Production of 265Sg in the 248Cm(22Ne,5n)265Sg reaction and decay properties of two isomeric states in 265Sg

Two isomeric states of 265Sg, i.e., 265Sga and 265Sgb, proposed in Ch. E. Düllmann and A. Türler were produced in the 248Cm(22Ne,5n)265Sg reaction. Decay properties of 265Sga^,b were investigated with a rotating-wheel apparatus for α and spontaneous fission (SF) spectrometry under low background conditions attained by a gas-jet transport system coupled to the RIKEN gas-filled recoil ion separator. Based on genetically correlated α-α(-α) and α-SF decay chains, 18 and 24 events were assigned to 265Sga and 265Sgb, respectively. The half-life T_1/2 and α-particle energy E_α of 265Sga were measured to be 8.5-1.6+2.6 s and 8.84 ± 0.05 MeV, respectively, and those of 265Sgb were 14.4-2.5+3.7 s and 8.69 ± 0.05 MeV. As a daughter product of 265Sga ^,b, the decay properties of the 3-s isomeric state in 261Rf, i.e., 261Rfb, were also derived: T_1/2 = 2.6-0.5+0.7 s, E_α = 8.51 ± 0.06 MeV, and SF branch b_SF = 0.82 ± 0.09. These results confirm and refine the decay pattern suggested for the decay chain 269Hs → 265Sga^,b → 261Rfa^,b → 257No → in Düllmann and Türler. The production cross sections for 265Sga and 265Sgb were determined to be 180-60+80 and 200-50+60 pb at 117.8 MeV, respectively, and they are discussed by comparing with the literature data as well as the theoretical prediction.