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1.1 This test method covers procedures for measuring reaction rates by the activation reactions  ⁴⁶Ti(n,p) ⁴⁶Sc + ⁴⁷Ti(n, np)⁴⁶Sc.

1.2 The reaction is useful for measuring neutrons with energies above approximately 4.4 MeV and for irradiation times up to about 250 days (for longer irradiations, 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 and health practices and determine the applicability of regulatory limitations prior to use.

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 1675°C, and can be obtained with satisfactory purity.

5.4 ⁴⁶Sc has a half-life of 83.79 days.³ The  ⁴⁶Sc decay⁴ emits a 0.8893 MeV gamma 99.984 % of the time and a second gamma with an energy of 1.1205 MeV 99.987 % of the time.

5.5 The isotopic content of natural titanium recommended for  ⁴⁶Ti is 8.25 %.³

5.6 The radioactive products of the neutron reactions   ⁴⁷Ti(n,p)⁴⁷Sc (τ_1/2 = 3.3492 d) and   ⁴⁸Ti(n,p)⁴⁸Sc (τ_1/2 = 43.67 h), might interfere with the analysis of  ⁴⁶Sc.

5.7 Contaminant activities (for example,   ⁶⁵Zn and  ¹⁸²Ta) might interfere with the analysis of  ⁴⁶Sc. See Sections 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 and 8 barns, respectively⁵; 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 cross section versus neutron energy for the fast-neutron reactions of titanium which produce   ⁴⁶Sc [that is, ^NatTi(n,X)⁴⁶Sc]. Included in the plot is the  ⁴⁶Ti(n,p) reaction⁶ and the   ⁴⁷Ti(n,np) contribution to the  ⁴⁶Sc production,⁷ normalized (at 14.7 MeV)⁸ per   ⁴⁶Ti atom. This figure is for illustrative purposes only to indicate the range of response of the  ⁴⁶Ti(n,p) reaction. Refer to Guide E1018 for descriptions of recommended tabulated dosimetry cross sections.

FIG. 1 ^NatTi(n,X)⁴⁶Sc Cross Section (Normalized per Ti-46 Atom)