A Search for Naturally Occurring Superheavy Elements

Abstract

IN a continuing effort to measure neutron emission in natural samples for evidence of superheavy elements, several ores, minerals, concentrates, and special samples have been examined in our neutron multiplicity counter1. This counter, containing twenty3He detectors in a paraffin matrix, enables the evaluation of the emitted neutron multiplicity spectrum of large samples (volume 20 1) with little or no chemical processing. Such measurements provide an effective tool in the search for superheavy elements, since either their decay or the decay of daughter nuclides is expected to proceed by spontaneous fission. Furthermore, the parameter v (average number of prompt neutrons emitted in the fission act) has been estimated2,3 to be very high for superheavy nuclides; for example, v (298114 or296112)≃10 in contrast to v ≲ 4 for all known spontaneously fissioning nuclides. In addition to providing a unique indicator, this predicted high value of v enhances the sensitivity for detecting superheavy elements. A neutron multiplicity counter with a single neutron counting efficiency ɛ° = 0.30 would exhibit an efficiency of ɛ(>3)=0.62 for observing multiplicities of three or greater and ɛ(>4)=0.35 for observing multiplicities of four or greater in a fission event in which ten neutrons were emitted. On the basis of a capability for detecting 1.0 fission event per day for a nuclide with a half life of 108 yr (approximately the shortest half life for a nuclide to have survived geological times), the maximum sensitivity of the counter for such nuclides can be estimated to be ˜5 × 1010 atoms or ˜10−15 g g−1 in a 25 kg sample.