PB-206+ N RESONANCES FOR E = 25-600 KEV - S-WAVE, P-WAVE, AND D-WAVE DOORWAY STATES AND M1 GROUND-STATE RADIATIVE STRENGTH IN PB-207

High resolution neutron transmission and differential scattering measurements have been performed on Pb206 and the results for E=25-600 keV are presented. Data analyses were performed utilizing multilevel R-matrix codes. Resonance parameters (i.e., E, 1, J, and on) were deduced for a large fraction of the 223 resonances observed. In addition to the previously known doorway in the s-wave channel, the p-wave neutron strength function exhibits significant changes near 40 and 145 keV indicative of doorway states in the p12 and p32 channels, respectively. These results are in good agreement with those observed in a study of the Pb207+n reaction. It is suggested that these doorway states arise from a (d52, 3-) particle-core excitation. The d-wave strength function shows indications of a doorway at about E=425 keV. The latter represents doorway resonances in the d32 and d52 channels which probably arise from a recoupling of the particle-core excitation that has been used to explain the s-wave doorway. A cumulative plot of the number of s-wave resonances vs E shows considerable curvature which indicates an increase of about 12% in the level density per 100 keV of excitation. These data were analyzed in terms of a constant temperature model with a nuclear temperature of about 0.9 MeV. The model reproduced the cumulative plot of d-wave resonances reasonably well up to E 500 keV, but underestimated the number of p-wave resonances. This indicates a parity dependence of the level density formula for this nucleus. Many of the resonances which had previously been thought to contribute to the ground-state M1 radiative strength are in fact formed by s and d waves, and hence, decay by E 1 radiation. We deduce a considerably smaller amount of M1 radiation for Ex=6738-7340 keV in Pb207 than had been reported earlier. NUCLEAR REACTIONS Pb206(n), (n,n), E=25-600 keV; measured T(E), (E,). Pb207 deduced doorway states, resonance parameters, J, n, neutron strength functions, level densities, M1 ground-state radiative strength. © 1979 The American Physical Society.