Beta-decay studies for applied and basic nuclear physics
Résumé
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.