【国外标准】 Standard Test Method for Measuring Fast-Neutron Reaction Rates by Radioactivation of Copper

5.1 Refer to Guide E844 for the selection, irradiation, and quality control of neutron dosimeters. 5.2 Refer to Practice E261 for a general discussion of the measurement of fast neutron fluence rate with threshold detectors. The general shape of the 63Cu(n,α) 60Co cross section is also shown in Fig. 1 (3, 4, 5) along with a comparison to the current experimental database (6). This figure is for illustrative purposes only to indicate the range of the response of the 63Cu(n,α)60Co reaction. Refer to Guide E1018 for descriptions of recommended tabulated dosimetry cross sections. FIG. 1 63Cu(n,α)60Co Cross Section with EXFOR Experimental Data Note 1: The cross section appropriate for use under this standard is from the IRDFF-II library (5) which, up to an incident neutron energy of 20 MeV, is drawn from the RRDF-2002 library (3) and is identical to the adopted cross section in the IRDF-2002 library (4). See Guide E1018. 5.3 The major advantages of copper for measuring fast-neutron fluence rate are that it has good strength, is easily fabricated, has excellent corrosion resistance, has a melting temperature of 1083°C, and can be obtained in high purity. The half-life of   60 Co is long and its decay scheme is simple and well known. 5.4 The disadvantages of copper for measuring fast neutron fluence rate are the high reaction apparent threshold of 4.5 MeV, the possible interference from cobalt impurity (>1 μg/g), the reported possible thermal component of the (n,α) reaction, and the possibly significant cross sections for thermal neutrons for   63Cu and 60Co [that is, 4.50(2) and 2.0(2) barns, respectively], (7), which will require burnout corrections at high fluences. 1.1 This test method covers procedures for measuring reaction rates by the activation reaction 63Cu(n,α) 60Co. The cross section for 60Co produced in this reaction increases rapidly with neutrons having energies greater than about 4.5 MeV. 60Co decays with a half-life of 5.2711(8)2 years (1)3,4 and emits two gamma rays having energies of 1.173228(3) and 1.332492(4) MeV (1). The isotopic content of natural copper is 69.174(20) % 63Cu and 30.826(20) % 65Cu (2). The neutron reaction, 63Cu(n,γ)64Cu, produces a radioactive product that emits gamma rays [1.34577(6) MeV (E1005)] which might interfere with the counting of the 60Co gamma rays. 1.2 With suitable techniques, fission-neutron fluence rates above 109 cm−2·s−1 can be determined. The 63Cu(n,α)60Co reaction can be used to determine fast-neutron fluences for irradiation times up to about 15 years, provided that the analysis methods described in Practice E261 are followed. If dosimeters are analyzed after irradiation periods longer than 15 years, the information inferred about the fluence during irradiation periods more than 15 years before the end of the irradiation should not be relied upon without supporting data from dosimeters withdrawn earlier. 1.3 Detailed procedures for other fast-neutron detectors are referenced in Practice E261. 1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.