Preprint / Chemical Physics and Chemistry JINRP122004159 P122004159

Chemical Identification of Dubnium as a Decay Product of Element 115 Produced in the Reaction $\rm {^{48}Ca}+{^{243}Am}$

Abstract: The results of an experiment designed to identify $^{268}$Db as the terminal isotope in the $\alpha$decay chain of element 115 produced via the ${\rm {^{243}Am}}({\rm {^{48}Ca}},3n){\rm {^{288}115}}$ reaction are presented. The $^{243}$Am target was bombarded with a beam dose of $3.4\cdot 10^{18}$ $^{48}$Ca projectiles at an energy of 247 MeV at the center of the target. The reaction products were collected in the surface layer of a copper catcher block, which was removed with a lathe and then dissolved in concentrated HNO$_{3}$. The group5 elements were separated by sorption onto Dowex $50{\times} 8$ cationexchange resin with subsequent desorption using 1 M HF, which forms anionic fluoride complexes of group5 elements. The eluent was evaporated onto a 0.4 $\mu$m thick polyethylene foil that was placed between a pair of semiconductor detectors surrounded by $^{3}$He neutron counters for measurement of $\alpha$ particles, fission fragments, and neutrons. In the course of the experiment, we observed 15 spontaneous fission events with $T_{1/2}=32_{7}^{+11}$ h, which we attribute to $^{268}$Db. The production cross section for the $\rm {^{243}Am}+{^{48}Ca}$ reaction was $4.2_{1.2}^{+1.6}$ pb. These results agree with the original element115synthesis experiment, where $^{268}$Db was first observed as the terminal isotope following the five consecutive $\alpha$ decays from the $^{288}$115 parent nucleus in the Dubna gasfilled separator. The data from the present experiment give independent evidence for the synthesis of element 115 as well as element 113 via the $\rm {^{243}Am}+{^{48}Ca}$ reaction.

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Language: rus

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