Identification of excited states in the deformed proton emitter La117 (travel and subsistence)

Only about 300 of the predicted 7000 atomic nuclei are stable, yet most of our understanding of nuclear physics is based on the measured properties of the stable (and near-stable) nuclei. For example, the arrangement of nucleons in specific shells, in a manner analogous to electrons in atomic structure, is one of the concepts at the heart of nuclear structure physics. The introduction of the spin-orbit interaction by Mayer, Haxel, Suess, and Jenssen was able to explain the existence of shell gaps and magic numbers in nuclei. Recent observations, however, have challenged the accepted shell structure, and have suggested that the well-known sequence of single-particle states does not persist in exotic nuclei which lie far from the line of beta stability. Instead, shifts in the sequence of single-particle levels conspire to cause different shell gaps, producing new and unexpected phenomena. The reasons for these alterations are presently of paramount importance in the field of nuclear-structure physics. In order to understand the structure of exotic nuclei, it is important to measure the properties of nuclei far from stability, near and at the particle driplines. The driplines delimit the existence of nuclei. The neutron dripline lies 20 or 30 mass units away from stability, and is still far from being experimentally accessible. Conversely, the proton dripline lies closer to stability and, using state-of-the art experimental techniques, it is now possible to study nuclei at the proton dripline in experiments. The structure of the nuclei at the proton dripline will be used to test our models of the behaviour of nucleus and its constituents, and to search for new phenomena caused by a severe excess of protons. Specifically the research proposed here will study a very proton-rich nucleus in the rare-earth region - La117. Nuclei in this region present ideal candidates to be studied because they are expected to possess novel structural phenomena, owing to the occupation of very similar orbitals by the the outermost neutrons and protons. With the technique of recoil-decay tagging in this region, it is possible to study the exotic proton-rich rare-earth nuclei over a whole range of isotopes, not just in individual cases, so that systematic effects will be studied at the proton dripline. Our objective is to study the structure of La117 by identifying its low-lying excited states using gamma-ray spectroscopy. In addition, we will further investigate the proton-decay properties of La117; although this decay mode has been studied previously, the configuration of the proton-decaying state is still unclear. The experiment to study La117 has been approved by the Programme Advisory Panel at Jyvaskyla Accelerator Laboratory in Finland using the Jurogam gamma-ray spectrometer and the RITU recoil-mass spectrometer. Here, we request funds for travel and subsistence to carry out the experiment.