Temporal variation of Radon measurements in three wells in the Phlegraean Fields, using LR-115 Type II Nuclear Track Detector

<strong>Radon-222 (222Rn), formed within the 238U chain by decay of 226Ra, is the main radioactivity source of groundwater. Radon has three radioactive isotopes but only 222Rn is of interest having a half-life of 3.8 days, since 219Rn and 220Rn are short-lived isotopes (3.8 s and 55.6 s, respectively).</strong> <strong>The values of radon and temperature measured in three wells in the Phlegraean Fields in the 1980s, 1990s and early 2000s are reported.</strong> <strong>The wells are: Damiani hot well, Costagliola cold well, Tortorelli hot well.</strong> <strong>Measur at Tortorelli were interrupted in 1993, because of technical problems, while for Damiani and Costagliola were interrupted in 2006</strong> <strong>To measure radon content we used the track-etch method. </strong> <strong>This technique uses a particle sensitive cellulose nitrate film (Kodak LR-115 type II) as the detector. The measured track density (Track/cm2 /day). </strong> <strong>A 2 x 4 cm strip of alpha-particle sensitive film is fixed into the internal top of a bell-shaped brass cylinder, long 0.2m, opened at its lower end, into which gas is permitted to flow. </strong> <strong>The cylinder was positioned about 30 cm above the water, so that the film strip can record the traces made by the radon expelled from the water.</strong> <strong>The method is commonly used in wells because water collects radon as it migrates through the rocks not only about the measurement point but for a wide area. </strong> <strong>The time interval between measurements was about 10-15 days for the cold well (Costagliola well) and about 7 days for the hot wells (Damiani and Tortorelli). </strong> <strong>The sensitive films were treated with 10% NaOH at 60°C for 90 minutes in the laboratory to enlarge the recorded alpha-tracks. The track shape depends on the energy and angle of incidence of alpha tracks</strong> <strong>Tracks were counted using a microscope with a magnification of 160X. </strong> <strong>Low radon content is detected in the cold well (Costagliola; temperature ranges between 20-27°C) , whilst radon contents in the hot wells (Damiani and Tortorelli; temperature 44°-52°C and 60-64°C, respectively).</strong> <strong>The well temperature was measured when the films were changed using a K-type thermocouple</strong>