Comparison of measurement methods for radium-226 on manganese-fiber

Richard N. Peterson, William C. Burnett, Natasha Dimova, Isaac R. Santos

Limnol. Oceanogr. Methods 7:196-205 (2009) | DOI: 10.4319/lom.2009.7.196

ABSTRACT: Acrylic fibers impregnated with MnO2 (Mn-fiber) have become a valuable tool for concentrating dissolved radium for oceanographic applications. With four naturally-occurring radium isotopes (223Ra, 224Ra, 226Ra, and 228Ra) of vastly different half-lives (3.6 days to 1600 years), radium can be a powerful tool for tracing terrestrial water discharges into the ocean and studying coastal mixing processes. Several techniques have been outlined in the literature describing the measurement of 226Ra on Mn-fiber via its gaseous daughter, 222Rn. We present a proven, air-tight cartridge design that allows one to use these measurement techniques. We then review the procedures for three radon-based nondestructive measurement techniques for 226Ra on Mn-fiber (via RAD7, RaDeCC, and Rn emanation line systems) and perform an intercomparison among them, using the standard technique of γ-spectrometry as a reference. We find that all methods statistically agree in terms of measured activity. The Rn emanation line and the RaDeCC systems (both based on Lucas cell counting) provide the lowest measurement uncertainties and minimum detectable activities (MDAs) for a given counting time. The RAD7 technique, on the other hand, offers the advantage of being an automated system, thus requiring minimal user interaction. The standard γ-spectrometry technique, while more time-consuming and sample destructive, has the advantage of providing a simultaneous measurement for 228Ra.