Nuclear structure ofPb208fromPb207+n resonances

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Abstract
Resonance structure in the Pb207 + n system has been investigated by measuring the neutron total cross section with high energy resolution and the partial radiative cross sections for transitions to the ground-state and the first-excited state in Pb208. A detailed analysis of resonance parameters was carried out up to a neutron energy of 700 keV. The nuclear level density shows a strong parity dependence. The doorway in the s-wave neutron strength function has been firmly established with an escape width equal to the corresponding widths in the neighboring isotopes. The total magnetic dipole strength detected between the neutron separation energy and 8.0 MeV is B(M1)↑=5.8 μN2, thus smaller than the lowest theoretical estimate for that region. Above that energy an additional 1 μN2 is observed, but more strength may have escaped detection because the sensitivity of the experiment decreases; thus the ‘‘missing’’ strength may be partly hidden at these higher energies. Radiative widths for the E1 decay of resonances to the first-excited state of Pb208 show a doorway structure which can be related to the properties of known bound states.