New developments in collinear resonance ionisation spectroscopy for sensitive measurement of radioactive atoms and molecules

Abstract

Spectroscopic methods utilised for the study of exotic nuclei in cutting-edge experimental physics experiments are necessarily highly selective, sensitive and low-background techniques that generate results quickly. This is due to the fact that the artificial radioactive species under study often have half-lives under 1 s, are measured with low rates that can reach several atoms per second, and compete with stable neighbouring isotopes and isobaric contaminants that have far greater abundance than the isotope of interest. For this reason, the methods developed for such experiments are ideally suited to the challenges of detecting and measuring trace radioisotopes in environmental samples. Such isotopes are present in soil, groundwater and the atmosphere as a result of anthropogenic nuclear operations, such as nuclear waste storage and reprocessing of nuclear fuel. Many of these isotopes are present in part-per-billion quantities or less, making their quantification difficult with conventional techniques. Nevertheless, developing routine methods of quantifying concentrations of artificial isotopes in the environment is essential for understanding the impact of nuclear facilities on the wider world, and ensuring the safety of such facilities. The collinear resonance ionisation spectroscopy technique, employed at ISOLDE, CERN for measuring fundamental nuclear properties, has been adapted for the measurement of trace radioactive substances. In the first part of this thesis, a new facility at the University of Manchester has been designed, constructed, developed and tested. The ARIES facility (Analysis of RadioIsotopes in Environmental Samples) was developed to be optimised for the analysis of gaseous radioisotopes emitted into the atmosphere by nuclear operations; in particular, it will be employed in the future for the measurement of atmospheric concentrations of krypton-85. The second part of this thesis presents results from an experiment which took place at the CRIS beamline at ISOLDE, in which laser spectroscopy was performed for the first time on short-lived radioactive molecules - radium monofluoride (RaF). Low-lying vibronic transitions of this molecule are determined, along with the ionisation potential and the lifetime of the first excited state. These results benchmark a novel technique in the detection and study of radioactive molecules.

Date of Award	1 Aug 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Kieran Flanagan (Supervisor) & Giles Edwards (Supervisor)