Fragmentation of magnetic dipole strength inPb208

Abstract

Fragmentation of the $M1\mathrm{}$ strength in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ at energies near the ($\gamma , n$) threshold is studied. It is shown that the 2p-2h configuration can provide a mechanism for fragmenting the 1p-1h giant $M1\mathrm{}$ excitation; however, our results do not predict as much spreading of the $M1\mathrm{}$ strength as has been suggested by experiment. The 2p-2h mechanism is also unable to explain the large $M1\mathrm{}$ strength recently observed at 4.84 MeV in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$.