Broad resonances and beta-decay

TL;DR

This paper investigates how broad resonances and the decay matrix element influence the energy spectrum in beta-decay, highlighting the importance of considering direct decay to continuum states near nuclear driplines.

Contribution

It introduces a schematic model showing that beta-decay directly to continuum states can significantly affect observed spectra, expanding the understanding of decay mechanisms near driplines.

Findings

Beta-decay lineshape distortion partly due to phase space and matrix element effects.

Direct decay to continuum states can be identified through specific signatures in R-matrix fits.

Analysis of $^8$B decay illustrates the model's application to real nuclear systems.

Abstract

Beta-decay into broad resonances gives a distorted lineshape in the observed energy spectrum. Part of the distortion arises from the phase space factor, but we show that the beta-decay matrix element may also contribute. Based on a schematic model for p-wave continuum neutron states it is argued that beta-decay directly to the continuum should be considered as a possible contributing mechanism in many decays close to the driplines. The signatures in R-matrix fits for such decays directly to continuum states are discussed and illustrated through an analysis of the beta-decay of $^8$B into $2^+$ states in $^8$Be.