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Register a new userMain parameters of the 118Sn compound-state cascade gamma-decay
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J. Honzatko
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Main properties of the excited states of $^{118}$Sn manifesting themselves in cascade gamma-decay of its compound state were studied. As in other heavier nuclei studied earlier, qualitative interpretation of the totality of the observed properties of this nucleus is impossible without accounting for coexistence and interaction of quasi-particle and collective nuclear excitations and their considerable influence on the main parameters of the process under study.
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Two-step cascades from the 192Os(n th,gamma)193Os reaction were studied in gamma-gamma coincidence measurement. The decay scheme of 193Os was established up to the excitation energy ~3 MeV. The excitation spectrum of intermediate levels of most intense cascades was found to be practically harmonic.
The statistical model of compound-nucleus reactions predicts that the fluctuations of the partial $gamma$-decay widths for a compound-nucleus resonance are governed by the Porter-Thomas distribution (PTD), and that consequently the distribution of total $gamma$-decay widths is very narrow. However, a recent experiment [Koehler, Larsen, Guttormsen, Siem, and Guber, Phys. Rev. C 88, 041305(R) (2013)] reported large fluctuations of the total $gamma$-decay widths in the $^{95}$Mo$(n,gamma)^{96}$Mo* reaction, contrary to this expectation. Furthermore, in recent theoretical works it was argued that sufficiently strong channel couplings can cause deviations of the partial width distributions from PTD. Here, we investigate whether the combined influence of a large number of nonequivalent $gamma$-decay channels, each of which couples weakly to the compound-nucleus resonances, can modify the statistics of the partial widths. We study this effect in neutron scattering off $^{95}$Mo within a random-matrix model that includes coupling to the entrance neutron channel and to the large number of $gamma$ channels. Using realistic coupling parameters obtained from empirical models for the level density and the $gamma$ strength function, we find that the PTD describes well the distribution of partial widths for all decay channels, in agreement with the statistical-model expectation. Furthermore, we find that the width of the distribution of the total $gamma$-decay widths is insensitive to wide variations in the parameters of the $gamma$ strength function, as well as to deviations of the partial-width distributions from the PTD. Our results rule out an explanation of the recent experimental data within a statistical-model description of the compound nucleus.
A new and independent determination of the Gamow-Teller branching ratio in the beta-decay of 21Na is reported. The value obtained of 5.13 +- 0.43 % is in agreement with the currently adopted value and the most recent measurement. In contrast to previous experiments, the present method was based on the counting of the parent 21Na ions and the resulting 351 keV gamma-rays without coincident beta-particle detection.
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The 48Ti on 40Ca reactions have been studied at 300 and 600 MeV focusing on the fusion-evaporation (FE) and fusion-fission (FF) exit channels. Energy spectra and multiplicities of the emitted light charged particles have been compared to Monte Carlo simulations based on the statistical model. Indeed, in this mass region (A about 100) models predict that shape transitions can occur at high spin values and relatively scarce data exist in the literature about coincidence measurements between evaporation residues and light charged particles. Signals of shape transitions can be found in the variations of the lineshape of high energy gamma rays emitted from the de-excitation of GDR states gated on different region of angular momenta. For this purpose it is important to keep under control the FE and FF processes, to regulate the statistical model parameters and to control the onset of possible preequilibrium emissions from 300 to 600 MeV bombarding energy.
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