Electromagnetic Transition Rate Studies in 28Mg

Synopsis

In-beam reaction experiments performed at TRIUMF, Canada's particle accelerator centre, allow for precision measurements of nuclei far from stability. Using the TRIUMF-ISAC Gamma-Ray Escape Suppressed Spectrometer (TIGRESS) in conjunction with the TIGRESS Integrated Plunger for charged particle detection, electromagnetic transition rates of these nuclei can be performed. These measurements provide a probe of nuclear wavefunctions and tests of theoretical models using the well-understood electromagnetic interaction.
 
Of particular interest are neutron rich Mg isotopes far from stability as the nuclear shell model's single particle energy state description breaks down, closing the N=20 shell gap. In this region, occupation of single particle energy states is inverted with respect to the predicted configuration, motivating this region to be called the island of inversion. Nuclei in the island of inversion exhibit collective behaviour in which multiple particle transitions play a significant role. This collectivity is seen in highly excited states of nuclei approaching the island of inversion, and can be observed through electromagnetic transition strength measurements.
 
In this talk, I will discuss our experimental approach to studying the island of inversion, focusing on the approved experiment for measuring the lifetime of the first excited state in 28Mg. This experiment will use the Recoil Distance Method to exploit the Doppler shift of gamma rays emitted in flight along with Monte Carlo simulations using the Geant4 simulation framework to determine the best fit lifetime of the state. Finally, I will discuss how the same experimental setup can be used to probe lifetimes in excited states in 30-32Mg in future experiments.