Doppler-shift lifetime measurements in 46Ti and 50Cr

Abstract

Abstract The lifetimes of nine states in 46Ti and fourteen states in 50Cr have been measured through the Doppler-shift attenuation method. The states were populated by the 46Ti(p, p′γ) and 50Cr(p, p′γ) reactions at Ep = 7 MeV. Thick targets (≈ 300 keV) were used to provide adequate averaging over many compound-nucleus levels. Singles γ-ray spectra were obtained with 33 and 55 cm3 Ge(Li) detectors at θγ = 0°, 90° and ≈ 160°, and lifetimes were extracted from the observed centroid shifts. An alternative method of analysis, involving a simulation of profiles of Doppler-shifted peaks with six free parameters gave considerably more accurate results. Both methods were tested by measuring known lifetimes in 58Ni. In addition, the lifetimes of three states in 52Cr were determined. A comparison of the energy spectra and electromagnetic decay properties of these nuclei to shell-model calculations revealed the failure of the simple ( f 7 2 ) 6 picture. A startling example of this failure is the fact that the 22+(E2)21+ rate in 46Ti appears to be a factor of ⪆ 25 faster than that in the cross-conjugate nucleus 50Cr.