Spectroscopic studies beyond the N=152 neutron gap: Decay of ₁₀₁²⁵⁵Md and ₁₀₁²⁵⁶Md

The isotopes ²⁵⁵Md and ²⁵⁶Md were produced by the irradiation of ²⁵³Es with 35–45 MeV α particles by (α,n) and (α,2n) reactions and were removed from the target by a helium jet system. α, γ, and α-γ coincidence spectra were measured with Si and Ge(Li) detectors. From the EC decays of ²⁵⁵Md and ²⁵⁶Md, levels in ²⁵⁵Fm and ²⁵⁶Fm were deduced. Favored α decay of ²⁵⁵Md was found to populate the 7/2^-[514] single-particle state in ²⁵¹Es, thus establishing the 7/2^-[514] as the ²⁵⁵Md ground state. Several γ rays were observed in the ²⁵⁶Md α-γ coincidence spectrum. ²⁵⁶Fm is the heaviest nucleus in which excited intrinsic states have been identified.