Magnetic dipole strength functions in heavy deformed nuclei

Abstract

The isovector spin-flip M1 strength function in the deformed heavy nuclei 156Gd and 238U 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 90Zr and 208Pb. With the model parameters fixed in this fashion, our calculations predict large quantities of spin-flip M1 strength (10–20 µ2N) between 5 and 10 MeV excitation in 156Gd and 238U; 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.