Unexpected increase of Be7 decay rate under compression

Abstract

It is important to understand the effect of compression on the decay rate of $^{7}\mathrm{Be}$ because of its significance in calculating $^{7}\mathrm{Be}$ decay rate at the solar core and corresponding $^{8}\mathrm{B}$ neutrino flux. We have measured that the decay rate of $^{7}\mathrm{Be}$ is faster in the smaller spatial confinement of Pd lattice compared to the larger spatial confinement of Pb lattice by (0.82 \ifmmode\pm\else\textpm\fi{} 0.16)%, indicating the effect of compression on the decay rate of $^{7}\mathrm{Be}$ ion, because low and similar electron affinities of Pd and Pb cannot produce any observable effect. Similar results were observed earlier by applying high external pressure on $^{7}\mathrm{BeO}$ lattice. The density functional calculations underpredict the increase of $^{7}\mathrm{Be}$ decay rate under compression by a large factor, although they can account for the effect of electron affinity reasonably well. The unexpectedly large increase (\ensuremath{\sim}1%) of $^{7}\mathrm{Be}$ decay rate under compression (25--40 GPa) compared to the state-of-the-art calculations could have implications on the calculated $^{7}\mathrm{Be}$ decay rate at the solar core.