Strongly deformed nuclei near the magic proton shell 82?

The sudden change of the isotope phase shift in the Hg isotopes is explained by studying the deformation energy with the Strutinsky shell correction method. It is shown that going from the spherical isotope ²⁰⁴Hg to the isotope ¹⁸⁴Hg a small negative deformation (up to β₂ = −0.19) is built up. Between the mass numbers 186 and 182 the deformation is shifted through the γ instability valley to larger positive deformations (β₂ ≈ 0.3). The experimentally observed anomaly can be explained with the theoretical isotope shift constant, if this change of ground state deformations is taken into account.