Our spectroscopy group at McGill University uses laser techniques to study fundamental nuclear properties - radii, spins, and moments. The techniques are borrowed from atomic physics. In an atomic spectrum, a transition line splits into a number of components (the hyperfine structure), whose wavelengths depend on the size, shape, and spin of the nucleus. A lot of the really interesting phenomena (sudden changes of nuclear shape, for example) occur in exotic nuclei which lie far from nuclear stability. This means that our studies must be done on radioactive nuclei produced in reactions at particle accelerators. The challenge is therefore to find ways of studying very small samples (a few atoms, in some cases) of isotopes that may have lifetimes of only a few minutes, or seconds. We collaborate with members of a number of European laboratories in the COMPLIS experiment at the ISOLDE on-line isotope separator at CERN Geneva. In this work, we collect a sample of an isotope on some foil, produce a tiny cloud of the material collected with a heating laser, and with carefully tuned pulsed lasers, selectively ionize a single element.The tuning of one of the pulsed lasers provides our spectral information, and we analyse the results to give us information on nuclear radius change. The figure below shows such measurements made in medium mass and heavy nuclei. The sudden jumps in radii occur at masses where the isotope changes between oblate and prolate shapes.
We are also collaborating with members of the University of Manitoba , Argonne National Laboratory , and Texas A & M in the Canadian Penning Trap project, which will make extremely precise measurements of nuclear mass. Here we store the ions we produce in a sequence of two ion traps; in the final trap, the ions orbit in a magnetic field, and their orbital frequency determines the mass. At our McGill home base, we have a fully equipped laser spectroscopy lab (with Nd:YAG, excimer, pulsed dye and CW dye lasers) and are using these mainly to do spectroscopy on ions confined in radiofrequency quadrupole traps. We have shown recently that it is possible to obtain useful spectroscopic information on trapped clouds of only about 20 ions.