Nuclear Structure Studies of Exotic Nuclei via the Strength of e2 Transitions; Advanced Time-Delayed γγ Spectroscopy at the Extreme

We report preliminary results from ultra-fast time-delayed γγ(t) measurements on exotic nuclei just below ¹⁰⁰Sn. The measurements were performed at the LISE spectrometer in GANIL. Nuclei of ⁹⁴Ru and ⁹⁶Pd were populated in the isomeric states via the fragmentation of energetic ¹¹²Cd beam. Preliminary lifetime or lifetime limits are reported for the 6⁺, 4⁺, and 2⁺ states in ⁹⁶Pd and the 4⁺ and 2⁺ states in ⁹⁴Ru. These results indicate an unexpected and strong quenching of the B(E2) strength for the 4⁺ to 2⁺ E2 transition in ⁹⁶Pd in comparison with model predictions and the equivalent B(E2) strength in ⁹⁴Ru. The sequence of quenched B(E2) rates for the 8⁺ → 6⁺ E2 transition in ⁹⁴Ru, 4⁺ → 2⁺ E2 transition in ⁹⁶Pd and for the 8⁺ → 6⁺ E2 transition in ⁹⁸Cd, seems to represent a systematic pattern along the N=50 neutron number just below Z=50 and could imply a weak N=50 shell closure when approaching the doubly magic ¹⁰⁰Sn.