Nuclear structure in the vicinity of shell closures far from stability

The status of experimental approach to "1"0"0Sn and "7"8Ni is reviewed. Revised single particle energies for neutrons are deduced for the N=Z=50 shell closure and evidence for low lying I"#pi#=2"+ and 3"- states is presented. Moderate E2 polarization charges of 0.1 e and 0.6 e are found to reproduce the experimental data when core excitation of "1"0"0Sn is properly accounted for in the shell model. For the neutron rich Ni region no conclusive evidence for an N=40 subshell is found, whereas firm evidence for the persistance of the N=50 shell at "7"8Ni is inferred from the existence of seniority isomers. The disappearance of this isomerism in the mid #nu#g_9_/_2 shell is discussed. The spectroscopy of "2"1"6Th disproves the existence of a Z=92 shell gap as predicted by some recent mean field calculations. Inversion of the #pi#h_9_/_2 and f_7_/_2 orbitals at Z=90 is ascribed to the coupling of the f_7_/_2 (and i_1_3_/_2) protons to the low-lying 3"- state (#Planck constant##omega#_3=1.69 MeV). (orig.)Invited talk 'Tours Symposium on Nuclear Physics IV, TOURS 2000' to be published in AIP conf. proc.SIGLEAvailable from TIB Hannover: RO 801(2000-26) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Energy and efficiency calibration of an array of six Euroball Cluster detectors used for beta-decay studies

The use of an array of 6 euroball cluster detectors, i.e. 42 large-volume germanium detectors, for beta-decay studies is described. The solid angle with respect to a source placed in the center of the array amounts to 65% of 4#pi# sr. The total photo-peak efficiency for 1.33 MeV #gamma#-rays is 10.2(5)%, without ''adding back'' the Compton-scattered events. For this #gamma#-ray energy, the energy resolution of the entire setup is 2.8 keV. The performance of the array up to #gamma#-ray energies of 8 MeV is discussed, and alternative ways of determining the photo-peak efficiency are presented. (orig.)13 refs.Available from TIB Hannover: RO 801(98-37) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

#beta#-decay of "4"0Ti

The #beta#-decay of "4"0Ti was studied. The Fermi and Gamow-Teller strength function was deduced from the observed #beta#-delayed emission of protons and #gamma#-rays and from the measured half-life of 55(2) ms. The results are compared to shell-model predictions and are used to estimate the neutrino-capture rate of the solar-neutrino detector ICARUS. (orig.)Available from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Nuclear structure near the doubly-magic "1"0"0Sn

The single particle (hole) energies in "1"0"0Sn, as extrapolated by a shell model analysis of the neighbouring nuclei, show a remarkable similarity to those in "3"6Ni, one major shell lower. This is borne out in nearly identical I"#pi#=2"+ excitation energies, implying E(2"+)#approx =#3 MeV in "1"0"0Sn, and a large neutron effective E2 charge #epsilon##>=#1.6#epsilon#. In contrast a small proton polarisation charge #delta##epsilon##<=#0.3#epsilon# is found, pointing to a large isovector charge. Mean field predictions for single particle energies show substantial deviations from the experimental extrapolation. From the experimental two-proton hole spectrum in "9"8Cd an improved empirical interaction is extracted for the #pi#(p_1_/_2,g_9_/_2) model space yielding a good description of the N=50 isotones "9"5Rh to "9"8Cd. In "1"0"4Sn, for the first time in this region, strong E3 transitions with B(E3)#>=#17 W.u. were identified, indicating E(3"-)#approx =#3 MeV in "1"0"0Sn. New experimental devices, as the Ge-cluster cube and total absorption spectrometers, applied in a pioneering experiment to the #beta#"+/EC decay of "9"7Ag, have led to a consistent picture of the Gamow-Teller quenching around "1"0"0Sn. The experimental results are discussed in the framework of various shell model approaches by using both empirical and realistic interactions. (orig.)Available from TIB Hannover: RO 801(98-62) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Beta-decay of "4"0Ti and "4"1Ti and implication for solar-neutrino detection

The #beta#-decay of "4"0Ti and "4"1Ti was studied by measuring the #beta#-delayed proton- and #gamma#-emission. The half-lives for "4"0Ti and "4"1Ti were determined to be 54(2) and 82(3) ms, respectively. The experimental #beta#-decay strengths are compared with shell-model calculations and results from other measurements. The integrated Gamow-Teller strengths for "4"0Ti and "4"1Ti were found to be quenched, compared to the calculations, by factors of 0.79(3) and 0.93(3), respectively. Based on the experimental "4"0Ti #beta#-decay strength, the neutrino absorption cross-section and induced neutrino event rates for "4"0Ar were determined to be 14.3(3) x 10"-"4"3 cm"2 and 9.4#+-#0.2(stat.)_-_1_._6"+"1"."3(syst.) SNU, respectively. (orig.)Available from TIB Hannover: RO 801(98-19) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Beta-decay of "5"6Cu

By measuring positrons and #beta#-delayed #gamma#-rays emitted from mass-separated sources, the decay of "5"6Cu(4"+,T_z=-1,T=1) to states in the doubly-magic nucleus "5"6Ni was studied for the first time. The half-life of "5"6Cu was measured to be 78(15) ms, and four #beta#-delayed #gamma#-rays were assigned to its decay. The resulting experimental data on Fermi and Gamow-Teller strength are compared with shell-model predictions. (orig.)Available from TIB Hannover: RO 801(98-12) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Beta-delayed proton decay of a high-spin isomer of "9"4Ag

We have observed the high-spin states in "9"3Rh populated by delayed-proton emission following the #beta# decay of "9"4Ag. The existence of a second isomer in "9"4Ag with I#>=#17, T1/2=0.42(5) s, whose #beta#-decay energy is at least 15.5 MeV, has been established. This state features most likely the highest spin ever observed for #beta#-decaying nuclei. (orig.)SIGLEAvailable from TIB Hannover: RO 801(03-08) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Interfaces of nuclear structure studies-decay vs. in-beam experiments

The common interface of #beta#-decay and particle-decay experiments and in-beam studies following fusion, relativistic fission and projectile fragmentation is defined by the search for the best way to extract nuclear structure information. For a few examples selected from the exotic regions of nuclei around "1"0"0Sn and between "6"8Ni and "7"8Ni it is demonstrated, that complementary spectroscopic data extracted by various methods lead to an understanding of the shell structure at these keypoints of the nuclidic chart. (orig.)24 refs.SIGLEAvailable from TIB Hannover: RO 801(99-16) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Beta decay of medium and high spin isomers in "9"4Ag

The very neutron-deficient isotope "9"4Ag was produced at the GSI on-line mass separator by using the reaction "5"8Ni("4"0Ca,p3n). The #beta#-decay properties of "9"4Ag were studied by detecting for the first time #beta#-delayed #gamma# rays and #beta#-#gamma#-#gamma# coincidences. Both the population of excited levels in the daughter nucleus "9"4Pd and the #beta#-decay half-life of "9"4Ag were investigated. The major part of the feeding was assigned to the decay of an I"#pi#=(7"+) isomer with a half-life of (0.36#+-#0.03) s. A weak #beta#-decay branch was found to populate high-spin levels in the "9"4Pd daughter with I#>=#18. It is tentatively assigned to the decay of a high-spin parent state in "9"4Ag with I#>=#17 and a half-life (0.3#+-#0.2) s. The measured #beta#-decay properties as well as the level structure of "9"4Ag and "9"4Pd are discussed in comparison with shell-model predictions. (orig.)SIGLEAvailable from TIB Hannover: RO 801(2002-19) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Structure of high spin states in "1"0"4Sn - E2 and E3 polarization of the "1"0"0Sn core

High spin states in "1"0"4Sn were identified in the reaction "5"8Ni("5"0Cr,2p2n) at 200 MeV and 205 MeV beam energies. The #gamma#-ray energies, intensities, multipolarities, and lifetimes of high spin states were measured with the GASP spectrometer array in combination with a plunger apparatus by means of the recoil distance Doppler shift method. The deduced level scheme and transition probabilities are compared to the results of large-scale shell model calculations using three independent two-body interactions. The agreement of the level energies is satisfactory, except for a cascade of dipole transitions at high spins. The general good agreement found for E2 transition strengths implies a large effective neutron polarization charge. The shell-model calculations do not account for the measured enhanced E3 transitions for which a core excited octupole phonon admixture is indicated. (orig.)Available from TIB Hannover: RO 801(98-18) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman