A lanthanum-bromide array for precision electromagnetic-transition measurements in light nuclei at the Birmingham MC40 cyclotron.

One of the greatest challenges in nuclear physics is to understand how the nuclear force (the strong interaction on the nuclear scale) results in the range of properties observed in nuclei. The strong interaction on the nuclear scale is a manifestation of the same interaction on a sub-nucleon level, where the quarks and gluons are the appropriate degrees of freedom. How these map on to the features of the nuclear force is the domain of ab initio (first principles) approaches to nuclear theory. There are several such methods, some of which use chiral effective field theory to generate the interactions, others which take an approach of modelling the nucleon-nucleon interaction of free protons and neutrons and then embedding that in the nucleus. All are able to produce calculations of light nuclei up to mass 12, e.g. carbon-12, and are (in some cases) progressing to heavier systems. In order to make further progress there is a need for experimental data to test and discriminate between the approaches. For some systems these data exist, for others, particularly for excited states of carbon-12, the data do not exist. Also, for systems where there are data, often the precision is insufficient to provide challenge to theory. The aim of the present equipment grant is to develop a UK-based facility capable of delivering precision measurements of electromagnetic transition rates. Such measurements are a key experimental observable which all theories can compute and hence can be tested. We will construct a facility around our existing MC40 cyclotron to combine gamma-ray detection with current charged particle detector technology and instrumentation to create this scientific opportunity. The funding is to purchase an array of Lanthanum Bromide scintillator detectors to permit precision electromagnetic decay measurements.

The direct beneficiaries of this research are those who are involved in the development of models of light nuclei - namely, ab inito type calculations. As part of the development of this proposal we have had discussions with groups active in: No-Core Shell Model, Chiral Effective Field Theory (on the lattice), Greens-Function Monte Carlo, Antisymmeterised Molecular Dynamics (AMD) and Fermionic Molecular Dynamics (FMD). The Birmingham group has a strong record of working with the theory community, particularly in Japan and Germany, in developing an understanding of light nuclei. The results of the current research will be communicated in the highest ranked journals possible. A second strand revolves around public understanding of Science. Part of the research programme focuses on the Holye state in carbon-12. The Hoyle state is responsible for the synthesis of carbon in stars; understanding its structure is a challenge which has an impact not only on nuclear science, but on the origins of carbon based life itself. The understanding which emerges from the current research will be communicated through both the scientific and popular press.