KEK ISOTOPE SEPARATION SYSTEM FOR beta DECAY SPECTROSCOPY OF R-PROCESS NUCLEI

Neutron-rich isotones with neutron shell closure N = 126 on the r-process path are supposed to be progenitors which form a peak around A = 195 in the r-abundance element distribution. Their beta decay properties are considered to play critical roles for better understanding where the heavy elements such as gold and platinum were made in the universe. We are now advancing a project to construct KEK Isotope Separation System to study beta decay properties and nuclear structures of neutron-rich nuclei around N = 126 experimentally. Those isotopes will be obtained via multi-nucleon transfer reactions induced by low-energy beams. For the study of the rare channel reaction products, it is essential to select both the element and mass number of them. We will adopt a gas catcher system combined with the laser resonance ionization and ISOL, which collect all reaction products and select the atomic number and mass of them efficiently. That system allows us to measure their beta decay properties by two-layer plastic scintillators and germanium detectors.