Measuring the plasma physics impact on nuclear reaction cross-sections and lifetimes (plasma strand project)

Supervisor: Dr Chris Murphy (University of York) & Andrew Simons (AWE)

Fusion in supernovae or neutron star collisions are responsible for generating around half of all material consisting of elements with atomic weights above that of iron (>56). [1]  Full understanding of the processes for the observed nuclear abundances is only possible with solid predictions of the masses, nuclear interaction cross-sections, and decay rates.  The majority of current data on these parameters is derived from accelerator-based experiments where highly ionised beams of ions are incident on neutral targets which, while instructive, does not represent the highly-ionised, thermal astrophysical environments in which these fusion reactions ordinarily occur.

The process of nuclear decay resulting in ejection of an atomic electron (mediated via a virtual photon between the nucleus and the orbital) is known as internal conversion (IC).  This de-excitation channel is supressed – or completely removed – as the material enters the plasma state, due to a reduction in the number of atomic electrons present.  A reverse process is possible, where the energy released by an electronic de-excitation (or capture) event is able to excite the nucleus through the mediation of a virtual photon.  These reverse processes these processes are known as nuclear excitation by electron transition (capture) or NEET (NEEC).

NEEC and NEET calculations are not well-constrained by experimental data due to the challenges associated with measurements in extreme conditions.  Recent work at the University of York [2] has been able to generate calculation tools which aid in the design of both accelerator and laser-based NEEC and NEET experiments.

This project will use these theoretical and computational tools in order to design a laser-plasma experiment in order to observe NEEC and/or NEET reactions.  The experiment will be carried out at a high-power laser facility chosen based on feasibility of measurement and availability of access to the facility.  The measurements will be designed to both attempt an early measurement of this important process, but also understand better the experimental constraints on such a measurement.  Understanding of these processes will lead to an improved understanding of the nuclear physics relevant to fusion in stars, supernovae, and neutron star mergers.

Training in experimental laser-plasma physics will be provided through in-house experience in the YPI labs, as well as through experience gained at the Central Laser Facility at the Rutherford Appleton Laboratory.  Experience in data analysis and interpretation will be gained through the taught programme in the CDT as well as through analysis of the experimental data obtained as part of the project.

Regular (written and oral) updates to our collaborators will be delivered by the student with the support of the supervisor which will build capability and confidence in scientific communication.  This will be demonstrated further by conference presentations which will increase visibility and future employment opportunities.

Since most undergraduate programmes do not cover laser-plasma interactions, and nuclear physics in plasma conditions, specific experience of the field is not required.  An enthusiasm for collaborative science and teamwork will be important for the successful candidate.

[1]  Physics Today 71, 1, 30 (2018);

[2] Optimising the Experimental Approach to Nuclear Excitation by Electron Capture  B Wallis PhD Thesis, York (2022)

The project will mainly be based in York, but will involve experimental campaigns at high power laser labs which are almost always collaborative.  This might include travel to Oxfordshire, Berkshire, France, Romania and the USA amongst other laboratories and universities.  There will also be the opportunity to attend summer schools and conferences internationally.

This project is offered by University of York. For further information please contact Dr Chris Murphy (