Abrupt structural transition in exotic molybdenum isotopes unveils an isospin-symmetric island of inversion
Ji Soo Ha, F. Recchia, S. M. Lenzi, H. Iwasaki, D. D. Dao, F. Nowacki, A. Revel, P. Aguilera, G. de Angelis, J. Ash, D. Bazin, M. A. Bentley, S. Biswas, S. Carollo, M L Cortes, Robert Elder, R. Escudeiro, P. Farris, A. Gade, T. N. Ginter, M. Grinder, J. Li, D. R. Napoli, S. Noji, J. Pereira, S. Pigliapoco, A Pompermaier, A. Poves, K. Rezynkina, A. Sanchez, R. Wadsworth, D. Weißhaar
Abstract
Abstract Like electrons in atoms, protons and neutrons in nuclei occupy orbitals in a shell structure with energy gaps at magic numbers. Radioactive-beam experiments revealed the disappearance of magic numbers in some neutron-rich isotopes. In these nuclei, configurations involving particles excited across the shell gap gain correlation energy, becoming the ground state. Neutron-rich regions of the nuclear chart that exhibit this property are known as “Islands of Inversion”. Here we present the lifetime measurement of the first 2 + states in 84 Mo ( N = Z ) and 86 Mo ( N = Z + 2) revealing an unexpected sharp structural change between them defining the edge of the region of deformation around 80 Zr. Similarly to the neutron-rich N = 40 Island of Inversion near 64 Cr where cross-shell excitations dominate, we identify this region as an Island of Inversion with symmetrical proton and neutron excitations that we term “Isospin-Symmetric Island of Inversion”. Three-nucleon forces are suggested to drive Mo isotope structural changes.