Neutron resonance spectroscopy:Bi209

Abstract

Neutron total cross section vs energy measurements were made for several thicknesses of bismuth metal. The results of the resonance parameter evaluation for 30 levels (12 $s$ and 18 $p$) to 75 keV are given. Parameters for the $p$ levels, and for three weak $s$ levels were determined using a transmission area analysis. An $R$-matrix multilevel shape analysis fitting was used to obtain the final choice resonance parameters for the nine dominant $l=0\mathrm{}$ levels. The experimental points and $R$-matrix fit curve to 75 keV are shown. The ($E_0,J,{\Gamma }_n$) choices for these nine levels are (0.800, 5, 4.6), (2.312, 4, 19.5), (5.112, 5, 5.4), (12.15, 4, 270), (15.54, 4, 118), (27.08, 4, 24), (33.34, 4, 240), (45.58, 5, 160), and (69.18, 5, 520), where $E_0$ is in keV and ${\Gamma }_n$ is in eV. On the basis of these levels, we obtain for the $s$ and $p$ strength functions $10{}_{}{}^4{}_{}{}^{}S_0^{}{}_{}{}^{}=\left({0.62}_{-0.20\mathrm{}}^{+0.36\mathrm{}}\right)$ and $10{}_{}{}^4{}_{}{}^{}S_1^{}{}_{}{}^{}=\left({0.13}_{-0.04\mathrm{}}^{+0.06\mathrm{}}\right)$. A channel radius of 9 fm was used to calculate $S_1$ and the evaluation ignores the possibility that some $p$ levels were missed below 75 keV.