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

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 9C [Phys. Rev. C 37 (1988) 766] and the decay of its mirror nucleus 9Li [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 9C and 9Li to the high lying region (between 11-12 MeV) in the daughter nuclei 9B and 9Be. 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 9C [Nucl. Phys. A 692 (2001) 427] and 9Li [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 9C [Nucl. Phys. A 692 (2001) 427, Phys. Rev. C 61 (2000) 064310] gave BGT values of 1.58(16) and 1.20 (15) for the transition 9C → 9B (12.2 MeV) whereas the only early determination for 9Li→ 9Be (11.81 MeV) [Nucl. Phys. A 510 (1990) 189] gave 5.6 (1.2). The experiments on 9C employed coincidence detection of charged particles thereby allowing a detailed analysis, whereas the older 9Li experiment only included singles spectra. The only previous 9Li 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.