Measurements of cross sections and decay properties of the isotopes of elements 112, 114, and 116 produced in the fusion reactionsU233,238,

Abstract

We have studied the dependence of the production cross sections of the isotopes 282,283 112 and 286,287 114 on the excitation energy of the compound nuclei 286 112 and 290 114. The maximum cross section values of the xn-evaporation channels for the reaction 238 U͑ 48 Ca, xn͒ 286−x 112 were measured to be 3n = 2.5 −1.1 +1.8 pb and 4n = 0.6 −0.5 +1.6 pb; for the reaction 242 Pu͑ 48 Ca, xn͒ 290−x 114: 2n ϳ 0.5 pb, 3n = 3.6 −1.7 +3.4 pb, and 4n = 4.5 −1.9 +3.6 pb. In the reaction 233 U͑ 48 Ca,2-4n͒ 277-279 112 at E * = 34.9± 2.2 MeV we measured an upper cross section limit of xn ഛ 0.6 pb. The observed shift of the excitation energy associated with the maximum sum evaporation residue cross section ER ͑E * ͒ to values significantly higher than that associated with the calculated Coulomb barrier can be caused by the orientation of the deformed target nucleus in the entrance channel of the reaction. An increase of ER in the reactions of actinide targets with 48 Ca is consistent with the expected increase of the survivability of the excited compound nucleus upon closer approach to the closed neutron shell N = 184. In the present work we detected 33 decay chains arising in the decay of the known nuclei 282 112, 283 112, 286 114, 287 114, and 288 114. In the decay of 287 114͑␣͒ → 283 112͑␣͒ → 279 110͑SF͒, in two cases out of 22, we observed decay chains of four and five sequential ␣ transitions that end in spontaneous fission of 271 Sg ͑T ␣/SF = 2.4 −1.0 +4.3 min͒ and 267 Rf ͑T SF ϳ 2.3 h͒, longer decay chains than reported previously. We observed the new nuclide 292 116 ͑T ␣ =18 −6 +16 ms, E ␣ = 10.66± 0.07 MeV͒ in the irradiation of the 248 Cm target at a higher energy than in previous experiments. The observed nuclear decay properties of the nuclides with Z = 104-118 are compared with theoretical nuclear mass calculations and the systematic trends of spontaneous fission properties. As a whole, they give a consistent pattern of decay of the 18 even-Z neutron-rich nuclides with Z = 104-118 and N = 163-177. The experiments were performed with the heavy-ion beam delivered by the U400 cyclotron of the FLNR ͑JINR, Dubna͒ employing the Dubna gas-filled recoil separator.

Chemistry of superheavy elements

“…This chemistry experiment was the first and independent confirmation of nuclear decay chains reported earlier from FLNR experiments about the synthesis of element 287 114 and 291 116 [32,35]. A third experiment [250] was carried out with a higher gas-flow rate which yielded two atoms of 283 Cn deposited at −29 • C and −39…”

“…These experiments provided a breakthrough and led to the (only for elements 114 and 116 officially accepted) discovery of elements up to 118 [30,31]; an overview is given in [32,33]. Results from a 48 Ca on 238 U experiment at SHIP [34] support data about the synthesis and decay of 3.8-s 283 Cn [35]. The synthesis of the most neutron-deficient know isotope of element 114, 285 114 (T 1/2 ≈ 0.1 s) [36], was achieved in an experiment at the Berkeley Gas-filled Separator (BGS).…”

“…This isotope, as we know it today, predominantly shows α-decay with a half-life of 3.8 s and is produced with a cross section of about 2 pb [32,35] or less [34]. Even if the authors published the observation of Cn, today, we must conclude that these early experiments did not convincingly identify 283 Cn, mostly because of false assumptions about decay properties (T 1/2 = 3 min, SF) and assuming a too high cross section; all based on the knowledge of the early 2000s.…”

“…A break-through came at the FLNR when Eichler and coworkers [40,41] used the reaction 48 Ca on 242 Pu to produce 0.48-s 287 114 with a cross section of 3.5 pb [32,35]. The α-decay daughter 283 Cn was transported in a He/Ar gas mixture which was highly purified and circulated in a closed gas loop.…”

Towards relativistic ECP / DFT description of chemical bonding in E112 compounds: spin-orbit and correlation effects in E112X versus HgX (X=H, Au)

“…[4,5]; however, their results can be affected by severe basis set limitations and simplified treatment of some relativistic contributions, so that studies of these systems by alternative techniques are desirable. Note also that the importance of the chemical identification of E112 has increased in the last years because of the controversial data on the detection of the long-lived 283 112 isotope [18,19].…”