High spin states in (72,73)krypton and exit channel selection using neutron coindicidence with gammasphere

Spectroscopic investigations of the N = Z system, ⁷²Kr and N = Z + 1 system ⁷³Kr were performed using the national γ-ray facility Gammasphere. The systems were populated via the 2p2 n and 2pn channels of the ³⁶Ar + ⁴⁰Ca reaction at a nominal Ar beam energy of 145 MeV. An array of 15 liquid scintillation neutron detectors was installed in Gammasphere for the purpose of exit channel selection. The present work represents the first use of Gammasphere in conjunction with an array of neutron detectors and the first use of Gammasphere with complex trigger conditions. The investigations yielded improved spectroscopic data as well as the design of an optimum array for use with Gammasphere. The high spin data in ⁷²Kr and ⁷³Kr were considerably extended. The data were compared with the predictions of pairing and deformation self-consistent total Routhian surface calculations. The nonobservation of a backbend in ⁷²Kr, and the anomolously large alignment in the (π, α) = (+, +1/2) band in ⁷³Kr are not understood either in the context of the current calculations or the heavier isotopes ^74,76Kr mid ^75,77Kr. Despite the improved data on ⁷²Kr and ⁷³Kr, no hard spectroscopic evidence regarding the shape of either isotope was obtained. An improved measurement of the lifetime of the isomeric (9/2⁺) state in ⁷³Kr was possible by means of a backed target measurement.