Precise study of the final-state continua inLi8andB8decays

Abstract

We studied \ensuremath{\beta}-delayed singles-\ensuremath{\alpha} spectra from $^{8}\mathrm{Li}$ and $^{8}\mathrm{B}$ decays with special emphasis on a careful calibration of the energy scale. $^{8}\mathrm{Li}$ and $^{8}\mathrm{B}$ activities were produced by $^{7}\mathrm{Li}$($d,p$) and $^{6}\mathrm{Li}$($^{3}\mathrm{He}$,$n$) reactions, respectively, and deposited in thin C foils. Delayed \ensuremath{\alpha}'s were counted in thin, cooled Si detectors with small solid angles to reduce summing with \ensuremath{\beta}'s. The energy scale and detector response were calibrated with spectroscopic grade radioactive sources. We extracted the $^{8}\mathrm{Li}$ and $^{8}\mathrm{B}$ final-state continuum shapes from our spectra by using $R$-matrix analyses that included effects of lepton-recoil broadening and detector response. Our results are in excellent agreement with a recent measurement using $^{8}\mathrm{B}$'s implanted in a Si counter and in good agreement with our reanalysis of the older Wilkinson-Alburger $^{8}\mathrm{Li}$ and $^{8}\mathrm{B}$ data, but disagree with a recent $^{8}\mathrm{B}$ experiment using a coincidence technique.