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

Abstract We report changes in mean-square charge radii, δ 〈 r 2 〉 , magnetic moments and quadrupole moments for three multi-quasi particle isomers; 97m2 Y, 176m Yb and 178m1 Hf. All the isomers are observed to display a decrease in 〈 r 2 〉 compared to the lower-lying nuclear state on which the isomer is built. The decreases in 〈 r 2 〉 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.