The problem of the nuclear stability of superheavy chemical elements began to attract a great deal of attention soon after the methods of calculating their nuclear deformation energy had been developed and significant fission barriers had been predicted for superheavy nuclei having proton and neutron numbers close to the magic numbers 2 = 114 and N = 184.Experiments to produce superheavy nuclei in heavy-ion reactions have so far been unsuccessful. However, some data show that the possibilities of producing cold compound nuclei were not used in the 48Ca-induced reactions. Therefore the corresponding experiments should be repeated. It is not excluded that superheavy element (SHE) nuclei could be produced in deep inelastic transfer reactions involved in the system Cm + 2 3 8 ~.Consideration of the mechanisms of nucleosynthesis and halflife calculations show that there is a small probability for superheavy nuclei to exist in nature. In studies of the tracks of cosmic-ray nuclei in meteoritic olivines some long tracks, supposedly due to nuclei with 2 = 110, have been observed. Their flux is nearly 300 times smaller than those of the thorium-uranium group nuclei.Searches for superheavy elements in some primitive meteorites and hot brines have resulted in the detection of a spontaneously fissioning nuclide, possibly belonging to a new island of stability. The low concentration of this nuclide (about g/g (1 part in in the Allende meteorite) makes its identification difficult. Searches should be made for geological samples whose formation process might lead to a greater concentration of the hypothetical superheavy elements relative to the average concentration in the Earth's crust. 248

Abstract

The water rich in heavy volatile metals form the Cheleken Penninsula hot springs was passed through a column containing 850kg of anion exchange resin. The spontaneous fission activity (SF) of the samples was measured by neutron multiplicity detectors. The counting rate of spontaneous fission events was 0.5 per day for 9 kg of saturated resin. After 170kg of the resin had been treated with acid solutions and hydroxides had been precipitated from the eluate with alkali, the counting rate for the precipitate was about five per day. From measurements of the ~/SF ratio it is concluded that the activity cannot be traced back to a contamination by actinides, except to a contamination by pure 25zCf, which, however, seems to be unlikely. Thus the explanation of the observed effect as being due to the spontaneous fission of a new naturally occurring isotope of a superheavy element is considered to be the most probable one.

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