Upper Limits for the Production of Superheavy Elements in the Reaction of ¹³⁶Xe with ^nat. U

Abstract

We tried to produce superheavy elements (SHE) in deepinelastic reactions of 136 Xe with nat U. Four irradiations of thick U-targets with increasing beam intensities (i. e. temperatures in the target) were performed. After a chemical separation sulfide precipitates were obtained. The spontaneous fission activity was determined by fission fragment/fission neutron coincidence counting with a lowbackground detector. We observed zero spontaneous fission decays due to superheavy elements in about two years counting time. This yields an upper limit for the production of SHE of < 1 · 10"" cm 2 in the half-life range of 1 to 200 day. Furthermore, the production cross-section of some actinoides was obtained.