2005 International Nuclear Atlantic Conference - INAC 2005 Santos, SP, Brazil, August 28 to September 2, 2005 ASSOCIAÇÃO BRASILEIRA DE ENERGIA NUCLEAR - ABEN ISBN: 85-99141-01-5 GAMMA-RAY MEASUREMENTS IN UPPERMOST SOIL PROFILE OF A GRAZING AREA AROUND LONDRINA CITY, PARANÁ STATE, BRAZIL Rodrigo O. Bastos 1 , Avacir C. Andrello 2 and Carlos R. Appoloni 3 Laboratório de Física Nuclear Aplicada – Departamento de Física - CCE Universidade Estadual de Londrina – Campus Universitário Rodovia Celso Garcia Cid s/n, Cx. Postal 6001 86051-990 Londrina, PR 1 rbastos@uel.br 2 acandrello@uel.br 3 appoloni@uel.br ABSTRACT Using high-resolution γ-ray spectrometry, soil profiles were measured to assess the depth distribution of 232 Th, 238 U, 226 Ra, 40 K and 137 Cs. The surveyed soil is the Latossolo Vermelho Distroférrico, clayey texture, in a soft wave relief area used for grazing, near Londrina city, Paraná, Brazil. Knowledge of radioelement depth distributions is important to understand their behavior along soil history, and in the same time, give clues about it, from pedogenesis to more recent events, such as weathering, erosion or interaction with biosphere. Five points were sampled, three of them in increment depths of 0 to 5 cm, 5 to 10 cm, 10 to 15 cm, 15 to 20 cm, 20 to 35 cm, and for two of them the increment 35-50 cm was collected either. These totalized 27 samples, each of them dried in open air during 48 hours, sieved through 2mm mesh, sealed in 1-litre plastic Marinelli beakers, and measured in the laboratory. It was employed a standard gamma ray spectrometry electronic chain, with a 66% relative efficiency HPGe detector. Measurement of the efficiency in the range from 60 to 1800 keV was carried out with certified IAEA 375 soil sample. From the measured γ-ray spectra, activity concentrations were determined for 232 Th (from 15.4 to 25.1 Bq kg -1 ), 238 U (from 11.0 to 18.9 Bq kg -1 ), 226 Ra (from 4.0 to 10.9 Bq kg -1 ), 40 K (from 36.0 to 133.9 Bq kg -1 ) and 137 Cs (from 0.0 to 2.2 Bq kg -1 ). Average values and respective deviations are 21.0 + 2.6 Bq kg -1 for 232 Th, 13.8 + 1.7 Bq kg -1 for 238 U, 7.8 + 1.9 Bq kg -1 for 226 Ra, 72.8 + 30.5 Bq kg -1 for 40 K, and 0.8 + 0.8 Bq kg -1 for 137 Cs. Depth distributions of each radioelement are presented and possible relations among activities are analyzed. 1. INTRODUCTION During the last century radioactivity has been the subject of several fundamental and applied researches. Nowadays many nuclear techniques are available to researchers all over the world and applications have been found in all environmental sciences. In this paper, high-resolution γ-ray spectrometry was employed to measure soil profiles and assess the depth distribution of 232 Th, 238 U, 226 Ra, 40 K and 137 Cs. Knowledge of radioelement depth distributions is important to understand their behavior along soil history, and in the same time, give clues about it, from pedogenesis to more recent events, such as weathering, erosion or interaction with biosphere. Investigations on terrestrial natural radiation have received particular attention worldwide and led to extensive surveys in many counties. Surveying all over the world has many motivations, from rock and regolith mapping [1] to evaluation of radiometric and dosimetric quantities [2]. Although information of radioelement content in common rock types are referred elsewhere [3], data on soil derived from those rocks is very rare [4]. In Brazil, although many studies on terrestrial radiation by gamma-ray measurements have been executed [5, 6, 7, 8, 9 and others], scarce data are available about variation of natural radioisotopes in the uppermost soil profiles. Most research on this subject regards to cesium profiles [10].