UCLA

This dissertation presents a search for the low lying transition in the 229Th nucleus. This nucleus is expected to have an exceptionally low energy and long-lived isomeric level just above the ground state which could be amenable to laser spectroscopy. We utilize 229Th doped LiSrAlF6 crystals to achieve high densities adequate for broadband synchrotron excitation. The charge state of the doped thorium atoms (4+) ensures a radiative decay upon de-excitation of the nucleus, necessary for fluorescence detection. Additionally; we built a pulsed VUV laser system, utilizing four wave difference frequency mixing in Xe, to continue interrogation of the 229Th:LiSrAlF6 crystals with improved sensitivities to longer lifetimes for the decay from the isomeric level. And finally, we utilize a 233U source along with superconducting single photon nanowire detectors (SNSPD's) in attempt to measure the internal conversion (IC) decay channel available to neutral 229Th. If successful, the experiment can provide the lifetime of the IC decay and can potentially provide energy bounds on the isomeric level.