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

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 ${\sigma }_0=(7200\mathrm{}\pm 200)$, $E_0=(0.176\mathrm{}\pm 0.002)$ ev, and $\Gamma =(0.115\mathrm{}\pm 0.002)$ ev with a value of (5.3±0.7) added as a "constant" term in the total cross section. (Energy is in ev and cross sections in units of ×${10}^{-24\mathrm{}}$ ${\mathrm{cm}}^2$/atom.) The silver resonance levels have been remeasured with essential agreement with the previous results. Three levels are well defined at (5.1±0.1) ev, (16±1) ev, and (45±4) ev. Antimony has also been checked and the upper "level" has been partially resolved into two levels at (15±1) ev and (21±1.5) ev. The other level is at (5.8±0.15) ev and there is no indication of higher energy levels. Manganese is found to have a strong level at (300±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 $\sigma =\left[\right(2.26\mathrm{}\pm 0.4)+(2.24\pm 0.05\left)E^{\frac{1}{2}}\right]$ The iridum curve shows high detail. This includes strong levels at (0.64±0.015) ev, (1.27±0.04) ev, (5.2±0.2) ev, and (8.7±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 $\sigma =\left[\right(14\mathrm{}\pm 6)+(64\pm 2)E^{-\frac{1}{2}}$. Further analysis has been made for most of the resonances.