Fast-timing Measurements in $^{100}$Zr Using LaBr$_{3}$(Ce) Detectors Coupled with Gammasphere

E R Gamba ,T Lauritsen,O Yordanov,D Seweryniak,V Vedia,S Lalkovski,S Bottoni,P Copp,J Sethi,I Burrows,S Ilieva,G Fernández Martínez,A D Ayangeakaa ,M P Carpenter ,D J Hartley ,R V F Janssens ,F G Kondev ,J Anderson ,D M Cullen ,R S Ilieva ,P.h Regan ,T Daniel ,S J Zhu ,C Shand ,Jack P Greene ,J Rohrer ,M Rüdigier ,Laila Gurgi ,John Simpson ,M Smoleń ,Cristina Niță ,E A Stefanova ,T Berry ,I Lazarus ,M D Reed ,V.f.e Pucknell ,Thilo Kroll ,Z Podolyák ,G Lotay ,A M Bruce ,G J Lane ,R J Carrol ,M Carmona-Gallardo

doi:10.5506/aphyspolb.49.555

Abstract

In order to investigate the evolution of nuclear deformation in the region of the chart of nuclides around mass numbers A similar or equal to 110 and A similar or equal to 150, an experiment was performed at the Argonne National Laboratory where the gamma-decay radiation emitted from the fission fragments of Cf-252 was measured using 51 Gammasphere detectors coupled with 25 LaBr3 (Ce) detectors. In this work, a short description of the experimental setup is presented together with some preliminary results from the fast-timing analysis of the 4(+) state of the nucleus Zr-100. A lifetime value of tau = 50(28) ps was obtained using the Generalized Centroid Shift Method. This result agrees with the literature value of tau = 53(4) ps within one standard deviation.

Highlights

Important information about the evolution of the deformation across the nuclear chart can be obtained from lifetime measurements of low-lying excited states in nuclei
A second data set contained the fast-timing information which consisted of 2-fold events in the LaBr3(Ce) array, in coincidence with at least one gamma ray detected in Gammasphere
The black dotted lines are the gate limits used to obtain the time distributions shown in Fig. 3, taken to the left-hand side of the peak in order to minimize the contribution of the peak at 511 keV

Summary

Introduction

Important information about the evolution of the deformation across the nuclear chart can be obtained from lifetime measurements of low-lying excited states in nuclei. The lifetime of the first excited states is an essential ingredient in the calculation of the reduced transition probability B(E2) which gives, in turn, the quadrupole moment related to the deformation parameter β2 In this experiment, a source of 252Cf was used in order to populate the regions around mass numbers A 110 and A 150. Gamma rays emitted from the fission fragments were detected using a hybrid detector array made of 51 HPGe detectors from Gammasphere and 25 LaBr3(Ce) scintillator detectors These scintillator detectors were used in the past to measure lifetimes in the sub-nanosecond range [2, 3] and they have been used in many successful experiments, for example during the EXILL-FATIMA campaign [3] and at RIKEN [4]. The 25 scintillator detectors are part of the UK NuSTAR Collaboration [5, 6] and in this experiment they were coupled for the first time to a fully digital acquisition system

The setup

Preliminary results

Conclusions