Measurement And Analysis Of Natural Radioactive Elements Ra-226and Rn-222in Thermal Groundwater

Radioactive elements226Ra and222Rn, which are part of the decay products of234U decay series, are now found to be abundant in natural species, and they have good effect on human health. Excessive226Ra and222Rn and their daughter can cause increasing incidence of lung cancer and endanger human body health. With the development and utilization of the underground hot water resources, the content of226Ra,222Rn radioactive elements and their features in water has also been gradually concerned by people.The method of emanation-flicker according to national standard is used to measure the content of natural radioactive elements226Ra and222Rn in thermal groundwater in this paper. The related parameters which are required for the measuring instruments and methods are also discussed to determine the optimal working state of instrument and measuring minimum error method, and to ensure the accuracy of test results.Strata of Archaean, mesoproterozoic erathem, Permian System, Jurassic systerm, cretaceous system and Neogene System are widely distributed in the Yanshan area in the northern part of North China. The fault zone of east-west and nearly east-west area are cut by the north-east and nearly north-east fault zone which is formed in the late, the tectonic fracture developed and the geological structure are complex. The groundwater mainly occurs in the metamorphic volcanic rock and clastic rock fissure water aquifer rock group, and the main recharge sources is meteoric waters. Thermal groundwater mostly occurs in fault belts or near magmatic rock, exposes as hot springs.Several springs (Baimiao spring, Chicheng spring, Tangzimiao spring, Zaoxitang spring, Dongyaotou spring in Zhangjiakou; Hongtangsi spring, Sandaoying spring, Shanwanzi spring, Qijia spring in Chengde; Zhangzi spring in Qinghuangdao; Songshan spring and Songshan artesian well in Beijing) which are mineralization type of hot water with good water quality are chosen to tested. The measured temperature range is40-80℃, and the salinity is between300-1300mg/L. All the springs’ pH are greater than8, belongs to alkaline water. The hydrochemical type is mainly of Na-SO4type and Na-SO4·HCO3type. F-content is between1.58to26.5mg/L, metasilicic acid content is31.1to96.3mg/L.The226Ra contents in13samples range from0.034to0.034Bq/L,222Rn contents, from3.62to131.1Bq/L. The226Ra,222Rn contents in the hot groundwater are related to hydrodynamic conditions. When the flow rate is large, the226Ra content is very low while the222Rn content is high. On the other hand, when the flow is small, the contents of226Ra are higher. The226Ra content is low when the hot groundwater temperature is high. On the contrary, when the temperature is low, the content of226Ra in water is high. The content of226Ra in water is low when the sum of saturation index of calcite and barite converges to zero. On the contrary, the content of226Ra in water is high. All water samples of thermal groundwater age are estimated within100years with the method of radium-radon measurement.