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.

Close

PrevNext

View figure in article