Measurement of radon in soils of Lima City - Peru during the period 2016-2017/Medicion del radon 222 en suelos de la provincia de Lima - Peru durante el periodo 2016-2017

Lima City is situated on alluvial fan deposits of rivers flowing through geological formations that contain different levels of uranium. In this paper, a study is made on the average spatial and temporal behavior of radon gas in soils of Lima City. Radon concentration was determined using the LR-115 type 2 track detector during 36 periods, of 14 days each, in twenty holes distributed in the fifteen districts of Lima City. Radon concentration in soil pores ranged from 0.1 to 64.3 kBq/[m.sup.3] with an average value of 5.6 kBq/[m.sup.3]. The average radon concentration in soil gas was about two times lower in winter than in the other seasons. High radon values during October/November 2017 were related to the earthquakes perceived in Lima City in that period. The highest radon concentrations were found in areas of alluvial deposits whose parental material has been removed from the Quilmana and Huarangal volcanics by the Chillon and Huaycoloro Rivers. Soil gas radon concentrations were even higher in areas closer to volcanic and less distant from rivers. During the period of maximum flooding of the Chillon, Rimac and Lurin rivers, due to the natural phenomenon "El Nino Costero", anomalous high soil radon concentrations were observed in most of the measurement sites located near rivers. These high radon values were associated with ground vibrations caused by rock and debris avalanches in rivers and creeks. Keywords: soil gas radon; emanation; Lima; LR-115 detector; Nino Costero; river floods; alluvial deposits; igneous rocks. Medicion del radon 222 en suelos de la provincia de Lima - Peru durante el periodo 2016-2017 La ciudad de Lima esta situada sobre depositos de abanicos aluviales de rios que fluyen a traves de formaciones geologicas que contienen diferentes niveles de uranio. En este trabajo se realiza un estudio sobre el comportamiento espacial y temporal promedio del gas radon en suelos de la ciudad de Lima. La concentracion de radon se determino utilizando el detector de trazas LR-115 tipo 2 durante 36 periodos, de 14 dias cada uno, en veinte hoyos distribuidos en los quince distritos de la Ciudad de Lima. La concentracion de radon en los poros del suelo estuvo comprendida entre 0.1 y 64.3 kBq/[m.sup.3] con un valor promedio de 5.6 kBq/[m.sup.3]. La concentracion promedio de radon en el gas del suelo fue aproximadamente dos veces menor en invierno que en las otras estaciones. Los altos valores de radon durante octubre/noviembre de 2017 se relacionaron c