Standard Test Method for Measuring Fast-Neutron Reaction Rates by Radioactivation of Titanium
5.1 Refer to Guide E844 for the selection, irradiation, and quality control of neutron dosimeters.
5.2 Refer to Test Method E261 for a general discussion of the determination of fast-neutron fluence rate with threshold detectors.
5.3 Titanium has good physical strength, is easily fabricated, has excellent corrosion resistance, has a melting temperature of 1668°C, and can be obtained with satisfactory purity.
5.4 46Sc has a half-life of 83.787 (16)3 days(1).4 The 46Sc decay emits a 0.889271 (2) MeV gamma 99.98374 (35) % of the time and a second gamma with an energy of 1.120537 (3) MeV 99.97 (2) % of the time.
5.5 The isotopic content of natural titanium recommended for 46Ti is 8.25 %. (2)
5.6 The radioactive products of the neutron reactions 47Ti(n,p)47Sc (τ1/2 = 3.3485 (9) d) (1) and 48Ti(n,p)48Sc (τ1/2 = 43.67 h), (2) might interfere with the analysis of 46Sc.
5.7 Contaminant activities (for example, 65Zn and 182Ta) might interfere with the analysis of 46Sc. See 7.1.2 and 7.1.3 for more details on the 182Ta and 65Zn interference.
5.8 46Ti and 46Sc have cross sections for thermal neutrons of 0.59 ± 0.18 and 8.0 ± 1.0 barns, respectively (3); therefore, when an irradiation exceeds a thermal-neutron fluence greater than about 2 × 1021 cm–2, provisions should be made to either use a thermal-neutron shield to prevent burn-up of 46Sc or measure the thermal-neutron fluence rate and calculate the burn-up.
5.9 Fig. 1 shows a plot of the Russian Reactor Dosimetry File (RRDF-2002) cross section (4) versus neutron energy for the fast-neutron reactions of titanium which produce 46Sc [that is, natTi(n,X)46Sc]. This cross section is identical, for energies up to 20 MeV, to what is found in the latest International Atomic Energy Agency (IAEA) International Reactor Dosimetry and Fusion File, IRDFF-1.05 (5). Included in the plot is the 46Ti(n,p) reaction and the 47Ti(n,np) contribution to the 46Sc production, normalized per 46Ti atom using the natural abundances (2). This figure is for illustrative purposes only to indicate the range of response of the natTi(n,p) 46Sc reaction. Refer to Guide E1018 for descriptions of recommended tabulated dosimetry cross sections. Fig. 2 compares the cross section for the 46Ti(N,p)47Sc reaction to the current experimental database (6, 7). Fig. 3 compares the cross section for the 47Ti(N, np+d) reaction to the current experimental database (6, 7).
FIG. 1 NatTi(n,X)46Sc Cross Section (Normalized per Ti-46 Atom Using Natural Abundance Data)
FIG. 2 46Ti(n,p)46Sc Cross Section, from RRDF-2002/IRDFF-1.05, with EXFOR Experimental Data
FIG. 3 47Ti(n,np+d)46Sc Cross Section, from RRDF-2002/IRDFF-1.05, with EXFOR Experimental Data
1.1 This test method covers procedures for measuring reaction rates by the activation reactions 46Ti(n,p)46Sc + 47Ti(n, np)46Sc + 47Ti(n,d)46Sc.
Note 1: The cross section for the 47Ti(n,np+d) reaction is relatively small for energies less than 12 MeV and is not easily distinguished from that of the 46Ti(n,p) reaction. This test method will apply to the composite natTi(n,X)46Sc reaction that is typically used for dosimetry purposes.
1.2 The reaction is useful for measuring neutrons with energies above approximately 4.4 MeV and for irradiation times, under uniform power, up to about 250 days (for longer irradiations, or for varying power levels, see Practice E261).
1.3 With suitable techniques, fission-neutron fluence rates above 109 cm–2·s–1 can be determined. However, in the presence of a high thermal-neutron fluence rate, 46Sc depletion should be investigated.
1.4 Detailed procedures for other fast-neutron detectors are referenced in Practice E261.
1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.6 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.
1.7 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.
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