Decay properties of 265Sg(Z=106) and 266Sg(Z=106)

The presently known most neutron-rich isotopes of element 106 (seaborgium, Sg), 265Sg and 266Sg, were produced in the fusion reaction 22Ne+248Cm at beam energies of 121 and 123 MeV. Using the On-Line Gas chemistry Apparatus OLGA, a continuous separation of Sg was achieved within a few seconds. Final products were assayed by α-particle and spontaneous fission (SF) spectrometry. 265Sg and 266Sg were identified by observing time correlated α-α-(α) and α-SF decay chains. A total of 13 correlated decay chains of 265Sg (with an estimated number of 2.8 random correlations) and 3 decay chains of 266Sg (0.6 random correlations) were identified. Deduced decay properties were T1/2=7.4-2.7+3.3 s (68% c.i.) and Eα=8.69 MeV (8%), 8.76 MeV (23%), 8.84 MeV (46%), and 8.94 MeV (23%) for 265Sg; and T1/2=21-12+20 s (68% c.i.) and Eα=8.52 MeV (33%) and 8.77 MeV (66%) for 266Sg. The resolution of the detectors was between 50-100 keV (full width at half maximum). Upper limits for SF of ≤35% and ≤82% were established for 265Sg and 266Sg, respectively. The upper limits for SF are given with a 16% error probability. Using the lower error limits of the half-lives of 265Sg and 266Sg, the resulting lower limits for the partial SF half-lives are T1/2SF(265Sg)≥13 s and T1/2SF(266Sg)≥11 s. Correspondingly, the partial α-decay half-lives are between T1/2α(265Sg)=4.7 endash 16.5 s (68% c.i.) and T1/2α(266Sg)=9 endash 228 s (68% c.i.), using the upper and lower error limits of the half-lives of 265Sg and 266Sg. The lower limit on the partial SF half-life of 266Sg is in good agreement with theoretical predictions. Production cross sections of about 240 pb and 25 pb for the α-decay branch in 265Sg and 266Sg were estimated, respectively. copyright 1998 The American Physical Society