Lifetime measurements of yrast states in ^{mathbf {178}}Pt using the charge plunger method with a recoil separator

Abstract

Lifetime measurements in ^{178}Pt with excited states de-exciting through gamma -ray transitions and internal electron conversions have been performed. Ionic charges were selected by the in-flight mass separator MARA and measured at the focal plane in coincidence with the 4_1^+rightarrow 2_1^+257,keV gamma -ray transition detected using the JUROGAM 3 spectrometer. The resulting charge-state distributions were analysed using the differential decay curve method (DDCM) framework to obtain a lifetime value of 430(20) ps for the 2_1^+ state. This work builds on a method that combines the charge plunger technique with the DDCM analysis. As an alternative analysis, ions were selected in coincidence with the ^{178}Pt alpha decay (E_{mathrm {alpha}} = 5.458(5) MeV) at the focal plane. Lifetime information was obtained by fitting a two-state Bateman equation to the decay curve with the lifetime of individual states defined by a single quadrupole moment. This yielded a lifetime value of 430(50) ps for the 2_1^+ state, and 54(6) ps for the 4_1^+ state. An analysis method based around the Bateman equation will become especially important when using the charge plunger method for the cases where utilising coincidences between prompt gamma rays and recoils is not feasible.