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Multi-dimensional tunneling description of subbarrier fusion including neck degree of freedom (1991)

Schneider, J. ; Wolter, H. H.

Springer

The European physical journal 339 (1991), S. 177-188

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ISSN: 1434-601X

Keywords: 24.90.+d ; 25.70.Jj

Source: Springer Online Journal Archives 1860-2000

Topics: Physics

Notes: Abstract Subbarrier fusion of heavy ions is treated as a multidimensional tunneling problem on a potential energy surface spanned by the relevant degrees of freedom in the fusion process. In addition to the radial separation these are taken to be the deformation of the two nuclei and the formation of noses or a neck between them. An initial wave packet is constructed on this surface and is then propagated in time by the Hamiltonian of the system. Thus the dynamical evolution is treated in a fully quantum-mechanical way using degrees of freedom which are adapted to the fusion process. In this way one can clearly ascertain the effects of the spreading of the wave packet (zero point motion and internal excitation), the rôle of barriers and saddle points, and the tunneling process. We have applied the model to the fusion of the symmetric system58Ni+58Ni where we can reasonably limit the number of coordinates. Neck formation is found to be very important for the fusion enhancement and we even obtain a quantitative description of the data. In addition the time dependent wave packet method provides a very intuitive picture of the fusion process which helps to discuss the different approaches to subbarrier fusion in a unified way.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01282947

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Occurrence of methylated tin and dimethyl mercury compounds in a mangrove core from Sepetiba Bay, Brazil (1992)

Quevauviller, P ; Donard, O F X ; Wasserman, J C ; [et al.]

New York, NY [u.a.] : Wiley-Blackwell

Applied Organometallic Chemistry 6 (1992), S. 221-228

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ISSN: 0268-2605

Keywords: Mangrove ; methylation ; organotins ; dimethylmercury ; anoxic conditions ; methyltins ; Chemistry ; Organic Chemistry

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology

Notes: Analyses of organotin and organic mercury compounds have been performed in a sediment core from Sepetiba Bay, Brazil, in order to investigate possible methylation pathways in a mangrove environment. The results have revealed that the physico-chemical conditions existing in this type of environment (high organic inputs, anaerobic conditions, microbial activity, etc.) account for high methyltin concentrations (mono-, di- and trimethyltin) in the sediments, which are dependent upon the total load of metal released (e.g. from anthropogenic sources). Furthermore, the presence of dimethylmercury and not monomethylmercury in the samples demonstrated a new pathway of transformation of mercury in the environment: this compound, thought to be unstable in sediment, is assumed to be stabilized by a conjunction of factors, such as high sulphide levels, anoxic conditions and constant inputs of methane into the medium.

Additional Material: 5 Ill.