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

Abstract

Lifetime measurements in 178Pt with excited states de-exciting through γ-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→2+1 257keV γ-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 178Pt alpha decay (Ealpha=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 γ rays and recoils is not feasible.