Clarification of large-strength transitions in the $\ensuremath{\beta}$ decay of $^{11}\mathrm{Be}$

Clarification of large-strength transitions in the $β$ decay of ${}^{11}{Be}$

J. Refsgaard, J. Büscher, A. Arokiaraj, H. O. U. Fynbo, R. Raabe, and K. Riisager

Phys. Rev. C 99, 044316 – Published 25 April 2019

Abstract

The shape and normalization of the $β$ -delayed $α$ spectrum from ${}^{11}{Be}$ was measured by implanting ${}^{11}{Be}$ ions in a segmented Si detector. The spectrum is found to be dominated by a well-known transition to the $3 / 2^{+}$ state at $E_{x} = 9.87 MeV$ in ${}^{11}B$ . A significant increase in the observed decay strength towards the higher end of the $Q_{β}$ window means, however, that the $9.87 MeV$ state cannot alone be responsible for the transition. Using the $R$ -matrix framework we find that the inclusion of an extra $3 / 2^{+}$ state at $E_{x} = 11.49 (10) MeV$ is required to obtain a satisfactory description of the spectrum. Both states show large widths towards $α$ decay, exhausting significant fractions of the Wigner limit, a typical signature of $α$ clusterization. The observed Gamow-Teller strength indicates large overlaps between the two states and the ground state of ${}^{11}{Be}$ .