URANIUM ISOTOPES IN SEDIMENTS AS AN INDICATOR OF MOBILITY OF RADIOACTIVITY IN SAN MARCOS RIVER, CHIHUAHUA, MEXICO

Nowadays, the environmental problems are becoming more relevant and important. The main problems are related to the contamination of the water due to the presence of some toxic elements, which modify its quality. In the State of Chihuahua, Mexico there exist radio anomalies containing uranium minerals. Two uranium outcrops are placed within San Marcos Region which is located to the northwest of Chihuahua City. From this region grow up the San Marcos River, which is an effluent of one of the main rivers that supply water to agriculture; the Sacramento River. The aim of this study was to evaluate the radioactivity in sediments along the San Marcos River. Isotopic uranium was measured by alpha spectrometry, using a PIPS detector. Five samples were taken downstream from San Marcos dam. Activity concentration of ²³⁸U and ²³⁴U ranged from 23 to 16.6 Bq kg^-1 and from 34.1 to 15.7 Bq kg^-1, respectively. Uranium was in equilibrium in all samples, the activity ratio ²³⁸U / ²³⁴U was around 1. From results, it was observed that uranium concentrations in sediments decrease in the same way that downstream of river.