In-beam investigation and the structure of states in "1"1"3Sn

The results of in-beam investigations of "1"1"3Sn using the (p,n), (p,3n), (#alpha#,n) and (#alpha#,2n) reactions are summarized. Excited states have 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 the 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 and 2d_3_/_2 shells, the negative-parity states as the coupling of one 1h_1_1_/_2 neutron to the two- or four-quasiparticle neutron excitations in the even-mass "1"1"2Sn core. For the 25/2"+ isomer the three-quasiparticle neutron configuration #nu#(h"2_1_1_/_2g"-"1_7_/_2) has been proposed on the basis of a shell-model analysis using the mass formula formalism. The experimentally observed yrast states in _5_0"1"1"3Sn_6_3 are compared with the corresponding states in the valence-mirror nucleus _6_3"1"4"5Eu_8_2 giving remarkable similarities although the parameters for the shell-model calculations differ considerably. The analysis of nearest-neighbour spacing distributions of 5/2"+ states in "1"1"3Sn does not allow definite conclusions about regularity or chaos. (orig.)59 refs.Available from TIB Hannover: RR 1847(95) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

The COMBAS fragment separator of radioactive nuclei and the FOBOS 4#pi#-detector for charged particles

The projectile-like fragment separator COMBAS is being designed at the Flerov Laboratory of Nuclear Reactions, JINR Dubna, for providing radioactive nuclear beams. COMBAS is a compact achromatic beam line with a high resolving power of 4360. It accepts fragments within 6.4 msr solid angle and with a momentum spread of 10%. The method of isotopic separation is based on a combination of magnetic rigidity and energy loss analysis. The separated radioactive beam is planned to be transported either into a time-projection chamber in the regime gas target - gas detector or to a secondary target positioned in the centre of the FOBOS 4#pi#-array or to another set-up. The FOBOS detector is intended for heavy ion reaction studies in the bombarding energy range of 10-100 AMeV at the cyclotron U-400M of the FLNR. Presently, only primary cyclotron beams are used because COMBAS is not yet complete. FOBOS consists of a gas-detector ball of 30 position-sensitive avalanche counters and 30 axial ionization chambers behind them and an outer scintillator shell of 210 CsI(Tl) counters surrounding the gas detectors. An array of 96 phoswich counters cover the very forward angles. All charged reaction products can be measured in a wide dynamic range and in a geometry convering a substantial part of 4#pi#. First data have been taken concerning fission and emission of intermediate-mass fragments in the reactions "7Li (43 AMeV) on "2"3"2Th and "1"4N (34 AMeV) on "1"9"7Au. (orig.)15 refs.SIGLEAvailable from TIB Hannover: RR 1847(103) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman