Three-cluster states in the spectrum of Be-8 (1) - Structure and beta-decay of B-8 to 16.6 MeV state

The structure and spectrum of the three-cluster states in Be-8 around 16-20 MeV was studied in the framework of the hyperspherical harmonic method. Fo r that purpose we have developed a potential formalism for T-p and He-3-n ( 3 + 1) scattering and mechanism for the three-body mixed isospin calculatio ns. We have studied the mechanism of the isospin mixing for 1(+), 2(+) doub lets in Be-8 and found a sharp sensitivity of isospin mixing to the experim entally not well defined parameters of the 3 + 1 intercluster interaction. The matrix elements of the beta-decay of B-8 to 2(+) doublet 16.6, 16.9 MeV were calculated and estimates were made for the probability of electron ca pture to 17.64 MeV state. It is found that about 90% of the Gamow-Teller (G T) sum rule is concentrated in the three-cluster 2(+) and 1(+) states, situ ated below the three-body thresholds, within narrow boundaries (16.5-19.0 M eV), (C) 2000 Elsevier Science B.V. All rights reserved.