Radon variability in borehole from Multi-Parametric Geophysical Observatory of NW Himalaya in relation to...

Radon has been measured continuously at an interval of 15 min at 10 m depth in a 68 m deep borehole. Five years of high resolution data of radon sampled at 15 min shows a complex trend with strong seasonal and diurnal trends. This temporal variation of radon has high emanation during summer and low concentration in winter. Diurnal radon variability was observed mainly during March-June and September-November each year. The existence of these diurnal periodicities in radon is related to the borehole temperature gradient i.e. difference between external atmospheric and internal borehole temperature at 10 m depth in the air column. The measured radon values are characterized by a diurnal cycle with a maximum in the afternoon and a minimum in the morning in all the seasons except in winter and during rainy periods. Minimum radon variations are recorded in the winter months primarily in December and January. Sudden unsystematic jumps in radon counts are observed each year in the rainy period (July and August). The atmospheric temperature was found to positively correlate with radon emanation. The data set of the borehole indicates a good correlation between atmospheric temperature and radon concentration that is observed throughout the year except in the rainy season. The spectra of radon and atmospheric temperature time series of 5 years data clearly show prominent and clear peaks at 1 and 2 cycles per day.