Wigner’s Equation Passes the Test
Eugene Wigner won the 1963 Nobel Prize “for his contributions to the theory of the atomic nucleus and the elementary particles, particularly through the discovery and application of fundamental symmetry principles”. Among his contributions was a simple quadratic equation known as the Isobaric Multiplet Mass Equation (IMME). The IMME relates the masses of the members in a multiplet of nuclear states that have same nuclear structure but different numbers of protons and neutrons.
Recently, a breakdown of the IMME was reported in the quintet consisting of states in 20Mg, 20Na, 20Ne, 20F, and 20O based on a precise new measurement of the 20Mg mass and adopted data on the other members. A group of nuclear theorists was unable to explain the breakdown using their most sophisticated models, leading to a conundrum. Either some of the experimental data was inaccurate, or a mysterious nuclear structure effect was causing the anomaly.
A group working at NSCL set out to measure the energy (hence, the mass) of the 20Na state using the beta decay of 20Mg to populate it and the SeGA array to detect its gamma-ray de-excitation. They were able to measure the mass of the 20Na state to a much higher precision than before and found that the previously adopted value was inaccurate. By applying the new value, they showed that the IMME is revalidated. Wigner passed away in 1995, but perhaps he would be amused.
Publication: Revalidation of the isobaric multiplet mass equation for the A=20 quintet, B. E. Glassman, D. Perez-Loureiro, C. Wrede et al., Physical Review C 92, 042501(R) (2015)