Laser Excitation of the 229-Th Nuclear Isomer

Georgia Tech Research Corporation, Atlanta GA

Investigators

Abstract

AMO technologies of ion trapping and cooling and high resolution spectroscopy will be applied to the manipulation of a nuclear excited state. While typical nuclear excitation energies are in the keV to MeV range, there are several exceptional cases where the excitation energies are much lower. The Thorium-229 isotope, uniquely, has an excited state in the UV optical spectrum. The nuclear transition is likely to be exceptionally sensitive to variation of fundamental constants, due to the interplay of the strong and electroweak interactions inside this nucleus. Additionally, it offers a prospect of an optical clock substantially less sensitive to external electromagnetic field perturbations, including black-body radiation. In preliminary work triply-charged ions of Thorium 232 (232Th3+) have been confined and laser cooled in an rf Paul trap. We will now trap and laser cool 229Th3+. The isomer state search will be assisted by the electron-nuclear coupling (the so-called electron-bridge mechanism), via multi-photon excitation with harmonics of an ultra-fast laser. Once the transition has been found, optical spectroscopy of the electronic states of the isomer will be performed. This should determine the enhancement factor for the search of time variation of fine structure constant alpha in this system, resolving an ongoing theoretical controversy. This research will have broad impact across several areas of physics and technology. Laser excitation and coherent manipulation of nuclear states would establish a new bridge between atomic and nuclear physics, with the promise for new technologies, particularly in the area of precision metrology. In addition, this research will provide training and expertise for a new generation of scientists working on the boundaries of atomic, optical and nuclear physics.