Isobaric-Spin Mixing inBe8States

Abstract

The ${\mathrm{Li}}^7({\mathrm{He}}^3, d){\mathrm{Be}}^8$ reaction has been studied using a magnetic spectrometer in order to obtain precise values for the widths of the isobaric-spin-mixed states at 16.6 and 16.9 MeV in ${\mathrm{Be}}^8$. The results are $\Gamma \mathrm{}\left(16.6\right)=113\mathrm{}\pm 3$ keV and $\Gamma \mathrm{}\left(16.9\right)=77\mathrm{}\pm 3$ keV. These values specify the isobaric-spin amplitudes of the wave functions for these states and show that, while the mixing is not complete, it is quite substantial. This mixing gives rise to interference effects that are manifest in such reactions as ${\mathrm{B}}^{10}(d, \alpha ){\mathrm{Be}}^8$. It is pointed out that attempts to infer a cross-section ratio $\frac{\sigma \mathrm{}\left(16.6\right)\mathrm{}}{\sigma \mathrm{}\left(16.9\right)\mathrm{}}$ from such a reaction by taking the areas under the peaks in an experimental energy spectrum can be seriously in error if the interference effects are neglected. The excitation energies for the states were found to be 16.627±0.005 MeV and 16.901±0.005 MeV.