The Hoyle Family: break-up measurements to probe α-condensation in light nuclei

The 12C Hoyle state is a candidate for α-condensation, due to its large volume and αcluster structure. This paper discusses precision break-up measurements and how they can elucidate α-condensate structures. Two experiments are discussed in detail, firstly concerning the break-up of 12C and then the decays of heavier nuclei. With more theoretical input, and increasingly complex detector setups, precision break-up measurements can, in principle, provide insight into the structures of states in α-conjugate nuclei. At present, such searches have not delivered evidence for α-condensation in 12C or 16O

Theoretical approaches to the 3α break-up of 12C

Abstract Two recent experiments have indicated that the break-up of the 12C Hoyle state is dominated by the sequential 8Be(g.s.) + α decay channel. The rare direct 3α decay was found to contribute with a branching ratio of less than 0.047% (95% C.L.). However, the ability of experimentalists to successfully disentangle these two competing decay channels relies on accurate theoretical predictions of how they each manifest in phase space distribution of the three break-up α-particles. The following paper reviews the current theoretical approaches to calculating the break-up of the Hoyle state and introduces a semi-classical WKB approach, which adequately reproduces the results of more sophisticated calculations. It is proposed that a more accurate upper limit on this branching ratio may be obtained if these new theoretical results are taken into account when analysing experimental data

Convolutional neural networks for challenges in automated nuclide identification

Improvements in Radio-Isotope IDentification (RIID) algorithms have seen a resurgence in interest with the increased accessibility of machine learning models. Convolutional Neural Network (CNN)-based models have been developed to identify arbitrary mixtures of unstable nuclides from gamma spectra. In service of this, methods for the simulation and pre-processing of training data were also developed. The implementation of 1D multi-class, multi-label CNNs demonstrated good generalisation to real spectra with poor statistics and significant gain shifts. It is also shown that even basic CNN architectures prove reliable for RIID under the challenging conditions of heavy shielding and close source geometries, and may be extended to generalised solutions for pragmatic RIID

An improved upper limit on the direct 3α decay of the Hoyle state

The structure of the Hoyle state, a near-threshold 0+ state of extreme astrophysical significance in 12C has long been investigated. An experiment was performed to measure the branching ratio for the decay of this state directly into 3 α-particles. Such a branching ratio is expected to be a good observable for whether the resonance can be described as a dilute gas of α- particles known as an α-condensate. This experiment gave the best upper limits to date for this direct decay via the improvement of the traditionally used DDΦ model to isotropic decay to the available phase space. The new DDP2 model includes three-body penetrabilities and gives a limit of < 0.026% (95% C.L.), a factor of 5 improvement over the previous experimentally obtained limit