Spectroscopy of neutron-rich nuclei populated in the spontaneous fission of {sup 252}Cf and {sup 248}Cm.

Spontaneous fission provides a very natural production mechanism for neutron-rich nuclei. The large excesses of neutrons over protons in heavy systems near the valley of stability, coupled with the tendency for the charge-to-mass ratio to be preserved in the fission process, results in fission fragments that lie well to the neutron-rich side of stability. The excitation energy of the primary fragments produced at scission results in the evaporation of neutrons (Fig 1) to produce secondary fragments whose excitation energy is dissipated through {gamma}-ray emission. In the last few years the study of such {gamma} rays has produced a dramatic increase in the available information on the structure of neutron-rich nuclei. This renaissance in fission-fragment spectroscopy has been due primarily to the much increased resolving power of large arrays of germanium {gamma}-ray detectors such as Euroball and Gammasphere. Through the improved detection efficiency and high granularity, these arrays have made it possible to obtain reasonable rates for the detection of three coincident {gamma} rays out of the cascades of multiplicity ten that are typically produced in spontaneous fission. In addition to the determination of the energies of excited levels, developments in spectroscopic techniques have allowed for information to be deduced regarding the spins and parities [1,2] and lifetimes [3,4] of such states of extreme isospin. In this paper we present research that has been carried out using the Euroball and Eurogam arrays to detect {gamma} rays emitted from spontaneously fissioning {sup 248}Cm and {sup 252}Cf. The paper focuses on three sub-areas of current activity, namely, the measurement of yields of secondary fragment pairs, the measurement of state lifetimes at around spin 10, and recent measurements of g-factors of excited states in fission fragments