The new isotopes258105,257105,254Lr and253Lr

Abstract

Evaporation residues from the heavy-ion fusion reaction50Ti on209Bi were investigated. They were separated from the projectile beam by the velocity filter SHIP and identified after implantation into an array of position-sensitive surface-barrier detectors by analyzing their α-decay chains. Spontaneous fission was also observed. Four new α emitters,258105 (T1/2=4.4-0.6+0.9s),257105 (T1/2= 1.4-0.3+0.6s),254Lr (T1/2= 13-2+3s), and253Lr (T1/2=1.3-0.3+0.6s) could be identified. For the isotope257105 we obtained a spontaneous-fission branch of about 20%. A spontaneous-fission activity with a halflife comparable to that for the α decay of258105 was explained as fission of258104, formed by electron capture from258105. An excitation function for evaporation-residue production was measured for bombarding energies in the range of ECM=184.4 MeV to ECM=196.6 MeV. Nearly all evaporation residues we observed, could be attributed to the 1n and 2n deexcitation channels. The maximum cross sections were σ(1n)=c/2.9±0.3) nbarn, and σ(2n)=c/2.1±0.8) nbarn, respectively. We could measure the total kinetic energy of the fission fragments of258104 to be TKE=(220±15) MeV, a value that fits into empirical systematics based on a Z2/A1/3 dependence. © 1985 Springer-Verlag.