1、Designation: E2450 11Standard Practice forApplication of CaF2(Mn) Thermoluminescence Dosimeters inMixed Neutron-Photon Environments1This standard is issued under the fixed designation E2450; the number immediately following the designation indicates the year oforiginal adoption or, in the case of re
2、vision, the year 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 practice describes a procedure for correcting aCaF2(Mn) thermoluminescence dosimeter (TLD) re
3、ading forits response to neutrons during the irradiation. The neutronresponse may be subtracted from the total TLD response togive the gamma-ray response. In fields with a large neutroncontribution to the total response, this procedure may result inlarge uncertainties.1.2 More precise experimental t
4、echniques may be applied ifthe uncertainty derived from this practice is larger than thelevel that the user can accept. These more precise techniquesare not discussed here. The references in Section 8 describesome of these techniques.1.3 This practice does not discuss effects on the TLDreading from
5、neutron interactions with the material surround-ing the TLD and used to ensure a charged particle equilibrium.These effects will depend on the isotopic composition of thesurrounding material and its thickness, and on the incidentneutron spectrum (1).21.4 The values stated in SI units are to be regar
6、ded asstandard.2. Referenced Documents2.1 ASTM Standards:3E170 Terminology Relating to Radiation Measurements andDosimetryE666 Practice for CalculatingAbsorbed Dose From Gammaor X RadiationE668 Practice for Application of Thermoluminescence-Dosimetry (TLD) Systems for DeterminingAbsorbed Dosein Radi
7、ation-Hardness Testing of Electronic DevicesE720 Guide for Selection and Use of Neutron Sensors forDetermining Neutron Spectra Employed in Radiation-Hardness Testing of ElectronicsE721 Guide for Determining Neutron Energy Spectra fromNeutron Sensors for Radiation-Hardness Testing of Elec-tronicsE722
8、 Practice for Characterizing Neutron Fluence Spectrain Terms of an Equivalent Monoenergetic Neutron Fluencefor Radiation-Hardness Testing of ElectronicsE1854 Practice for Ensuring Test Consistency in Neutron-Induced Displacement Damage of Electronic PartsF1190 Guide for Neutron Irradiation of Unbias
9、ed ElectronicComponents3. Terminology3.1 Definitions:3.1.1 absorbed dosesee Terminology E170.3.1.2 exposuresee Terminology E170.3.1.3 kermasee Terminology E170.3.1.4 linear energy transfer (LET)the energy loss per unitdistance as a charged particle passes through a material.Electrons resulting from
10、gamma-ray interactions in a 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!F
11、E!(1)where:F(E) = the neutron fluence, andM(E) = the apparent dose (light output) in the TLD causedby neutrons of energy E.4. Significance and Use4.1 Electronic devices are typically tested for survivabilityto gamma radiation in pure gamma-ray fields. Testing elec-tronic device response against neut
12、rons is more complex sincethere is invariably a gamma-ray component in addition to theneutron field. The gamma-ray response of the electronic deviceis typically subtracted from the overall response to find the1This practice is under the jurisdiction of ASTM Committee E10 on NuclearTechnology and App
13、lications and is the direct responsibility of SubcommitteeE10.07 on Radiation Dosimetry for Radiation Effects on Materials and Devices.Current edition approved Nov. 1, 2011. Published November 2011. Originallyapproved in 2005. Last previous edition approved in 2006 as E2450-06. DOI:10.1520/E2450-11.
14、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, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Docume
15、nt Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.device response to neutrons. This approach to the testingrequires a determination of the gamma-ray exposure in themixed field. To enhance the neutron
16、effects, the radiation fieldis sometimes selected to have as large a neutron component aspossible.4.2 CaF2(Mn) TLDs are often used to monitor the gamma-ray dose in mixed neutron/gamma radiation fields. Since thedosimeters are exposed along with the device under test to themixed field, their response
17、 must be corrected for neutrons. In afield rich in neutrons, the uncertainty in the interpretation of theTLD response grows. In fields with relatively few neutrons, thetotal TLD response may be used to make a correction forgamma response of the device under test. Under this condition,the relative un
18、certainty in the TLD neutron response is notlikely to drive the overall uncertainty in the correction to theelectronic device response.4.3 This practice gives a means of estimating the responseof CaF2(Mn) TLDs to neutrons. This neutron response is thensubtracted from the measured response to determi
19、ne the TLDresponse due to gamma rays. The procedure has relatively highuncertainty because the neutron response of CaF2(Mn) TLDsmay vary depending on the source of the material, and thisprocedure is a generic calculation applicable to CaF2(Mn)TLDs independent of their manufacturer/source. The neutro
20、nresponse given in this practice is a summary of CaF2(Mn) TLDresponses reported in the literature. The associated uncertaintyenvelops the range of results reported, and includes the varietyof CaF2(Mn) TLDs used as well as the uncertainties in thedetermination of the neutron response as reported by v
21、ariousauthors.4.4 Should the user find the resulting uncertainties too largefor his purposes, the neutron response of the particularCaF2(Mn) TLDs in use must be determined. This practice doesnot supply guidance on how to determine the neutron responseof a specific batch of TLDs.4.5 Neutron effects o
22、n electronics under test are usuallyreported in terms of 1-MeV(Si) equivalent fluence (E722).Neutron effects of TLDs, as discussed here, are reported inunits of absorbed dose, since they are corrections to thegamma-ray dose.5. Exposure Procedure5.1 Determine the neutron and gamma-ray environments.Ca
23、lculate the relative neutron response of the TLDs. If thisresponse is negligible, document this maximum bound of theTLD response to the neutron environment. No further mea-surements are required for the purpose of documenting theneutron sensitivity of the TLDs.5.2 Expose the TLD along with the devic
24、e under test (seePractice E1854 and Guide F1190). 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 neutron spectrum must be known (s
25、ee Guides E720and E721). This may be determined in a separate exposure. Aneutron monitor should be used on the irradiation along withthe device under test (see Practice E1854). The device undertest must not significantly perturb the neutron spectrum.5.4 Practice E668 provides information on the cali
26、brationand use of CaF2(Mn) dosimeters for use in X-ray and gammaradiation fields as well as for electrons in a designated energyrange. The guidance in this standard is to adopt, for use inmixed neutron-gamma radiation fields, these same calibration,handling, and read-out techniques for CaF2(Mn) TLDs
27、. Inparticular, the CaF2(Mn) TLDs that are used in a mixedneutron photon field should only be calibrated in a well-characterized gamma-only radiation source. See Section 9 ofE668.6. Neutron Sensitivity of CaF2(Mn)6.1 Thermal Neutrons:6.1.1 Thermal neutron responses of CaF2(Mn) ranging from0.06 to 0.
28、89 GyCaF2(Mn) (6 to 89 radCaF2(Mn) per1012n/cm2are reported (2). The sensitivity may depend onseveral factors, one of the most important parameters being themanganese doping of the TLD. The sensitivity may also be afunction of dosimeter size, since the dosimeter surface-to-volume ratio affects the p
29、ortion of the charged particles bornwithin the TLD that deposit their dose outside the TLD.Horowitz (3) reported a thermal neutron response of 0.34Gy(CaF2) (34 radCaF2) per 1012n/cm2for CaF2(Mn), with2 % Mn by weight, for TLD of dimensions 0.165 by 0.165 by0.083 cm.NOTE 1Thermal neutron response is
30、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. For the Co-60 gamma energy, the conversion fromGy(air) to Gy(CaF2) is 0.975. Thus, in a Co-60 source, Gy(CaF2) is 0.
31、0085times 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 energy-de
32、pendentfast-neutron response is displayed in Fig. 1 and listed in Table1. For the purpose of this practice, the fast-neutron response isthe response due to a neutron with an energy above 0.4 eV.Table 1 is the Rinard (4) response function multiplied by 1.2.The factor of 1.2 was used to scale the resp
33、onse function togive an optimal fit to a variety of measured data. See Fig. 2 forthe quality of this coverage. Use this response to calculate thefast 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 unce
34、rtainty in thisresponse as 50 % of the calculated value.6.3 Subtract the thermal and fast neutron responses from themeasured responses to obtain the gamma-ray response of theTLD:DG5 DMeas2 DThermal2 DFast(3)6.3.1 The uncertainties are uncorrelated and should beadded in quadrature:sDG5=sDMeas21sDTher
35、mal21sDFast2(4)E2450 1127. Reporting7.1 The gamma-ray dose is reported after the neutroncorrections are made to the TLD response. Sometimes anadditional correction is made to convert from units of dose inCaF2(Mn) to dose in the material of the device under test (seePractice E666).7.2 The corrections
36、 for neutron response shall be retainedby the measuring laboratory and be made available uponrequest. The documentation for the correction should referenceinformation used from fast or thermal neutron monitors and theneutron spectrum used to characterize the radiation field.7.3 If the correction for
37、 neutron response to the TLD isnegligible (5 %), a correction need not be made. The lack ofcorrection, and the reasons, shall be stated.7.4 The uncertainty in the dose reported from the TLDmeasurement shall include the uncertainty due to neutroneffects.8. Precision and Bias8.1 None of the uncertaint
38、y attributable to the neutroncorrection process addressed in this practice is derived bystatistical techniques. Therefore, all the uncertainty is Type B.FIG. 1 Fast-Neutron Sensitivity of CaF2(Mn) TLDsTABLE 1 Fast Neutron Sensitivity of CaF2(Mn) TLDsEnergy(MeV)ResponseGy(CaF2)/ncm-2Energy(MeV)Respon
39、seGy(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 2.02E+00 1.75E-131.07E-05 3.22E-16 4.09E-02 5.56E-15 2.4
40、7E+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 1.83E-01 2.24E-14 6.70E+00 4.99E-129.61E-04 2.68E-16 2.2
41、4E-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 6.08E-01 6.49E-144.31E-03 1.03E-15 7.43E-01 6.11E-147.10
42、E-03 1.40E-15 9.07E-01 8.04E-14E2450 113The level of uncertainty is quite large, since it encompasses therange of response of CaF2(Mn) independent of a specificmanufacturer or TLD batch. The uncertainty in the reportedgamma-ray dose will depend on the relative amounts ofneutrons and gamma rays in th
43、e exposure field.8.2 See Practice E668 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 the light output from oneGy(CaF2) as deliver
44、ed in the neutron field divided by the lightoutput of the TLD from one Gy(CaF2) as delivered in a Co-60gamma ray field. There is a significant variation seen in theresponse. The shaded area represents the 1 s range of valuesspecified by this practice. Reference (11) suggests an averagevalue of 0.29
45、6 0.18 for neutrons below 10 MeV. For reactorfields based on235U fission, a lower value would be moreappropriate, such as 0.12 6 0.1. Thus, the light output of theCaF2(Mn) in235U fission radiation fields is approximated by:light 5 KDGCaF2Mn! 1 0.12 DNCaF2Mn!# (5)where K is the proportionality consta
46、nt for the light output ofthe TLD reader as determined by the calibration in thegamma-only radiation field, thus making the total light outputproportional to the gamma-ray dose, DG, plus 12 % of theneutron dose DN.9. Keywords9.1 dosimetry; gamma; LET; mixed-field; neutron; TLDAPPENDIX(Nonmandatory I
47、nformation)X1. LET DEPENDENCE OF LIGHT OUTPUT OF TLDSX1.1 Both neutrons and gamma rays produce ionizing dosein CaF2(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
48、 rays and for neutrons. Gamma raysproduce electrons, which have a low LET. The heavy ionsresulting from neutron interactions have high LET, i.e. a highdensity of the ionizing energy that may enhance recombinationeffects. The high LET of the dose results in increased chargerecombination and tends to
49、suppress the neutron response inthe TLD. Fig. X1.1 (12) shows the relative efficiency forconversion of absorbed dose into TLD light (h) as a function ofLET/density (L/r). Fig. X1.1 is normalized to a Co-60 effi-ciency of 1.0. The figure shows that the heavy charged particlesproduced by neutron interactions in TLD material have agreatly reduced efficiency.The data in Fig 2 is reported as measured and calculated by various authors, including Rinard (4), Schraube (5), Scarpa (6), Blum (7), Handloser (8), Goldstein (9), andHenniger (10).FIG. 2 Relati
