This paper reports a high-precision test of isospin symmetry in three nuclei with mass number A = 62: 62Ge, 62Ga and 62Zn. Isospin symmetry is the idea that protons and neutrons behave nearly the same under the strong force, apart from their electric charge. The experiment checked whether a key measurable, the proton part of an electric quadrupole transition (called the proton E2 matrix element Mp), follows the simple linear rule expected when isospin is conserved. The three measured Mp values fall on a straight line within the experimental uncertainties, supporting isospin symmetry in this triplet.

The team produced beams of 62Ge, 62Ga and 62Zn at the RIKEN Radioactive Isotope Beam Factory and hit thin gold (197Au) and carbon (12C) targets to excite the nuclei. They used the BigRIPS and ZeroDegree spectrometers to select and identify the reaction products and the DALI2+ gamma-ray array to detect the emitted gamma rays. By measuring inelastic scattering cross sections on two different targets and comparing the results under identical experimental conditions, they extracted nuclear deformation lengths (δN) and the reduced transition probabilities B(E2; 0+1 → 2+1). These B(E2) values are about 1400 e2fm4 for all three nuclei, and the inferred proton matrix elements Mp are all close to 37–38 e·fm2.

Why this matters: B(E2) values and Mp probe the wave functions of protons and neutrons inside the nucleus. For a triplet of states with the same total isospin, isospin symmetry predicts Mp should change linearly with the isospin projection Tz = (N−Z)/2. Deviations from that linearity would signal isospin-breaking effects in the nuclear wave functions. Because the three nuclei were measured in the same setup and analyzed together, many systematic errors cancel. The authors therefore claim this is the most accurate test to date of isospin symmetry rules using transition matrix elements in this mass region.