The decay of the (7{sup +}) and (21{sup +}) isomers of the N=Z isotope {sup 94}Ag was studied at the GSI on-line mass separator by measuring {beta}-delayed protons, {gamma} rays, proton-{gamma} and ...proton-{gamma}-{gamma} coincidences as well as the {beta}-strength distribution. We have observed high-spin (up to 39/2) states in {sup 93}Rh populated by proton emission following the {beta} decay of the {sup 94}Ag isomers. The major part of the population is related to the {beta} decay of the known (7{sup +}) isomer whose half-life is 0.61(2) s. The assignment of the high-spin (21{sup +}) isomer in {sup 94}Ag with a half-life of 0.39(4) s has been confirmed. The excitation energy and {beta}-decay energy of the (21{sup +}) isomer were measured to be at least 5.4 and 17.7 MeV, respectively. At this excitation energy, the (21{sup +}) isomer is expected to be unbound to direct one-proton, two-proton, or {alpha} decays. The remarkably long half-life of the (21{sup +}) isomer with the highest spin and excitation energy ever observed for {beta}-decaying nuclei makes a new textbook example of a nuclear high-spin trap. The branching ratios for {beta}-delayed proton emission are about 20% and 27% for the decays of the (7{sup +}) and (21{sup +}) isomers, respectively. The properties of the experimentally identified {sup 93}Rh levels are discussed in comparison to shell-model predictions.
Proton radioactivity from {sup 105}Sb has been reinvestigated at the GSI on-line mass separator. The nucleus was produced in the reaction {sup 50}Cr({sup 58}Ni,1p2n), and collected with a tape ...transport system. A double-sided Si strip detector was used for proton spectroscopy. The direct proton decay of {sup 105}Sb reported in an earlier experiment at Berkeley was not observed. The present data imply an upper limit {approx}10{sup -3} for the ground-state proton decay branching ratio for proton energies higher than 430 keV.
{beta} decay of {sup 95}Ag Harissopulos, S.; Galanopoulos, S.; Skouras, L. D. ...
Physical review. C, Nuclear physics,
08/2005, Letnik:
72, Številka:
2
Journal Article
We studied the {beta}-decay properties of the N=Z+1 nucleus {sup 95}Ag by measuring {beta}-delayed {gamma} rays and {beta}-{gamma}-{gamma} coincidences with a plastic scintillator as {beta} detector ...and a Ge-detector array. The {sup 95}Ag nuclei were produced by means of the {sup 58}Ni({sup 40}Ca,p2n) reaction and separated with the GSI online mass separator. The previously reported level scheme of the {sup 95}Pd daughter nucleus was extended considerably. The deduced level scheme is compared with different shell-model calculations with or without breaking the {sup 100}Sn core.
We investigated the prompt dipole {gamma}-ray emission, related with entrance channel charge asymmetry effects, in the {sup 32}S+{sup 100}Mo and {sup 36}S+{sup 96}Mo fusion reactions at E{sub ...lab}=196 MeV and 214.2 MeV, respectively, with the aim to probe its evolution with incident energy. These reactions populate, through entrance channels having different charge asymmetries, the {sup 132}Ce compound nucleus at an excitation energy of 117 MeV with identical spin distribution. Fusion events were selected by detecting high-energy {gamma} rays in coincidence with evaporation residues. The center-of-mass differential {gamma}-ray multiplicity spectra of the considered reactions were found to be identical within the experimental uncertainties in the whole energy range. This result, associated with that reported for the same reaction pair at higher beam energy where a larger giant dipole resonance yield was evidenced for the more charge asymmetric system, implies an increasing trend of the prompt dipole {gamma}-ray emission with incident energy. Calculations based on a collective bremsstrahlung analysis of the reaction dynamics are presented and compared with the experimental findings.
Decay modes of excited nuclei are investigated in \(^{78,82}\)Kr + \(^{40}\)Ca reactions at 5.5 MeV/nucleon. Charged products were measured by means of the \(4\pi\) INDRA array. Kinetic-energy ...spectra and angular distributions of fragments with atomic number 3 \(\le Z \le\) 28 indicate a high degree of relaxation and are compatible with a fission-like phenomenon. Persistence of structure effects is evidenced from elemental cross-sections (\(\sigma_{Z}\)) as well as a strong odd-even-staggering (o-e-s) of the light-fragment yields. The magnitude of the staggering does not significantly depend on the neutron content of the emitting system. Fragment-particle coincidences suggest that the light partners in very asymmetric fission are emitted either cold or at excitation energies below the particle emission thresholds. The evaporation residue cross-section of the \(^{78}\)Kr + \(^{40}\)Ca reaction is slightly higher than the one measured in \(^{82}\)Kr + \(^{40}\)Ca reaction. The fission-like component is larger by \(\sim\) 25% for the reaction having the lowest neutron-to-proton ratio. These experimental features are confronted to the predictions of theoretical models. The Hauser-Feshbach approach including the emission of fragments up to \(Z\) = 14 in their ground states as well as excited states does not account for the main features of \(\sigma_{Z}\). For both reactions, the transition-state formalism reasonably reproduces the \(Z\)-distribution of the fragments with charge 12 \(\le Z \le\) 28. However, this model strongly overestimates the light-fragment cross-sections and does not explain the o-e-s of the yields for 6 \(\le Z \le\) 10. The shape of the whole \(Z\)-distribution and the o-e-s of the light-fragment yields are satisfactorily reproduced within the dinuclear system framework which treats the competition between evaporation, fusion-fission and quasifission processes. The model suggests that heavy fragments come mainly from quasifission while light fragments are predominantly populated by fusion. An underestimation of the cross sections for 16 \(\le Z \le\) 22 could signal a mechanism in addition to the capture process.
A systematic study of the population probabilities of nanosecond and microsecond isomers produced following the projectile fragmentation of U-238 at 750 MeV/nucleon has been undertaken at the SIS/FRS ...facility at GSI. Approximately 15 isomeric states in neutron-deficient nuclei around A similar to 190 were identified and the corresponding. isomeric ratios determined. The results are compared with a model based on the statistical abrasion-ablation description of relativistic fragmentation and simple assumptions concerning gamma cascades in the final nucleus (sharp cutoff). This model represents an upper limit for the population of isomeric states in relativistic projectile fragmentation. When the decay properties of the states above the isomer are taken into account, as opposed to the sharp cutoff approximation, a good agreement between the experimental and calculated angular momentum population is obtained.
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