Transition strengths and deformation in 77Kr.

Abstract

High spin states in $^{77}\mathrm{Kr}$ were populated using the $^{48}\mathrm{Ti}$${(}^{32}$S,2pn${)}^{77}$Kr reaction with a 106 MeV $^{32}\mathrm{S}$ beam from the Florida State University Tandem-LINAC accelerator. Three Compton-suppressed Ge detectors at 95\ifmmode^\circ\else\textdegree\fi{} and one at 18\ifmmode^\circ\else\textdegree\fi{} were used to determine \ensuremath{\gamma}-\ensuremath{\gamma} coincidence relations, directional correlation ratios and Doppler-shift attenuation lifetimes. The level scheme for the positive-parity band agrees with previous studies up to spin 37/${2}^{+}$. New levels at 9913 keV (41/${2}^{+}$) and 11 760 keV (45/${2}^{+}$) have been identified. The negative-parity band was extended to a probable spin state of 27/${2}^{\mathrm{\ensuremath{-}}}$, with three new levels identified. The kinematic and dynamic moments of inertia in the positive-parity band converge to a rather constant value of (22--24) ${\mathrm{\ensuremath{\Elzxh}}}^{2}$/MeV. The transition quadrupole moments average about 2.6 e b in this band and decrease somewhat after the \ensuremath{\pi}${\mathit{g}}_{9/2}$ alignment. The magnetic transition strengths alternate with signature and increase to about a nuclear magneton after the alignment. The kinematic moment of inertia in the negative-parity band increases with rotational frequency and exhibits the beginnings of a band crossing at \ensuremath{\Elzxh}\ensuremath{\omega}\ensuremath{\approxeq}0.55 MeV, while the transition quadrupole moments decrease steadily with frequency. Cranking model calculations with the Nilsson plus BCS potential were performed for the quasiparticle energies and electromagnetic transition rates for both the positive- and negative-parity bands. The experimental data were reproduced well. As for the positive-parity band, \ensuremath{\beta}(3qp)>\ensuremath{\beta}(1qp) has been shown to be necessary in addition to \ensuremath{\gamma}(3qp)>0 to reproduce the signature dependence of the energies and B(M1) values.