On radon emanation as a possible indicator of crustal deformation

Radon emanation has been monitored in shallow capped holes by a Tracketch method along several active faults and in the vicinity of some volcanoes and underground nuclear explosions. The measured emanation shows large temporal variations that appear to be partly related to crustal strain changes. This paper proposes a model that may explain the observed tectonic variations in radon emanation, and explores the possibility of using radon emanation as an indicator of crustal deformation. In this model the emanation variation is assumed to be due to the perturbation of near-surface profile of radon concentration in the soil gas caused by a change in the vertical flow rate of the soil gas which, in turn, is caused by the crustal deformation. It is shown that, for a typical soil, a small change in the flow rate (3 · 10⁻⁴ cm sec⁻¹) can effect a significant change (a factor of 2) in radon emanation detected at a fixed shallow depth (0.7 m). The radon concentration profile has been monitored at several depths at a selected site to test the model. The results appear to be in satisfactory agreement.     

Distribution of radon sources and effects on radon emanation in granitic soil at Ben Lomond,California

The abundance and distribution of radioelements on bulk and microscopic scales were investigated in residual granitic-derived soil at a facility for investigating the movement of radon into structures. In bulk soil samples, Ra concentrations range from 0.6 to 1.3 pCi/g, and variations in Ra, Th, and K appear to be controlled mainly by heterogeneities inherited from the parent granitic rock, which contains abundant dikes and inclusions. U in soil and parent rock is concentrated in primary minerals (mainly zircon and sphene), and in secondary sites that are of greater importance for Rn emanation. The main U-bearing secondary sites are weathered sphene, grain boundary coatings, weathered biotite and plagioclase, as well as dense Fe-rich coatings and a REE-phosphate mineral present in near-vertical fracture zones in saprolite underlying shallow loam. Elevated U in these sites generally correlates with high Ti, Al, Fe, and/or P. Preferential distribution of U and Ra on grain boundaries and porous weathered minerals is reflected in relatively high Rn emanation rates in the soil. Highest emanation occurs between 1.3 and 2.3 m depth, where fine pedogenic phasesgibbsite and amorphous silica and Fe-OOH—are most abundant; it is related to fixation of Ra by these phases, which precipitate close to the surface and accumulate at these depths by illuviation. Separation of Ra from U may occur locally, given remobilization of U-series elements from secondary sites, and large differences between Ra and U sorption capabilities of several phases present in the soil. Concentration of U along permeable fracture zones in saprolite suggests that contribution of soil-gas Rn from depth (> 2 m) could be significant to Rn availability near the surface.     

Theory of alpha recoil effects on radon release and isotopic disequilibrium

Using the present understanding of the mechanisms of release from rocks and soils of recoiling products of alpha emission, physical predictions can be made of the fraction of these nuclei that are directly freed and the fraction that can subsequently be freed by the action of water. The fractions depend on the size and nature of the grains in which the recoiling nuclei originate, the size and shape of the pore spaces, the nature of the surrounding grains, the decay lifetime of the recoiling nuclei, and the time sequence of the presence of water. For simplified assumptions quantitative predictions are made of Rn emanation rates and of isotopic disequilibrium.     

Seasonal variations in soil radon emanation: long-term continuous monitoring in light of seismicity

Soil gas radon release patterns have been monitored continuously for more than 3 years in the Eastern Mediterranean Province (EMP) (Southern Turkey), alongside regional seismic events, providing a multidisciplinary approach. In the period from January 2008 to January 2011, 14 earthquakes M _L ≥4 occurred in the study area. By monitoring the sites for more than 3 years, the site-characteristic patterns of soil radon emanation of each site have become evident. Radon emanation data show seasonal (semi-annual) variation characteristics; high soil radon values are between May and October and low soil radon values are between November and April. With available rainfall data, the soil gas radon data can be more reliably evaluated. It is shown in this paper that if radon emanation data are available over sufficiently long periods of time and baseline data (and their seasonal variations) are known with certainty for each monitoring site, then the observation of positive anomalies might provide a correlation or connection to seismic activity.     

Upgrading of high moisture content lignite

Summary Removal of inherent moisture from run-of-mine lignite was tested by lock-feeding the lignite, which was previously sized by screening into 25 kg autoclaves. High pressure, up to 4.053 MPa (588 psi), saturated steam was then introduced into the pressure reactor. Reaction time, pressure, temperature and depressurization rates were strictly controlled for each reactor test run. Results indicate that about 80% of lignite total moisture was removed, including some of the inherent moisture, yielding a nonoxidized, and thus stable, lignite product. Some reduction of noncombustible portions of the lignite also took place. The conclusion reached as a result of the tests is that the steam-drying process can be successfully applied to reducing moisture in lignite, and may be considered for additional studies on acceleration of the coalification process.     

Predicting moisture content of soil from thermal properties using artificial neural network

Monitoring of soil moisture contents is an important practice for irrigation water management. The benefit of periodic soil water content data includes improved irrigation scheduling in order to optimize water usage for improved crop productivity. However, the in situ equipment for measuring soil water contents have high maintenance and operation cost and are highly affected by neighboring soil conditions, and some have overwhelming calibration and data interpretation, whereas the common standard laboratory procedure requires much effort and can be time-consuming for large dataset. The objective of this study is to evaluate the applicability of artificial neural network (ANN) to predict moisture content of soil using available or measured thermal properties (thermal conductivity, thermal diffusivity, specific heat, and temperature) of soil. We used both multilayered perception (MLP) and radial basis function (RBF) types of ANN. The study area is a farmland situated within the premises of the University of Ibadan campus. Thermal properties were measured with KD2 Pro at 42 points along seven transects. Soil samples were also collected at these points to determine their moisture contents in the laboratory. ANN analysis carried out effectively predicted the soil moisture content with very low root-mean-square error (RMSE) and high correlation coefficient (R) of approximately 0.9 for the two methods evaluated. The overall results suggest that ANN can be incorporated to predict the moisture content of soil in this area where thermal properties are known.     

Reconnaissance soil-gas radon survey over the faulted crystalline area of Ile-Ife, Nigeria

Tropical rain forest areas are well known for problems with geological mapping because of the dense vegetation and thick overburden. The application of soil-gas radon measurements was carried out over known and suspected fault zones in the basement terrains of Ile-Ife, southwestern Nigeria. Radon concentration in the area ranged from 25.6 to 6,227.8 pCi/l, with distinct contrasts and overlap in concentrations among soil groups derived from various rock types. Radon concentrations in the soil exhibit a strong dependence on the local geology and reflect the bedrock geochemistry. Relatively high radon soil-gas concentrations of between 4,000 and 6,227.8 pCi/l were found directly on the axis of the known and suspected strike slip faults. The use of the radon-222 technique confirms its application as a useful tool in geological and structural mapping in basement terrains largely covered by relatively thick overburdens.     

Influence of soil moisture content on surface albedo and soil thermal parameters at a tropical station

Half hourly data of soil moisture content, soil temperature, solar irradiance, and reflectance are measured during April 2010 to March 2011 at a tropical station, viz., Astronomical Observatory, Thiruvananthapuram, Kerala, India (76°59’E longitude and 8°29’N latitude). The monthly, seasonal and seasonal mean diurnal variation of soil moisture content is analyzed in detail and is correlated with the rainfall measured at the same site during the period of study. The large variability in the soil moisture content is attributed to the rainfall during all the seasons and also to the evaporation/movement of water to deeper layers. The relationship of surface albedo on soil moisture content on different time scales are studied and the influence of solar elevation angle and cloud cover are also investigated. Surface albedo is found to fall exponentially with increase in soil moisture content. Soil thermal diffusivity and soil thermal conductivity are also estimated from the subsoil temperature profile. Log normal dependence of thermal diffusivity and power law dependence of thermal conductivity on soil moisture content are confirmed.     

Influence of radon on the acidification of atmospheric precipitation

Mechanisms of the acidification of precipitation at the expense of radiochemical effects were considered. The results of natural measurements of physicochemical and metrological parameters (pH, T, and radiation background) of atmospheric precipitation (rain and snow) are reported. The possible influence of radon radioactivity (decay energy) on physicochemical processes in the atmosphere was analyzed. A hypothesis was proposed on the mechanism of this process.     

Relationships between radium and radon occurrence and hydrochemistry in fresh groundwater from fractured crystalline rocks, North Carolina (USA)

Naturally-occurring radionuclides (uranium, radium, and radon), major dissolved constituents, and trace elements were investigated in fresh groundwater in 117 wells in fractured crystalline rocks from the Piedmont region (North Carolina, USA). Chemical variations show a general transition between two water types: (1) slightly acidic (pH 5.0–6.0), oxic, low-total dissolved solids (TDS) waters, and (2) near neutral, oxic to anoxic, higher-TDS waters. The uranium, radium, and radon levels in groundwater associated with granite (Rolesville Granite) are systematically higher than other rock types (gneiss, metasedimentary, and metavolcanic rocks). Water chemistry plays a secondary role on radium and radon distributions as the ²²²Rn/²²⁶Ra activity ratio is correlated with redox-sensitive solutes such as dissolved oxygen and Mn concentrations, as well as overall dissolved solids content including major divalent cations and Ba. Since ²²⁴Ra/²²⁸Ra activity ratios in groundwater are close to 1, we suggest that mobilization of Ra and Rn is controlled by alpha recoil processes from parent nuclides on fracture surfaces, ruling out Ra sources from mineral dissolution or significant long-distance Ra transport. Alpha recoil is balanced by Ra adsorption that is influenced by redox conditions and/or ion concentrations, resulting in an approximately one order of magnitude decrease (~ 20,000 to ~ 2000) in the apparent Ra distribution coefficient between oxygen-saturated and anoxic conditions and also across the range of dissolved ion concentrations (up to ~ 7 mM). Thus, the U and Th content of rocks is the primary control on observed Ra and Rn activities in groundwater in fractured crystalline rocks, and in addition, linked dissolved solids concentrations and redox conditions impart a secondary control.     

Determination of hydrogen content in geological samples using elastic recoil detection analysis (ERDA)

The present study illustrates the interest of using the elastic recoil detection analysis (ERDA) method to characterize any geological sample matrix with respect to hydrogen. ERDA is combined with Rutherford back scattering (RBS) and particle induced X-ray emission (PIXE), allowing the simultaneous characterization of the matrix with respect to major and trace elements (Z > 15). Analyses are performed by mapping of a 4 × 16 μm² incident beam of ⁴He⁺ on large areas (50 × 200 μm²). The method is almost not destructive and requires no calibration with respect to well known hydrous samples. Hydrous and nominally anhydrous phases in contact with each other in the same sample may both be characterized. The depth of the analyses is limited to several μm beneath the surface, allowing tiny samples to be investigated, provided their sizes are larger than the incident beam. Our setup has been improved in order to allow H determination on a micrometric scale with a 5-15% relative uncertainty and a detection limit of 94 wt ppm H₂O. We present multi-elemental mappings on a large panel of samples: (1) natural and analogue synthetic glasses from Stromboli volcano (0.44-4.59 wt% H₂O), natural rhyolitic glasses (1466-1616 wt ppm H₂O); (2) magmatic rhyolitic melt inclusions from Guadeloupe Island (4.37-5.47 wt% H₂O) and their quartz host crystal (2020 ± 230 wt ppm H₂O); (3) nominally anhydrous natural (82-260 wt ppm H₂O) and experimentally hydrated (240-790 wt ppm H₂O) olivines; natural clinopyroxenes (159-716 wt ppm H₂O); natural orthopyroxenes (201-452 wt ppm H₂O); a natural garnet (90 wt ppm H₂O). Results show that ERDA is a strong and accurate reference method that can be used to characterize geological sample from various matrix compositions from high to low water contents. It can be used to calibrate other methods of microanalysis such as Fourier Transform Infrared Spectroscopy (FTIR) or secondary ion mass spectrometry (SIMS).     

Relation between "terra rossa" from the Apulia aquifer of Italy and the radon content of groundwater: Experimental results and their applicability to radon occurrence in the aquifer

 The radon-222 (²²²Rn) activity in groundwater of the Apulian karstic aquifer in southern Italy is as great as 500 Becquerel per liter (Bq/L) locally. Normal radium-226 (²²⁶Ra) activity in the limestone and calcareous dolomites of the aquifer is not enough to explain such a high level. Laboratory investigations identified high ²²⁶Ra activity in the "terra rossa," the residuum occupying fissures and cavities in the bedrock, and also the relation between (1) ²²⁶Ra-bearing bedrock and "terra rossa" and (2) ²²²Rn in water. The "terra rossa" is the primary source of the radon in the groundwater. The experimental results show the need to characterize the "terra rossa" of Apulia on the basis of ²²⁶Ra activity and also to study the distribution and variations in ²²²Rn activity over time in the aquifer. Received, January 1996 · Revised, March 1997, September 1997, June 1998 · Accepted, July 1998     

Study of radium content and radon exhalation rates in soil samples of northern India

Radon is a radioactive hazardous and ubiquitous gas. It has been recognized to be one of the major contributors to natural radiation even causing lung cancer if present at enhanced levels. There are large variations in data available in the literature for radium content and radon exhalation rates of various materials. It is a well-documented fact that radon exhalation from the ground surface depends upon a number of parameters such as soil grain size, soil porosity and radium content. For this purpose, in this study the so-called can technique has been used to measure radium content and exhalation rates of radon in soil samples collected from different places of Aligarh, Etah and Mathura districts of Uttar Pradesh??a province in northern India. These districts lie within the subtropical region of the Indo-Gangetic plains. The values of effective radium content are found to vary from 8.11 to 112.83?Bq?kg^?1 with a mean value of 33.21?Bq?kg^?1 and a standard deviation of 28.15. The values of mass exhalation rates of radon vary from 0.76?×?10^?6 to 15.80?×?10^?6?Bq?kg^?1?day^?1 with a mean value of 4.21?×?10^?6?Bq?kg^?1?day^?1, while the surface exhalation rates vary from 1.97?×?10^?5 to 41.03?×?10^?5?Bq?m^?2?day^?1 with a mean value of 10.93?×?10^?5?Bq?m^?2?day^?1.     

膨胀土壤标准吸湿含水率及其试验方法

提出了土壤标准吸湿含水率的概念，说明了其物理意义，并给出了试验标准。通过试验结果可以看出，土壤标准吸湿含水率与膨胀土的蒙脱石含量、阳离子交换量、比表面积之间是线性相关的，反映了膨胀土的本质属性。土壤标准吸湿含水率不仅在膨胀土的分类中，而且在细粒材料的表面物理性质方面具有很大的应用前景。     

Mineralogy of poorly crystalline aluminium phases in the B horizon of Podzols in southern Sweden

Poorly crystalline Al components of the clay fraction are often neglected in soil mineralogical studies. In this study 7 B horizons from podzolised soils in Sweden were analysed using a combination of infrared (IR) spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and selective extractions. It was found that most Bhs and Bs horizons contained allophane, imogolite and more or less hydroxy-interlayered vermiculite. Some Bhs and Bs horizons also contained small amounts of kaolinite and/or gibbsite. In one acid Bh horizon organically complexed Al was the only reactive Al fraction of importance. The vertical patterns of vermiculite and allophane/imogolite suggested that both had formed during the podzolisation process, but due to different mechanisms. The pattern of kaolinite and gibbsite occurrences indicated that these minerals were mostly inherited from the parent material. Oxalate and pyrophosphate extractions suggested that allophane and imogolite constituted the most important reactive inorganic Al fraction in the soils. This shows that allophane and imogolite seem to be the typical, rather than the occasional, reactive inorganic Al phases that form in the B horizon as a result of podzolisation.     

昔格达土混合填料最优含水量研究

昔格达地层的沉积地质历史环境决定了昔格达地层的多旋回性及其泥岩的近饱和特性。因此昔格达土填料作为一种混合填料，具有与其它一般单一岩土填料不一样的工程特征。随着混合填料中各组分的变化，尤其是粘粒百分含量的变化，其含水量也将发生变化，对直接填料最优含水量的确定带来困难。而最优含水量的确定，既是路、坝基填方工程选料的需要，也是工程施工质量检验的需要。因此，填料最优含水量的研究具有一定的工程意义和实践价值。文章运用工程地质反分析的方法，从昔格达土的物理性质着手，通过对昔格达土混合填料工程力学性质特性与其含水量的关系的研究，发现昔格达土混合填料的最大干密度Pdmax、压实度及力学强度(c、Ф)值与含水量之间具有较好的相关性。从而得到了昔格达混合填料的最优含水量，并且这个最优含水量与随机混合的昔格达土填料的天然含水量较为接近。由此得出具有稳定混合比的天然昔格达土混合填料适于用作路、坝基填料的结论。并为工程选料和施工质量检验提供了参考依据。