Beta decay ofB14

Abstract

A target of BeO, enriched to 94% in $^{10}\mathrm{Be}$, has been bombarded with 31-MeV $^{6}\mathrm{Li}$ ions, and delayed activities were measured by means of a fast beam chopper and a NaI(Tl)-plastic $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\beta}$ coincidence detecting system. $\ensuremath{\gamma}$ rays corresponding to the known activities $^{11}\mathrm{Be}$, $^{12}\mathrm{B}$, $^{13}\mathrm{B}$, $^{16}\mathrm{N}$, $^{20}\mathrm{F}$, and $^{20}\mathrm{Na}$ were observed in coincidence with $\ensuremath{\beta}$ rays. In addition, the spectrum contained $\ensuremath{\gamma}$ rays of 6.1 and 6.7 MeV decaying with ${T}_{\frac{1}{2}}=16.1\ifmmode\pm\else\textpm\fi{}1.2$ msec. The 6.1-MeV $\ensuremath{\gamma}$ rays are in coincidence with $\ensuremath{\beta}$ rays having ${E}_{max}=14.0\ifmmode\pm\else\textpm\fi{}0.7$ MeV. This activity is assigned to $^{14}\mathrm{B}$ produced in the $^{10}\mathrm{Be}(^{6}\mathrm{Li},2p)^{14}\mathrm{B}$ reaction. Based on the observed $\ensuremath{\gamma}$-ray intensities the $^{14}\mathrm{B}$ $\ensuremath{\beta}$-ray branches to $^{14}\mathrm{C}$ states at 6.09 (${1}^{\ensuremath{-}}$), 6.73 (${3}^{\ensuremath{-}}$), and 7.34 (${2}^{\ensuremath{-}}$) MeV are 81 \ifmmode\pm\else\textpm\fi{} 9%, ${8.6}_{\ensuremath{-}4.0}^{+1.7}$%, and 11%, respectively, where an allowance of 5% has been made for a probable ground-state $\ensuremath{\beta}$-ray branch. It is deduced that $^{14}\mathrm{B}$ has a spin-parity of ${J}^{\ensuremath{\pi}}={2}^{\ensuremath{-}}$ consistent with recent shell-model calculations. The experimental $log\mathrm{ft}$ values for the \ensuremath{\beta} decay of $^{14}\mathrm{B}$ are also in good agreement with theory.RADIOACTIVITY $^{14}\mathrm{B}$: measured ${T}_{\frac{1}{2}}$, ${E}_{\ensuremath{\gamma}}$, ${E}_{\ensuremath{\beta}}$, $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\beta}$ coin; deduced ${J}^{\ensuremath{\pi}}$ of $^{14}\mathrm{B}$, $\ensuremath{\beta}$ branches, $log\mathrm{ft}$ values; compared with theory.