1、Designation: E265 15Standard Test Method forMeasuring Reaction Rates and Fast-Neutron Fluences byRadioactivation of Sulfur-321This standard is issued under the fixed designation E265; 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 () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope1.1 This test method de
3、scribes procedures for measuringreaction rates and fast-neutron fluences by the activationreaction32S(n,p)32P.1.2 This activation reaction is useful for measuring neutronswith energies above approximately 3 MeV.1.3 With suitable techniques, fission-neutron fluences fromabout 5 108to 1016n/cm2can be
4、measured.1.4 Detailed procedures for other fast-neutron detectors aredescribed in Practice E261.1.5 This standard does not purport to address all of thesafety problems, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health p
5、ractices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E170 Terminology Relating to Radiation Measurements andDosimetryE181 Test Methods for Detector Calibration and Analysis ofRadionuclidesE261 Practice for Determining Neutron Flu
6、ence, FluenceRate, and Spectra by Radioactivation TechniquesE720 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
7、Elec-tronicsE844 Guide for Sensor Set Design and Irradiation forReactor Surveillance, E 706 (IIC)E944 Guide for Application of Neutron Spectrum Adjust-ment Methods in Reactor Surveillance, E 706 (IIA)E1018 Guide for Application of ASTM Evaluated CrossSection Data File, Matrix E706 (IIB)3. Terminolog
8、y3.1 Definitions:3.1.1 Refer to Terminology E170.4. Summary of Test Method4.1 Elemental sulfur or a sulfur-bearing compound is irra-diated in a neutron field, producing radioactive32Pby means ofthe32S(n,p)32P activation reaction.4.2 The beta particles emitted by the radioactive decay of32Pare counte
9、d by techniques described in Methods E181 andthe reaction rate, as defined in Practice E261, is calculated fromthe decay rate and irradiation conditions.4.3 The neutron fluence above 3 MeV can then be calcu-lated from the spectral-averaged neutron activation crosssection, , as defined in Practice E2
10、61.5. Significance and Use5.1 Refer to Guides E720 and E844 for the selection,irradiation, and quality control of neutron dosimeters.5.2 Refer to Practice E261 for a general discussion of thedetermination of fast-neutron fluence and fluence rate withthreshold detectors.5.3 The activation reaction pr
11、oduces32P, which decays bythe emission of a single beta particle in 100 % of the decays,and which emits no gamma rays. The half life of32P is 14.284(36)3days (1)4and the maximum beta energy is 1710.66 (21)keV (1).1This test method is under the jurisdiction ofASTM Committee E10 on NuclearTechnology a
12、nd Applicationsand is the direct responsibility of SubcommitteeE10.07 on Radiation Dosimetry for Radiation Effects on Materials and Devices.Current edition approved June 1, 2015. Published August 2015. Originallyapproved in 1970. Last previous edition approved in 2013 as E265 07(2013). DOI:10.1520/E
13、0265-15.2For 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 Document Summary page onthe ASTM website.3The non-boldface number in parentheses after the nuc
14、lear data indicates theuncertainty in the last significant digit of the preceding number. For example, 8.1 s(5) means 8.1 6 0.5 seconds.4The boldface numbers in parentheses refer to the list of references at the end ofthis test method.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700,
15、 West Conshohocken, PA 19428-2959. United States15.4 Elemental sulfur is readily available in pure form andany trace contaminants present do not produce significantamounts of radioactivity. Natural sulfur, however, is composedof32S (94.99 % (26),34S (4.25 % (24) (2), and trace amountsof other sulfur
16、 isotopes. The presence of these other isotopesleads to several competing reactions that can interfere with thecounting of the 1710-keV beta particle. This interference canusually be eliminated by the use of appropriate techniques, asdiscussed in Section 8.6. Apparatus6.1 Since only beta particles o
17、f32Pare counted, proportionalcounters or scintillation detectors can be used. Because of thehigh resolving time associated with Geiger-Mueller counters,their use is not recommended. They can be used only withrelatively low counting rates, and then only if reliable correc-tions for coincidence losses
18、 are applied.6.2 Refer to Test Methods E181 for preparation of apparatusand counting procedures.7. Materials and Manufacture7.1 Commercially available sublimed flowers of sulfur areinexpensive and sufficiently pure for normal usage. Sulfur canbe used directly as a powder or pressed into pellets. Sul
19、furpellets are normally made at least 3 mm thick in order to obtainmaximum counting sensitivity independent of small variationsin pellet mass. A 0.8 g/cm2pellet can be considered infinitelythick for the most energetic beta particle from32P(see Table 1).Due to the relatively long half-life of32P, it
20、may not bepractical to use a pellet more than once.Aperiod of at least oneyear is recommended between uses. However, see 8.2 regard-ing long-lived interfering reaction products.7.2 Where temperatures approaching the melting point ofsulfur are encountered (113C), sulfur-bearing compoundssuch as ammon
21、ium sulfate (NH4)2SO4, lithium sulfate Li2SO4,or magnesium sulfate MgSO4can be used. These are suitablefor temperatures up to 250, 850, and 1000C, respectively. Thereduced sensitivity of these compounds offers no disadvantagesince high temperatures are usually associated with a high-neutron fluence
22、rate. The sulfur content by weight of(NH4)2SO4is 24 %, of Li2SO4is 29.2 %, and of MgSO4is26.6 %.7.3 The isotopic abundance of32S in natural sulfur is 94.996 0.26 atom % (2,3).8. Sample Preparation and Irradiation8.1 Place sulfur in pellet or powdered form in a uniformfast-neutron flux for a predeter
23、mined period of time. Recordthe beginning and end of the irradiation period.8.2 Table 2 lists competing reaction products that must beeliminated from the counting. Those resulting from thermal-neutron capture, that is,33P,35S, and37S, can be reduced by theirradiation of the sulfur inside 1 mm-thick
24、cadmium shields.This should be done whenever possible in thermal-neutronenvironments. Those reaction products having relatively shorthalf-lives, that is,31S,34P,31Si, and37S, can be eliminated bya waiting period before the counting is started. A delay of 24 his sufficient for the longest lived of th
25、ese, although shorterdelays are possible depending on the degree of thermalizationof the neutron field. Finally, those with relatively low betaparticle energies, that is,33P and35S, can be eliminated by theinclusion of a 70-mg/cm2aluminum absorber in front of thedetector. For particularly long decay
26、 times, an absorber must beused because the35S becomes dominant. Note that the use ofan internal (windowless) detector maximizes the interferencein counting from35S.8.3 Irradiated sulfur can be counted directly, or may beburned to increase the efficiency of the counting system.Dilution may be used t
27、o reduce counting system efficiency formeasurements of high neutron fluences.8.4 Burning the sulfur leaves a residue of32P that can becounted without absorption of the beta particles in the sulfurpellet. Place the sulfur in an aluminum planchet on a hot plateuntil the sulfur melts and turns to a dar
28、k amber color. At thispoint the liquid gives off sulfur fumes. Ignite the fumes bybringing a flame close to the dish, and allow the sulfur to burnout completely. In order to reduce the sputtering that can leadto variations in the amount of32P remaining on the planchet,the hot plate must be only as h
29、ot as necessary to melt the sulfur.In addition, air flow to the burning sulfur must be controlled,such as by the placement of a chimney around the sulfur. Countthe residue remaining on the dish for beta activity.NOTE 1The fumes given off by the burning sulfur are toxic. Burningshould be done under a
30、 ventilating hood.8.5 An alternative to burning is sublimation of the sulfurunder a heat lamp. Removal of the sulfur is very gradual, andthere is no loss of32P from sputtering.8.6 Counting of dilute samples is useful for measuring highneutron fluences, although it is applicable to virtually allirrad
31、iation conditions. Use lithium sulfate, reagent grade orbetter, as the target material because of its high melting point(860C), good solubility in water, and minimum production ofundesirable activation products. Prepare a dry powder byspreading about 10 g of Li2SO4in a weighing bottle and placeTABLE
32、 1 Sulfur Counting Rate Versus Mass for a Pellet of25.4-mm DiameterSample Mass, g Relative Counting Rate0.4 0.460.6 0.580.8 0.661.0 0.731.2 0.781.4 0.821.6 0.861.8 0.892.0 0.912.2 0.932.4 0.942.6 0.952.8 0.963.0 0.973.2 0.983.4 0.993.6 0.993.8 1.04.0 1.0E265 152in a drying oven for 24 h at 150C. Pla
33、ce the dried Li2SO4ina dessicator for cooling and storage. Prepare a phosphoruscarrier solution by dissolving 21.3 g of (NH4)2HPO4in waterto make 1 L of solution. Prepare a Li2SO4sample forirradiation by placing about 150 mg of material in an air-tightaluminum capsule or other suitable container. Fo
34、llowing theirradiation, accurately weigh a sample of about 100 mg anddissolve in 5 mL of phosphorus carrier solution to minimizeadsorption of32Pon the glass container.Adrop of concentratedHCl may be used to speed solution of the sample. Place thesolution in a volumetric flask and add additional phos
35、phoruscarrier solution to bring the total volume to 100 mL. Prepare asample for counting by pipetting 0.050 mL of the32P solutiononto a standard planchet and evaporating in air to dryness.Counting procedures and calculations are the same as in othermethods with the exception that an aliquot factor o
36、f 2000 mustbe introduced for the 0.050-mL sample removed from the100-mL flask.9. Calibration9.1 Calibration is achieved by irradiation of sulfur in afast-neutron field of known spectrum and intensity, and mea-suring the resulting32P activity to determine a countingsystems efficiency. This calibratio
37、n is specific for a givendetector system, counting geometry, and sulfur pellet size andmass or sample preparation. It is, however, valid for subse-quent use in measuring activities in any arbitrary spectrum, andtherefore, may be used with activation data from other foils indetermining neutron energy
38、 spectra as described in PracticeE721 and Practice E944.9.2235U fission and252Cf spontaneous fission neutronsources of known source strength have been used for directfree-field calibrations (9).9.3 Once a sulfur counting system is calibrated, it must bemonitored to ensure that the calibration remain
39、s valid. Thereare several isotopes that can be used as reference standards forthis monitoring. One is234Pa, having a maximum beta energyof about 2000 keV, comparable to the 1710-keV beta from32P.It is obtained as a daughter of238U, that can be dispersed as apowder in plastic granules and formed to t
40、he shape of astandard pellet. The concentration of238U can be varied toobtain the desired counting rate. Uranium alpha particles canbe prevented from reaching the detector by use of a 7-mg/cm2absorber. Another useful isotope is210Bi that produces betaparticles having a maximum energy of 1161 keV. It
41、 is obtainedas a daughter of210Pb, and sources are commercially available.10. Activity and Fluence by Detector Efficiency Method10.1 Using a sulfur sample irradiated in a calibration neu-tron field, determine the efficiency, , for the detector system: 5Cfexptd# tiN s 1 2 exp2tc#!1 2 exp2ti#!(1)where
42、:C = counts recorded in detector, less background,f= correction for coincidence losses, if needed, =32P decay constant, = 5.625 107s1,td= decay time, s,tc= count time, s,ti= duration of irradiation, s,N = number of32S atoms in pellet,s= spectrum-averaged cross section for32S in the calibra-tion neut
43、ron field, cm2=1024b, and = neutron fluence, n/cm2.10.1.1 Fig. 1 shows a plot of sulfur cross section as afunction of energy. Fig. 2 shows a plot of the uncertainty in thesulfur cross section as a function of energy. (See Guide E1018for the recommended cross section source.) The spectrum-averaged cr
44、oss section for252Cf fission neutrons is about 74.10mb, and for235U fission is about 68.2 mb. (See Table 2 andRefs (4,6,7,8,10,11,12,13,14,15).)10.1.2 The correction for coincidence losses, f, is a functionof the particular counting system, and may be already ac-counted for by the system electronics
45、 if “live time” is used (seeMethods E181). Coincidence loss corrections can be large,especially when Geiger-Mueller counters are used.TABLE 2 Neutron-induced Reactions in Sulfur Giving Radioactive ProductsReactionCross Section Cross Section (mb)ProductHalflife(1,2,3)MaximumEnergy ofProductBeta (MeV)
46、(1,4)AverageEnergy ofProductBeta(MeV) (1,4)IsotopicAbundanceofTarget (%)(2)Library(5) Material ID ThermalA235UThermalFissionFastB252CfFission1.32S(n,p)32P RRDF-2008 1625 . 68.2 74.10 14.284d (36)1.71066(21)0.6955 (3) 94.99 (26)2.32S(n,2n)31S JENDL-4.0 1625 . 7.760 1062.51052.572 s(13)5.3956( +)1.997
47、5( +)94.99 (26)3.33S(n,p)33P JENDL-4.0 1628 2 1 57.46 58.72 25.383d (40)0.2485 (11) 0.0764 (5) 0.75 (2)4.34S(n,p)34P JENDL-4.0 1631 . 0.8001 1.080 12.43 s(8)5.374 (5) 2.30 (9) 4.25 (24)5.34S(n,)31Si JENDL-4.0 1631 . 3.281 4.067 157.3 m(3)1.4905 (4) 0.595231 4.25 (24)6.34S(n,)35S JENDL-4.0 1631 256 9
48、 0.2753 0.2710 87.37 d(4)0.16714 (8) 0.04863 4.25 (24)7.36S(n,)37S JENDL-4.0 1637 236 6 0.2511 0.2508 5.05 m(2)4.86530(25)0.800 (16) 0.01 (1)AThe thermal cross section corresponds to neutrons with a velocity of 2200 m/s or energy of 0.0253 eV.BThe fast cross section corresponds to the spectrum-avera
49、ged cross section from the ENDF/B-VI (MAT=9228, MF=5, MT=18)235U thermal fission spectrum (6,7) andthe ENDF/B-VI (MAT=9861, MF=5, MT=18)252Cf spontaneous fission spectrum (6-8).E265 153NOTE 2Because of self-absorption in counting thick pellets intact,detection efficiency is not sensitive to small variations in pellet mass butis rather a function of the pellet dimensions. The detection efficiencyshould be determined for each different pellet size that is to be used. Thevalue of N in Eq 1 can be taken to be the arithmetic mean
