Search for Superheavy Elements and Actinides Produced by Secondary Reactions in a Tungsten Target

Abstract

Evidence was presented earlier by the authors (Nature 229: with atomic number 112. This evidence came principally from the observation of spontaneous fission activity in a Hg source separated from a W target irradiated with 24 GeV protons, and it was subsequertly shown that, at a later stage, 70% of the fission acttvity was due to /sup 252/Cf. The origin of the remaining 30% was unexplained. Experiments have since been carried out with other targets, the results of which are described. As the previous evidence was based on the possible production of eka-Hg, the chief aim of the experiments was to separate eka-Hg from the W target. As well as looking for possible superheavy elements a search was made for actinides. Details are given of the chemical separation mcthods. Counting experiments gave no evidence of superheavy elements and no known transplutonium elements were observed. It was, of course, not certain that the eka-element would follow its homologue in the chemical procedures, and it is possible this could be the reason for the negative results. The later experiments thus still did not explain the origin of the fission activity observed in the Hg source in the earlier experiments. It is concludedmore » that the secondary rcaction process is unlikely to be a useful way of producing superheavy elements, and that future experiments must rely on direct heavy ion reactions. (UK)« less