A charge plunger device to measure the lifetimes of excited nuclear states where transitions are dominated by internal conversion

L Barber,C Müller-Gatermann,J Sarén,R Julin,D O’Donnell,P Rahkila,J Sinclair,G Beeton,J Uusitalo,J Vilhena,T Grahn,S Juutinen,P Spagnoletti,G Zimba,A Illana,P Ruotsalainen,J Ojala,M Bowry,H Tann,J Sorri,J Heery,J Pakarinen,M Sandzelius,R.‐D Herzberg ,Minna‐Liisa Luoma ,Α Dewald ,B S Nara Singh ,J F Smith ,P T Greenlees ,D M Cullen ,J M Keatings

doi:10.1016/j.nima.2020.164454

Abstract

A charge plunger device has been commissioned based on the DPUNS plunger (Taylor et al., 2013) using the in-flight mass separator MARA at the University of Jyväskylä. The 152Sm(32S,4n)180Pt reaction was used to populate excited states in 180Pt. A lifetime measurement of the 21+ state was performed by applying the charge plunger technique, which relies on the detection of the charge state-distribution of recoils rather than the detection of the emitted γ rays. This state was a good candidate to test the charge plunger technique as it has a known lifetime and depopulates through a converted transition that competes strongly with γ-ray emission. The lifetime of the 21+ state was measured to be 480(10)ps, which is consistent with previously reported lifetimes that relied on the standard γ-ray techniques. The charge plunger technique is a complementary approach to lifetime measurements of excited states that depopulate through both γ-ray emission and internal conversion. In cases where it is not possible to detect Doppler-shifted γ rays, for example, in heavy nuclei where internal conversion dominates, it may well be the only feasible lifetime analysis approach.

Highlights

The measurement of lifetimes of excited nuclear states has historically provided a useful experimental observable for assessing nuclear models
The charge plunger device was commissioned through a measurement of the lifetime of the 2+1 yrast state in 180Pt
The two-foil plunger DPUNS [6] was adapted to function as a charge plunger by replacing the degrader foil with a nat.Ni charge reset foil of thickness 0.29 mg cm−2

Summary

Introduction

The measurement of lifetimes of excited nuclear states has historically provided a useful experimental observable for assessing nuclear models. Such lifetimes allow for reduced transition rates between states to be determined, in principle allowing for the nuclear wavefunctions of the states they connect to be probed. For lifetimes of the order of a picosecond, a common experimental approach is to use a plunger device to collect recoil-distance Doppler shift (RDDS) data [1,2]. This approach relies on detecting γ-rays that are Doppler-shifted due to emission from nuclei travelling at different velocities. The ratio between the intensities of the γ rays emitted before and after passing through the degrader foil can be used as a function of plunger distance to determine the lifetime of interest

Methods

Results

Conclusion