Neutron-proton pairing competition in nuclei; Metastable state decays in the proton dripline nuclei Nb and Tc

Garnsworthy, A. B.*; Regan, P. H.*; Cceres, L.*; Pietri, S.*; Sun, Y.*; Rudolph, D.*; Grska, M.*; Podolyk, Z.*; Steer, S. J.*; Hoischen, R.*; Heinz, A.*; Becker, F.*; Bednarczyk, P.*; Doornenbal, P.*; Geissel, H.*; Gerl, J.*; Grawe, H.*; Grbosz, J.*; Kelic, A.*; Kojouharov, I.*; Kurz, N.*; Montes, F.*; Prokopowicz, W.*; Saito, Takehiko*; Schaffner, H.*; Tashenov, S.*; Werner-Malento, E.*; Wollersheim, H. J.*; Benzoni, G.*; Blank, B. B.*; Brandau, C.*; Bruce, A. M.*; Camera, F.*; Catford, W. N.*; Cullen, I. J.*; Dombrdi, Zs.*; Estevez, E.*; Gelletly, W.*; Ilie, G.*; Jolie, J.*; Jones, G. A.*; Jungclaus, A.*; Kmiecik, M.*; Kondev, F. G.*; Kurtukian-Nieto, T.*; Lalkovski, S.*; Liu, Z.*; Maj, A.*; Myalski, S.*; Pftzner, M.*; Schwertel, S.*; Shizuma, Toshiyuki; Simons, A. J.*; Walker, P. M.*; Wieland, O.*; Xu, F. R.*

The low-lying structures of the self-conjugate () nuclei Nb and Tc have been investigated using isomeric-decay spectroscopy following the projectile fragmentation of a Ag beam. These represent the heaviest odd-odd nuclei in which internal decays have been identified to date. The resulting level schemes shed light on the shape evolution along the line between the doubly-magic systems Ni and Sn and support a preference for states in odd-odd nuclei at low excitation energies associated with a neutron-proton pairing gap. Comparison with Projected Shell Model calculations suggests that the decay in Nb may be interpreted as an isospin-changing isomer.