Doppler-shift lifetime measurements in $^{94}$Sr using the TIGRESS Integrated Plunger

Neutron-rich Sr isotopes are characterized by a sudden onset of quadrupole deformation at neutron number $N=60$ demonstrated by a dramatic drop in excitation energy of the first $2^+_1$ state. Though the emphasis is usually put on the sudden onset of collectivity at $N=60$, it is equally surprising that there is no onset of collectivity when adding up to 8 neutrons beyond the $N=50$ shell closure, as indicated by a previous measurement of low $B(E2)$ values of $\approx 10$~W.u.~in even-even Sr isotopes from $^{90}$Sr to $^{96}$Sr [1]. A high precision Doppler shift lifetime measurement of the first excited state in $^{94}$Sr using the TIGRESS Integrated Plunger (TIP) [2] can help elucidate whether the onset of collectivity is as sudden as generally assumed. An experiment aimed towards a high-precision ($<10$\%) measurement of the $B(E2,2^+_1\rightarrow 0^+_1)$ reduced transition probability in $^{94}$Sr was performed in December 2015 using inelastic scattering near the Coulomb barrier coupled with an recoil distance method lifetime measurement of a radioactive $^{94}$Sr beam. The device, experimental approach, analysis, and preliminary results will be presented and discussed. [1] Mach et al., Nucl. Phys. A 523 (1991) 197; [2] Voss et al., Nucl. Inst. and Meth. A 746 (2014)