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

T. Goigoux (1) , Ch. Theisen (1) , B. Sulignano (1) , M. Airiau (1) , K. Auranen , H. Badran , R. Briselet (1) , T. Calverley , D. Cox , F. Déchery (1) , F. Defranchi Bisso , A. Drouart (1) , Z. Favier (1) , B. Gall (2) , T. Grahn , P.T. Greenlees , K. Hauschild (3) , A. Herzáň , R.-D. Herzberg , U. Jakobsson , R. Julin , S. Juutinen , J. Konki , M. Leino , A. Lightfoot , A. Lopez-Martens (3) , A. Mistry , P. Nieminen , J. Pakarinen , P. Papadakis , J. Partanen , P. Peura , P. Rahkila , E. Rey-Herme (1) , J. Rubert (2) , P. Ruotsalainen , M. Sandzelius , J. Sarén , C. Scholey , J. Sorri , S. Stolze , J. Uusitalo , M. Vandebrouck (1) , A. Ward , M. Zielińska (1) , P. Jachimowicz , M. Kowal , J. Skalski

1 IRFU - Institut de Recherches sur les lois Fondamentales de l'Univers
2 IPHC - Institut Pluridisciplinaire Hubert Curien
3 IJCLab - Laboratoire de Physique des 2 Infinis Irène Joliot-Curie

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.

Domaines: Physique Nucléaire Expérimentale [nucl-ex]; Physique Nucléaire Théorique [nucl-th]

T. Goigoux, Ch. Theisen, B. Sulignano, M. Airiau, K. Auranen, et al.. First observation of high-K isomeric states in $^{249}$Md and $^{251}$Md. Eur.Phys.J.A, 2021, 57 (12), pp.321. ⟨10.1140/epja/s10050-021-00631-4⟩. ⟨hal-03339483⟩