Nuclear properties fission barriers

Decay properties of transuranium nuclides lead to the understanding of proton excess heavy nuclei verification of the proton drip line, nuclear structure of large deformed nuclei such as octupole and hexadecapole deformation, and fission barrier heights. There are several textbooks and review articles on nuclear decay properties of transuranium nuclei (e.g., Hyde et al. 1964 Seaborg and Loveland 1985 Poenaru 1996). Theoretical nuclear models of heavy nuclei are presented by Rasmussen (1975) and the nuclear structure with a deformed single-particle model is discussed by Chasman et al. (1977). Radioactive decay properties of transuranium nuclei are tabulated in the Table of Isotopes (Firestone and Shirley 1996). Recent nuclear and decay properties of nuclei in their ground and isomeric states are compiled and evaluated by Audi et al. (1997), while the calculated atomic mass excess and nuclear ground-state deformations are tabulated by MoUer et al. (1995). 

The nuclear models that resulted in the prediction of an island of superheavy nuclei have evolved in response to experimental measurements of the decay properties of the heaviest elements. While the prediction of a spherical magic N = 184 is robust and persists across the models [8], the shell closure associated with Z — 114 is weaker, and different models place it at higher atomic numbers, from Z = 120 to 126 [60-69] or even higher [70] (see Nuclear Structure of Superheavy Elements ). Interpretation of the decay properties of the heaviest elements may support this [71, 72], but the most part decay and reaction data do not conclusively establish the location of the closed proton shell. Because of this, the domain of the superheavy elements can be considered to start at approximately Z = 106 (seaborgium), the point at which the liquid-drop fission barrier has vanished [9]. For our purposes, the transactinide elements (Z > 103) will be considered to be superheavy (see Nuclear Structure of Superheavy Elements ). 

At temperatures up to 1000°C, molten fluorides exhibit low vapor pressure (benign chemical reactivity with air and moisture. Molten fluorides also trap most of the fission products (including Cs and 1) as very stable fluorides, and thus act as an additional barrier to accidental fission product release. Fluorides of the metals other than U, Pu, or Th are used as diluents and to keep the melting point low enough for practical use. Consideration of nuclear properties alone leads one to prefer as diluents the fluorides of Be, Bi, Li, Pb, Zr, Na, and Ca, in that order. 

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