Studies of closed shell nuclei using radioactive beams

点击翻译按钮获取中文摘要

One of the puzzling topics in modern nuclear structure is how nuclei "collectivize", or what determines the emergence of nuclear collectivity from shell model degree of freedom. This topic can be investigated in closed shell nuclei that are spherical in their ground state and exhibit a rotational character at relatively low excitation energies. The research program proposed here involves a series of experiments with the objective of searching for highly collective states in the A-even Sn isotopes that posses a closed shell at proton number 50. The main goal of the experiment is to study and fully characterize the proton two particle-two hole (2p-2h) excitations, and to search for proton four particle-four hole (4p-4h) excitations in the low-lying states of the 116-122Sn isotopes. These experiments will take advantage of the unique, high-quality, high-intensity beams of radioactive 116-122In ions available from the ISAC I facility at TRIUMF. The 8pi spectrometer in conjunction with a suite of ancillary detectors will be used. This world class experimental set-up will lead to comprehensive spectroscopy of low-lying states in the Sn isotopes. In such experiments beta decay spectroscopy offers unparalleled sensitivity to weak decay branches, in some cases at the 10-6 level. This is essential for observing collective transitions, which will be of low energy and have to compete with high energy, non-collective decay branches. A proposal entitled "Search for highly collective states in closed shell nuclei" to study the structure of low-lying collective states in 116-122Sn has been approved by the Subatomic Physics - Experiments Evaluation Committee at TRIUMF in July 2010 through a rigorous peer review process. This program will provide projects that are ideally suited for training highly qualified personnel at Simon Fraser University and collaborating institutes.