Measurements of radioactive gases are critical in environmental monitoring, nonproliferation testing, and medical applications. NIST has been asked by multiple stakeholders to provide measurement traceability to the SI (unit Bq) by expanding on traditional gas counting capabilities and developing new methods to meet outstanding challenges. In particular, we seek to develop absolute assay the activity of radioactive gases (Kr, Xe, H) not only at the traditionally high levels (~ MBq) normally done by metrology institutes, but also at low levels (< mBq) needed to provide metrological traceability for environmental and nonproliferation measurements. Gas handling and dilution techniques will need to be developed to make measurements possible over the necessary activity ranges for the disparate applications, while maintaining traceability to the SI with low overall uncertainty (~ 0.1 %).

Longer-term plans include development of complementary absolute activity methods, such as coincidence counting and defined solid angle counting, as well as atom counting methods such as cavity ringdown spectroscopy. A potential scientific impact would be to combine atom counting with decay counting on the same sample to produce a novel measurement of half-lives, e.g. for radioactive dating.