イランのデホランの温浴施設での高レベルの自然電離放射線

High level of natural ionizing radiation at a thermal bath in Dehloran, Iran.

• Mohammademad Adelikhah
• Amin Shahrokhi
• Stanislaw Chalupnik
• Edit Tóth-Bodrogi
• Tibor Kovács

抄録

自然背景放射線の被曝の半分以上はラドン同位体とその崩壊生成物に由来することが証明されている。ラドンとその崩壊生成物の吸入は呼吸器系への照射を引き起こし、肺がんのリスクを増加させる。本研究では、デフローラン(イラン)にある温泉施設の入浴剤中のラドン及びトリウムの濃度を調査した。また、温泉水中の溶存Ra濃度を測定した。さらに、温泉水で灌漑された農地土壌中の豊富な自然起源放射性核種の活性濃度を測定し、他の源泉からの水で灌漑された土壌サンプルと比較することで、温泉のスタッフ,患者,観光客が被曝する自然放射線の放射線学的影響の可能性を推定した。また、土壌中の天然放射性核種の濃度と温泉水の利用との関連性を調べることも本研究の主要な目的の一つであった。土壌中の主要な3種類の天然起源放射性核種の放射能濃度を測定したところ、K, Ra, Raはそれぞれ101±8〜240±12, 276±7〜322±12, 20±7〜80±10Bq.kgであった。温泉水で灌漑された土壌サンプルでは、Ra及びRaのより高い活性濃度が記録された。すべての温泉で同じ源泉を使用しているため、異なる温泉の水サンプル中の溶存Ra濃度も0.42±0.20Bq.lと推定された。45日間（占有時間と空室時間を含む）の個人浴場の室内ラドン濃度は1880±410から2450±530 Bq.mの間で測定され、温泉ギャラリーのラドン濃度は790±135から1050±120 Bq.mの間で測定されたが、トリウム濃度は検出限界を下回っていた。調査中の温泉の換気と集中加熱システムは効率が悪いため、治療室と浴場のラドン濃度が高い。観光客とスタッフのラドン吸入に起因する最大放射線量は、それぞれ0.13mSv.yrと5.5mSv.yrと推定され、イランの国の規制値（5mSv.yr）をわずかに超えている。被ばく時間は、観光客については年間15時間、作業員については年間1468時間と推定された。

It has been proven that more than half of the exposure to natural background radiation originates from radon isotopes and their decay products. The inhalation of radon and its decay products causes the irradiation of respiratory tracts, thus increasing the risk of lung cancer. In this study, the concentrations of radon and thoron in thermal baths at a spa in Dehloran (Iran) were investigated. The concentrations of dissolved Ra in samples of water from thermal baths were also measured. Additionally, the activity concentrations of abundant naturally occurring radionuclides in farmland soils irrigated with water from hot springs was measured and compared with other soil samples irrigated with water from other sources to estimate possible radioecological effects of natural radiation staff, patients and tourists at the spa are exposed to. In addition, the search for a link between the concentration of naturally occurring radionuclides in soil and the use of water from hot springs for irrigation was one of the main goals of the study. The activity concentrations of three major naturally occurring radionuclides in soil samples were measured; the ranges for K, Ra and Ra were 101 ± 8 to 240 ± 12, 276 ± 7 to 322 ± 12 and 20 ± 7 to 80 ± 10 Bq.kg, respectively. Higher activity concentrations of Ra and Ra were recorded in soil samples irrigated with hot spring water. The water from the same spring was used in all thermal baths so concentrations of dissolved Ra in water samples from different thermal baths were approximated to also be 0.42 ± 0.20 Bq.l. The indoor radon concentrations in the private thermal baths over a period of 45 days (including both occupied and vacant time) were measured to be between 1880 ± 410 and 2450 ± 530 Bq.m and the radon concentrations in the spa galleries were measured to be between 790 ± 135 and 1050 ± 120 Bq.m, however, thoron concentrations were below the detection limit. The ventilation and centralized heating systems at the spa under investigation are inefficient so the radon concentrations in the therapy rooms and baths are high. The maximum radiation doses originating from the inhalation of radon for tourists and the staff were estimated to be 0.13 and 5.5 mSv.yr, respectively, which is slightly over the national limit in Iran (5 mSv.yr). The exposure duration was estimated 15 and 1468 h per year for visitors and workers, respectively.

© 2020 The Authors.