Determination of lifetimes of nuclear excited states using the Recoil Distance Doppler Shift Method in combination with magnetic spectrometers

M Doncel,B Quintana,A Gadea,O Möller,D Mengoni,N Pietralla,A Dewald,J J Valiente-Dobón,V Modamio

doi:10.1140/epja/i2017-12382-6

Abstract

.The current work presents the determination of lifetimes of nuclear excited states using the Recoil Distance Doppler Shift Method, in combination with spectrometers for ion identification, normalizing the intensity of the peaks by the ions detected in the spectrometer as a valid technique that produces results comparable to the ones obtained by the conventional shifted-to-unsifted peak ratio method. The technique has been validated using data measured with the gamma -ray array AGATA, the PRISMA spectrometer and the Cologne plunger setup. In this paper a test performed with the AGATA-PRISMA setup at LNL and the advantages of this new approach with respect to the conventional Recoil Distance Doppler Shift Method are discussed.

Highlights

The use of Ge detector arrays coupled with large acceptance magnetic spectrometers allows to measure the γrays in coincidence with the reaction products identified in most cases unequivocally
This plunger, to be used with a Ge array coupled to a magnetic spectrometer, was commissioned for the first time in a CLARA-PRISMA campaign at the Laboratori Nazionali di Legnaro [4,5] where the CLARA array composed of 25 clover detectors was sucessfully coupled to the large acceptance magnetic spectrometer
Several successful measurements were performed with this plunger to determine lifetimes of excited states in neutron-rich nuclei at the CLARAPRISMA setup such as 50Ca and 51Sc isotopes [6] and 44,46Ar [7], as well as for example 70–74Zn [8] or 63–65Co [9] at the AGATA-PRISMA [10] setup

Summary

Introduction

The use of Ge detector arrays coupled with large acceptance magnetic spectrometers allows to measure the γrays in coincidence with the reaction products identified in most cases unequivocally. The use of an ion tracking spectrometer, such as PRISMA, where A and Z are determined on an eventby-event basis, allows to develop a different approach to determine the lifetime using only one of the peaks, the shifted or the unshifted one In this case, the normalization is done considering the number of nuclei populated in the reaction and detected in the spectrometer (NI ). The main difference between the two methods is that in the conventional method one needs to measure accurately the intensity of both peaks to deduce the decay curve as defined in eq (2) while in the present approach where the number of ions is accurately measured by a spectrometer, the number of useful experimental data increases since two independent normalized decay curves for the shifted and unshifted peaks can be defined, as it can be seen in eq (3) This method can be useful to determine the lifetime of excited states when using a magnetic spectrometer in measurements with low statistics, as expected in future radioactive facilities, or when one of the peaks could not be accurately determined due to low statistics or contaminants from other γ transitions. As will be discussed in the following, this normalization of the decay curve with the number of ions NI overcomes the problem of the degrader Coulomb excitations when using the differential RDDS method

Measurements with the AGATA γ-ray array and the PRISMA spectrometer

Lifetime determination of the first excited states in the 72Zn isotope

Conclusions