Quantum preequilibrium multistep direct calculations for nucleon scattering on spherical and deformed nuclei: a microscopic approach

Preequilibrium multistep direct (MSD) double differential cross sections are calculated for medium energy inelastic neutron scattering (11-18 MeV) on 208Pb and 238U. A microscopic approach is used, since no adjustable parameters are involved. Cross section are expressed as a sum of DWBA transition amplitudes computed with the microscopic two-body interaction M3Y. Final target states are expressed as particle-hole excitations built from single particle states obtained within the HF+BCS theory applied with Skyrme force

Isomeres de forme dans les noyaux pairs-pairs : premiere selection de candidats dans la region de masses A < 208

SIGLECNRS RP 148 (748) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Lifetime measurement for the 21+ state in Sm 140 and the onset of collectivity in neutron-deficient Sm isotopes

Background: The chain of Sm isotopes exhibits a wide range of nuclear shapes and collective behavior. While the onset of deformation for N > 82 has been well studied both experimentally and theoretically, fundamental data is lacking for some Sm isotopes with N < 82. Purpose: Electromagnetic transition rates represent a sensitive test of theoretical nuclear structure models. Lifetime measurements are furthermore complementary to Coulomb excitation experiments, and the two methods together can give access to spectroscopic quadrupole moments. Method: The lifetime of the 2+ 1 state in 140Sm was measured with the recoil-distance Doppler shift technique using the reaction 124Te( 20Ne, 4n) 140Sm at 82 MeV. Theoretical calculations were performed based on a mapped collective Hamiltonian in five quadrupole coordinates (5DCH) and the Gogny D1S interaction. Results: The lifetime of the 2+ 1 state in 140Sm was found to be 9.1(6) ps, corresponding to aB(E2; 2+ 1 → 0+ 1 ) value of 51(4) Weisskopf units. The theoretical calculations are in very good agreement with the experimental result. Conclusions: The B(E2; 2+ 1 → 0+ 1 ) value for 140Sm fits smoothly into the systematic trend for the chain of Sm isotopes. The new beyond-mean field calculations are able to correctly describe the onset of collectivity in the Sm isotopes below the N = 82 shell closure for the first time

Lifetime measurements in 138Nd

Lifetimes of several short-lived excited states in 138Nd were measured with the ROSPHERE array at IFIN-HH, Bucharest, using the recoil-distance Doppler shift technique following the 123Sb(19F,4n) reaction. The resulting electromagnetic transition probabilities are compared to large-scale shell model calculations and to constrained Hartree-Fock-Bogoliubov calculations with the Gogny D1S interaction, configuration mixing, and a five-dimensional collective Hamiltonian formalism. The onset of collectivity in Nd isotopes below the N = 82 shell closure and the deformation induced by the alignment of protons and neutron holes in the h11/2 orbitals are discussed