The β-decay of Li-9 to the high lying states in Be-9

Abstract

Mirror β-transitions should have similar strengths as long as binding energy, Coulomb energy and other explicitly breaking effects are small. However, large β-decay asymmetries have been observed in the decay of C-9 [Phys. Rev. C 37 (1988) 766] and the decay of its mirror nucleus Li-9 [Nucl. Phys. A 510 (1990) 189]. These asymmetries could be the indication of structural differences between mirror states. We have focussed on the beta-decays of C-9 and Li-9 to the high lying region (between 11-12 MeV) in the daughter nuclei B-9 and Be-9. The difficulty in the study of these decays is that they are accompanied by the emission of three particles and one needs to determine the breakup mechanism to extract information about the position, width and feeding of the states. The β-decays of C-9 [Nucl. Phys. A 692 (2001) 427] and Li-9 [Phys. Lett. B. 576 (2003) 22] to the high lying region of the daughter nuclei have been remeasured with setups that allow the study of the complete kinematics of the processes and, hence, the breakup mechanism of the states in the daughter nuclei can be determined. The most recent experiments on C-9 [Nucl. Phys. A 692 (2001) 427, Phys. Rev. C 61 (2000) 064310] gave B(GT) values of 1.58(16) and 1.20 (15) for the transition C-9 → B-9 (12.2 MeV) whereas the only early determination for Li-9 → Be-9 (11.81 MeV) [Nucl. Phys. A 510 (1990) 189] gave 5.6(1.2). The experiments on C-9 employed coincidence detection of charged particles thereby allowing a detailed analysis, whereas the older Li-9 experiment only included singles spectra. The only previous Li-9 experiment where α-particle coincidences were measured [Nucl. Phys. A 366 (1981) 449] did not have sufficient angular resolution and no detailed analysis of the breakup mechanism was performed.