6,115 research outputs found

    The contrasting fission potential-energy structure of actinides and mercury isotopes

    Full text link
    Fission-fragment mass distributions are asymmetric in fission of typical actinide nuclei for nucleon number AA in the range 228A258228 \lnsim A \lnsim 258 and proton number ZZ in the range 90Z10090\lnsim Z \lnsim 100. For somewhat lighter systems it has been observed that fission mass distributions are usually symmetric. However, a recent experiment showed that fission of 180^{180}Hg following electron capture on 180^{180}Tl is asymmetric. We calculate potential-energy surfaces for a typical actinide nucleus and for 12 even isotopes in the range 178^{178}Hg--200^{200}Hg, to investigate the similarities and differences of actinide compared to mercury potential surfaces and to what extent fission-fragment properties, in particular shell structure, relate to the structure of the static potential-energy surfaces. Potential-energy surfaces are calculated in the macroscopic-microscopic approach as functions of fiveshape coordinates for more than five million shapes. The structure of the surfaces are investigated by use of an immersion technique. We determine properties of minima, saddle points, valleys, and ridges between valleys in the 5D shape-coordinate space. Along the mercury isotope chain the barrier heights and the ridge heights and persistence with elongation vary significantly and show no obvious connection to possible fragment shell structure, in contrast to the actinide region, where there is a deep asymmetric valley extending from the saddle point to scission. The mechanism of asymmetric fission must be very different in the lighter proton-rich mercury isotopes compared to the actinide region and is apparently unrelated to fragment shell structure. Isotopes lighter than 192^{192}Hg have the saddle point blocked from a deep symmetric valley by a significant ridge. The ridge vanishes for the heavier Hg isotopes, for which we would expect a qualitatively different asymmetry of the fragments.Comment: 8 pages, 9 figure

    Cooling of a Compact Star with a LOFF Matter Core

    Get PDF
    Specific heat and neutrino emissivity due to direct URCA processes for quark matter in the color superconductive Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) phase of Quantum-Chromodynamics have been evaluated. The cooling rate of simplified models of compact stars with a LOFF matter core is estimated.Comment: 3 pages, 1 figure, to appear in the proceedings of the Helmoltz International Summer School of Theoretical Physics on Dense Matter in Heavy Ion Collisions and Astrophysics, JINR, Dubna, Russia, 21 Aug - 1 Sep 200
    corecore