A procedure is presented by which the proton-neutron symmetry breaking in first excited 2+ stats of even- even nuclei can be estimated. The procedure involves calculations within the proton-neutron version of the interacting Boson model, and comparison with experimental data. The results of applying this procedure to even-even nuclei with 44 < Z < 80 are presented. In many cases, the amount of symmetry breaking, expressed in terms of the F-spin quantum number, is of the order to 10 percent.
"Proton-neutron symmetry breaking in even-even nuclei", Proc. SPIE 2867, International Conference Neutrons in Research and Industry, (27 February 1997); doi: 10.1117/12.267943; https://doi.org/10.1117/12.267943