Decay properties of heavy mendelevium isotopes

Abstract

We investigated the nuclear properties of several mendelevium isotopes produced in the reactions of heavy ions with 245Esg. We measured the alpha particles, spontaneous fissions (SF), and photons emitted by counting samples resulting from chemical and/or mass separations. The 256Md half-life is (78.1 ± 1.8) min; it decays primarily by electron capture (EC), but also by alpha emission (11 ± 3)% of the time. The 256Md ground state has J ≤ 2 (probably Jπ = 1-), and a mass excess of (87.611 ± 0.053) MeV. The 257Md half-life is (5.523 ± 0.050) h; it decays primarily by EC, but also by alpha emission (15.2 ± 2.6)% of the time and by SF less than 1% of the time. The 256Md mass excess is (88.989 ± 0.003) MeV. The 258Mdg (Jπ = 8-) half-life is (51.50 ± 0.29) d. It decays by alpha emission; the sum of SF, EC, and β- decay branches is less than 3 × 10-3 %. The alpha decay of 258Mdg populates 254Esm (0.60 ± 0.08)% of the time. The 256Mdg mass excess is (91.691 ± 0.007) MeV. The half-life of Jπ = 1- 258Mdm is (57.0 ± 0.9) min. It decays by EC; the branch for decay by alpha emission is less than 1.2%. The sum of SF and β- decay branches is less than 30%. The half-life of 259Md is (1.60 ± 0.06) h; it decays primarily by SF. The alpha decay branch of 259Md is less than 1.3%. From the 259Md half-life we calculated a SF hindrance factor associated with the 7 2-[514] proton configuration of 3.6 × 106. From our data we proposed partial level schemes for 252Es, 253Es, and 254Es. © 1993.