An efficiency calibration for 210Pb and 7Be measurements by gamma-ray spectrometry in atmospheric filters

Abstract

Natural radionuclides, especially 210Pb and 7Be, condensed on suspended particulate matter in the atmosphere (commonly called aerosols) have been widely used to study a large variety of relevant atmospheric processes. A rapid and non-destructive analysis of 210Pb and 7Be is possible by direct measurement of their 46.5 and 477.6 keV γ-rays, respectively. In this work we have developed an original method to find an empirical function which relates the full-energy peak efficiency with energy in a rectangular geometry for energies above 150 keV. For the energy range below 150 keV only the 46.5 keV of the gamma photon of 210Pb was of interest in this work. A dusty Reference Material (phosphate rock) containing high levels of 238U-series radionuclides, especially 226Ra, was used as calibration sample. This solid matrix (grain size smaller than 63 μm) was taken to impregnate homogenously the filters so that the real geometry of measurement was reproduced. 210Pb and 7Be activity concentrations in surface air were determined in samples collected from July 2004 to June 2005 at three different locations of the Huelva province (South West of Spain): urban, rural, and industrialized areas. 7Be and 210Pb activities have been determined in the PM 10 and TSP fractions of surface aerosols. The radiometric measurements were performed by low-level gamma spectrometry with a thin window coaxial germanium detector.