Abstract

In this review we will present the results of recent beta -decay studies using the total absorption technique that cover topics of interest for applications, nuclear structure and astrophysics. The decays studied were selected primarily because they have a large impact on the prediction of (a) the decay heat in reactors, important for the safety of present and future reactors and (b) the reactor electron anti-neutrino spectrum, of interest for particle/nuclear physics and reactor monitoring. For these studies the total absorption technique was chosen, since it is the only method that allows one to obtain beta -decay probabilities free from a systematic error called the Pandemonium effect. The total absorption technique is based on the detection of the gamma cascades that follow the initial beta decay. For this reason the technique requires the use of calorimeters with very high gamma detection efficiency. The measurements presented and discussed here were performed mainly at the IGISOL facility of the University of Jyväskylä (Finland) using isotopically pure beams provided by the JYFLTRAP Penning trap. Examples are presented to show that the results of our measurements on selected nuclei have had a large impact on predictions of both the decay heat and the anti-neutrino spectrum from reactors. Some of the cases involve beta -delayed neutron emission thus one can study the competition between gamma - and neutron-emission from states above the neutron separation energy. The gamma -to-neutron emission ratios can be used to constrain neutron capture (n,gamma ) cross sections for unstable nuclei of interest in astrophysics. The information obtained from the measurements can also be used to test nuclear model predictions of half-lives and Pn values for decays of interest in astrophysical network calculations. These comparisons also provide insights into aspects of nuclear structure in particular regions of the nuclear chart.

Highlights

  • Our knowledge of the properties of atomic nuclei is derived almost entirely from studies of nuclear reactions and radioactive decays

  • In this article we have presented a review of the impact of our total absorption studies of β decays that are relevant for reactor applications

  • The measurements presented have been performed at the IGISOL facility of the University of Jyväskylä employing the high isotopic purity beams provided by the JYFL Penning Trap

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Summary

Introduction

Our knowledge of the properties of atomic nuclei is derived almost entirely from studies of nuclear reactions and radioactive decays. The ground and excited states of nuclei exhibit many forms of decay but the most common are α, β and γ -ray emission. A glance at the Segrè Chart reveals that it is the most common way for the ground states of nuclei to decay and it is frequently the observation of such β decays that brings us our first knowledge of a particular nuclear species and its properties. Characteristic α and γ -ray spectra exhibit a series of discrete lines It requires sophisticated detection and analysis techniques to determine the excitation energies of the states involved, their lifetimes and the transition rates between states. A knowledge of β-decay transition probabilities is of particular importance for application to (a) tests of nuclear model calculations, (b) the radioactive decay heat in reactors, (c) the reactor electron anti-neutrino spectrum and (d) reaction network calculations for nucleosynthesis in explosive stel-

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TAGS measurements
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Decay heat
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Neutrino applications
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Nuclear structure
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Astrophysical applications
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Summary, future and conclusions
Findings
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Full Text
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