A new tool to explore exotic nuclear structure: Forty years of after the discovery of magnesium- 31 (31Mg), TRIUMF's ability to produce the world's highest spin-polarization for rare nuclei has successfully enabled Japanese and Canadian researchers to clarify this rare isotope's exotic structure. High spin polarization makes it possible to efficiently measure a rare nuclei's basic, but hard-to-know, quantum numbers–the spins and parities of the ground and excited states of a resulting nucleus from the b-decay of the polarized nucleus. As reported in Physics Letters B (2017), one of the highlights from this new method is the finding of “shape coexistence” in 31Mg. Here, states with various types of shape coexist in a narrow and low excitation energy region. Shape coexistence can be seen as a result of subtle competition between a persistent spherical shape due to the neutron magic number 20, and prevalence of deformation due to nuclear correlations.