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 211 Pb has been developed and extended using lithium-drifted germanium detectors and sum–coincidence techniques. A more detailed level scheme for 211 Bi has been produced with greater precision in the determination of the energies and intensities of the 16 gamma rays observed.The alpha decays of 211 Bi and 211 Po have been studied using solid-state detectors with a resolution of 15.5 keV at 6 MeV. The alpha branching of 211 Bi to the 350-keV level in 207 Tl has been found to be 16.43 ± 0.04% and that of 211 Po to the 570-keV level in 207 Bi to be 0.50 ± 0.07%. The beta–alpha branching ratio in the decay of 211 Bi 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 207 Tl 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 207 Tl decay or 0.002 9 ± 0.000 4 photons per 211 Pb decay.A decay scheme for the entire active deposit is given.