Abstract

Cross sections have been measured for the reaction 208Pb(γ,p) leading to the low-lying ( 1 2 + , 3 2 + ) and ( 11 2 − , 5 2 + ) doublets and 7 2 + state in 207Tl using a high energy-resolution tagged photon beam of 41 to 57 MeV. The data are compared with results obtained with the reaction 208Pb(e,e′p) in the same recoil-momentum range. The recoil-momentum distributions derived from the (γ,p) data do not coincide with those obtained from the (e,e′p) data. Distorted-wave impulse-approximation (DWIA) calculations of which the input is constrained by the (e,e′p) data underestimate the (γ,p) data by typically one order of magnitude. An estimate of meson-exchange currents (MEC) effects using the Siegert theorem brings the DWIA-calculations close to the data. Random-phase approximation calculations also give a fair account of the data, but in this case MEC-effects are predicted to be less important.

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