ELECTROMAGNETIC TRANSITION STRENGTHS IN PB206 PB207 AND PB208 FROM THRESHOLD PHOTONEUTRON CROSS-SECTION MEASUREMENTS

The photoneutron cross sections for Pb206, Pb207, and Pb208 have been measured for photon energies up to 40 keV above threshold. Several resonances were resolved for each isotope. Most of the resonances seen in the Pb207 and Pb208 spectra correspond to resonances detected by neutron-capture or total cross-section measurements on Pb206 and Pb207, respectively. Values for Γγ0, the ground-state γ-ray width, were determined for a number of resonances in each target. By comparison with the neutron-capture experiments, the multipolarities of the γ-ray transitions were determined, and an average γ-ray transition strength was obtained. The M1 transition strengths for Pb206 and Pb207 were found to be markedly enhanced over the expected value. One E2 transition in Pb208 was found to have a strength of 0.14 Weisskopf units, and there is a possibility of two other E2 transitions with similar strength. © 1969 The American Physical Society.