Synthesis and study of decay properties of the doubly magic nucleus 270Hs in the 226Ra + 48Ca reaction

title: Synthesis of elements 115 and 113 in the reaction 243Am + 48Ca
abstract: The results of two experiments designed to synthesize element 115 isotopes in the {sup 243}Am+{sup 48}Ca reaction are presented. Two new elements with atomic numbers 113 and 115 were observed for the first time. With 248-MeV {sup 48}Ca projectiles, we observed three similar decay chains consisting of five consecutive {alpha} decays, all detected in a total time interval of 30 s. Each chain was terminated by a spontaneous fission (SF) with a high-energy release and a lifetime of about a day. With 253-MeV {sup 48}Ca projectiles, we registered a different decay chain of consecutive {alpha} decays detected in a time interval of 0.5 s, also terminated by spontaneous fission, but after 1.8 h. The decay properties of the eleven new {alpha}- and SF-decaying nuclei are consistent with expectations for consecutive {alpha} decays originating from the parent isotopes {sup 288}115 and {sup 287}115, produced in the 3n- and 4n-evaporation channels, respectively. Support for the assignment of the atomic numbers of all of the nuclei in the {sup 288}115 decay chain was obtained in an independent experiment in which a long-lived spontaneous fission activity, {sup 268}Db (15 events), was found to be chemically consistent with the fifth group of the periodic table.more » The odd-odd isotope {sup 288}115 was observed with largest cross section of about 4 pb. In the SF decay of {sup 268}Db, a total kinetic energy of 230 MeV and a neutron multiplicity per fission of 4.2 were measured. The decay properties of the 11 new isotopes with Z=105-115 and the production cross sections are in agreement with modern concepts of the role of nuclear shells in the stability of superheavy nuclei. The experiments were carried out at the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research.« less

title: Discovery of enhanced nuclear stability near the deformed shells N=162 and Z=108.
abstract: In bombardments of [sup 248]Cm with [sup 22]Ne we discovered two new isotopes, [sup 265]106 and [sup 266]106, by establishing genetic links between their [alpha] decays and spontaneous fission (SF) or [alpha] decays of the daughter nuclides. We measured [ital E][sub [alpha]]=8.63[plus minus]0.05 MeV for [sup 266]106 and a half-life of 1.2 s for its daughter [sup 262]104. For [sup 265]106 we measured [ital E][sub [alpha]]=8.71 to 8.91 MeV. From these [alpha] energies we estimated [alpha] half-lives of 10--30 s for [sup 266]106 and 2--30 s for [sup 265]106. We estimated SF branches of 50% or less for both isotopes. The decay properties of [sup 266]106 establish the existence of enhanced nuclear stability near the predicted deformed shells [ital N]=162 and [ital Z]=108.

title: Experiments on the synthesis of element 115 in the reaction am-243(ca-48, xn) x-115-291

title: Measurements of cross sections for the fusion-evaporation reactions pu-244(ca-48, xn) 114-(292-x) and cm-245(ca-48, xn) 116-(293-x)
abstract: We have studied the excitation functions of the reactions 244Pu(48Ca,xn). Maximum cross sections for the evaporation of 3–5 neutrons in the complete-fusion reaction 244Pu+48Ca were measured to be s3n=2 pb,s4n =5 pb, ands5n=1 pb. The decay properties of 3 n-evaporation product 289114, in the decay chains observed at low 48Ca energy coincide well with those previously observed in the 244Pu+48Ca and248Cm+48Ca reactions and assigned to288114. Two isotopes of element 114 and their descendant nuclei were identified for the first time at higher bombarding energies: 288114 (Ea=9.95 MeV, T1/2=0.6 s) and 287114 (Ea=10.04 MeV,T1/2 =1 s). We also report on the observation of new isotopes of element 116, 290,291116, produced in the245Cm +48Ca reaction with cross sections of about 1 pb. A discussion of self-consistent interpretations of all observed decay chains originating at Z=118, 116, and 114 is presented.

title: Synthesis of the New Element with Z=117
abstract: The synthesis of the new chemical element with atomic number Z=117 is presented. The isotopes 293117 and 294117were produced in fusion reactions between 48Ca and 249Bk. The 249Bk was produced in the High Flux Isotope Reactor and chemically separated at Oak Ridge. Decay chains involving eleven new nuclei were identified by means of the Dubna Gas Filled Recoil Separator. The measured decay properties show a strong rise of stability for super-heavy nuclei toward N=184.

title: Experiments on synthesis of superheavy nuclei by reactions with Ge ions