Pairing-quadrupole interplay in the neutron-deficient tin nuclei: First lifetime measurements of low-lying states in 106,108Sn

Low-Energy Coulomb Excitation for the Shell Model

“…The first hints of the intruder character of the 0 + 2 states in the Zn isotopes came from E0 measurements in the stable even-even [64][65][66][67][68] Zn isotopes [27], a feature further supported by the results of multi-step Coulomb-excitation experiments on 66,68 Zn [14,28]. However, only for 68 Zn has the key 2 + 3 E2 0 + 2 matrix element been determined, which, when combined with other matrix elements involving the 0 + 2 state, leads to a Q 2 invariant significantly different from that of the ground state [28].…”

“…As shown in Figure 3b, a decrease of the 0 + 2 state energy between N = 36 and N = 40, similar to those observed in the Ge and Zn chains, is evident also in the Ni isotopes. According to Monte-Carlo Shell-Model (MCSM) calculations with the A3DA effective interaction in the p f g 9/2 d 5/2 model space [40], the 0 + 2 states in 64,66,68 Ni are oblate deformed and result from neutron 2p-2h excitation across the N = 40 gap, similar to their counterparts in the Ge isotones. The V-shaped trend of the 0 + 2 excitation energies with the vertex at N = 40 does not persist for 70 Ni and beyond, as different configurations start to appear at low excitation energy.…”

“…The V-shaped trend of the 0 + 2 excitation energies with the vertex at N = 40 does not persist for 70 Ni and beyond, as different configurations start to appear at low excitation energy. Specifically, proton 2p-2h excitations across the energy gap at Z = 28 are suggested [40,41] to dominate the structure of the 0 + 4 state in 64,66 Ni, the 0 + 3 state in 68 Ni and the 0 + 2 state in 70 Ni. MCSM calculations predict that these predominantly π(2p-2h) states have well-deformed prolate shapes, resulting from an interplay of type-I and type-II shell evolution.…”

Low-Energy Coulomb Excitation for the Shell Model

“…The V-shaped trend of the 0 + 2 excitation energies with the vertex at N = 40 does not 269 persist for 70 Ni and beyond, as different configurations start to appear at low excitation 270 energy. Specifically, proton 2p − 2h excitations across the energy gap at Z = 28 are 271 suggested [41,42] to dominate the structure of the 0 + 4 state in 64,66 Ni, the 0 + 3 state in 68 74,76 Zn [43,44]. The obtained B(E2) values hint at the importance 284 of triaxiality also in neutron-rich Zn isotopes, whose ground states were suggested to be 285 rather diffuse in the γ degree of freedom [43].…”

“…The experimental values of the Q 2 and Q 3 cos 3δ invariants for the 0 + 1,2 states were According to MCSM calculations with the A3DA effective interaction in the p f g 9/2 d 5/2 266 model space [41], the 0 + 2 states in 64,66,68 Ni are oblate deformed and result from neutron 267 2p − 2h excitation across the N = 40 gap, similar to their counterparts in the Ge isotones.…”