Production and Discovery of Neutron Rich Isotopes by Fragmentation of ¹⁹⁸Pt

The properties of neutron-rich heavy isotopes near the N = 126 shell closure are important for our understanding of nuclear physics and play a fundamental role in astrophysical processes such as the r-process. Despite their importance, the N = 126 isotones for atomic numbers less than lead are poorly studied due to the lack of sufficiently high production cross sections. In order to establish a footing in this region and eventually reach out toward the location of the r-process pathway and beyond, it is desirable to perform experiments studying the production of neutron rich isotopes in the Hf-Pt region.

Production cross sections were measured for over 70 fragments produced by an 85 MeV/u ¹⁹⁸Pt beam incident on a beryllium target, including three nuclei first observed in this work: ^{191, 192}Hf and ¹⁸⁹Lu. Event-by-event particle identification of A, Z, and q for the reaction products was performed by employing energy loss, time of flight, magnetic rigidity, and total kinetic energy measurements. Due to the existence of multiple charge up to C-like ions, a new analysis method was created, incorporating Monte Carlo calculations of charge state fractions for a given charge state of the projectile-residue just after the reaction. For the first time, charge-state probability distribution functions after the reaction have been deduced from experimental data.

This talk will discuss one possible method of rare-isotope production near N = 126 and the ability of a fragmentation residue to retain electrons from the primary beam.