Radon signals at the Roded site, Southern Israel

Abstract

Abstract. 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, illustrate this situation. The monitoring of radon in the last 10 years or more has been carried out in massive meta-diorite of the Precambrian basement block of Roded. The measurement is conducted using an alpha detector at a resolution of 15-min, placed in a borehole at a depth of 9 m, within a PVC casing to that depth. Systematic temporal variation patterns, manifested as large relative signals are composed of sub-diurnal (SDR) radon, multi-day (MD) and annual (AR) signals. The overall variation is 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 at 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 at an 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) Continuous Wavelet Transform (CWT) analysis shows an overall annual structure with a modulation of the S1 and S2 periodicities; (b) Moving-time-window Fourier spectral analysis showing that the amplitudes of S1Correspondence to: G. Steinitz (steinitz@gsi.gov.il) and S2 vary in an annual pattern, with relatively high values in summer. The phase of S1, S2 and S3 shows a systematic multi-year variation. It is suggested that the significant signatures of the periodic phenomena and their modulations reflect a direct link with the solar radiation tide.

Influence of a component of solar irradiance on radon signals at 1 km depth, Gran Sasso, Italy

“…The measured signal was decomposed using a 25-h sliding average revealing two types of signals in the radon time series-daily radon (DR) signals and MD signals, similar to those encountered in several other sites and locations [15][16][17]25]. The MD signals, with amplitudes of over 10 kcounts/15-min, span 2 or more days and are non-periodic.…”

“…Geophysical analysis of these relatively long time series measured with a high time resolution (within 1 h) demonstrates that Rn signals in air confined within rock units are characterized by systematic recurrence of signal patterns in the temporal, geological and geographical domains, at a depth of more than 100 m. The main types recognized are multi-year, annual radon (AR; periodic), MD and daily radon (DR; periodic) signals [14,15,25,34] as well as intense variation lasting several hours [16,17]. Examination of the patterns suggested that -variation patterns in the subsurface regime cannot be accounted for by simple and direct time varying processes in the gas system such as emanation, diffusion, absorption and advection; -absence of above surface atmospheric influence, in particular pressure; and -periodicity in the DR signal is characterized by solar tide frequencies S1 (24-h), S2 (12-h) and S3 (8-h) [31], implying an external above surface driving mechanism.…”

“…At these levels, the air pressure regime is related to the local atmospheric barometric pressure while temperature tends to show stabile patterns reflecting the rock temperature at depth. Radon signals characterized by systematical recurrence of patterns in the temporal, geological and geographical domains have been reported from tunnels and boreholes in France [10], from Tenerife at a depth of more than 800 m [11][12][13] and from the desert in Israel at a depth of more than 100 m [14][15][16][17].…”

Investigation of temperature and barometric pressure variation effects on radon concentration in the Sopronbánfalva Geodynamic Observatory, Hungary

“…Thus, the amount of radon exhalation depends on the elastic properties and porosity of the rocks and on the local fracture system (e.g. Holub and Brady, 1981;Kies et al, 2002Kies et al, , 2005Vaupoti c et al, 2010) and shows large temporal variations due to meteorological and hydrological effects (Garavaglia et al, 1999;Vargas and Ortega, 2006;Papp et al, 2008;Smetanova et al, 2010;Steinitz and Piatibratova, 2010;Szab o et al, 2013). Analysis of temporal variations in the radon gas concentration is a useful tool to study geodynamic processes associated with tectonic (Garavaglia et al, 1998Aumento, 2002;Omori et al, 2007;Mahajan et al, 2010;Utkin and Yurkov, 2010) and volcanic (Toutain and Baubron, 1999;Viñas et al, 2007) activities as well as in looking for a warning sign for earthquakes (Igarashi et al, 1995;Yong and Wei, 1995;Garavaglia et al, 1999;Virk et al, 2000;Crockett et al, 2006;Kawada et al, 2007;Inan et al, 2008;Yasuoka et al, 2009;Crockett and Gillmore, 2010;Cigoliní et al, 2015).…”

“…Radon gas, which is continuously produced in rocks and soils, migrates into the air. The migration is mainly affected by convection and molecular diffusion (Steinitz and Piatibratova, 2010;Szab o et al, 2013). Thus, the amount of radon exhalation depends on the elastic properties and porosity of the rocks and on the local fracture system (e.g.…”