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.