First observation of high-K isomeric states in $$^{249}$$ 249 Md and $$^{251}$$ 251 Md

Decay spectroscopy of the odd-proton nuclei $$^{249}$$ Md and $$^{251}$$ Md has been performed. High-K isomeric states were identified for the first time in these two nuclei through the measurement of their electromagnetic decay. An isomeric state with a half-life of 2.8(5) ms and an excitation energy $$\ge 910$$ keV was found in $$^{249}$$ Md. In $$^{251}$$ Md, an isomeric state with a half-life of 1.4(3) s and an excitation energy $$\ge 844$$ keV was found. Similarly to the neighbouring $$^{255}$$ Lr, these two isomeric states are interpreted as 3 quasi-particle high-K states and compared to new theoretical calculations. Excited nuclear configurations were calculated within two scenarios: via blocking nuclear states located in proximity to the Fermi surface or/and using the quasiparticle Bardeen–Cooper–Schrieffer method. Relevant states were selected on the basis of the microscopic-macroscopic model with a deformed Woods–Saxon potential. The most probable candidates for the configurations of K-isomeric states in Md nuclei are proposed.