Electrostatic spectrometers utilized in high-resolution beta-spectroscopy
studies such as in the Karlsruhe Tritium Neutrino (KATRIN) experiment have to
operate with a background level of less than 10^(-2) counts per second. This
limit can be exceeded by even a small number of Rn-219 or Rn-220 atoms being
emanated into the volume and undergoing alpha-decay there. In this paper we
present a detailed model of the underlying background-generating processes via
electron emission by internal conversion, shake-off and relaxation processes in
the atomic shells of the Po-215 and Po-216 daughters. The model yields electron
energy spectra up to 400 keV and electron multiplicities of up to 20 which are
compared to experimental data.Comment: 7 figure
