There are three kinds of radioactive radon gases in nature, even though the word radon(Rn) often means ~(222)Rn. The two others are thoron( ~(220)Rn) and actinon (~(219)Rn) and all of the three are decay products of the natural radioactive chains of Uranium, Thorium and Actinium. Since the half-life of ~(219)Rn is too short (4.0 seconds) and there has been little study done on it. The study of radon in water started about 90 years ago since its existence in mineral springs was confirmed. Until the early 1950s radon research in water was measured with the fontactoscope. After that, liquid scintillation counter(LSC) was used in the measurement of radon in water: the toluene-extracted and LSC method since it was developed, and the method spread rapidly and made good progress. With the spread of the method more and more concern has been shown regarding the effects of environmental radiation in daily life. Radon research is presently being performed in environmental science, geochemical science, medical science, physics, biology and technology with many other applications. The studied of radon in water resources, especially as hydrological tracer and in hot springs have been carried out and will be reported here.
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