Recoil distance method lifetime measurement of the 2(1)(+) state in Sr-94 and implications for the structure of neutron-rich Sr isotopes
A high precision lifetime measurement of the 2(1)(+) state in 94Sr was performed at TRIUMF's ISAC- II facility by coupling the recoil distance method implemented via the TIGRESS integrated plunger with unsafe Coulomb excitation in inverse kinematics. Due to limited statistics imposed by the use of a radioactive 94Sr beam, a likelihood ratio chi(2) method was derived and used to compare experimental data to Geant4 simulations. The B(E2; 2(1)(+)-> 0(1)(+)) value extracted from the lifetime measurement of 7.80(- 0.40)(+0.50)(stat.)+/- 0.07(sys.) ps is approximately 25% larger than previously reported while the relative error has been reduced by a factor of approximately 8. A baseline deformation has been established for Sr isotopes with N <= 58 which is a necessary condition for the quantum phase transition interpretation of the onset of deformation in this region. A comparison to existing theoretical models is presented.