ポリエチレン保存容器から大気への拡散を考慮した水中ラドン濃度推定法の開発  [in Japanese] Development of Estimation Method of <sup>222</sup>Rn Level in Water Considering Its Diffusion from Polyethylene Bottle to Atmosphere  [in Japanese]

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Author(s)

    • 川端 訓代 KAWABATA Kuniyo
    • 鹿児島大学総合教育機構アドミッションセンター|鹿児島大学大学院理工学研究科 Admission Center, Institute for Comprehensive Education, Kagoshima University|Graduate School of Science and Engineering, Kagoshima University

Abstract

<p>岩石から放出されるラドンは水に対する溶解度が高く,地殻内では流体とともに移動する.ラドンの放出量は岩石の亀裂や流体と岩石の接触比に比例して増減するため,亀裂発生や歪状態の変化など地殻内情報を得るために地下水中のラドン濃度が測定されている.水中ラドンは,採取後に壊変に加え大気への拡散によって減少し続けるため採取地にて測定が行われてきた.本実験では水中ラドン濃度測定を実験室で行うため,ポリエチレン保存容器内から大気へ放出するラドンの拡散係数を求め採取時の水中ラドン濃度の推定を試みた.鹿児島県桜島の三つの温泉水を試料とし,保存容器内の水中ラドン濃度の時間変化から拡散係数を推定した.その結果,1.6〜2.4 × 10<sup>−11</sup> m<sup>2</sup>s<sup>−1</sup>(平均: 1.90 × 10<sup>−11</sup> m<sup>2</sup>s<sup>−1</sup>)の拡散係数が得られた.これらの値は既往研究におけるポリエチレン素材フィルムを透過する際のラドンの拡散係数と似た値を示しており妥当な値を得たと考えられる.本研究で提示した式は,推定値の誤差を小さくするためラドンの半減期以内に測定を行うことが必要となる.推定値誤差として,推定値残差が測定値幅を上回ることから,本実験で得た予測式を用いる場合,最大推定値残差(約20%)を付することが適切である.</p>

<p><sup>222</sup>Rn is a radioactive noble gas that occurs naturally in Earth's crust as an intermediate step in the normal radioactive decay chain of uranium series. A high concentration of radon exposure in air and water causes damage to human cells, therefore the radon concentration in buildings and the diffusive coefficient of shield films have been studied. On the other hand, Radon shows a high solubility for water, and thus a high mobility through groundwater in Earth's crust. The concentration of radon in crustal fluid and groundwater can provide a clue to understand the state of crustal deformation as crack formation and change in the strain state, because its release rate depends mainly on the rock surface area. The radon concentration in groundwater is usually measured on the sampling site, due to a decrease after sampling by its continuous decay and diffusion to air. To measure the radon concentration at a laboratory, we tried to estimate a diffusion coefficient of the radon for a polyethylene bottle used for keeping water samples in this study. We collected water samples from three hot springs at Sakurajima district in Kagoshima, Japan. We estimated the diffusion coefficient by measuring the radon concentration in the water at different times after several hours of keeping. The estimated diffusion coefficients are 1.6 - 2.4 × 10<sup>−11</sup> m<sup>2</sup>s<sup>−1</sup> (averaged: 1.9 × 10<sup>−11</sup> m<sup>2</sup>s<sup>−1</sup>). The values are similar to those from an experiment using polyethylene films, suggesting that the diffusion coefficient obtained in this study is reasonable. Concerning the error on the estimated diffusion coefficient obtained here, we used maximum residual value range of the estimated value, 20 %, because the residual error on the estimated values was larger than that on the measurement.</p>

Journal

  • BUNSEKI KAGAKU

    BUNSEKI KAGAKU 68(5), 333-338, 2019

    The Japan Society for Analytical Chemistry

Codes

  • NII Article ID (NAID)
    130007662343
  • NII NACSIS-CAT ID (NCID)
    AN00222633
  • Text Lang
    JPN
  • ISSN
    0525-1931
  • NDL Article ID
    029747505
  • NDL Call No.
    Z17-9
  • Data Source
    NDL  J-STAGE 
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