The Edinburgh nuclear physics group has led new research indicating the surface of heavy atomic nuclei comprises a thin "skin" of neutrons, having an average (root mean square) radius around 0.15 millionths of a nanometre larger than that of the protons. A paper co-authored by the School's Prof. Dan Watts has been published as an Editor's Suggestion and features in the commentary section of the current issue of Physical Review Letters.
Dan explains the background to the paper:
"The experiment provides the first measurement of the neutron skin using an electromagnetic probe. This allows a new level of precision in the determination of neutron skin properties and has different systematic errors to other attempts. The neutrons in the nuclear surface were measured to have a more diffuse distribution than the protons. The new results discriminate between nuclear theories in common use but also provide new constraints on how nuclear matter behaves as it is compressed. This information guides the latest theories of neutron stars affecting the predicted star radius for a given mass, possible star cooling mechanisms and gravitational wave emission. The neutron skin is like a mini laboratory for neutron star physics!"
The initial data analysis was carried out by Claire Tarbert who now works as a medical physicist, developing new diagnostic devices for the UK National Health Service.
"This paper arose out of a project I worked on with Dan Watts that formed the basis of my PhD thesis. I’m really pleased to see it published, its been a great project to be a part of.
"I now work for the NHS as a medical physicist. My current role involves collaborating with clinicians, other physicists, and engineers to develop new medical devices (either pieces of software or hardware) mainly for ophthalmic applications. While my knowledge of neutron skins doesn’t come up too often in this job, I find that I use the other skills that I developed during my nuclear physics PhD on an almost daily basis. Through developing hardware for nuclear physics experiments, performing Monte Carlo simulations and data analysis, I gained programming skills and an understanding of electronic and mechanical engineering. That experience, together with the scientific writing skills I picked up as I put together my thesis, I now find invaluable." Claire Tarbert, NHS Medical Physicist
Neutron skin of 208Pb from coherent pion photoproduction: C.M. Tarbert, D.P. Watts, D.I. Glazier et al