NEARLY COMPLETE LEVEL SCHEME OF SN-116 BELOW 4.3 MEV

The level scheme of Sn-116 has been studied by combining the results of Sn-115(n,gamma)Sn-116 and Sn-116(n,n'gamma)Sn-116 experiments. Both experiments were performed using isotopically enriched samples and Ge gamma-ray detectors. Based on the thresholds of gamma-ray excitation functions measured for the Sn-116(n,n'gamma) reaction and the precise gamma-ray energies from the capture reaction, 100 levels were observed below 4.3 MeV excitation energy. Approximately half of these were not known previously. Forty-eight of these levels have unique or tentative spin-parity assignments, and for ten more the spin has been restricted to a single value. The spin-parity for most other levels below 4.3 MeV excitation has been restricted to a few values. These spin-parity assignments and limitations were derived mainly from (n,n'gamma) angular distribution measurements, together with additional information obtained from the cross section magnitudes in both experiments. Above 4.3 MeV excitation energy, 55 additional levels are proposed, based only on the Sn-115(n,gamma) results. No J-pi information is available for these higher-lying levels beyond the fact that they most probably all have J less-than-or-equal-to 4. The level scheme below 4.3 MeV from the current work, together with known high-spin levels up to 5.4 MeV seen in other experiments, are compared to the combined predictions of the two-broken-pair model, the interacting boson model, and the deformed collective model. In addition, several states have been phenomenologically identified as proton 1p-lh and collective quadrupole-octupole two-phonon excitations. It is concluded from the good agreement between experiment and these models that all levels in Sn-116 with J less-than-or-equal-to 6 up to an excitation of 4.0 MeV and J less-than-or-equal-to 3 up to 4.3 MeV may have been experimentally identified. The nearest-neighbor spacing distribution is intermediate between that of a Gaussian orthogonal ensemble and that of a Poisson distribution, with a slight preference for the former. The neutron separation energy was determined to be 9563.47 +/- 0.11 KeV.