Natural gamma-ray spectrometry as a tool for radiation dose and radon hazard modelling M. Verdoya a , P. Chiozzi a , P. De Felice b , V. Pasquale a,Ã , M. Bochiolo a , I. Genovesi a a Dipart. Studio Territorio Risorse, Settore di Geofisica, Universita ` di Genova, Viale Benedetto XV 5, I-16132 Genoa, Italy b Instituto Nazionale Metrologia Radiazioni Ionizzanti ENEA, Centro Ricerche Casaccia, Via Anguillarese, 301 S.M. Galeria, I-00100 Rome, Italy article info Keywords: Spectrometry Natural radioactivity Absorbed dose rate Radon potential abstract We reviewed the calibration procedures of gamma-ray spectrometry with particular emphasis to factors that affect accuracy, detection limits and background radiation in field measurements for dosimetric and radon potential mapping. Gamma-ray spectra were acquired in western Liguria (Italy). The energy windows investigated are centred on the photopeaks of 214 Bi (1.76 MeV), 208 Tl (2.62 MeV) and 40 K (1.46 MeV). The inferred absorbed dose rate and the radon flux are estimated to be lower than 60 nGy h 1 and 22 Bq m 2 h 1 , respectively. & 2009 Elsevier Ltd. All rights reserved. 1. Introduction Radiometric surveys cover many different scientific and practical interests, ranging from basic geophysics to mineral exploration and environmental radiation monitoring. The envir- onmental aspects of natural radioactivity, above all regarding radon effects and exposure to ionising radiation, is a topic of growing interest during the last years (see e.g. A ˚ kerblom and Linde ´ n, 1996; Bellotti et al., 2007 and references therein). Natural radioactivity originated from uranium, thorium and potassium, which are hold in variable quantities above all in the rocks forming the Earth’s crust, is the major cause of natural, potentially hazardous, gamma-ray exposure. Albeit aerial gamma-ray spectrometry can provide an overview and mapping of radioelement concentrations over wide regions (e.g. Aydin et al., 2006), only ground, high-resolution measure- ments yield detailed mapping over relatively small rock outcrops, and allow cheap and fast monitoring of environmental radio- activity even in a rough terrain. In this paper, we present results of natural radioactivity from a ground gamma-ray survey carried out in the Alpine geological units of western Liguria (Italy) (Fig. 1). Gamma-ray spectrometry results were used for assessment of absorbed dose rates. Moreover, uranium concentration was considered as a radon potential indicator in the different geological environments and was used for preparing radon prognosis maps. Particular care was paid to the calibration of the gamma-ray apparatus, with reference to the assessment of the background radiation. Since the surveyed area has a rough topography, we evaluated the variation of background radiation with elevation. The interest for the study area is above all based on the presence of several lithotypes, spanning from sedimentary, to metasedimentary and metavolcanic rocks, the latter particularly known in literature for their abundance of radionuclides (see Verdoya et al., 2001; Bochiolo, 2007; Genovesi, 2007 and references therein). The stratigraphy consists of: (1) basement rocks (Late Carboniferous-Permian), embodying polimetamorphic terms (orthogneisses and granitoids), metasediments (phyllites, micaschists and quartzschists) and metavolcanics (metaandesites, metarhyolites and porphyric schists); (2) cover rocks (Trias- Miocene), formed by orthoquartzites, arkosic sandstones, and conglomerates, and by a calcareous-dolomitic succession, some- times alternate to arenaceous and marly terms. 2. Measurement technique 2.1. Instrumentation and calibration The type of spectrometer, detector volume, measurement times, and mode of measurement depend on the radiation environment and the type, size and distribution of radioactive sources. Portable, hand-held gamma-ray spectrometers are widely used in field studies for both regional and detailed mapping surveys aimed to estimate the surface concentrations of the radionuclides. Our portable apparatus for gamma-ray activity measurements (Satisgeo Brno, Czech Republic) consists of a thallium-activated sodium iodide scintillation detector of about 440 cm 3 together with a photomultiplier tube, a high-voltage supply and a signal preamplifier. It is thermally insulated and ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/apradiso Applied Radiation and Isotopes 0969-8043/$ - see front matter & 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.apradiso.2009.01.066 Ã Corresponding author. Tel.: +39 010 3538090; fax: +39 010 352169. E-mail address: pasquale@dipteris.unige.it (V. Pasquale). Applied Radiation and Isotopes 67 (2009) 964–968