ASTM E526-08

Refer to Guide E 844 for the selection, irradiation, and quality control of neutron dosimeters.

Refer to Test Method E 261 for a general discussion of the determination of fast-neutron fluence rate with threshold detectors.

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.

⁴⁶Sc has a half-life of 83.79 days. The ⁴⁶Sc decay 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.

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

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.

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.

⁴⁶Ti and ⁴⁶Sc have cross sections for thermal neutrons of 0.59 and 8 barns, respectively ; 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.

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) reaction and the ⁴⁷Ti(n,np) contribution to the ⁴⁶Sc production, normalized (at 14.7 MeV) 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 E 1018 for descriptions of recommended tabulated dosimetry cross sections.

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

Note 1—Since the cross section for the (n,np) reaction is relatively small for energies less than 12 MeV and is not easily distinguished from that of the (n,p) reaction, this test method will refer to the (n,p) reaction only.

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 E 261).

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 E 261.

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.