M. Monnin

Radon in soil-air and in groundwater related to major geophysical events: A survey

Abstract The various technical aspects of radon concentration measurements in the ground or in the groundwater are reviewed. The emphasis is put on the most convenient techniques particularly suited for in situ monitoring in the field. Some attention is paid to the thoron problem. Historical and most recent findings in the field of earthquake related radon anomalies are presented and briefly discussed. A similar approach is made to rarer volcanic cases that have been documented up to now. A short discussion regarding the various models that intend to provide satisfactory explanations is presented, supported, whenever it is possible, by experimental laboratory results. Finally a glimpse on the possible and future application of the method to hydrogeology is given.

Soil radon time series: Surveys in seismic and volcanic areas

Abstract Soil radon surveys have been performed in a long term monitoring basis with SSNTD (LR 115 type II), in order to observe possible fluctuations due to high magnitude seismic events and volcanic eruptions. Five-year radon time series are available in stations located in an intense seismic zone located along the Pacific coast of Mexico. The series analyses have been performed as a function of the local seismicity and geological characteristics. A discussion is intended to explain the lack of biunivocal relation between single radon peaks and earthquakes for the long term monitoring data using SSNTDs. Examples of short term radon anomalies obtained with continuous probes are also discussed as a function of local earthquakes and meteorological perturbations. Additionally, complementary results from recent changes in the activity pattern of an active volcano indicate that degassing process induced anomalous soil radon emanation correlated with the volcanic activity changes.

Short and long term radon in soil monitoring for geophysical purposes

Abstract The subduction of the Cocos Plate under the North America Plate defines a high risk seismic zone along the Pacific coast of Mexico. A seismic gap has been identified at the Guerrero State as a place where a large earthquake, up to MS=8.2, can occur within the next years. In this area an in-soil radon network, consisting of fixed SSNTD monitoring stations, has been operated during several years on a monthly exposure basis. A continuous radon probe that registers data on a short term basis is also operating since recently. The results of the two radon detection systems are compared and discussed as a function of the local seismic activity observed at the Guerrero coastal zone.

Variations of radon in soils induced by external factors

Experiments were designed to evaluate, in a controlled way, some of the variations that can be expected in radon concentration in soil due mainly to meteorological factors and to close spacing monitoring in the field. Electronic continuous radon monitoring and the track-etch method were used to record the radon α-decay. The radon emanation in daily measurements and in long term surveys showed a general effect modulated by temperature and pressure variations. Radon monitoring in soil for nearby stations showed that a 10% range of variation can be expected with the track-etch method and as a result of non-homogeneous emanation pattern of the soil.

Methods of automatic scanning of SSNTDs

Abstract The methods of automatic scanning of solid state nuclear track detectors are reviewed. The paper deals with transmission of light, charged particles, chemicals and electrical current through conventionally etched detectors. Special attention is given to the jumping spark technique and breakdown counters. Eventually optical automatic devices are examined.

Research on variation of radon and gamma-background as a prediction of earthquakes in the Caucasus

For prediction of earthquakes in the Caucasus, a network of measurement sites for radon and gamma-background is established. The sites are established in the galleries of Krasnodar and Stavropol regions. The setups of measuring gamma-background and Rn in the soil air were built in galleries near settlement Kholmsky. The detector of Rn in soil operates in the gallery near Pyatigorsk. Gamma-setup is being mounted. Moreover, solid state nuclear track detectors (SSNTD) are operating in several points, including a mud volcano. They are exchanged every month. The preliminary data show correspondences between background radiation levels, and seismic and atmospheric phenomena.

Radon-in-soil variations related to volcanic activity

Two active volcanoes, the Popocatepetl in Mexico, and the Piton de la Fournaise on the island of La Reunion, France, have been monitored for soil radon for several years. The Popocatepetl, located 60 km from Mexico City, started an eruptive period in December, 1994. Two radon-in-soil monitoring stations are operated there, since 1993. The behaviour of soil radon showed an increase as a function of the eruptive phase. The Piton de la Fournaise volcano has also been under survey for several years. A radon network based on 20 Clipperton II automatic probes was set on July, 1994. Since then, the volcano has entered a quiescence phase. Thus it has been possible to draw the pattern of the radon behavior under the influence of atmospheric conditions.

Volcanic monitoring for radon and chemical species in the soil and in spring water samples

Abstract Soil radon has been monitored at two fixed stations in the northern flank of Popocatepetl Volcano, a high risk volcano located 60 km SE from Mexico City. Water samples from three springs were also studied for radon as well as major and trace elements. Radon in the soil was recorded using track detectors. Radon in the water samples was evaluated using the liquid scintillation method and an Alphaguard. The major elements were determined through conventional chemical methods and trace elements using an ICP-MS equipment. Soil radon levels were low, indicating a moderate diffuse degassing through the flanks of the volcano. Groundwater radon had almost no relation with the eruptive stages. Water chemistry was stable in the reported time (2000–2002).

Physical models related to radon emission in connection with dynamic manifestations in the upper terrestrial crust: A review

Abstract Radon emissions that are enhanced by forthcoming geophysical events as earthquakes or volcanic activity have been observed all over the World. Many of these observations have been carried out with equipments using Solid State Nuclear Tracks Detectors as sensors. However, such radon “anomalies” are not one-to-one events and the technique has not yet reached the necessary level of confidence. In the mean time, the data collected by scientists are casting some light on the involved phenomena. Radon emissions are now recognized as a rather complicated set of successive steps involving many aspects of geophysics and chemistry. Several models have been proposed as an explanation of the experimental field data. They are reviewed in this paper; ranging from radon outgassing related to fumaroles to radon emission related to the particular behaviour of aquifers in volcanic areas.

Visualization of latent damage trails

Abstract The article starts with a very brief summary on the nature of the latent track in organic and inorganic detectors. The first real part deals with the chemical etching technique. The possible mechanisms involved in the track revealing processes are shortly described. Emphasis is then put on the technology of track etching. A very general procedure is described. Starting from this basis a study of each step is undertaken: conception and description of various etching baths, nature of the etchant according to the detector structure, influence of the etching parameters such as concentration, temperature, time, stirring, influence of interruptions in the process and of the reaction products. Typical examples are given. The sensitivity of the detectors depending on the etching technique is examined. Peculiar methods such as TINT, TINCLE, perforated detectors, multilayer detectors and thin foil techniques are described. One then makes an approach of the electrochemical etching under a very similar scheme: equipment, influence of the electrical field characteristics, nature and concentration of etchant, sensitivity. The second part of the paper deals with the so-called decoration techniques, namely, silver chloride crystals, fluorescent and/ or dyed detectors, silver precipitation in glasses. The latter is just mentioned whereas the two former techniques are described in more detail: the working principles are explained from the theoretical point of view, the technological behaviour and properties of those detectors are described together with their possible applications. The use of “mixed techniques” forms the conclusion of the part on track revealing. The last part of the text is devoted to the observation techniques of revealed tracks. All the detectors can be viewed under an optical microscope. The microscopy technique relevant to SSTND observations is described: light and dark field illumination, transmitted and reflected light, contrast enhancement techniques, special devices, etc. Eventually, the use of the transmission and stereo electron microscopes is considered and the specific fields of application of these techniques are reviewed.