Fifteen years experience in measuring 224Ra and 223Ra by delayed-coincidence counting

The RaDeCC (TM) system has proved to be a robust method of measuring Ra-223 and Ra-224 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 Ra-223 and Ra-224 are recorded in a scintillation cell. These data are used to activate electronic gates in the delayed coincidence system, which separate events due to Ra-223 from those due to 224Ra. The System combines a high detection efficiency with low background to accurately measure Ra-223 and Ra-224 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. (c) 2007 Elsevier B.V All rights reserved.