Nuclear Physicists publish 2 Cosmic gamma-ray papers in same PRL issue

Gavin Lotay and a Wolf-Rayet star in the background.

Edinburgh Nuclear Physicists working at US and European accelerators report key nuclear astrophysical reaction measurements affecting cosmic γ-ray emission line intensities, in 2 papers in same issue of prestigious Physical Review Letters journal.

Modern satellite telescopes are revealing detailed information on cosmic γ-ray emission. Distinctive γ-ray lines, associated with the radioactive decays of specific nuclear isotopes in our galaxy, are tracers that tell us that the process of production of elements, known as nucleosynthesis, is ongoing in the cosmic environment, and in our own galaxy. There remain key uncertainties as to the origins of these radio-isotopes due to orders of magnitude uncertainties in the nuclear reaction rates at the burning temperatures in stars. These reactions only take place at very low energies by quantum tunnelling, and the reactions can be ignited by the existence of single resonances located in the burning energy region known as the Gamow window.

The Edinburgh Nuclear Physics Group is internationally renowned for its work on explosive nuclear astrophysical reactions, and in particular on its links with the properties of unstable (sometimes known as exotic) nuclei. In an experimental work led by Gavin Lotay, as part of his PhD Thesis work, and Professor Woods, performed at Argonne National Laboratory, Chicago, USA the world leading Gammasphere array was used to identify key low lying resonances for the first time, thereby reducing uncertainties in the nuclear reaction rates affecting production of the cosmic γ-ray emitter 26Al by nearly a factor of a million! These results clearly demonstrate that low energy reactions on massive Wolf-Rayet stars, and the subsequent flow of material into the cosmos from stellar winds, is the most likely source of the majority of the 26Al material observed in satellite missions. This was reported in the prestigious journal Physical Review Letters [1], the image shows Gavin Lotay and a Wolf-Rayet star in the background.

In the same Physical Review Letters issue Professor Woods, Dr Aliotta, and Dr Davinson, as part of an international team reported the observation of a broad astrophysical resonance that had been predicted by nuclear theoreticians, but whose absence had been something of a mystery. This resonance was observed using accelerated radioactive beams, a vital modern approach that allows us to study for the first time key nuclear reactions that take place in the Universe in hot, dense, exploding stars such as novae, but reproduced here on the surface of the earth [2]. This result increases the destruction rate of the radioisotope 18F, in novae burning, and may explain the surprising failure of satellite missions to observe its presence through cosmic γ-ray emission.

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