Development of a regenerative radon-in-water radioactivity standard

NBS has developed a prototype standard that generates samples of radium-free 222Rn gas dissolved in distilled water. This standard is intended to be used for quality control of the US Environmental Protection Agency's program to survey drinking water. It consists of a generator and delivery system which can accurately dispense solutions of 222Rn with known concentration into, for example, a liquid scintillation vial containing scintillation cocktail. The prototype consists of a source of 226Ra which is deposited on an ion exchange filter and sandwiched between two layers of thin polyethylene tape and immersed in water in a specially constructed accumulation chamber. The chamber is then flushed and 222Rn is allowed to accumulate for a measured time and flushed again into a large syringe from which the standard is dispensed. From the measurements made at NBS over the past two years, the 222Rn in the ion exchange filter-polyethylene sandwich, and therefore, the concentration of radon dissolved in the water, can be predicted accurately. Other characteristics of the system will be reported. (orig.)