Speaker
Description
The beta decay of 8B into 8Be is of interest both from nuclear structure and astrophysical point of view. For astrophysics, the 8B decay is the main source of solar neutrinos with energy higher than 2 MeV mainly coming from the intense (88%) beta branch of the 8B decay to the 3 MeV state of 8Be.
From the nuclear structure point of view, the 2+ 8B ground state is the only well-established proton halo state known. Its +/EC decay can give access to the 2+ doublet at 16.6 and 16.9 MeV in 8Be observed in reaction studies more than fifty years ago [1]. These states have dominant configurations as 7Li+p and 7Be+n, respectively and constitute the highest mixed isospin doublet known as stated in [2]. This assumption is able to describe well the experimental reaction data, however direct determination is missing. The beta decay of 8B feeding the 2+ states of 8Be offers a valuable avenue for probing the isospin composition of the doublet by the determination of the selective Fermi and Gamow-Teller (GT) components. However, resolving the feeding to the 2+ doublet poses challenges due to the low beta feeding.
We have performed an experiment at the ISOLDE-CERN facility's decay station to study the 8B decay. Thanks to relevant target development we achieved high statistics, allowing for first time a good separation of the population of the doublet. In this contribution, a comprehensive description of the results of experiment IS633 will be presented. We apply two methods to deduced the Fermi and GT strengths to the doublet. From these two analyses, the isospin mixing of the doublet is determined [3].
[1] C. P. Browne et al., Phys. Lett. 23 (1966) 371.
[2] P. von Brentano, Phys. Rep. 264 (1996) 57.
[3] D. Fernandez Ruiz et al., submitted.