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

摘要

Natural radionuclides, especially ~(210)Pb 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 ~(210)Pb and ~7Be is possible by direct measurement of their 46.5 and 477.6 keV y-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 keVonly the 46.5 keV of the gamma photon of ~(210)Pb was of interest in this work. A dusty Reference Material (phosphate rock) containing high levels of ~(238)U-series radionuclides, especially ~(226)Ra, was used as calibration sample. This solid matrix (grain size smaller than 63 μrn) was taken to impregnate homogenously the filters so that the real geometry of measurement was reproduced. ~(210)Pb 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 ~(210)Pb 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.