The dynamics of Rn-222 cyclic flow within the shallow geological subsurface media as a daily temporal variated source for exhalation into the air.

Extensive research on the dynamics of radon gas (Rn-222) originating from the radioactive decay of radium (Ra-226) in geological subsurface media, sheds light on its periodic release into the atmosphere. Radon is a product of the uranium-238 decay chain found within rock and soil grains. While only a fraction of the generated radon escapes (emanates) into porous spaces due to nuclear recoil, it serves as the source for subsurface gas flows and for cyclic exhalation into the soil-atmosphere interface. Ongoing study of radon movement in shallow and deep subsoil, and its emergence at the surface, reveals complete semi-diurnal, diurnal, and seasonal gas flow cycles in the subsoil. Complementary emissions occur nocturnally as radon is released into the atmosphere. Moreover, two natural driving forces govern complex semi-diurnal and diurnal flows below and above the surface. Subsurface gas movement in porous media exhibits nonlinear behavior influenced by surface temperature gradients, resulting in downward flow to depths of up to 100 m. This flow exhibits daily periodicity with depth-dependent time delays, correlating with the diurnal surface temperature cycle. Additionally, pore gas transport into and out of open boreholes responds linearly to semi-diurnal barometric pressure changes, known as barometric pumping. Beyond subsurface phenomena, Europe and Australia increasingly employ nocturnal radon measurements to study atmospheric stability and air quality, assuming that variations in local stationary near-surface radon concentrations reflect atmospheric mixing processes. Recognizing mechanisms governing radon's temporal changes within geological subsurface media highlights the need for continuous underground radon monitoring to validate variations in daily radon exhalation to the surface. On the other hand, monitoring radon at considerable depths minimizes climatic contributions and enhances the ability to discern non-periodic pre-seismic radon signals, independent of atmospheric compulsion. This research offers potential insights into seismic precursors and the complex interplay between subsurface geodynamics and atmospheric conditions.

Effect of atmospheric temperature on underground radon: A laboratory experiment.

The effect of atmospheric temperature on underground radon flow was investigated in a customized climate-controlled laboratory (CCL) system, which enabled us to isolate the impact of ambient atmospheric temperature variations on underground radon transport. The soil thermal gradients that developed, following atmospheric warming, acted as the driving force for the diffusive radon flow, resulting in a decrease in the radon concentration along the experimental column setup at a rate of ∼70 Bq∙m-3 per oC∙m-1 (∼0.4% of the radon concentration). When the ambient temperature decreased, compared to the soil temperature, an air-soil temperature difference developed along the column, which acted as a driving force for radon to flow along the column and promptly increased the radon concentration at a rate of ∼140 Bq∙m-3 per oC (∼0.8% of the radon concentration). The overall radon concentration changes under the experimental conditions were up to 30%. The changes in the molecular diffusion coefficient in the experimental temperature range were ∼7%, with thermal diffusion as a possible additional mechanism contributing to radon transport due to temperature. The cyclic changes in ambient temperature in the forced conditions experiments were found to be directly correlated with underground radon oscillations. The same frequency for ambient temperature and radon concentration, along the experimental column in low frequency warming-cooling cycles (i.e., 4-8 days), was found. This good correlation was lost at higher frequencies (two days or more), due to the asymmetrical response of radon to atmospheric warming and cooling. The results of this study explain some of the field observations in underground radon monitoring.

Monte Carlo modeling of scintillation detectors for continuous underground radon monitoring.

Nuclear simulation methods were applied to two systems that investigate radon transport within geological porous media: a) a laboratory system built to test, under controlled climate conditions, the effect of temperature on radon transport, and b) a field monitoring system comprising gamma and alpha detectors in an abandoned water well. The use of Monte Carlo simulations of NaI and BGO scintillation detectors in continuous underground radon measurements by gamma counting, to estimate the photon flux in the detector volume, is presented. The advantages of shielding side-view NaI detectors were demonstrated for a laboratory system containing ground phosphate rock, including avoiding high counting rates and reducing the effective source volume in radon transport studies. The gross gamma counting procedure was shown to result in a lower uncertainty than spectrometric measurement, by at least a factor of two, despite it being a simpler and more suitable procedure for field measurements. The calculation of simulated source volumes for a BGO detector in a borehole and the measurements in the field support the assumption that the gamma signal comes primarily from radon flowing in the bedrock's air-filled pores. As a practical outcome of this study, positioning the detector a few cm off-center from the borehole's axis increased the gamma counting efficiency; however, measurements in groundwater taken too close to the iron casing had a lower detection efficiency. The conversion factor from the scintillator signal to the radon activity concentration, for the laboratory system, was calculated. Monte Carlo simulations demonstrated the advantages of the gross counting procedures using gamma scintillation detectors in field underground high-frequency radon monitoring.

The role of atmospheric conditions in CO2 and radon emissions from an abandoned water well.

Boreholes and wells are complex boundary features at the earth-atmosphere interface, connecting the subsurface hydrosphere, lithosphere, and biosphere to the atmosphere above it. It is important to understand and quantify the air exchange rate of these features and, consequently their contribution as sources for greenhouse gas (GHG) emissions to the atmosphere. Here, we investigate the effect of atmospheric conditions, namely atmospheric pressure and temperature, on air, CO2, and radon transport across the borehole-ambient atmosphere interface and inside a 110-m deep by 1-m diameter borehole in northern Israel. Sensors to measure temperature, relative humidity, CO2, and radon were placed throughout a cased borehole. A standard meteorological station was located above the borehole. Data were logged at a high 0.5-min resolution for 9 months. Results show that climatic driving forces initiated 2 different advective air transport mechanisms. (1) Diurnal and semidiurnal atmospheric pressure cycles controlled daily air transport events (barometric pumping); and (2) There was a correlation between borehole-atmosphere temperature differences and transport on a seasonal scale (thermal-induced convection). Barometric pumping was identified as yielding higher fluxes of vadose zone gases than thermal-induced convection. Air velocities inside the borehole and CO2 emissions to the atmosphere were quantified, fluctuating from zero up to ~6 m/min and ~5 g-CO2/min, respectively. This research revealed the mechanisms involved in the process throughout the year and the potential contribution role played by boreholes to GHG emissions.

Detailed effects of particle size and surface area on 222Rn emanation of a phosphate rock.

The dependency of radon emanation on soil texture was investigated using the closed chamber method. Ground phosphate rock with a large specific surface area was analyzed, and the presence of inner pores, as well as a high degree of roughness and heterogeneity in the phosphate particles, was found. The average radon emanation of the dry phosphate was 0.145 ± 0.016. The emanation coefficient was highest (0.169 ± 0.019) for the smallest particles (<25 µm), decreasing to a constant value (0.091 ± 0.014) for the larger particles (>210 µm). The reduction rate followed an inverse power law. As expected, a linear dependence between the emanation coefficient and the specific surface area was found, being lower than predicted for the large specific surface area. This was most likely due to an increase in the embedding effect of radon atoms in adjacent grains separated by micropores. Results indicate that knowledge of grain radium distribution is crucial to making accurate emanation predictions.

High Resolution Marine Magnetic Survey of Shallow Water Littoral Area.

The purpose of this paper is to present a system developed for detection andaccurate mapping of ferro-metallic objects buried below the seabed in shallow waters. Thesystem comprises a precise magnetic gradiometer and navigation subsystem, both installedon a non-magnetic catamaran towed by a low-magnetic interfering boat. In addition wepresent the results of a marine survey of a near-shore area in the vicinity of Atlit, a townsituated on the Mediterranean coast of Israel, about 15 km south of Haifa. The primarypurpose of the survey was to search for a Harvard airplane that crashed into the sea in 1960.A magnetic map of the survey area (3.5 km² on a 0.5 m grid) was created revealing theanomalies at sub-meter accuracy. For each investigated target location a correspondingferro-metallic item was dug out, one of which turned to be very similar to a part of thecrashed airplane. The accuracy of location was confirmed by matching the position of theactual dug artifacts with the magnetic map within a range of ± 1 m, in a water depth of 9 m.