THE STRUCTURE OF SN-113 FROM PROTON AND ALPHA-PARTICLE INDUCED REACTIONS

The results of in-beam investigations of Sn-113 using the (p,n), (p,3n ), (alpha,n) and (alpha,2n) reactions are summarized. Excited states h ave been identified until E-x = 4715 MeV and J(pi) = (27/2(-)). For a large number of levels mean lifetimes tau have been determined with th e DSA method, For the J(pi) = 25/2(+) state at E-x = 4059 MeV, tau = 1 .0(4) ns has been measured with the gamma-RF method, The experimental results are compared with the predictions of shell-model calculations. Most of the positive-parity states may be considered as one- or three -quasiparticle neutron excitations of the 2d(5/2), 1g(7/2), 3s(1/2) an d 2d(3/2) shells, the negative-parity states as the coupling of one 1h (11/2) neutron to the two- or four-quasiparticle neutron excitations i n the even-mass Sn-112 core. For the 25/2(+) isomer the three-quasipar ticle neutron configuration nu(h(11/2)(2) g(7/2)(-1)) has been propose d on the basis of a shell-model analysis using the mass-formula formal ism. The experimentally observed yrast states in Sn-113(50)63 are comp ared with the corresponding states in the valence mirror nucleus Eu-14 5(63)82 giving remarkable similarities although the parameters for the shell-model calculations differ considerably. The analysis of nearest -neighbour spacing distributions of experimentally obtained 5/2(+) sta tes in Sn-113 does not allow definite conclusions about regularity or chaos.