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

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

Pure nickel in the form of foil or wire is readily available, and easily handled.

⁵⁸Co has a half-life of 70.86 days and emits a gamma ray with an energy of 0.8107593-MeV.

Competing activities ⁶⁵Ni(2.5172 h) and ⁵⁷Ni(35.60 h) are formed by the reactions ⁶⁴Ni(n,γ) ⁶⁵Ni, and ⁵⁸Ni(n,2n)⁵⁷Ni, respectively.

A second 9.04 h isomer, ^58mCo, is formed that decays to 70.86-day ⁵⁸Co. Loss of ⁵⁸Co and ^58mCo by thermal-neutron burnout will occur in environments ^, having thermal fluence rates of 3 × 10¹² cm⁻²·s⁻¹ and above. Burnout correction factors, R, are plotted as a function of time for several thermal fluxes in Fig. 1. Tabulated values for a continuous irradiation time are provided in Hogg, et al.

Fig. 2 shows a plot of cross section versus energy for the fast-neutron reaction ⁵⁸Ni(n,p) ⁵⁸Co. This figure is for illustrative purposes only to indicate the range of response of the ⁵⁸Ni(n,p) reaction. Refer to Guide E 1018 for descriptions of recommended tabulated dosimetry cross sections.

Note 1—The data is taken from the Evaluated Nuclear Data File, ENDF/B-VI, rather than the later ENDF/B-VII. This is in accordance with E 1018, section 6.1, since the later ENDF/B-VII data files do not include covariance information. For more details see Section H of reference 8.

FIG. 2 ⁵⁸Ni(n,p)⁵⁸Co Cross Section

1.1 This test method covers procedures for measuring reaction rates by the activation reaction ⁵⁸Ni(n,p)⁵⁸Co.

1.2 This activation reaction is useful for measuring neutrons with energies above approximately 2.1 MeV and for irradiation times up to about 200 days in the absence of high thermal neutron fluence rates (for longer irradiations, see Practice E 261).

1.3 With suitable techniques fission-neutron fluence rates densities above 10⁷ cm⁻²·s⁻¹ can be determined.

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.

Note—The burnup corrections were computed using effective burn-up cross sections of 1650 b for ⁵⁸Co(n,γ) and 1.4E5 b for ^58mCo(n,γ).