ISBN 9783843926751

978-3-8439-2675-1, Reihe Physik

Hannah Duckwitz
Systematic Nuclear Structure Investigations of 84Sr and 86Sr under Application and Advancement of Gamma-Ray Spectroscopic Methods

169 Seiten, Dissertation Universität Köln (2016), Softcover, A5

Zusammenfassung / Abstract

To investigate the low-spin structure of 84Sr and 86Sr two fusion evaporation experiments with a (p,2n) reaction have been performed. The data of the experiments (85Rb(p,2n)84Sr, YRAST Ball spectrometer, Yale University and 87Rb(p,2n)86Sr, HORUS spectrometer, University of Cologne) have been evaluated in terms of Gamma-ray spectroscopy, i.e. the level scheme was built up, branching ratios were determined, nuclear spin and parity assignments were made after GammaGamma angular correlation analyses. A code for the calculation of branching ratios has been developed. In the past, a general error for the uncertainties of branching ratios was assumed. Through the inclusion of all possible error sources, the absolute errors of the branching ratios were now precisely calculated. For both nuclei under investigation, it was possible to enlarge the previously known level scheme information.

In addition, lifetimes were determined by means of the Doppler Shift Attenuation Method. In 86Sr a new method for lifetime determinations, using Doppler attenuated peak shapes, was applied for the first time. In this approach, spectra of a feeding and a deexciting transition of the level of interest are used to determine level lifetimes without any line shape analysis of the feeding transition. The feeding of the level is included via the spectral difference of the feeding and the deexciting transitions. Another code has been developed to automate the sequence of steps up to the derivation of mean level lifetimes with the Spectral Difference Method.

In cases where all necessary input variables were known, reduced transition strengths were calculated with Monte Carlo simulated probability density functionals. It is stressed that linear error propagation for the calculation errors of reduced transition strengths is not universally applicable here.

As both nuclei lie in the vicinity of the N equal to 50 neutron shell closure and on a possible proton subshell closure of the 2p3/2 orbit, they are expected to show excitations which are explainable within the Nuclear Shell Model. Calculations for 84Sr, 86Sr, and 88Sr have been performed in a truncated model space for protons and neutrons with the empirical JUN45 residual interaction by M. Honma (2009) and were compared to the experimental findings. Finally, the experimental results were placed and discussed systematically in the framework of the strontium and neighbouring isotopic chains for N smaller than 50.