Cold fusion reproducibility

Several years ago, there was much discussion of a cold fusion process involving electrolysis of deuterium containing water with palladium electrodes. Independent investigators have had little luck duplicating the experiment and the original developers cannot reliably reproduce their results. 

On March 23, 1989, the University of Utah held a press conference that shook the energy world. Electrochemists Stanley Pons and Martin Fleischmann announced reproducible cold fusion 10% more energy released than supplied. They passed an electric current through palladium and platinum wires in a container of heavy water and lithium sulfate. Cold fusion is nuclear fusion at ambient temperature. When the two hydrogen atoms in a water molecule are replaced with deuterium (called heavy hydrogen because it has one proton and one neutron), it is called heavy water. 

To explain the small cross sections for SHE synthesis and in particular the fast decrease of the cold fusion cross sections, the concept of extra push has been developed. In this model, the barrier for complete fusion is shifted dynamically above the Coulomb barrier until the experimental cross section is reproduced (Hessberger et al. 1985). The barrier shift is explained (in terms of a macroscopic approach) as a result of dynamical hindrance of the nuclei on their way to fusion (Swiatecki 1982 Armbruster 1989). However, for the transactinide elements known to exist only due to shell effects, the application of a macroscopic model to explain all structure effects related to their production is questionable if not wrong (Miinzenberg 1988). In contrast to the extra push concept, experiment shows that the maximum of the excitation function shifts toward a smaller excitation energy for heavier systems, with Cn being the coldest compound nucleus ever produced at an excitation energy of only 10 MeV (Hofmann et al. 1996). 

McKubre, M.C.H., Crouch-Baker, S., Hauser, A.K. et al. (1995) Concerning reproducibility of excess power production. Proceedings of the 5th International Conference on Cold Fusion, IMRA, France (ed. S. Pons), pp. 17-33. 

In hot-fusion reactions, the cross section for producing heavy-element nuclides is determined by the probability that the highly excited compound nucleus will avoid fission in the deexcitation process. Cold fusion near the reaction barrier is qualitatively different the formation of the compound nucleus comes about in two separate steps [105, 107]. The reacting nuclei come into contact, captured into a dinuclear configuration, which is separated from an equilibrated compound nucleus by a potential-energy barrier which is not reproduced by the one-dimensional Coulomb-barrier model [94, 95, 210, 219, 220]. This extra barrier diverts the trajectory of the reaction through multidimensional deformation space toward quasifission, making reseparation much more likely than complete fusion. 

Besides the effect of shell stabilization in the entrance channel on the of the compound nucleus, the mechanism of " Ca-induced hot-fusion reactions shares another aspect of the character of cold-fusion reactions. While deexcitation of the hot compound nuclei is dominated by the competition between fission and neutron emission, attempts to reproduce the evaporation-residue cross sections by a simple r /ry treatment results in values that are much higher than those that are observed experimentally [300-302]. It is necessary to invoke a significant dynamical hindrance to fusion and a two-step mechanism [303, 304] to reproduce the cross sections for " Ca-induced reactions that result in transactinide nuclides [305, 306], which increases as the atomic number of the target nuclide increases. Like the cold-fusion reaction intermediate, the reaction trajectory from nuclei in contact to a compound nucleus can be diverted into a more probable path leading to quasifission, even though the potential energy of the compound nucleus is lower than or approximately equal to that of the reacting nuclei in contact [8, 105,123,174,220, 301, 307-312]. Only a small number of dinuclear intermediates reach the compact shape associated with the compound nucleus. 

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