminology E 170.3.1.2 exposuresee Terminology E 170.3.1.3 kermasee Terminology E 170.3.1.4 linear energy transfer (LET)the energy loss per unitdistance as a charged particle passes through a material.Electrons resulting from gamma-ray interactions in a
11、materialgenerally have a low LET. Heavy charged particles resultingfrom neutron interactions with a material generally have a highLET.3.1.5 neutron sensitivity m(E)the ratio of the detectorreading, that is, the effective neutron dose, to the neutronfluence. Thus,mE! 5ME!FE!(1)where:F(E) = the neutro
12、n fluence, andM(E) = the apparent dose (extra light output) in the TLDcaused by neutrons of energy E.4. Significance and Use4.1 Electronic devices are typically tested for survivabilityagainst gamma radiation in pure gamma-ray fields. Testingtheir response against neutrons is more complex since ther
13、e isinvariably a gamma-ray component to the neutron field. The1This practice is under the jurisdiction of ASTM Committee E10 on NuclearTechnology and Applications and is the direct responsibility of SubcommitteeE10.07 on Radiation Dosimetry for Radiation Effects on Materials and Devices.Current edit
14、ion approved May 1, 2006. Published May 2006. Originallyapproved in 2005. Last previous edition approved in 2005 as E 2450-05.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontac
15、t ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.gamma-ray response of th
16、e device is subtracted from theoverall response to find the response to neutrons. This testingthus requires a determination of the gamma-ray exposure in themixed field. To enhance the neutron effects, the field issometimes selected to have as large a neutron component aspossible.4.2 CaF2(Mn) thermol
17、uminescent detectors are often usedto monitor the gamma-ray dose for this type of testing. Sincethey are exposed along with the device under test to the mixedfield, their response must be corrected for neutrons. In a fieldrich in neutrons, the uncertainty in the TLD response grows,but this may be un
18、important since the gamma-ray effects on thedevice under test may be relatively small. In fields withrelatively few neutrons, the TLD response may be used tomake a relatively large correction for gamma response on thedevice under test. Under this condition, the relative uncertaintyin the TLD respons
19、e shrinks.4.3 This practice gives a means of estimating the responseof CaF2(Mn) to neutrons. This neutron response is thensubtracted from the measured response to give the response togamma rays. The procedure has relatively high uncertaintybecause the neutron response of CaF2(Mn) may vary depend-ing
20、 on the source of the material, and this procedure is ageneric calculation applicable to CaF2(Mn) independent ofsource. The neutron response given in this practice is asummary of responses reported in the literature. The associateduncertainty envelops the range of results reported, and includesthe v
21、ariety of TLDs used as well as the uncertainties in thedetermination of the neutron response as reported by variousauthors.4.4 Should the user find the resulting uncertainties too largefor his purposes, the neutron response of the particular TLDs inuse must be determined. This practice does not supp
22、ly guid-ance on how to determine the neutron response of a specificbatch of TLDs.4.5 Neutron effects on electronics under test are usuallyreported in terms of 1 MeV equivalent fluence (E 722).Neutron effects of TLDs, as discussed here, are reported inunits of absorbed dose, since they are correction
23、s to thegamma-ray dose.5. Exposure Procedure5.1 Determine the neutron and gamma-ray environments.Calculate the relative neutron response of the TLDs. If thisresponse is negligible, document this result. No further mea-surements are required for the purpose of neutron sensitivity ofthe TLDs.5.2 Expos
24、e the TLD along with the device under test (seePractice E 1854 and Guide F 1190). If there is a non-negligiblefast-neutron or thermal-neutron response, a fast-neutron moni-tor (for example, nickel) or thermal-neutron monitor (forexample, gold) must also be exposed with the device undertest.5.3 The n
25、eutron spectrum must be known (see Guides E 720and E 721). This may be determined in a separate exposure.The device under test must not significantly perturb the neutronspectrum.5.4 Practices E 668 and E 1854 provide information on thecalibration and use of CaF2(Mn) dosimeters.6. Neutron Sensitivity
26、 of CaF2(Mn)6.1 Thermal Neutrons:6.1.1 Thermal neutron responses of CaF2(Mn) ranging from0.06 to 0.89 Gy(CaF2(Mn) (6 to 89 rad (CaF2(Mn) per1012n/cm2are reported (2). The sensitivity may depend on themanganese doping of the TLD. The sensitivity may also be afunction of dosimeter size, since the dosi
27、meter surface-to-volume ratio affects the portion of the charged particles bornwithin the TLD that deposit their dose outside the TLD.Horowitz (3) calculates a thermal neutron response of 0.34Gy(CaF2) (34 rad (CaF2) per 1012n/cm2for CaF2(Mn (2 % byweight) for TLD of dimensions 0.165 by 0.165 by 0.08
28、3 cm.NOTE 1Thermal neutron response is typically reported in terms ofTLD response relative to a Co-60 equivalent Roentgen (R)/n/cm2. ForCo-60 decay gamma rays, the conversion from Roentgen to Gy(air) is0.00869 Gy(air)/R. The conversion from Gy(air) to Gy(CaF2) is 0.975.Thus Gy(CaF2) is 0.0085 times
29、the exposure in Roentgen.6.1.2 A value of 0.45 6 0.45 Gy (45 6 45 rad) (1 s)(CaF2(Mn) per 1012thermal n/cm2shall be used for CaF2(Mn)TLDs.NOTE 2The variation in measured thermal neutron sensitivities forCaF2(Mn) is as large as the average sensitivity.6.2 Fast NeutronsA recommended fast-neutron respo
30、nseis displayed in Fig. 1 and listed in Table 1. For the purpose ofthis practice, the fast-neutron response is the response due toall neutrons above 0.4 eV. Table 1 is the Rinard (4) responsefunction multiplied by 1.2. The factor of 1.2 was used to scalethe response function to give an optimal fit t
31、o a variety ofmeasured data. See Fig. 2 for the quality of this coverage. Usethis response to calculate the fast neutron response in Gy-(CaF2).Response 5*RE! FE!dE (2)where R(E) is taken from Table 1 and F(E) is the neutronspectrum in ncm-2MeV-1. Take the 1 s uncertainty in thisresponse as 50 % of t
32、he calculated value.6.3 Subtract the thermal and fast neutron responses from themeasured responses to obtain the gamma-ray response:DG5 DMeas2 DThermal2 DFast(3)6.3.1 The uncertainties are added in quadrature:sDG5=sDMeas21sDThermal21sDFast2(4)7. Reporting7.1 The gamma-ray dose is reported after the
33、neutroncorrections are made. Sometimes an additional correction ismade to convert from dose CaF2(Mn) to dose in the material ofthe device under test (see Practice E 666). The corrections forneutron response shall be retained by the measuring laboratoryand be made available upon request.7.2 If the co
34、rrection is negligible (5 %), a correction neednot be made. The lack of correction, and the reasons, shall bestated.7.3 The uncertainty in the dose reported from the TLDmeasurement shall include any uncertainty due to neutroneffects.E24500628. Precision and Bias8.1 None of the uncertainty attributab
35、le to this practice isderived by statistical techniques. Therefore, all the uncertaintyis Type B. The level of uncertainty is quite large, since itencompasses the range of response of CaF2(Mn) independentof manufacturer or batch. The uncertainty in the reportedgamma-ray dose will depend on the relat
36、ive amounts ofneutrons and gamma rays in the exposure field.8.2 See Practice E 668 for a description of the statistical(Type A) uncertainties involved with TLD use.8.3 Fig. 2 shows the relative neutron sensitivity ofCaF2(Mn) as determined by various authors. The relativeneutron response is given as
37、the light output from one neutronGy(CaF2) divided by the light output of the TLD to oneGy(CaF2) in a Co-60 gamma ray field. There is a large range ofresponse. The shaded area represents the 1 s range of valuesFIG. 1 Fast-Neutron Sensitivity of CaF2(Mn) TLDsTABLE 1 Fast Neutron Sensitivity of CaF2(Mn
38、) TLDsEnergy(MeV)ResponseGy(CaF2)/ncm-2Energy(MeV)ResponseGy(CaF2)/ncm-2Energy(MeV)ResponseGy(CaF2)/ncm-24.14E-07 9.78E-16 1.50E-02 2.33E-15 1.11E+00 9.18E-141.13E-06 9.78E-16 1.93E-02 3.17E-15 1.35E+00 1.15E-132.38E-06 6.72E-16 2.48E-02 4.02E-15 1.65E+00 1.31E-135.04E-06 4.63E-16 3.19E-02 1.22E-14
39、2.02E+00 1.75E-131.07E-05 3.22E-16 4.09E-02 5.56E-15 2.47E+00 2.69E-132.26E-05 2.28E-16 5.25E-02 2.05E-14 3.01E+00 5.64E-134.78E-05 1.69E-16 8.65E-02 9.67E-15 3.68E+00 1.17E-121.01E-04 1.36E-16 1.23E-01 3.74E-14 4.49E+00 2.08E-122.14E-04 8.42E-17 1.50E-01 2.41E-14 5.49E+00 3.32E-124.54E-04 1.51E-16
40、1.83E-01 2.24E-14 6.70E+00 4.99E-129.61E-04 2.68E-16 2.24E-01 2.46E-14 8.19E+00 6.59E-121.23E-03 3.83E-16 2.73E-01 4.87E-14 1.00E+01 8.10E-121.59E-03 4.67E-16 3.34E-01 6.47E-14 1.22E+01 9.18E-122.04E-03 5.66E-16 4.08E-01 7.24E-14 1.49E+01 8.05E-122.61E-03 6.84E-16 4.98E-01 6.77E-143.36E-03 8.42E-16
41、6.08E-01 6.49E-144.31E-03 1.03E-15 7.43E-01 6.11E-147.10E-03 1.40E-15 9.07E-01 8.04E-14E2450063specified by this practice. Reference (11) suggests an averagevalue of 0.29 6 0.18 for neutrons below 10 MeV. For reactorfields based on235U fission, a lower value would be moreappropriate, such as 0.12 6
42、0.1. Thus, the light output of theCaF2(Mn) is approximated by:light 5 KDGCaF2Mn! 1 0.12 DNCaF2Mn!# (5)where the total light output is proportional to the gamma-raydose DGplus 12 % of the neutron dose DN.9. Keywords9.1 dosimetry; gamma; LET; mixed-field; neutron; TLDAPPENDIX(Nonmandatory Information)
43、X1. LET DEPENDENCE OF LIGHT OUTPUT OF TLDSX1.1 Both neutrons and gamma rays produce dose inCaF2(Mn). Only a few percent of the absorbed energy isreleased in the form of light when the TLD is heated. Theefficiency of the conversion of absorbed dose into light isdifferent for gamma rays and for neutro
44、ns. Gamma raysproduce electrons, which have a low LET. The heavy ionsresulting from neutron interactions have high LET. This tendsto suppress the neutron response. Fig. X1.1 (12) shows therelative efficiency for conversion of absorbed dose into TLDlight (h) as a function of LET/density (L/r). Fig. X
45、1.1 isnormalized to a Co-60 efficiency of 1.0. The figure shows thatthe heavy charged particles produced by neutron interactions inTLD material have a greatly reduced efficiency.X1.2 Calculations (4, 10) of the neutron response of TLDsto neutrons have taken this LET dependence into account. Fig.X1.1
46、 shows substantial variation (even for a given LET) in theefficiency for producing a measurable response. This gives riseto a large uncertainty in the sensitivity of TLDs to neutrons.Additionally, other aspects of the recoil ions also affect theneutron sensitivity. See Ref (13) for a description of
47、theseconsiderations.X1.3 The neutron sensitivity of TLDs may be dependent onthe structure of the material. Small variations in manufacturingprocess, the introduction of ppm contaminants, the annealingprocedure used, and irradiation with large neutron fluencesmay change the neutron sensitivity. These
48、 effects are ignored inthis practice except to the extent that they are bounded by thecorrections in Section 6.As measured and calculated by various authors, including Rinard (4), Schraube (5), Scarpa (6), Blum (7), Handloser (8), Goldstein (9), and Henniger (10).FIG. 2 Relative Neutron Sensitivity
49、of CaF2(Mn)E2450064REFERENCES(1) DePriest, K. R., and Griffin, P. J., “Neutron Contribution to CaF2:MnThermoluminescent Dosimeter Response in Mixed (n/g) Field Envi-ronments,” IEEE Trans. Nucl. Sci., Vol 50, No. 6, December 2003, pp.2393-2398.(2) Horowitz, Y. S., Thermoluminescence and Thermoluminescent Dosim-etry, Vol II, Chapter 2, Table 8.(3) Horowitz, Y. S., “Thermal Neutron Sensitivity of Other TL Materials,”Thermoluminescence and Thermoluminescent Dosimetry, Vol II,Chapter 2.IV.A.4.(4) Rinard, P., and Simons, G., “Calculated Neutron Sensitiviti
