Magnetic-moment measurements by the transient-field and recoil-in-vacuum techniques in fpg-shell nuclei

Abstract

Picosecond-lifetime nuclear-state g factors are challenging to measure, with the transient-field (TF) and recoil-in-vacuum (RIV) techniques best able to probe them. The TF is experienced by a swift ion traversing a polarised ferromagnetic material, while RIV relies on hyperfine interactions between the nucleus and its electrons that occur in isolated ions. Both techniques often require independent calibration, a key limitation in their use. The objective of this thesis is to improve the precision of g-factor measurements with these techniques. This was achieved by developing procedures that minimise systematic uncertainty in TF measurements to obtain reliable relative g factors, and then scaling them by developing atomic-structure calculations that enabled absolute g factors to be determined from RIV measurements focused on Na-like ions.

Relative TF measurements were used to determine the first-excited-state g-factor ratio between Mg-24 and Mg-26, which was then scaled using a literature value of g(Mg-24), obtained using RIV, to determine g(Mg-26). TF measurements were also performed to obtain first-excited-state g-factor ratios between the stable even-A isotopes of Ge and Se, with the first-ever simultaneous measurement performed on isobaric nuclides (Ge-74, Se-74) in a cocktail beam.

An ab initio approach to modelling Fe-56 first-excited-state time-differential RIV data focused on Na-like ions was developed. Time-differential Ge-76 and time-integral Fe-54,56 first-excited-state data were also analysed. The analysis utilised a Monte-Carlo simulation of atomic decays to model the hyperfine interaction through time.

The combined use of relative TF and calibration-independent RIV measurements allowed the determination of precise absolute g-factor values. These were used to interrogate TF-strength calibrations, and shell-model predictions. Together, TF and RIV procedures presented in this work were effective in determining accurate g-factor values with improved precision in picosecond-lifetime nuclear states.