Results from the First {sup 249}Cf + {sup 48}Ca Experiment

Oganessian, Y T ; Utyonkov, V K ; Lobanov, Y V ; Abdullin, F S ; Polyakov, A N ; Shirokovsky, I V ; Tsyganov, Y S ; Mezentsev, A N ; Iliev, S ; Subbotin, V G ; Sukhov, A M ; Ivanov, O V ; Voinov, A A ; Subotic, K ; Zagrebaev, V I ; Itkis, M G ; Moody, K J ; Wild, J F ; Stoyer, M A ; Stoyer, N J ; Laue, C A ; Shaughnessy, D A ; Patin, J B ; Lougheed, R W

Lawrence Livermore National Laboratory

关键词: Isotopes;    Nuclear Models;    Decay;    Irradiation;    Excitation;   

DOI  :  10.2172/15007307
RP-ID  :  UCRL-ID-151619
RP-ID  :  W-7405-ENG-48
RP-ID  :  15007307

美国|英语

来源: UNT Digital Library

【 摘 要 】

The present paper reports the results of an attempt aimed at the synthesis of element 118 in the reaction {sup 249}Cf({sup 48}Ca,3n){sup 294}118. The experiment was performed employing the Dubna Gas-filled Recoil Separator and the U400 heavy-ion cyclotron at FLNR, JINR, Dubna. In the course of a 2300-hour irradiation of an enriched {sup 249}Cf target (0.23 mg/cm{sup 2}) with a beam of 245-MeV {sup 48}Ca ions, we accumulated a total beam dose of 2.5 x 10{sup 19} ions. We detected two events that may be attributed to the formation and decay of nuclei with Z=118. For one event, we observed a decay chain of two correlated {alpha}-decays with corresponding energies and correlation times of E{sub {alpha}1} = 11.65 {+-} 0.06 MeV, t{sub {alpha}1} = 2.55 ms and E{sub {alpha}2} = 10.71 {+-} 0.17 MeV, t{sub {alpha}2} = 42.1 ms and, finally, a spontaneous fission with the sum of the kinetic energies of the fission fragments E{sub tot} = 207 MeV (TKE {approx} 230 MeV) and t{sub SF} = 0.52 s. In the second event chain, the recoil nucleus decayed into two fission fragments with E{sub tot} = 223 MeV (TKE {approx} 245 MeV) 3.16 ms later, without intervening {alpha} decays. The probabilities that these events were caused by the chance correlations of unrelated signals are negligible. Both events were observed at an excitation energy of the compound nucleus {sup 297}118 of E* = 30.0 {+-} 2.4 MeV, close to the expected maximum of the 3n-evaporation channel. The relationship between the decay energy Q{sub {alpha}} and decay period T{sub {alpha}} shows that sequential {alpha}-transitions in the first event correspond to the decay chain with Z = 118{_}116{_}114. Decay characteristics of the newly observed nuclides are compared with radioactive decay properties of the even-even isotopes with Z = 116, 114 and 112 previously produced in the reactions {sup 244}Pu, {sup 248}Cm + {sup 48}Ca and calculations made in various nuclear models.