Search

Abstract In atomic nuclei, the spin-orbit interaction originates from the coupling of the orbital motion of a nucleon with its intrinsic spin. Recent experimental and theoretical works have suggested a weakening of the spin-orbit interaction in neutron-rich nuclei far from stability. To study this phenomenon, we have investigated the spin-orbit energy splittings of single-hole and single-particle valence neutron orbits of 132Sn. The spectroscopic strength of single-hole states in 131Sn was determined from the measured differential cross sections of the tritons from the neutron-removing 132Sn(d, t)131Sn reaction, which was studied in inverse kinematics at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. The spectroscopic factors of the lowest 3 / 2 + , 1 / 2 + and 5 / 2 + states were found to be consistent with their maximal values of (2 j + 1) , confirming the robust N = 82 shell closure at 132Sn. We compared the spin-orbit splitting of neutron single-hole states in 131Sn to those of single-particle states in 133Sn determined in a recent measurement of the 132Sn(d, p)133Sn reaction. We found a significant reduction of the energy splitting of the weakly bound 3 p orbits compared to the well-bound 2 d orbits, and that all the observed energy splittings can be reproduced remarkably well by calculations using a one-body spin-orbit interaction and a Woods–Saxon potential of standard radius and diffuseness. The observed reduction of spin-orbit splitting can be explained by the extended radial wavefunctions of the weakly bound orbits, without invoking a weakening of the spin-orbit strength. [ABSTRACT FROM AUTHOR]

We have begun a program to measure (d,p) reactions on neutron-rich nuclei, probing the single-particle states near the and closed shells. We have measured the neutron transfer on two isotones, 82Ge and 84Se, at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. We have also performed a test measurement of transfer on 124Sn to develop the techniques to study the 2H(130,132Sn,p)131,133Sn reactions. Preliminary results for 85Se are consistent with 5/2+ ground state and 1/2+ first excited state assignments, and the successful measurement of the 2H(124Sn,p)125Sn reaction demonstrates the feasibility to measure the (d,p) reaction with neutron-rich 130,132Sn beams. [Copyright &y& Elsevier]

The study of neutron single-particle strengths in neutron-rich nuclei is of interest for nuclear structure and nuclear astrophysics. The distribution of single-particle strengths constrains the effective Hamiltonian and pairing interactions and determines neutron interaction rates that are crucial for understanding the synthesis of heavy nuclei in supernovae via the rapid neutron capture process. Particularly important are the neutron single-particle levels in nuclei near closed neutron shells. Radioactive ion beams from the Holifield Radioactive Ion Beam Facility have been used to study (d,p) reactions in inverse kinematics in order to probe neutron single-particle states in exotic nuclei. The results of a measurement with a 82Ge beam will be presented. [Copyright &y& Elsevier]