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| Titel |
Radon emanation of rock and soil samples: A tool for stratigraphy, geology, geophysical modelling and radon health hazard |
| VerfasserIn |
Frédéric Girault, Bharat P. Koirala, Mukunda Bhattarai, Sudhir Rajaure, Patrick Richon, Frédéric Perrier |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250035624
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| Zusammenfassung |
| Radium-226, the mother of radon-222, with a half-life of 1600 years, is intrinsically present
in all the rocks and soils in variable amount. However, a small part only of the radium atoms
is able to produce radon atoms in the porous media of the rock allowing this radon to escape
the rock media through the pore space. This fraction of radium is referred to as the radon
source term in rocks or soils, and is usually called the effective radium concentration (ECRa).
This parameter is expressed in Bq kg-1, where CRa is the radium-226 concentration and E
the emanation coefficient. Considering a sample, it is not possible to estimate its ECRa
value a priori. Therefore, this parameter has to be measured in the laboratory. The
method in the laboratory to obtain ECRa values is based on the measurement of the
concentration of radon in the inner air of a hermetically sealed container in which
one rock or one soil sample was previously placed. In order to measure this radon
concentration, Lucas scintillation flasks were used, and their radon content counted by a
photomultiplier (Stoulos et al., Journal of Environmental Radioactivity, 2003). This
method was compared in detail with another method using SSNTD (Solid-State
Nuclear Track Detector). Detailed investigations have been carried out, including
systematic effects such as the shape or volume of container, mass and preparation
method of the sample, using a large number of rock, soil and building material
samples (more than 800) collected in France and Nepal. Preliminary results will be
given based on this data set. With such a large sample, some effects of intrinsic
and external factors on the measurement technique and on the obtained results
could also be accurately studied: the effect of atmospheric pressure, of the ambient
temperature, or of the water content of the sample. ECRa measurements appear
to be particularly useful for human health hazards study on a considered natural
site, as well as for other applications. Indeed, some studies were performed in an
overpopulated area, more precisely in the Kathmandu Basin, Nepal, where sediments from
several terraces and scarps were sampled and analysed. In addition, ECRa values
exhibit characteristic patterns, and therefore can be used for stratigraphy studies.
Similarly, this parameter could be relevant in geological mapping, especially where it
is not particularly easy to discriminate the diverse encountered layers, as in the
Main Central Thrust (MCT) Zone of the Himalayan range. The measurement of
effective radium concentration is also important to assess health hazard, and for
detailed modelling of radon flux from the soil. Examples of such modelling will
be given in the case of the high radon flux observed in geothermal areas of the
Nepal Himalayas (Perrier et al., Earth and Planetary Science Letters, 2009; Girault
et al., Journal of Environmental Radioactivity, 2009). Thus, these various results
illustrate that it is useful to develop the knowledge of effective radium concentration in
different natural and artificial media, both for practical and fundamental problems. |
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