Slow Neutron Velocity Spectrometer Studies I. Cd, Ag, Sb, Ir, Mn

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Abstract

The Columbia Neutron Velocity Spectrometer has been completely redesigned and enlarged to permit 32 separate measurements to be made simultaneously with greatly improved resolution and precision. A detailed comparison between the experimentally measured cross section of Cd and the Breit-Wigner one-level formula gives excellent agreement for over a factor of 100 in energy and 1000 in cross section. The selected parameters are ${\ensuremath{\sigma}}_{0}=(7200\ifmmode\pm\else\textpm\fi{}200)$, ${E}_{0}=(0.176\ifmmode\pm\else\textpm\fi{}0.002)$ ev, and $\ensuremath{\Gamma}=(0.115\ifmmode\pm\else\textpm\fi{}0.002)$ ev with a value of (5.3\ifmmode\pm\else\textpm\fi{}0.7) added as a "constant" term in the total cross section. (Energy is in ev and cross sections in units of \ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}24}$ ${\mathrm{cm}}^{2}$/atom.) The silver resonance levels have been remeasured with essential agreement with the previous results. Three levels are well defined at (5.1\ifmmode\pm\else\textpm\fi{}0.1) ev, (16\ifmmode\pm\else\textpm\fi{}1) ev, and (45\ifmmode\pm\else\textpm\fi{}4) ev. Antimony has also been checked and the upper "level" has been partially resolved into two levels at (15\ifmmode\pm\else\textpm\fi{}1) ev and (21\ifmmode\pm\else\textpm\fi{}1.5) ev. The other level is at (5.8\ifmmode\pm\else\textpm\fi{}0.15) ev and there is no indication of higher energy levels. Manganese is found to have a strong level at (300\ifmmode\pm\else\textpm\fi{}40) ev and probably other unresolved higher energy levels. There is no indication of levels at lower energies where the cross section shows a normal $\frac{1}{v}$ type absorption with $\ensuremath{\sigma}=[(2.26\ifmmode\pm\else\textpm\fi{}0.4)+(2.24\ifmmode\pm\else\textpm\fi{}0.05){E}^{\frac{1}{2}}]$ The iridum curve shows high detail. This includes strong levels at (0.64\ifmmode\pm\else\textpm\fi{}0.015) ev, (1.27\ifmmode\pm\else\textpm\fi{}0.04) ev, (5.2\ifmmode\pm\else\textpm\fi{}0.2) ev, and (8.7\ifmmode\pm\else\textpm\fi{}0.3) ev. There is a low broad transmission dip for energies above about 20 ev, indicating several more levels may be present. A $\frac{1}{v}$-type absorption is observed in the thermal region with $\ensuremath{\sigma}=[(14\ifmmode\pm\else\textpm\fi{}6)+(64\ifmmode\pm\else\textpm\fi{}2){E}^{\ensuremath{-}\frac{1}{2}}$. Further analysis has been made for most of the resonances.

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