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\beta-delayed particle spectroscopy


Very high \beta-decay energies characterize nuclides far from stability for which the daughter nuclei have low nucleon-separation energies. Therefore the \beta-decay of exotic nuclei may feed excited states that are unbound with respect to the emission of nucleons or clusters of nucleons. This decay mode, discovered for \beta\alpha decay in 1916 and for \betap decay in the 1960’s, has already provided crucial nuclear structure information. The key point is that, if one knows the final state, one can derive the \beta-feeding to that state and the associated Fermi or Gamow-Teller matrix elements from the particle spectra. This gives information on the strong interaction within the nucleus. Beta-delayed particle emission is now well established and the mechanism governing the decay process is quite well understood. In light nuclei, where the level density is low and the levels are narrow, detailed and very precise information of the nuclear structure can be achieved at very low count rate (about 1/s or less). For heavier nuclei, the width of the individual levels is smaller than their spacing, but the emitted particles from these unbound states are nevertheless hardly resolvable. The structure of the nucleus is best described in terms of local averages and fluctuations around them. These fluctuations in nuclear level widths and spacing can be described by general statistical laws and are characteristic of the phenomenon of deterministic chaos in nuclei. Detailed spectroscopy of neutron-deficient nuclei from argon to krypton will be of interest to determine where and how the transition from order to chaos occurs.