Radon emanation of heterogeneous basin deposits in Kathmandu Valley,Nepal |
| |
| Authors: | Frédéric Girault Ananta Prasad Gajurel Frédéric Perrier Bishal Nath Upreti Patrick Richon |
| |
| Institution: | 1. Equipe de Géomagnétisme, Institut de Physique du Globe de Paris, UMR-7154 and Université Paris-Diderot, 1 rue Jussieu, F-75238 Paris Cedex 05, France;2. Department of Geology, Tri-Chandra Campus, Tribhuvan University, Ghantaghar, Kathmandu, Nepal;3. CEA, DAM, DIF, F-91297 Arpajon, France;4. Equipe de Géologie des Systèmes Volcaniques, Institut de Physique du Globe de Paris, UMR-7154, 1 rue Jussieu, F-75238 Paris Cedex 05, France;1. Division of Earth and Environmental Sciences, Korea Basic Science Institute (KBSI), Cheongju 28119, Republic of Korea;2. Department of Earth System Sciences, Yonsei University, Seoul 03722, Republic of Korea;3. Korea Institute of Nuclear Safety (KINS), Daejeon 34142, Republic of Korea;1. Helmholtz Centre Potsdam, German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany;2. Museum für Naturkunde, Leibniz-Institut Biodiversität- und Evolutionsforschung, Invalidenstrasse 43, 10115 Berlin, Germany;1. School of Physics, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia;2. Department of Environment, College of Science, Kufa University, Iraq;1. Low Level Radioactivity Laboratory, Institute of Nature and Environmental Technology, Kanazawa University, Nomi, Ishikawa 923-1224, Japan;2. National Research Institute of Fisheries Science, Fisheries Research Agency, Fukuura, Kanazawa, Yokohama 236-8648, Japan;3. Japan Marine Science Foundation, Minato, Mutsu, Aomori 035-0064, Japan;4. Institute of Medical, Pharmaceutical and Health Sciences, Kanazawa University, Kakuma, Kanazawa 920-1192, Japan;5. Marine Ecology Research Institute, Yamabuki, Shinjuku, Tokyo 162-0801, Japan;6. Graduate School of Fisheries Sciences, Hokkaido University, Minato-cho, Hakodate 041-8611, Japan |
| |
| Abstract: | Effective radium-226 concentration (ECRa) has been measured in soil samples from seven horizontal and vertical profiles of terrace scarps in the northern part of Kathmandu Valley, Nepal. The samples belong to the Thimi, Gokarna, and Tokha Formations, dated from 50 to 14 ky BP, and represent a diverse fluvio-deltaic sedimentary facies mainly consisting of gravelly to coarse sands, black, orange and brown clays. ECRa was measured in the laboratory by radon-222 emanation. The samples (n = 177) are placed in air-tight glass containers, from which, after an accumulation time varying from 3 to 18 days, the concentration of radon-222, radioactive decay product of radium-226 and radioactive gas with a half-life of 3.8 days, is measured using scintillation flasks. The ECRa values from the seven different profiles of the terrace deposits vary from 0.4 to 43 Bq kg?1, with profile averages ranging from 12 ± 1 to 27 ± 2 Bq kg?1. The values have a remarkable consistency along a particular horizon of sediment layers, clearly demonstrating that these values can be used for long distance correlations of the sediment horizons. Widely separated sediment profiles, representing similar stratigraphic positions, exhibit consistent ECRa values in corresponding stratigraphic sediment layers. ECRa measurements therefore appear particularly useful for lithologic and stratigraphic discriminations. For comparison, ECRa values of soils from different localities having various sources of origin were also obtained: 9.2 ± 0.4 Bq kg?1 in soils of Syabru–Bensi (Central Nepal), 23 ± 1 Bq kg?1 in red residual soils of the Bhattar-Trisuli Bazar terrace (North of Kathmandu), 17.1 ± 0.3 Bq kg?1 in red residual soils of terrace of Kalikasthan (North of Trisuli Bazar) and 10 ± 1 Bq kg?1 in red residual soils of a site near Nagarkot (East of Kathmandu). The knowledge of ECRa values for these various soils is important for modelling radon exhalation at the ground surface, in particular in the vicinity of active faults. Importantly, the study also reveals that, above numerous sediments of Kathmandu Valley, radon concentration in dwellings can potentially exceed the level of 300 Bq m?3 for residential areas; a fact that should be seriously taken into account by the governmental and non-governmental agencies as well as building authorities. |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
