On the nature of “three-phonon” excitations in 112Cd

The lifetimes of proposed 3-phonon states in 112Cd have been measured using the Doppler shift attenuation method (DSAM) following the (n,n′γ) reaction. The experimental results allow the determination of relevant B(E2) values which are compared to different theoretical descriptions. Collective enhancements favouring the interpretation of collectivity in the phonon model are observed for 3+ and 4+ members of the 3-phonon quintuplet. However, for the proposed 2+ member, this simple model fails most likely due to the subtle interplay between intruder, mixed-symmetry, and phonon states, and the decay pattern is strongly perturbed. The best overall agreement is obtained with IBM-2 calculations.