Fusion reaction 48Ca+249Bk leading to formation of the element Ts (Z=117)

The heaviest currently known nuclei, which have up to 118 protons, have been produced in 48Ca induced reactions with actinide targets. Among them, the element tennessine (Ts), which has 117 protons, has been synthesized by fusing 48Ca with the radioactive target 249Bk, which has a half-life of 327 d. The experiment was performed at the gas-filled recoil separator TASCA. Two long and two short α decay chains were observed. The long chains were attributed to the decay of 294Ts. The possible origin of the short-decay chains is discussed in comparison with the known experimental data. They are found to fit with the decay chain patterns attributed to 293Ts. The present experimental results confirm the previous findings at the Dubna Gas-Filled Recoil Separator on the decay chains originating from the nuclei assigned to Ts

Shape coexistence near the double-midshell nucleus Rh-111

The decay of Ru-111 obtained from fast on-line chemical and mass separation has been investigated by beta-gamma-t and gamma-gamma coincidence techniques. Earlier spin and parity assignments of Rh-111 levels based on extrapolations of level systematics are confirmed. in particular, the K=1/2 intruder band is supported by the hindrance of E2 transitions between deformed and spherical stales and enhancement of intraband E2 transitions. The excitation energies of intruder hand members in Rh isotopes show a minimum at Rh-109(64), with two neutrons less than Rh-111 at the N=66 midshell. This trend, which differs from the one in the higher-Z neighbouring elements Ag and Cd with minima at N=66, follows the evolution of deformation observed in the lower-Z elements Ru and Mo

Experimental study of the U238(S36,3-5n)Hs269-271 reaction leading to the observation of Hs270

The deformed doubly magic nucleus Hs270 has so far only been observed as the four-neutron (4n) evaporation residue of the reaction Mg26+Cm248, where a maximum cross section of 3 pb was measured. Theoretical studies on the formation of Hs270 in the 4n evaporation channel of fusion reactions with different entrance channel asymmetry in the framework of a two-parameter Smoluchowski equation predict that the reactions Ca48+Ra226 and S36+U238 result in higher cross sections due to lower reaction Q values, in contrast to simple arguments based on the reaction asymmetry, which predict opposite trends. Calculations using hivap predict cross sections for the reaction S36+U238 that are similar to those of the Mg26+Cm248 reaction. Here, we report on the first measurement of evaporation residues formed in the complete nuclear fusion reaction S36+U238 and the observation of Hs270, which is produced in the 4n evaporation channel, with a measured cross section of 0.8-0.7+2.6 pb at 51-MeV excitation energy. The one-event cross-section limits (68% confidence level) for the 3n, 4n, and 5n evaporation channels at 39-MeV excitation energy are 2.9 pb, while the cross-section limits of the 3n and 5n channel at 51 MeV are 1.5 pb. This is significantly lower than the 5n cross section of the Mg26+Cm248 reaction at similar excitation energy. © 2010 The American Physical Society

Experimental study of the U-238(S-36,3-5n)(269-271)Hs reaction leading to the observation of (270)Hs

The deformed doubly magic nucleus (270)Hs has so far only been observed as the four-neutron (4n) evaporation residue of the reaction Mg-26+Cm-248, where a maximum cross section of 3 pb was measured. Theoretical studies on the formation of (270)Hs in the 4n evaporation channel of fusion reactions with different entrance channel asymmetry in the framework of a two-parameter Smoluchowski equation predict that the reactions Ca-48+Ra-226 and S-36+U-238 result in higher cross sections due to lower reaction Q values, in contrast to simple arguments based on the reaction asymmetry, which predict opposite trends. Calculations using HIVAP predict cross sections for the reaction S-36+U-238 that are similar to those of the Mg-26+Cm-248 reaction. Here, we report on the first measurement of evaporation residues formed in the complete nuclear fusion reaction S-36+U-238 and the observation of (270)Hs, which is produced in the 4n evaporation channel, with a measured cross section of 0.8(-0.7)(+2.6) pb at 51-MeV excitation energy. The one-event cross-section limits (68% confidence level) for the 3n, 4n, and 5n evaporation channels at 39-MeV excitation energy are 2.9 pb, while the cross-section limits of the 3n and 5n channel at 51 MeV are 1.5 pb. This is significantly lower than the 5n cross section of the Mg-26+Cm-248 reaction at similar excitation energy