Three-cluster states in the spectrum of 8Be: structure, isospin mixing and β-decay of 8B to 16.6 MeV state

Abstract

The structure and spectrum of the three-cluster states in 8Be around 16–20 MeV was studied in the framework of the hyperspherical harmonic method. For that purpose we have developed a potential formalism for T-p and 3He-n (3 + 1) scattering and mechanism for the three-body mixed isospin calculations. We have studied the mechanism of the isospin mixing for 1+,2+ doublets in 8Be and found a sharp sensitivity of isospin mixing to the experimentally not well defined parameters of the 3 + 1 intercluster interaction. The matrix elements of the β-decay of 8B to 2+ doublet 16.6, 16.9 MeV were calculated and estimates were made for the probability of electron capture to 17.64 MeV state. It is found that about 90% of the Gamow-Teller (GT) sum rule is concentrated in the three-cluster 2+ and 1+ states, situated below the three-body thresholds, within narrow boundaries (16.5–19.0 MeV).