Gamma-Ray Studies in Boron-10

Gamma rays emanating from the 7.56-Mev level of ${\mathrm{B}}^{10}$ were analyzed with a five-crystal pair spectrometer. Cascade gamma rays were investigated by recording the spectra in coincidence with the 2.40, 0.72, 2.15, and 5.41-Mev gamma-ray transitions. The branching ratios for the decay of the 7.56-Mev level were found to be 76%, 9%, and 15% for 6.84, 5.41, and 2.40-Mev gamma rays, respectively. For the 2.15-Mev level, the respective branching ratios for 2.15, 1.43, and 0.41-Mev gamma rays were shown to be 16%, 29%, and 55%. The partial width for the 3.01-Mev transition was found to be less than 1% of the total width of the 5.16-Mev state in ${\mathrm{B}}^{10}$. Combining this result with the data of Meyer-Schützmeister and Hanna, the gamma-ray width of the 5.16-Mev level was found to be 0.51 ev and the alpha width $32<\mathrm{}{\Gamma }_{\alpha }<500\mathrm{}$ ev. Although the upper limit for the alpha width of the 5.16-Mev level is quite small, this result is shown to be consistent with the alpha transition being isotopic spin allowed. The conflict between our result $\frac{{\Gamma }_{\gamma 3.01}}{\Gamma }<0.01\mathrm{}$ and other evidence requiring larger relative partial gamma-ray widths may be resolved if the 5.16-Mev state in ${\mathrm{B}}^{10}$ is assumed to be a doublet.