M1Giant Resonance inPb208From Threshold Photoneutron Measurements

From threshold photoneutron cross-section and angular-distribution measurements on ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$, seven $1^{+}$ states have been detected, which have a total $M1\mathrm{}$ strength of 51 eV. This $M1\mathrm{}$ strength, centered at an excitation energy of 7.9 MeV and spread over a range of 700 keV, constitutes at least half and perhaps all of the total $M1\mathrm{}$ strength obtained from shell-model calculations.