Fifteen years experience in measuring Ra and Ra by delayed-coincidence counting

The RaDeCC™ system has proved to be a robust method of measuring ²²³Ra and ²²⁴Ra extracted from natural waters. Samples ranging in size from < 1 to > 1000 L are first concentrated onto Mn-fiber. The Mn-fiber is partially dried and placed into a circulation system with helium as the carrier gas. Alpha decays of the radon daughters of ²²³Ra and ²²⁴Ra are recorded in a scintillation cell. These data are used to activate electronic gates in the delayed coincidence system, which separate events due to ²²³Ra from those due to ²²⁴Ra. The system combines a high detection efficiency with low background to accurately measure ²²³Ra and ²²⁴Ra at concentrations on the order of 5 atoms per liter. Since this system was first deployed, numerous improvements in electronics and technique have occurred. In this paper I present tests we have conducted to confirm certain assumptions and improve the overall technique of sample collection and measurement.