The Gamow-Teller decay of "1"0"5Sn to three-particle states in "1"0"5In

The EC/#beta#"+ decay of "1"0"5Sn was reinvestigated by using "5"8Ni (5 MeV/u) + "5"0Cr reactions, chemically selective on-line mass separation and #gamma#-ray spectroscopy. The half-life of "1"0"5Sn has been determined as 34 #+-# 1 s. Out of 104 #gamma# transitions ascribed to the "1"0"5Sn decay, 89 have been placed in the decay scheme including 52 excited states of "1"0"5In. From the EC/#beta#"+ feeding of individual states, the distribution of the Gamow-Teller (GT) strength has been derived. It is shown that the main part of the GT strength is associated with the feeding of "1"0"5In levels having excitation energies above 3 MeV. This observation can be interpreted as a sign of dominant feeding of three-quasiparticle states in "1"0"5In, which correspond to the #pi#(g_9_/_2)"-"1 #nu#d_5_/_2 shell-model configuration spread over many levels. The sum of the GT strength deduced from the present gamma ray data of B_#SIGMA#(GT)=1.46 povides a lower limit to the total GT strength. Many weak transitions, mainly from high energy levels, may not have been detected in this study and therefore part of the strength may be missed. An indirect support for this conclusion has been obtained from the analysis of the indium KX-rays intensity. This analysis indicates about 50% contribution of the electron-capture to the beta decay of "1"0"5Sn, which is interpreted as a sign of a predominant feeding of the high-energy "1"0"5In states with B_#SIGMA#(GT)#>=#3. The observed GT distribution and strength will be compared to results obtained from a finite-Fermi-system theory and a large-basis shell-model calculation. The core-polarization and higher-order hindrance factors will be discussed. (orig.)SIGLEAvailable from TIB Hannover: RO 801(94-23) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Gamow-Teller strength in the #beta#-decay of "3"6Ca

The #beta#-decay of "3"6Ca has been studied at the projectile fragment separator at GSI Darmstadt. The Gamow-Teller strength function B(GT), deduced from the observed #beta#-delayed proton- and #gamma#-emission and from the measured half-life of 102(2) ms, is compared to results obtained from large-scale sd-shell model calculations. (orig.)SIGLEAvailable from TIB Hannover: RO 801(94-84) / 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

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

Gamow-Teller strength distribution in the beta-decay of "1"0"0Ag from total-absorption gamma spectrometry

The EC/#beta#"+-decay of the odd-odd nucleus "1"0"0Ag was studied by means of total absorption #gamma#-ray spectrometry. Most of the Gamow-Teller strength was found to be concentrated at an excitation energy of 5.6 MeV in "1"0"0Pd, the FWHM of this resonance being 1.5 MeV. The measured strength distribution which is interpreted within the BCS approximation as being due to the dominant population of four-quasiparticle excitations, resembles the distribution predicted by an advanced shell-model calculation for the "9"8Ag#->#"9"8Cd decay. (orig.)Available from TIB Hannover: RO 801(94-66) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Study of the #beta#-decays of "3"7Ca and "3"6Ca

The #beta#-delayed proton and #gamma#-ray emission of "3"7Ca and "3"6Ca was studied at the projectile fragment separator at GSI Darmstadt. In the "3"7Ga study, the #beta#-delayed #gamma#-decay was observed for the first time, and the half-life was redetermined, under essentially background-free conditions, as 181.1#+-#1.0 ms. The surprisingly high #GAMMA#_#gamma#/#GAMMA#_p values found for proton-unbound states in "3"7K drastically reduce former discrepancies between the Gamow-Teller strength value B(GT) measured in the "3"7Ca #beta#-decay and those deduced from the "3"7Cl(p, n)"3"7Ar mirror reaction. Our data provide evidence, on a level of 1.6 standard deviations, for isospin-mixing of the lowest T=3/2 level in "3"7K. In the "3"6Ca study, a complete #beta#-decay scheme, including the #beta#-delayed proton emission into the ground and first excited states of "3"5Ar as well as the #beta#-delayed #gamma#-decay, was measured for the first time. The "3"6Ca half-life was remeasured with improved accuracy to be 102#+-#2 ms. Our data exclude a 1"+ assignment for two near-threshold states in "3"6K that could be important resonances in "3"5Ar(p, #gamma#) reactions of astrophysical interest. The B(GT) distributions in "3"7","3"6Ca decays are compared to results obtained from large-scale sd shell-model calculations. (orig.)Available from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Nuclear structure from N #approx =# Z to N >> Z - "1"0"0Sn, "7"8Ni, "2"0"8Pb

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 "5"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 e#>=#1.6e. In contrast a small proton polarisation charge #delta#e#<=#0.3e is found, pointing to a large isovector charge. In "1"0"4Sn for the first time in this region strong E3 transitions with B(E3)#>=#17 Wu were identified, indicating E(3"-)#approx =#3 MeV in "1"0"0Sn. Isomer spectroscopy beyond "6"8Ni following fragmentation of a 60.3 A MeV "8"6Kr beam has provided first evidence on the neutron polarisation charge and the occupation of the #nu#g_9_/_2 orbital beyond N=40, which is at variance with shell model calculations using realistic interactions. The N=40 subshell effect seen in E(2"+) is not borne out in 2n separation energies. On the other hand the #nu#g_9_/_2-f_5_/_2 splitting of single quasiparticle energies in Ni, Fe and Cr isotopes, as deduced from M2 isomers, give no hint for deformation at Z<28, N#approx =#40. In neutron-rich nuclei around "2"0"8Pb a number of new isomers were observed in the fragmentation of a 1000 A MeV "2"3"8U beam, while 3"-excitations on high spin configurations in and adjacent to "2"0"8Pb were identified in inelastic collisions of "2"0"8Pb+"2"0"8Pb. E2 and E3 strengths from stretched configurations are compared to model expectations. (orig.)SIGLEAvailable from TIB Hannover: RO 801(98-41) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

The beta-decay of "2"0Mg and its implications for the astrophysical rp-process

We have studied the #beta#-delayed proton and #gamma#-decay of "2"0Mg, produced by means of 95 MeV/u "2"4Mg+Ni reactions and implanted into a detector array after electromagnetic separation at GANIL. The experimental data obtained for excitation energies, #beta#-decay branching ratios, log-ft values and J"#pi#-assignments are given. No feeding has been observed to the 2646 keV state in "2"0Na, which plays an important role in the "1"9Ne(p, #gamma#)"2"0Na breakout reaction from the hot CNO cycle. A large difference of log ft values for mirror states in "2"0Na and "2"0F was found. The experimentally determined level properties, including B(GT) values, are discussed with reference to model calculations performed within the complete sd-shell space. (orig.)Available from TIB Hannover: RO 801(93-47) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Beta decay of neutron-deficient even-mass indium isotopes: evidence for population of highly-excited states in the cadmium daughter nuclei

By using mass-separated sources, positrons as well as #beta#-delayed protons and #gamma# rays were measured from the #beta# decay of "1"0"2In(T_1_/_2=22#+-#1 s) and "1"0"0In(T_1_/_2=6.1#+-#0.9 s). In particular, the average #beta#"+/(#beta#"++EC) ratio for the decay of "1"0"2In was measured to be 0.76(4) and a detailed level scheme of "1"0"2Cd was constructed. Whereas no direct #beta#"+/EC feeding of the identified "1"0"2Cd levels was observed, there is evidence for population of "1"0"2Cd states at high excitation energy followed by statistical #gamma# decay. This feature, which has been deduced on the basis of the measured positron spectrum and the measured #beta#"+/(#beta#"++EC) ratio of the "1"0"2In decay, is compared to the decay properties of the heavier odd-odd indium isotopes "1"0"4In, "1"0"6In and "1"0"8In, and is also used to interpret the observed #beta#-delayed proton data of "1"0"2In and "1"0"0In. For the first time, large-space shell-model calculations have been performed for the Gamow-Teller decay of heavy odd-odd nuclei. The decay results from these calculations are in good overall agreement with the gross decay properties of "1"0"2In and "1"0"0In deduced from the experiment. (orig.)SIGLEAvailable from TIB Hannover: RO 801(94-38) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Beta-decay of "2"0Mg

The #beta#-decay of "2"0Mg was investigated. A secondary beam of "2"0Mg ions, produced in reactions between a 95 A x MeV "2"4Mg-beam and a "n"a"t".Ni-target, was isotopically separated by means of the LISE3 spectrometer at GANIL. This secondary beam was implanted into a silicon detector array surrounded by germanium #gamma#-detectors. The #beta#-delayed proton and #gamma#-ray data, measured for this short-lived nucleus (T_1_/_2=95#+-#3 ms), were incorporated into an improved "2"0Mg#->#"2"0Na decay scheme. The 2645 keV level in "2"0Na is of importance for the breakout from the astrophysical hot CNO-cycle and the onset of the rapid proton capture process via the reaction "1"9Ne(p,#gamma#)"2"0Na. An upper limit of 0.1% for the #beta#-decay feeding of the 2645 keV level and a lower limit for the corresponding log ft value of 6.24 were determined. The implications of this result for the spin and parity assignment of the 2645 keV state are discussed. Concerning the isobaric multiplet mass equation no significant deviation from its quadratic form was found. By comparing the "2"0Mg #beta#-decay into the proton-unbound 3001 keV state in "2"0Na and the isospin-mirrored decay into the particle-bound 3488 keV level in "2"0F, an asymmetry ft"+/ft"--1=1.69_-_0_._6_5"+"0"."8"6 was observed. (orig.)SIGLEAvailable from TIB Hannover: RO 801(94-52) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman