The ²¹⁰Pb bremsstrahlung in the background of lead shields

Abstract

Contemporary theories of dark matter predict that weakly interacting massive particles interact with matter by nuclear recoils leaving in the detector energies up 50 keV. The bremsstrahlung of 210Pb contributes to this spectral region. The 46.5 keV gamma intensity of Pb in the background can be easily reduced by inner lining, but the bremsstrahlung from the 1.2 MeV maximal energy beta decay will reach the lead shielded Ge detector. The spectrum of this bremsstrahlung is calculated by numerically fitting the beta spectrum and integrating the Koch-Motz formula. The absorption of the bremsstrahlung spectrum in the lead and detection efficiencies for Ge detector are calculated by the effective solid angle algorithm, using correction for photopeak/compton ratio of cross sections in Ge. By comparison with the measured spectrum, it is shown, that for the lead with 25 Bq/kg of 210Pb, up to 500 keV, the bremsstrahlung contribution to the background is about 20%. The calculated bremsstrahlung intensity is in good agreement with the experimental result derived in Max Planck Institute, Heidelberg. © 2007 American Institute of Physics.