On the decrease in charge radii of multi-quasi particle isomers

We report changes in mean-square charge radii, δ〈r2〉, magnetic moments and quadrupole moments for three multi-quasi particle isomers; 97m2Y, 176mYb and 178m1Hf. All the isomers are observed to display a decrease in 〈r2〉 compared to the lower-lying nuclear state on which the isomer is built. The decreases in 〈r2〉 occur despite the isomers showing increases in quadrupole moment. Possible mechanisms for the effect, which is now seen for six multi-quasi particle isomers, are discussed.