STUDIES IN THE DECAY OF THE ACTIVE DEPOSIT OF ACTINIUM: III. LEVELS IN 211Bi AND ITS DAUGHTER PRODUCTS

Abstract

Previous work on the decay of 211Pb has been developed and extended using lithium-drifted germanium detectors and sum–coincidence techniques. A more detailed level scheme for 211Bi has been produced with greater precision in the determination of the energies and intensities of the 16 gamma rays observed.The alpha decays of 211Bi and 211Po have been studied using solid-state detectors with a resolution of 15.5 keV at 6 MeV. The alpha branching of 211Bi to the 350-keV level in 207Tl has been found to be 16.43 ± 0.04% and that of 211Po to the 570-keV level in 207Bi to be 0.50 ± 0.07%. The beta–alpha branching ratio in the decay of 211Bi is 0.274 ± 0.004%. The data enable upper limits to be placed on any other alpha groups in the active deposit in the energy range 3–13 MeV.The gamma-ray spectrum of separated sources of 207Tl has been found to consist of a single transition of energy 898 ± 0.5 keV with an intensity of 0.002 4 ± 0.000 4 photons per 207Tl decay or 0.002 9 ± 0.000 4 photons per 211Pb decay.A decay scheme for the entire active deposit is given.