Sample bottle design improvements for radon emanation analysis of natural waters

The "radon emanation" method of analysis for Rn and Ra in natural waters has been used by scientists for more than 30 years. We have examined the use of a new plastic bottle design as a viable option and improvement to traditional glass designs. The advantages of the new design over that used previously in our laboratory include a larger volume, lower blank, less fragile nature, and ease of handling in the field. Extensive calibration of the new design yielded an average efficiency of 70.9 +/- 1.7% and showed that an accurate blank value can be determined for each sample based on its specific holding time. Based on a 5-L sample and a 60-min count time, minimum detectable activities (MDA) range from 1.0 to 1.2 mBq L for Rn and Ra, respectively. Memory effect experiments have shown that activity artifacts are negligible when reusing the sampling containers. In addition, intra- and inter-laboratory comparisons show that the new design gives reliable results.