Deformation of 113Cs from Proton-emission and Electromagnetic Transition Rates

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Abstract

Studying nuclei beyond the proton dripline can provide valuable information onthe structure of nuclei at the limits of stability, where the strong nuclear forcestarts to be overcome by Coulomb repulsion between protons. Simple experi-mental observables, such as excitation energies and lifetimes of excited states inthese proton-unbound nuclei can provide information on the nuclear wavefunc-tion. Experimental data, such as that presented in this work, can then be usedto improve models of nuclear structure at the proton dripline.This thesis presents data from a recoil-decay tagged differential plunger experi-ment undertaken at the University of Jyvaskyla in 2014. A fusion-evaporationreaction was used to populate excited states in the deformed ground-state protonemitter 113Cs. The JUROGAM-RITU-GREAT experimental setup was used tocorrelate gamma rays emitted from these excited states with protons emitted from 113Csand the differential plunger for unbound nuclear states (DPUNS) was placed atthe target position to measure the excited state lifetimes.The lifetime of the (11/2+) state in the most intense rotational band of 113Cs wasmeasured to be tau = 24(6) ps, while a limit of tau is less than or equal to 5 ps was found for the lifetime of the higher energy (15/2+) state. The lifetime of proton emission was measured to be tau = 24.2(2) microseconds.The experimental data were used to test the predictions of a nonadiabatic quasi-particle model for proton-emitting nuclei, which was employed to deduce thedeformation of the states in 113Cs. Wavefunctions from the nonadiabatic quasi-particle model were used to independently calculate proton-emission rates, gamma-ray transition rates and excited state energies as functions of deformation. The de-formation of 113Cs could then be extracted from the intersection of the differenttheoretical values and experimental observables. A deformation of beta2 = 0.22(6)was extracted from the (11/2+) excitation energy and lifetime. The deforma-tion values taken from the proton-emission rate and the lifetime limit of the(15/2+) state were also consistent with this value. The consistency of the differentdeformations calculated shows the effectiveness of the nonadiabatic quasiparticlemethod when used to calculate the properties of deformed ground-state proton-emitters.

Keyword(s)

Gamma-ray spectroscopy; Ground-state proton emission ; Plunger measurements; Proton-emission models; Recoil-decay-tagging

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