P.M. Stwertka

Inhibition of nucleon decay from high spin nuclei near the N = 82 shell closure

Abstract Statistical model calculations are shown to systematically overpredict the multiplicity of evaporated nucleons from Gd compound nuclei just above the N = 82 shell closure. Calculations for nuclei just below the shell closure, however, readily reproduce the data. A rapid neutron number dependence of the collective component of the total excitation energy is implied.

Structure in the 02+ excitation function in 12C + 12C scattering

Abstract Differential cross sections for 12 C + 12 C inelastic scattering to the 0 2 + state have been measured at several energies. The data are analysed in terms of DWBA calculations with no resonance contribution. In this description structure in the excitation function arises from barrier matching effects and interference between barrier and internal waves.

Angular-momentum limitations in the high-spin gamma-decay of medium-mass evaporation residues

Gamma-ray multiplicity measurements in coincidence with mass-separated evaporation residues are reported for the reaction 28 Si+ 54 Fe. The bombarding energy dependence [75 ⩽ E l ( 28 Si) ⩽ 145MeV] of the average gamma-ray multiplicity shows a saturation for the heaviest observed masses (80 and 79). Complementary information from partial-cross-section measurements, performed in the same energy range, is analyzed in the framework of the statistical model. A consistent description of both data sets suggests an enhanced alpha competition in the decay of the compound nucleus 28 Zr. The use of deformation-dependent optical-model transmission coefficients in statistical-model calculations at very high angular momenta is considered.

The onset of collectivity in nuclei near the N = 82, Z = 64 double closed shell☆

Abstract The high spin evolution of the quasi-continuum γ-rays has been studied in a series of nuclei, 145–148Gd, spanning the N = 82, Z = 64 double closed shell (146Gd). The study involves a new particle-γ coincidence technique which is sensitive to spin-energy correlated or rotational transitions in the continuum. The results indicate that collective rotational features exist in all these nuclei at high spin. This collective behavior seems to become dominant above J ∼ 42 h .

The validity of the compound nucleus mechanism in the 12C(16O, α) reaction at high energies☆

Abstract Excitation functions for several discrete states in 24 Mg excited in the 12 C( 16 O, α) reaction are studied from E( 16 O ) = 40 MeV to 150 MeV . A Hauser-Feshbach analysis is performed for states with J π = 0 + through 10 + and a consistent interpretation of these data is obtained in a compound nucleus model with reasonable critical angular momenta. We show that the energy dependence of the high spin selectivity is in agreement with the absence of selectivity recently reported for the 14 N( 14 N, α) reaction at high energy. Contrary to recent speculations, no compelling evidence for preequilibrium or direct processes in 16 O + 12 C reactions is found.