New measurements of the total cross section of ${\mathrm{Be}}^9$ (resolution 4 kev) give maxima of 7.75±0.20 barns ($\Gamma =25\mathrm{}$ kev) and 5.25±0.20 barns ($\Gamma =8\mathrm{}$ kev) for the 0.62 Mev and 0.81 Mev resonances, consistent with $J=3\mathrm{}$ and $J=2\mathrm{}$ for the respective compound state spin values. Elastic scattering angular distributions indicate that the 0.62-Mev resonance may be formed by $p$-wave neutrons with the $s$-wave potential scattering (${\delta }_0=-54.2\mathrm{}°$) spin-dependent and all channel spin 1, or possibly by $d$-wave neutrons with the resonance scattering all channel spin 2. Potential scattering phase shifts for ${\mathrm{B}}^{10}$ are ${\delta }_0=-53.5\mathrm{}°$ at 0.55 Mev; ${\delta }_0=-60.7\mathrm{}°$, ${\delta }_1=-4.0\mathrm{}°$ at 1.00 Mev; and ${\delta }_0=-66.9\mathrm{}°$, ${\delta }_1=-10.3\mathrm{}°$, and ${\delta }_2=-2.9\mathrm{}°$ at 1.50 Mev. The 0.43-Mev resonance in ${\mathrm{B}}^{11}$, agrees with a $J=2\mathrm{}$, $l=1\mathrm{}$ assignment, while the 1.28-Mev resonance is best fitted by $J=3\mathrm{}$, $l=2\mathrm{}$; with a mixing ratio of channel spin 2 equal to 10 times channel spin 1. Potential scattering is nearly all $s$-wave up to 1.50 Mev where ${\delta }_0=-90\mathrm{}°$. ${\mathrm{C}}^{12}$ has pure $s$-wave scattering at 0.55 Mev (${\delta }_0=-50.1\mathrm{}°$) and 1.00 Mev (${\delta }_0=-68.9\mathrm{}°$), and at 1.50 Mev a small amount of $p$-wave appears, (${\delta }_0=-79.4\mathrm{}°$, ${\delta }_1=-5.7\mathrm{}°$). In general the observed $s$-wave phase shifts are larger than those calculated from a hard sphere model, whereas the $p$- and $d$-wave phase shifts are smaller.

• Received 2 December 1954

DOI:https://doi.org/10.1103/PhysRev.98.669