Solid Earth Discussions www.solid-earth-discuss.net 1869-9537 2 1 2010 10.5194/sed-2-161-2010 http://www.solid-earth-discuss.net/2/161/2010/ http://www.solid-earth-discuss.net/2/161/2010/sed-2-161-2010.html http://www.solid-earth-discuss.net/2/161/2010/sed-2-161-2010.pdf 161 193 2010-06-22 Radon signals at the Roded site, southern Israel G. Steinitz Steinitz@gsi.gov.il O. Piatibratova Geological Survey of Israel, 30 Malkhe Israel St. Jerusalem 95501, Israel Temporal variations of radon in the geological environment (upper crust) are frequent and recognized as unique in terms of the signals encountered and for the lack of substantial and generally applicable explanations. The phenomena observed at the Roded site, located in arid southern Israel, emphasize this situation. Monitoring of radon during more than 10 years is carried out in massive meta-diorite of the Precambrian basement block of Roded. Measurement is conducted using an alpha detector at a resolution of 15-min, lowered in a borehole at a depth of 9 m, within a PVC casing to that depth. Systematic temporal variation patterns, manifesting large relative signals are composed of sub-daily (SDR) radon, multi-day (MD) and annual (AR) signals. The overall variation in dominated by the intense SDR signals which occur in some days, and may vary from background levels (5 counts or less) to peak values (attaining >1000 counts) and back to background in an interval of 6 to 12 h. Intervals of up to several tens of days without significant SDR signals interchange with times of intense daily occurrences of such signals. Their occurrence indicates very fast variations of radiation from radon at the point of measurement. The peak times, within the diurnal 24-h cycle of SDR signals occur preferentially in the interval of 14–16 h (UT+2). Spectral analysis indicates: (a) A diurnal periodicity composed of a primary 24-h and a secondary 12-h periodicity, which are attributed to the solar tide constituents S1 and S2. Tidal constituents indicative for gravity tide (O1, M2) are lacking; (b) An annual periodicity. A compound relation among the diurnal and annual periodicity is indicated by: (a) Wavelet (CWT) analysis showing an overall annual structure with a modulation of the S1 and S2 periodicities; (b) FFT analysis using consecutive 21.3-day long time intervals shows that the amplitudes of S1 and S2 vary in an annual pattern, with relatively high values in summer. The phase of S1 and S2 and S3 shows a systematic multi-year variation. Existing frames of reference of geophysical processes cannot explain the highly systematic phenomena. It is suggested that the significant signatures of the periodic phenomena and their modulations are reflecting a direct link with solar radiation tide. 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