Thermal neutron capture in isotopes of nickel

Abstract

The gamma-ray spectra associated with thermal neutron capture in targets of 5SNi, 6~ 62Ni, and 64Ni have been observed with a high-sensitivity pair-spectrometer. Level schemes for the four product nuclei are discussed, correlation of widths with neutron single-particle states examined, and estimates for M1 and E2 7-ray strength functions obtained.The stable isotopes of nickel, which range in mass number from 58 to 64, fall within a mass region commanding considerable interest. In particular, since four of the five naturally occurring isotopes provide even-even target nuclei, one might expect strong correlation between (d, p) single-particle strengths and reduced radiative widths for transitions to l, = 1 final states following thermal neutron capture. Since in the latter reaction much of the radiated strength is concentrated in a few high-energy ~ rays, the characteristics of such 7 rays, and associated energy levels, are well known. The low-energy 7 rays from thermal neutron capture in nickel isotopes have also been well established [1 6]. In addition, several studies of the nickel isotopes have been conducted by means of (d, p) reactions employing either polarized [7][8][9] or unpolarized [l(L13] deuterons. Summaries of energylevel information for nickel are available in recent compilations of the Nuclear Data Sheets [14][15][16][17]. In the present thermal-neutron-capture study, 7 rays of intermediate to high energy, 2 to 9 MeV, were examined by means of Ge(Li)-NaI(T1) pairspectrometer system of greatly improved sensitivity, as reported by Robertson et al. [18]. The remarkable reduction in continuum achieved by this system, in particular at intermediate photon energies, permitted detection of several low intensity y rays helpful in the understanding of decay characteristics, and, in gen-* Permanent Address: Nuclear Physics Division, Pinstech, P.O. Nilore, Rawalpindi, Pakistan eral, led to a more complete collection of information than available to date. Moreover, since the nickel isotopes were studied en bloc, both as constituents of a natural target and as enriched targets, it was possible to obtain accurate estimates of intensities and widths, which checked as consistent with known isotopic abundances and thermal neutron-capture cross sections. Improved Q-value estimates were correspondingly obtained for all isotopes studied.

Ni62(n,γ) andNi<

“…In fact, the thermal cross section obtained with the two choices is 16.2 barn for γ = 2.7 meV, but only 12.8 barn for γ = 2.4 meV. Previous measurements of the thermal cross section result in reported values between 14.0 and 21 barn [43][44][45][46][47][48][49][50], with the majority of values grouped around 14.5 barn [43,45,46,48,49]. Because of this large spread, these previous measurements cannot give us a hint on the correct γ value.…”

GRID lifetime measurements in59, 61, 63Ni following thermal neutron capture

“…The lineshapes of the strongest v-transitions depopulating seven levels in 59Ni, two levels in 61Ni and one level in 63Ni were investigated (see Table 1). These transitions were selected because of their rather larger intensities I s which had been determined in previous (n, 7) measurements [8][9][10]. The product of capture cross-section a, isotopic abundance and relative decay intensity I s is large enough (~ 1 b).…”

Thermal neutron capture?-ray spectroscopy of59Ni and61Ni

“…Considering an additional systematic calibration error of 25 ppm yields a total error of 225eV. Ishaq et al [3] found B, to be 8999.91 (20) keV. This discrepancy might be explained by the fact that the calibration reference energies of lSN used by Ishaq et al seem to be systematically higher than those of the recent 14Ni(n, y) study of Kennett et al [17].…”

“…Previous (n, ~) studies in the even-mass nickel targets [3] have shown deviations from this behaviour insofar as the primary spectra are dominated by very few strong transitions to low-lying negative-parity states which account for some 70%-90% of the primary flux. This direct mechanism thus dominates the capture process and leaves correspondingly little flux to higher excited states; this flux was not fully resolved up to now.…”