Short-lived Radon Daughter Deposition Activity on Ground Surface Carried by Rainfall

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This paper describes a convenient and easy method of evaluating the short-lived radon daughters, 214Pb(RaB) and 214Bi(RaC), deposition activity on ground surface carried by rainfall in situ. Data of variations in the deposition activity on ground surface calculated from the continuous gamma radiation made at several sites for a period of nine years are given together with data of precipitation.It is concluded from the observations that the annual Ra(B+C) deposition activity lies within the range 4, 600-12, 000pCicm-2y-1, which depends on the annual precipitation. From the annual mean radon (222Rn) exhalation rate (UNSCEAR 1982), the annual precipitation on the terrestrial parts of the earth (reference data), and the annual mean specific activity of Ra(B+C) in rainwater (observation), we calculate the ratio of Ra(B+C) atom deposited on the ground to 222Rn released from the ground. This ratio is less than 1%. This means that almost all of the short-lived radon daughters in the atmosphere are not caught by rain and decayed to the long-lived radon daughters in the atmosphere.