報告書番号

U95039

タイトル（和文）

天燃溶存希ガスを用いた地下水調査法の提案（その２）－水中のトラック法を用いた溶存ラドン測定による地下水流れの検出－

タイトル（英文）

DEVELOPMENT OF GROUNDWATER TRACING TECHNIGUEUSING NATURAL DISSOLVED NOBLE GASES (PART2). DETECTION OF FLWING SECTIONS OF GROUNDWATER BY MEASURING DISSOLVED RADOM USING AQUATIC ALPHA TRACK METHOD

概要 （図表や脚注は「報告書全文」に掲載しております）

大型地下構造物の建設に当たっては，事前に地下水への影響を評価する必要がある。その際，対象が岩盤の場合，地下水流れの評価は，岩盤地下水を対象として行うこととなる。例えば，対象岩盤が結晶質岩の場合には，割れ目を通した地下水となり，割れ目モデルによる解析評価が必要となる。現状では，各々の割れ目ごとに透水性について情報を得ることは難しく，原位置測定による透水係数と割れ目の統計データを基にした割れ目モデルによる解析しかできない状況にある。ここで提案する溶存ラドンを活用する手法では，微小区間においてラドン濃度を測定することが可能なために，個々の割れ目ごとに地下水の流動性を観測できる。このために，地下水流動評価に直接考慮しなければならない割れ目とそうでない割れ目とを区別しモデルの構築を可能とする計測法の有効性が確認された。

概要 （英文）

DISSOLVED RADON IN GROUNDWATER IA S GOOD TRACER TO TRACK MOVEMENT OF WATER IN A STRATUM. RADON LOGGING IS A VERY USEFUL TECHNIQUE FOR DETECTION OF GROUNDWATER MOVING IN A BOREHOLE. THIS USUALLY REQUIRES PROMPT MEASUREMENT OF RADON CONCENTRATION BECAUSE ALL ISOTOPES OF RADON HAVE SHORT HALF-LIVES. HOWEVER,PROMPT MEASUREMENT IS VERY DIFFICULT IN THE FILD BECOAUSE DISSOLVED RADON IN GROUNDWATER MUSTBE EXTRACTED INTO AN ORGANIC SOLVENT FOR RADIOACTIVE COUNTING AFTER SAMPLING. IN THIS STUDY,IN-SITU MEASUREMENT OF RADON WAS DEVELOPED WITHOUT SAMPLING GROUNDWATER. THE IN-SITU METHOD USES AN ALPHA-TRACK METHOD,WHICH IS COMMONLY USED TO MEASURE RADON CONCENTRATION IN THE AIR,TO MEASURE RADON DISSOLVED IN GROUNDWATER. SINCE ALPHA PARTICLES HAVE A VERY SHORT RANGE OF A FEW TENS OF MICROMETERS IN THE METHOD IS NOT USUALLY USED TO MEASUREG DISSOLVED RADON CONCENTRATIONS. MOREOVER,THERE HAVE NOT BEEN SOLID DETECTORS FOR ALPHA TRACKING IN WATER. HOWEVER,IF AN ALPHA-TRACK DETECTOR CAN BE PRODUCED TO MEASURE DISSOLVED RADON IN WATER,THE SHORT RANGE OF RADON IN WATER WILL BE A MERIT FOR TRACING GROUNDWATER MOVEMENT BECAUSE RADON DISSOLVED IN WATER CANNOT MAKE TRACKS ON THE SURFACE OF A SOLID DETECTOR WITHOUT RADON DIRECTLY TOUCHING THE DETECTOR. FURTHERMORE,THIS NEW ALPHA TRACK METHOD DOSE NOT REQUIRE PROMPT MEASUREMENT,BECAUSE RADON CONCENTRATION IS GIVEN AS THE INTEGRATED NUMBERS OF TRACKS WHILE SOLID DETECTORS ARE EXPOSED IN THE WATER. IN FACT,THE IN-SITU ALPHA-TRACK METHOD IN WATER CAN PROBABLY REVEAL WHETHER INDIVIDUAL CRACKS ARE PERMEABLE OR IMPERMEABLE IN GROUNDWATER SURVEYS OF CRYSTALLINEROCK. THE RESULTS OF ALPHA TRACK ARE CONSISTENT WITH A SERIES OF CRACKMAPPINGS,HYDRAULIC CONDUCTIVITY TESTS AND HYDRAULIC POTENTIAL MEASUREMENTS IN A SHOLLOW GROUNDWATER ZONE. BUT IN THE DEEP ZONE (

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