α-decaying neutron-deficient nuclei 195g,195mAt

Abstract

New neutron-deficient isotopes 195g,195mAt, which are far away from the β-stability line, have been produced in the 164Er( 36Ar,p4n) 195g,195mAt(E lab=199 MeV) reaction. The reaction products recoiling out of the 164Er (62.4% enriched) target were separated from the incident 36Ar beam by using a gas-filled-type recoil separator (GARIS) and were implanted onto a double-sided position-sensitive silicon detector (PSD) placed at the focal-plane of the GARIS after traversing a large micro-channel plate (MCP) assembly. The large-area MCP assembly was set 60.8 cm upstream from the PSD to measure the time of flight (TOF) and to roughly estimate the masses of the reaction products. A pulsed beam with a repetitive mode of 5-ms Beam-On and 5-ms Beam-Off was used. The fusion evaporation products were identified on the basis of genetic correlations in the evaporation residue-initiated α-decay chains. As a result, the new activity with a half-life of 84 -14 +20 ms and an α-energy of 7089±30 keV is assigned to the decay of the ground state of 195At ( 195gAt). Another new alpha line with a half-life of 26 -9 +31 ms and an α-energy of 7185±30 keV is assigned to the decay of an isomeric state in 195At ( 195mAt).