Research of Superheavy Element at RIKEN

An isotope of the 113$^{\mathrm{th}}$ element, $^{278}$113, were produced by the $^{209}$Bi($^{70}$Zn, $n)$ reaction using gas-filled recoil ion separator (GARIS). Three decay chains originating from $^{278}$113 were observed. Two of them consisted of four consecutive alpha decays followed by spontaneous fission (SF). One consisted of six consecutive alpha decays. These were assigned to the decay, $^{278}$113(alpha) $\to$ $^{274}$Rg(alpha) $\to$ $^{270}$Mt(alpha) $\to$ $^{266}$Bh(alpha) $\to$ $^{262}$Db(SF/alpha) $\to$ $^{258}$Lr(alpha) $\to$. The reaction $^{248}$Cm + $^{48}$Ca was studied using GARIS. Five decay chains terminated by SF were observed. The decay properties of the chains agree well with the chains observed, and assigned to $^{292}$Lv and $^{293}$Lv, at Dubna and at GSI in the same reaction. Possible new alpha decay branch of $^{284}$Cn and subsequent SF of possible new isotope $^{280}$Ds were observed.