Isospin dependence of mass-distribution shape of fission fragments of Hg isotopes

Using an improved scission-point model, the mass distributions are calculated for induced fission of even Hg isotopes with mass numbers A=174 to 196. With increasing A of a fissioning AHg nucleus the mass distribution evolves from symmetric for 174Hg, to asymmetric for isotopes close to 180Hg, and back to more symmetric for 192,194,196Hg. In the fissioning Hg isotopes their excitation energy weakly influences the shape of the mass distribution. In 180,184Hg, the mass distributions of fission fragments remain asymmetric even at high excitation energies

Muon Bremsstrahlung and Muonic Pair Production in Air Showers

The objective of this work is to report on the modifications in air shower development due to muon bremsstrahlung and muonic pair production. In order to do that we have implemented new muon bremsstrahlung and muonic pair production procedures in the AIRES air shower simulation system, and have used it to simulate ultra high energy showers in different conditions. The influence of the mentioned processes in the global development of the air shower is important for primary particles of large zenith angles, while they do not introduce significant changes in the position of the shower maximum.Comment: To be presented at the International Symposium on Very High Energy Cosmic Ray Interactions X

Shapes of the 192,190^{192,190}Pb ground states from beta decay studies using the total absorption technique

The beta decay of $^{192,190}$Pb has been studied using the total absorption technique at the ISOLDE(CERN) facility. The beta-decay strength deduced from the measurements, combined with QRPA theoretical calculations, allow us to infer that the ground states of the $^{192,190}$Pb isotopes are spherical. These results represent the first application of the shape determination method using the total absorption technique for heavy nuclei and in a region where there is considerable interest in nuclear shapes and shape effects

Shape Coexistence in the Relativistic Hartree-Bogoliubov approach

The phenomenon of shape coexistence is studied in the Relativistic Hartree-Bogoliubov framework. Standard relativistic mean-field effective interactions do not reproduce the ground state properties of neutron-deficient Pt-Hg-Pb isotopes. It is shown that, in order to consistently describe binding energies, radii and ground state deformations of these nuclei, effective interactions have to be constructed which take into account the sizes of spherical shell gaps.Comment: 19 pages, 8 figures, accepted in Phys. Rev.

Colloquium: Beta delayed fission of atomic nuclei

This Colloquium reviews the studies of exotic type of low-energy nuclear fission, the beta-delayed fission (bDF). Emphasis is made on the new data from very neutron-deficient nuclei in the lead region, previously scarcely studied as far as fission is concerned. These data establish the new region of asymmetric fission in addition to the previously known one in the transuranium nuclei. New production and identification techniques, which emerged in the last two decades, such as the wider use of electromagnetic separators and the application of selective laser ionization to produce intense isotopically or even isomerically pure radioactive beams are highlighted. A critical analysis of presently available DF data is presented and the importance of detailed quantitative DF studies, which become possible now, is stressed, along with the recent theory efforts in the domain of low-energy fission

Population of a low-spin positive-parity band from high-spin intruder states in 177Au : The two-state mixing effect

The extremely neutron-deficient isotopes 177,179Au were studied by means of in-beam γ-ray spectroscopy. Specific tagging techniques, α-decay tagging in 177Au and isomer tagging in 179Au, were used for these studies. Feeding of positive-parity, nearly spherical states, which are associated with 2d3/2 and 3s1/2 proton-hole configurations, from the 1i13/2 proton-intruder configuration was observed in 177Au. Such a decay path has no precedent in odd-Au isotopes and it is explained by the effect of mixing of wave functions of the initial state