High-spin study of the shell model nucleus 88Y⁴⁹

The near-yrast structure of the near-magic, odd-odd nucleus, 3988Y ⁴⁹, has been studied into the high-spin regime. Investigations were performed at the Wright Nuclear Structure Laboratory, Yale University, using the 74Ge(18O,p3n) and 76Ge(18O,p5n) fusion-evaporation reactions at beam energies of 60 and 90 MeV, respectively. Gamma-ray energy coincidence analyses using both double (γ2) and triple (γ3) fold coincidences, together with angular correlation measurements, have been used to extend the previously reported level scheme to an excitation energy of 8.6 MeV and a spin and parity of 19^(-). The presented level scheme is compared with predictions of a truncated valence space shell-model calculation, which assumes an inert 56Ni core with proton and neutron excitations allowed within the f_5/2, p_3/2, p_1/2, and g _9/2 single-particle states. The shell-model calculations show a reasonable comparison with the experimental data for the yrast, positive-parity states up to spin 18 â, with larger variations evident for negative-parity states with spins greater than 16. In spite of a significant increase in angular momentum input associated with the thin target 76Ge(18O,p5n) reaction channel, as compared to the backed target data using the 74Ge target, no additional discrete states were identified in the former data set, suggesting that the level scheme for this nucleus fragments significantly above the observed states, possibly indicating cross-shell excitations becoming dominant for I>19.