Contribution of 210Pb bremsstrahlung to the background of lead shielded gamma spectrometers

Lead, which is often used as a shielding material, contains ²¹⁰Pb (T_1/2=22.3 y). The 46.54 keV γ-intensity of ²¹⁰Pb can be easily reduced by an inner lining, but the bremsstrahlung caused by the β-decay of its daughter, ²¹⁰Bi, with a maximal electron energy of 1.16 MeV, will contribute to the gamma detector background. The spectrum of this bremsstrahlung is calculated by numerically fitting the β-spectrum and integrating the Koch–Motz formula. The absorption of the bremsstrahlung in the lead and detection efficiencies for the HPGe detector are calculated by the effective solid angle algorithm, using corrections for the photopeak/Compton ratio of cross-sections in Ge. By comparison with the measured background spectrum, it is shown that, for the lead with 25 Bq/kg of ²¹⁰Pb up to 500 keV of gamma spectrum, the bremsstrahlung contribution to the background is about 20% for our surface-based detector system. Also, we compared our calculations with a Monte Carlo simulation of another detector system with a shield containing 1 Bq/kg of ²¹⁰Pb and found that our analytical method gives a value of roughly two times higher than the Monte Carlo one for the total bremsstrahlung contribution. The quality of the analytical semi-empirical method is proved by the reasonable agreement with the experimental results published.