High Resolution Neutron Total Cross Research Articles

Average scattering matrix elements from high resolution neutron total cross sections forS32

A previous analysis of high resolution measurements of the total cross sections for 25- to 1100-keV neutrons on $^{32}\mathrm{S}$ in terms of an $l$-dependent optical model is extended to obtain model-independent but still $l$-dependent average scattering matrix elements from the data. The particular optical model obtained here is essentially the same as that deduced in the previous paper but the matrix elements are more amenable to future analyses with different models.NUCLEAR REACTIONS ($^{32}\mathrm{S}(n, n)$, ${E}_{n}=25\ensuremath{-}1100$ keV, average scattering matrix elements and optical model parameters for $l=0 \mathrm{and} 1$.

High resolution neutron total cross section measurement ofY89

Results of a high resolution neutron time-of-flight experiment for neutron energies $27\ensuremath{\le}E\ensuremath{\le}240$ keV on the target nucleus $^{89}\mathrm{Y} ({J}^{\ensuremath{\pi}}={\frac{1}{2}}^{\ensuremath{-}})$ are presented. The measurement employed a 5 nsec beam burst and a 250 m flight path. A multilevel shape analysis of the data was carried out. The parities of almost all observed resonances were easily determined, and for $s$ wave levels the $J$ values of most resonances were obtained. It was found that the $\ensuremath{\Sigma}{\ensuremath{\Gamma}}_{n}^{0}$ vs $E$ plot of the $l=0$, $J=1$ levels exhibited a significant change in slope over the 240 keV interval, which was interpreted as evidence for a ${1}^{\ensuremath{-}}$ doorway state. The analysis yielded an escape width ${\ensuremath{\Gamma}}^{\ensuremath{\uparrow}}=0.8$ keV and a spreading width ${\ensuremath{\Gamma}}^{\ensuremath{\downarrow}}=100$ keV, with the doorway state located at a neutron energy of 70 keV. No effect attributable to nonstatistical behavior was observed in the $p$ wave channel. Since most $s$ and $p$ wave levels were observed a relatively clean test could be made of the expected ratio of $s$ to $p$ wave level spacings. After estimating the number of missed levels (inferred through the use of the Porter-Thomas distribution), the experimental ratio of $s$ to $p$ wave spacings was found to be 2.74. This is in disagreement with the theoretical level density prediction of 2.06. The average $s$, $p$ strength functions and level spacings are ${S}_{0}=0.28\ifmmode\pm\else\textpm\fi{}0.05\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$, ${S}_{1}=2.64\ifmmode\pm\else\textpm\fi{}0.03\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$, ${〈D〉}_{l = 0}=4.0$ keV, ${〈D〉}_{l = 1}=1.46$ keV.NUCLEAR REACTIONS Neutron total cross section measurement of $^{89}\mathrm{Y}$, $27<E<240$ keV. Multilevel analysis, determined $E$, ${J}^{\ensuremath{\pi}}$, ${\ensuremath{\Gamma}}_{n}$ of resonances. Deduced $s$ and $p$ wave strength functions, doorway state parameters ${E}_{d}$, $\ensuremath{\Gamma}\ensuremath{\uparrow}$, $\ensuremath{\Gamma}\ensuremath{\downarrow}$.

S- and p-wave neutron spectroscopy : Part XIa. Level spacings in even intermediate elements

High resolution neutron total cross sections of separated isotopes of Ca 12, Ca 44, Cr 50, Cr 54, Ni 58, Ni 60, Ni 62, and Ni 64 have been measured using the Li 7(p, n)Be 7 reaction as the source of neutrons. The data have been fitted with a multilevel formula derived from the R Matrix Theory. Widths have been obtained for all recognizable s-wave resonances and for most of the p-wave resonances. The distributions of the reduced widths and local spacings of the s-wave resonances were found to be in good agreement with the combined Porter-Thomas and Wigner distributions. The average s-wave level spacings have been corrected to an excitation energy of 6 MeV and combined with data for Part VIII in this region in order to compare the behavior of the average level spacings with the predictions of various shell models. We obtain reasonably good agreement with both the Rosenzweig model and the model of Newson and Duncan if we assume that, at the excitation energies involved, a major shell is closed at 16 nucleons instead of 20. The data indicate that a dependence of the average level spacing on neutron excess exists but that it probably is not a simple exponential. Attempts to find triple and quadruple coincidences of the resonances due to the Ni, Cr, and Ca isotopes were unsuccessful.