Systematic Study of Tin Isotopes via High Resolution (p,t) Reaction Measurements

The tin isotopes provide a very good opportunity for experimental and theoretical studies of variations in nuclear properties with changing neutron number. Transfer reactions play an important role in our understanding of tin isotopes since these reactions are very sensitive to the neutron structure of the isotopic sequence N=60 (110Sn) to N=76 (126Sn). In the framework of a systematic study of the tin isotopes using (p,t) reactions in high resolution experiments at the Munich HVEC Tandem, with the Q3D spectrograph [1,2,3,4], the 118Sn(p,t)116Sn and 124Sn(p,t)122Sn reactions have been measured at an incident proton energies of 24.6 and 25 MeV, respectively. Angular distributions for 55 and 63 transitions to the final states of 116Sn and 122Sn, respectively, have been measured. A distorted-wave Born approximation (DWBA) analysis of the experimental differential cross sections, using conventional Woods-Saxon potentials and a semi-microscopic neutron pickup mechanism, has been carried out, allowing either the confirmation of previous spin and parity values or the assignment of new spin and parity to a large number of states. In Fig. 1 the angular distributions for the transitions to the observed 0+ states of 116Sn and 122Sn residual nuclei (dots) are compared with the DWBA calculations (solid lines). Zero-range one-step DWBA microscopic calculations of cross section angular distributions for the ground state and some excited states are in progress. These microscopic calculations make use of two-neutron spectroscopic amplitudes obtained from a shell model study of the 118,116Sn and 124,122Sn nuclei, respectively. The shell model calculations have been carried out within the framework of the seniority scheme, using a realistic effective interaction derived from the CD-Bonn nucleon-nucleon potential [5]. The model space has been truncated to states with seniority less than or equal to 4 to reduce the numerical work required by a complete basis diagonalization[6]. The energy spectra are also calculated and compared with experiment.(author)