Short-Lived Isotopes of Transfermium Elements: Studying Characteristics of Spontaneous Fissioning

Abstract

series of experiments performed in 2014–2015 using the SHELS separator and a beam of multicharged ions from the U-400 accelerator at the Flerov Laboratory of Nuclear Reactions (Joint Institute for Nuclear Research) in Dubna is described. In preparation for a large program of experiments with a beam of highly charged ions of ⁵⁰Ti, an experiment is performed to study the spontaneous fissioning (SF) of short-lived neutron-deficient isotope ²⁵⁶Rf formed in complete fusion reaction⁵⁰Ti + ²⁰⁸Pb = ²⁵⁶Rf + 2n. The half-life of ²⁵⁶Rf is measured along with the probability of its SF decay. The average number of neutrons per one event of ²⁵⁶Rf SF ($\bar v$= 4.47 ± 0.09) is obtained for the first time. The results from experiments to study the SF of short-lived neutron-deficient isotopes synthesized in complete fusion reaction ⁴⁸Ca + ²⁰⁴Pb → ²⁵²No* are presented as well. Two short-lived activities attributed to the SF of the ground and isomeric states of ²⁵⁰No are revealed. The half-life, total kinetic energies of fission fragments, and neutron multiplicities are measured for the obtained short-lived nuclei. The average numbers of neutrons per one SF event are $\bar v$= 4.38 ± 0.13 and $\bar v$= 3.90 ± 0.20, respectively, for SF activity with t_1/2 = 5.1 ± 0.3 and t_1/2 = 36 ± 3 μs.