Neutron-hole strength distributions in heavy nuclei: (II). The 144, 148, 152Sm( 3He, α) 143, 147, 151Sm and the 144, 148, 150, 152, 154Sm(p, d) 143, 147, 149, 151, 153Sm reactions

Abstract

Valence and deep-lying neutron-hole strengths corresponding to orbits near and well below the Fermi surface have been observed in high-resolution studies of the 144, 148, 152Sm( 3He, α) and of the 144, 148, 150, 152, 154Sm(p, d) reactions at 70 and 42 MeV bombarding energy, respectively. The explored excitation energy range was 28 MeV for the ( 3He, α) experiment and about 12 MeV in the (p, d) study. Complete angular distributions have been measured in both cases and the data was analyzed within the framework of the distorted waves Born approximation theory of direct reactions. For the neutron closed shell target ( 144Sm), in addition to the well-known fragmentation of the 2d 5 2 and 1g 7 2 valence-hole strength, a new bump observed around 7.6 MeV excitation energy is excited in both reactions. This structure corresponds to the 1g 9 2 inner-hole strength in 143Sm and the analysis of the ( 3He, α) data suggests that more than 50% of the l = 4 strength can be found between 6 and 12 MeV. When one goes to the heavier Sm isotopes, the energy spacing between valence-hole states located above and just below the N = 82 shell decreases strongly and disappears in 151Sm as a result of increasing deformation. Combining good energy resolution and detailed analysis of the two reactions, rather complete spectroscopic information is obtained for the valence-hole strength distributions. With regard to inner-hole states, the energy spectra exhibit a narrow structure whose centroid energy decreases from 4.4 to 2.9 MeV when the mass number increases from A = 147 to A = 153. The main peak displays an asymmetric shape with an extremely large high-energy tail. The 1h 11 2 hole strength is split into the Nilsson Orbitals. The narrow bumps are found to carry a large fraction of the l = 5 and l = 2 hole strengths in 147,149,151,152Sm isotopes. In the high-energy tail of the structures one observes overlapping and increasing spreading of the g 7 2 , 2d 5 2 and possibly 1g 9 2 inner-hole strengths due to the disappearance of the N = 82 shell gap between N = 83 and N = 89 neutron numbers. The experimental hole strengths distributions are compared where possible to the predictions of the quasiparticle-phonon nuclear model or to the simple Nilsson model.