The current status of precision measurements in allowed nuclear beta decay is reviewed, including neutron decay, with emphasis on their potential to look for new physics beyond the standard electroweak model. Experimental results are interpreted in the framework of phenomenological model-independent descriptions of nuclear beta decay as well as in some specific extensions of the standard model. The values of the standard couplings and the constraints on the exotic couplings of the general beta decay Hamiltonian are updated. The ratio between the axial and vector couplings obtained is ${C}_{A}∕{C}_{V}=\ensuremath{-}1.269\phantom{\rule{0.2em}{0ex}}92(69)$ under standard model assumptions. Particular attention is devoted to the discussion of the sensitivity and complementarity of different precision experiments in direct beta decay. The prospects and impact of recent developments of precision tools and of high intensity low-energy beams are also addressed.

Tests of the standard electroweak model in nuclear beta decay

Nuclear structure at the proton drip line: Advances with nuclear decay studies

In recent years, it has become possible to study experimentally the properties of many nuclei with a neutron number differing greatly from that of stable nuclei [see, e.g., (FHR 67), (Ley 70)]. The present survey deals with the information about nuclear structure that may be gained from the investigation of the beta-decay properties of nuclei far away from beta stability, where the energy available for beta decay is very large. The decay can therefore proceed to a very large number of excited levels of the kind that are observed as resonance or final states in the neutron-capture process. Because of the large number and density of final states it becomes expedient to deal with high-energy beta decay in the language of the statistical model [for general reviews, see Lynn (Lyn 68) and Vogt (Vog 68)], and to discuss the beta-decay rate in terms of a strength function.

The Beta Strength Function

The decay of 20Na: Measurements of isospin mixing and the weak vector coupling constant as well as other new decay data

The β-decay process allows one to understand better the interactions and behaviour of the nucleons inside the nucleus. The study of nuclei at the limits of stability has recently become a central focus of nuclear structure research. The main characteristic of β-decay far from stability is the large number of decay channels open. The decay process is well understood and the interpretation of the data yields a wide variety of spectroscopic information: level energies, spins, parities, widths and level densities. In this brief paper, a summary of the progress achieved over the last few decades in the study and identification of β-delayed particle precursors is given with special emphasis on the achievements in studies of β-delayed charged particles where the detection system allowed for refined spectroscopy studies. For instance, detailed studies have been conducted on many β-delayed proton precursors of the sd shell. The comparison with the best performing shell-model calculations shows that although overall agreement is obtained in BGT distributions, the density of the observed states is higher than predicted. This points to the need to include higher order configurations in the present sd shell calculations. The extension to heavier systems is desirable. The main challenges for the present and the next decade in this domain are outlined.

https://iopscience.iop.org/article/10.1088/0031-8949/2013/T152/014013/pdf

R.D. Macfarlane

Papers

Beta - neutrino correlations and longitudinal nuclear alignment in the decay of 20Na☆

Concerning the anomalous Fermi strength in the β+-decay of 20Na and mirror symmetry in the mass-20 multiplet☆

Crystal lattice effects in the 149Sm(n, α)146Nd reaction induced by thermal neutrons