X-ray fluorescence analysis in environmental radiological surveillance using HPGe detectors $ E. Herrera Peraza * , M. Renteria Villalobos, M.E. Montero Cabrera, A. Mun ˜oz Romero Department of Environmental Radiological Surveillance, Centro de Investigacio ´n en Materiales Avanzados (CIMAV), P.O. Box 31109, Miguel de Cervantes #120, Complejo Industrial Chihuahua, Chihuahua, Me ´xico Received 26 September 2003; accepted 1 May 2004 Available online 9 September 2004 Abstract X-ray fluorescence (XRF) has been proven to be a valuable tool for determining trace quantities of heavy metals, such as uranium and lead, in different types of samples. The present paper demonstrates the applicability of XRF spectrometry to measure the concentrations of these heavy metals in samples from natural ore and soil. The values of uranium concentrations in rock from the Pen ˜a Blanca uranium ore, in Chihuahua, Me ´xico, were calculated for the purpose of precertifying the rock powders samples. The comparison with other techniques, such as inductively coupled plasma atomic emission spectrometry, atomic absorption spectrometry, alpha spectrometry and electron microscopy, was used to complete the precertification process, so that the sample powders may be used as secondary standards. The source-sample- detector geometry and the incident angle are the most important factors for obtaining low detection limits. The selected system uses a 57 Co source of about 0.1 mCi to excite the K X-rays from uranium and lead. X-rays were recorded on a CANBERRA HPGe coaxial detector. The comparative results for two incident angles (908 and 1808) performed previously by other authors show that the best geometry is the backscattering geometry. In the present paper, using EGS4 code system with Monte Carlo simulation, it was possible to determine the location and distribution of background produced by the Compton edge in the optimized geometry. This procedure allowed to find the minimum detectable concentration of uranium and lead, which was experimentally calculated using standards. The possibility of performing in vivo measurements rapidly and easily, as well as the factors affecting accuracy and the minimum detectable concentration in several samples are also discussed. D 2004 Elsevier B.V. All rights reserved. Keywords: X-ray fluorescence; HPGe detectors; Environmental radiological surveillance 1. Introduction The toxicological effects of uranium and lead have been assessed in many studies [1–4]. Measurements of uranium and lead in soil, water and air have been conducted by the Environmental Division and specially by the Department of Environmental Radiological Surveillance of the Advanced Materials Research Centre (CONACyT contract C000/ C300/0736, 2002). Different regions and cities in the state of Chihuahua have been studied to determine the specific activities of the uranium-238 chain—including its daugh- ters, radium and radon—and the thorium chain, as well as their effects in human health. X-ray fluorescence is very appropriate for determining the concentrations of uranium and lead. However, monitoring of miners exposed to inhalation or ingestion of these metals in the State of Chihuahua, Mexico, is a very difficult task. This paper presents the results of the preliminary steps towards obtaining the optimal detector geometry for uranium and lead measurements, using XRF excited by a 57 Co gamma source and a HPGe detector. 0584-8547/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.sab.2004.05.028 $ This paper was presented at the International Congress on X-Ray Optics and Microanalysis (ICXOM XVII), held in Chamonix, Mont Blanc, France, 22–26 September 2003, and is published in the special issue of Spectrochimica Acta Part B, dedicated to that conference. * Corresponding author. Tel.: +52 614 439 4806; fax: +52 614 439 1112. E-mail address: eduardo.herrera@cimav.edu.mx (E. Herrera Peraza). Spectrochimica Acta Part B 59 (2004) 1695 – 1701 www.elsevier.com/locate/sab