ENERGY LEVELS OF RU-100

The nuclear-level structure of Ru100 has been investigated through study of the radioactive decay of 16-sec Tc100 and 20-h Rh100. The experimental techniques employed include two-parameter Ge(Li)-Ge(Li) coincidence spectroscopy and NaI(Tl) γ-γ angular-correlation measurements. Altogether, 24 excited states of Ru100 have been observed below 3.5 MeV. Examination of previous Ru(n,γ) data strongly suggests that at least seven of the observed levels are populated by primary Ru99(n,γ) transitions. The present results, combined with previous internal-conversion and angular-correlation data, yield unique spin-parity assignments for nine levels, four of which are 0+ (at 1130.4, 1740.6, 2051.5, and 2387 keV). Also, through selection-rule arguments, narrow limits have been placed on the spin-parity values for the remaining states, almost all of which are of low spin (≤2). The assignments deduced for the parent nuclei are 1+ for Tc100 and 1- for Rh100. The β branching of Tc100 is found to be anomalous in that the transitions to the lowest two 2+ levels are extremely hindered compared to those that proceed to the lowest two 0+ levels. © 1969 The American Physical Society.