Journal of Radioanalytical and Nuclear Chemistry, Vol. 269, No.2 (2006) 435–439 0236–5731/USD 20.00 Akadémiai Kiadó, Budapest © 2006 Akadémiai Kiadó, Budapest Springer, Dordrecht A method for analyzing low statistics high resolution spectra from 210 Pb in underground coal miners from Brazil A. L. A. Dantas, 1 * B. M. Dantas, 1 J. L. Lipsztein, 2 H. B. Spitz 3 1 Instituto de Radioproteção e Dosimetria, IRD-CNEN, Av. Salvador Allende s/n, 22780-160 Rio de Janeiro, Brazil 2 Instituto de Biologia Roberto Alcântara Gomes, UERJ, Av. 28 de Setembro n.87, 20551-030 Rio de Janeiro, Brazil 3 University of Cincinnati, 598 Rhodes Hall, 45221-0072 Cincinnati, USA (Received April 6, 2006) A survey conducted by the IRD-CNEN determined that some workers from an underground coal mine in the south of Brazil were exposed to elevated airborne concentrations of 222 Rn. Because inhalation of high airborne concentrations of 222 Rn can lead to an increase of 210 Pb in bone, in vivo measurements of 210 Pb in the skeleton were performed in selected underground workers from this mine. Measurements were performed using an array of high-resolution germanium detectors positioned around the head and knee to detect the low abundant 46.5 keV photon emitted by 210 Pb. The gamma-ray spectra were analyzed using a moving median smoothing function to detect the presence of a photopeak at 46.5 keV. The minimum detectable activity of 210 Pb in the skeleton using this methodology was 50 Bq. Introduction The major source of naturally occurring radiation exposure arises from inhalation of radon and its short- lived progeny, which deliver a substantial internal dose to the respiratory tract. 1 Studies of underground uranium miners have demonstrated that the skeleton of the persons who are chronically exposed to elevated concentrations of 222 Rn will accumulate 210 Pb, the long lived radioactive decay product of the noble gas, 222 Rn. 2 The 210 Pb deposited in the skeleton can arise from the decay of 222 Rn in the respiratory tract or by direct inhalation of 210 Pb as a free ion or attached to airborne dust particles. Lead is a chemical congener of calcium and, therefore, exhibits biokinetic properties similar to those of calcium. Thus, an intake of 222 Rn gas or 210 Pb particles will eventually lead to a deposition of 210 Pb in the skeleton, since the majority of calcium in the body is deposited in bone. 3 The head (skull) and knees are convenient locations on the body for measuring 210 Pb in vivo since detectors can easily be placed around these locations and the likelihood of cross contribution from 210 Pb in other organs or tissue is low. Likewise, the head and knees are regions of the body where a large fraction of bone surface area is found. 4 A radiological survey conducted in non-uranium mines by the Institute for Radiation Protection and Dosimetry (IRD) identified an underground coal mine, located in the south of Brazil having a high airborne concentration of 222 Rn. 5 The aim of this work was to investigate if underground coal miners from this mine have elevated 210 Pb levels in the skeleton resulting from occupational exposure to radon. In vivo measurements for 210 Pb in a group of underground coal miners were performed using an array * E-mail: adantas@ird.gov.br of four high resolution germanium detectors installed in a shielded, low radiation background room at the IRD- CNEN whole body counter. Detectors are positioned as close as possible around the head or over the knee to maximize detection efficiency. The count rate observed in the 46.5 keV region of the spectrum is converted to activity units (Bq) by calibrating the detector array using anthropometric phantoms of the knee and head that contain precisely known quantities of 210 Pb in bone. 6 Reliable detection of the low abundant (~4%), 46.5 keV photons from 210 Pb is especially challenging because the background spectrum can be highly variable and difficult to predict. Different from scintillation detector spectroscopy of low energy photons, in which the activity has to be quantified by a net positive count rate in a pre-determined region of the photon energy spectrum, high-resolution Ge detectors exhibit a small, but easily distinguishable, near Gaussian-shaped peak which, once resolved by an appropriate algorithm, allows for reliable in vivo measurements for 210 Pb even if the amount of radioactivity is low. In this work measurements were evaluated by first applying a moving median smoothing function to each of the gamma-ray spectra to determine the background in the 46.5 keV peak regions. The moving median smoothing function is insensitive to extremes and eliminates outlier peak channels in the spectrum, providing a new energy spectrum that reflects the background. 7 In addition, the background in the 46.5 keV region for each measured energy spectrum was estimated by determining the average number of counts immediately preceding and following the 46.5 keV 210 Pb region. Six of 32 workers who consented to be measured were found to have a detectable amount of 210 Pb in the skeleton as evidenced by a visible photopeak at 46.5 keV.