Measurement of Ra-224 and Ra-226 activities in natural waters using a radon-in-air monitor

We report a simple new technique for measuring low-level radium isotopes (R a-224 and Ra-226) in natural waters. The radium present in natural waters i s first preconcentrated onto MnO2-coated acrylic fiber (Mn fiber) in a colu mn mode. The radon produced from the adsorbed radium is then circulated thr ough a closed air-loop connected to a commercial radon-in-air monitor. The monitor counts alpha decays of radon daughters (polonium isotopes) which ar e electrostatically collected onto a silicon semiconductor detector. Count data are collected in energy-specific windows, which eliminate interference and maintain very low backgrounds. Radium-224 is measured immediately afte r sampling via Rn-220 (Po-216), and Ra-226 is measured via Rn-222 (Po-218) after a few days of ingrowth of Rn-222. This technique is rapid, simple, an d accurate for measurements of low-level Ra-224 and Ra-226 activities witho ut requiring any wet chemistry. Rapid measurements of short-lived Rn-222 an d Ra-224, along with long-lived Ra-226, may thus be made in natural waters using a single portable system for environmental monitoring of radioactivit y as well as tracing of various geochemical and geophysical processes. The technique could be especially useful for the on-site rapid determination of Ra-224 which has recently been found to occur at elevated activities in so me groundwater wells.