CIV. The photo-production of an isomeric state in207Pb

Abstract

Summary The 0·8 second activity produced in Pb by irradiation in the x-ray beam of a 23 Mev synchrotron was shown to arise from a disintegration of 208Pb by comparing the effects produced in a target of ‘natural’ Pb and a similar target of Pb enriched in the 208 isotope. The γ-rays emitted by the short-lived activity were investigated with a scintillation spectrometer. The resulting spectrum, and the half-life of the activity agree with the known spectrum and half-life associated with the i13/2 isomeric state in 207Pb. The reaction was thus determined to be 208Pb(γ, n)207*Pb. An estimate of the threshold for the production of the isomer was made by comparing, at different settings of the maximum x-ray energy from the machine, the intensity of the isomeric activity and the activity produced in Ag. The value thus obtained was 9.0±0−1 Mev. The threshold calculated from the ground state mass differences, the energy of the isomeric level and the centrifugal barrier corresponding to the orbital angular momentum...