Structure of Neutron-rich N = 126 Closed Shell Nuclei.

A series of experiments devoted to the study of the neutron-rich N∼426 region have been performed at GSI, Darmstadt, within the Rare Isotopes Investigations at GSI (RISING) project. The highlights of the experimental results from these highly successful experiments include the first observation of excited states in three neutron-rich N = 126 closed shell nuclei: (i) In ²⁰⁵Au₇₉ the conversion electron decay of the πh_11/2^-1 seconds lived isomeric state into the πd_3/2^-1 ground-state has been observed. In addition the yrast structure has been established up to spin-parity (19/2⁺) via the observation of the decay of an isomeric state with configuration π(h_11/2^-1)10(s_1/2^-1); (ii) In ²⁰⁴Pt₇₈, the yrast sequence has been observed following the internal decay of I^π = (5^-), (7^-) and (10⁺) isomeric states; (iii) In ²⁰³Ir₇₇ excited states have been observed following the decay of an isomeric state with structure ’similar’ to that in its ²⁰⁵Au isotone. Shell model calculations have been performed in order to get a deeper understanding of the structure of these N = 126 nuclei. It was found that in order to get a good description for all available information on the N = 126 isotones below lead, both on excitation energies and transition strengths, small modifications of the standard two-body matrix elements were required. [ABSTRACT FROM AUTHOR]