Magnetic dipole strength functions in heavy deformed nuclei

The isovector spin-flip M1 strength function in the deformed heavy nuclei ${}_{}{}^{156}{}_{}{}^{}\mathrm{Gd}$ and ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ is calculated in the quasiparticle random-phase approximation. Interaction parameters are adjusted to reproduce the energies of isobaric-analog and Gamow-Teller excitations observed in (p,n) charge-exchange reactions. A phenomenological spreading width for decay into background 2p2h states is introduced and adjusted to reproduce the M1 spin-flip strength function recently observed by elastic scattering of tagged photons on ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$ and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$. With the model parameters fixed in this fashion, our calculations predict large quantities of spin-flip M1 strength (10–20 ${\mathrm{\mu }}_{\mathit{N}}^2$) between 5 and 10 MeV excitation in ${}_{}{}^{156}{}_{}{}^{}\mathrm{Gd}$ and ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$; it is strongly fragmented and should be observable by tagged-photon elastic scattering and proton inelastic scattering but probably not in high resolution inelastic electron scattering.