Development of an alpha fast-slow coincidence counter for analysis of ²²³Ra and ²²⁴Ra in seawater

An alpha fast-slow coincidence counter has been designed and manufactured for measuring the low alpha activities of 223Ra and 224Ra in the seawater. In this work, Radium from the seawater was absorbed onto a column of MnO2 coated fiber (Mn fiber). The short-lived Rn daughters of 223Ra and 224Ra which recoil from the Mn fiber are swept into a scintillation detector where alpha decays of Rn and Po occur. Signals from the detector are sent to a delayed coincidence circuit which discriminates decays of the 224Ra daughters, 220Rn and 216Po, from decays of the 223Ra daughters, 219Rnand 215Po.