Neutron transmission and capture measurements and analysis of /sup 60/Ni from 1 to 450 keV

Abstract

High-resolution transmission and capture measurements of M Ni-enricned targets have been made at the Oak Ridge Electron Linear Accelerator (ORELA) from a few eV to 1800 keV in trarsmissior. and from 2.5 keV to 5 MeV in capture. The transmission data from I to 450 keV were analyzed with a muiti-level R-matrix code which uses the Bayes' theorem for the fitting process. This code provides the energies and neutron widths of toe resonances inside the 1-to 450-keV region as well as a possible parameterization for outside resonances to describe the smooth cross section in this region. The capture data were analyzed with a least-squares fitting code using the Breit-Wigner formula. From 2.S to 450 LeV, 166 resonances were seen in both sets of data. Correspondence between the energy scales shows a discontinuity around 300 keV which makes the matching of resonances at higher energies difficult. Eighty-nine resonances were seen in the capture data only. Average parameters for the '0 observed »wave resonances were deduced. The average level spacing D" was found to be equal to I5.2_± 1.5 keV, the strength function, S 0 , equal to (2.2 ± 0.6) X 10-4 and the average radiation width, H,, equal to 1.30 ± 0.07 eV. The staircase plot of the reduced level widths and the plot of the Lorentz-weighted strength function averaged over various energy intervals show possible evidence for doorway states. The level densities calculated with the Fermi-gas model for £ = 0 and for £ > 0 resonances were compared with the cumulative number of observed resonances, but the analysis is not conclusive. The average capture cross section as a function of the neutron incident energy is compared to the tail of the giant electric dipole resonance prediction. ? The experimental conditions of the capture measurements are given in Sect. 4 wiih a discussion of the various corrections applied to the raw data. The capture data analysis made with a least-squares fitting code using the Breit-Wigner formalism is reported in Sect. 5, Section 6 deals with problems encountered in the energy scales of the two sets of data. In Sect. 7, the resonance parameters obtained from the analysis of both data sets are reported and their uncertain ties discrised. Comparisons ?<iin previously reported resonance parameters for *°Ni are made in Sect. 8. The behavior of the average resonance parameters is analyzed in Sect. 9. Possible evidence for door way states is discussed. 2. TRANSMISSION MEASUREMENTS AND DATA PROCESSING The transmission measurements were made by the time-of-flight technique using neutron pulses from the ORELA v/ater-moderated tantalum target and a 78.203-m flight path. Measurements were made on two samples of *°Ni enriched to 99.7% with thicknesses of 0.00736 and 0.0744 atoms/barn. At the location o. the samples 9 m from the neutron target, the neutron beam was collimated to a diameter of 2.4 cm. A neutron house monitor was used to normalize the sample-in sample-out data to compensate for variations in the neutron production rate during the runs which were of _ f...

Uncertainties in radiative neutron-capture rates relevant to the $A\sim 80$ $r$-process peak

“…A temperature-dependent HFB plus combinatorial level 60 Ni(n,γ), data from Refs. [62,63]; (c) 61 Ni(n,γ), data from Ref. [64], (d) 62 Ni(n,γ), data from Refs.…”

Microscopic folding model analysis of the radiative(n,γ)reactions near theZ=28shell closure and the weaksprocess

“…The experimental (n, γ) cross sections of 58 Ni are taken from Refs. [41][42][43][44]. Perey et al [43] presented both energy-averaged and stellar-averaged cross section values for 58 Ni.…”

“…[41][42][43][44]. Perey et al [43] presented both energy-averaged and stellar-averaged cross section values for 58 Ni. The energy averaged cross sections are scattered and hence we have not plotted them.…”

Microscopic folding model analysis of the radiative $(n,γ)$ reactions near the $Z=28$ shell-closure and the weak s-process

“…The experimental values are from Refs. [26,[41][42][43][44][45][46][47][48][49][50]. Elements of nickel are used as important constituents of structural materials.…”