First measurements of g factors in even Kr isotopes

The g factors of the $2^+_1$ and $4^+_1$ states in $^{78,80,82,84,86}$Kr have been measured for the first time, using Coulomb excitation of isotopic Kr beams and the transient field technique.

The measured g factors of $2^+_1$ states in $^{78,80,82}$Kr are well described, in both magnitude and progression with neutron number, by the IBA–II model. Whereas the lighter isotopes show a dominant collective structure with g factor values close to Z/A, the large $g(2^+_1) = 1.12(14)$ value of $^{86}$Kr, with its closed N = 50 shell, is unequivocally dominated by specific proton configurations. The g factor of the $2^+_1$ state in $^{84}$Kr, with two holes in the $1g_{9/2}$ neutron orbit, reflects both proton and neutron components in the wave function.