中文摘要：

介绍了同步延时计数法，并应用其对辽河口水体中的223Ra和224Ra进行了测定，结合pH、DO、COD、叶绿素、营养盐等参数对223Ra和224Ra的放射性活度及其比值随盐度的变化和影响因素进行了讨论，继而以“镭同位素表观年龄模型”计算了辽河口水体的停留时间。结果表明：2010年4月，辽河口调查水域水体中的224Ra、223Ra随盐度变化趋势不保守，在盐度为10和26的海域出现了放射性活度高峰值，可能分别由悬浮颗粒物解吸和滨岸咸化的地下水排放等因素造成。水体停留时间随着离开河口距离的增大而增大，最大值出现在盐度为14的海域，达到8．34-d。

英文摘要：

Radium delayed coincidence countering system has become the state-of-the-art technique for short-lived radium isotopes （223 Ra, 224 Ra） measurement. In this paper, we described this system, and used it to measure 223 Ra, 224 Ra activities at the Liaohe River Estuary. Other parameters, like pH, DO, COD, petroleum hydrocarbon, chlorophyll and nutrients, were used to demonstrate the distribution and impact factors of isotopes activity and ratio versus salinity. Furthermore, the ＂Apparent Radium Age＂ model was applied to assess the water residence time at this area. 224Ra and ~23Ra were not conservative with salinity at the studying area in A- pril, 2010. Two peak activities at salinity 10 and 26 were caused by suspended particles desorption and submarine groundwater discharge, respectively. Water residence time increased with the distance. The oldest age was 8.34 days at the area with salinity of 14.