Probing the nature of the 2$^+$ excited state in $^{72}$Ni with lifetime measurements

We present the results of an experiment to measure the lifetimes of the $2^+_1$ excited state in $^{72}$Ni populated in a proton knockout reaction at intermediate energies using the recoil distance method. This experiment was performed at the NSCL during GRETINA campaign and the array was used for $\gamma$-ray detection. Measured $\gamma$-ray spectra were directly compared with GEANT4 simulations [1] accounting for the geometry of the experiment. The new result does not indicate increased collectivity in nickel isotopes above $N=40$ and is found to be in agreement with the recent MCSM calculations [2]. [1] P. Adrich et al., Nucl. Instrum. and Meth. A598 (2009) 454. [2] Y. Tsunoda, T. Otsuka, N. Shimizu, M. Honma and Y. Utsuno, Journal of Physics: Conference Series 445 (2013) 012028.