Speaker
Description
Measurement of 222Rn activity in water is important in many fields such as dosimetry, radiation protection, geology and volcanology. Various methods were developed to measure radon-in-water, namely: emanometry, gamma–ray spectrometry (GS), liquid scintillation counting (LSC) and track-etch techniques. Despite the importance of these measurement techniques, their long history and wide scale application, no primary standard for radon-in-water concentration currently exists. This impedes the establishment of a traceability chain for the radon-in-water measurements to a primary 222Rn standard as the calibrations are often performed usingother nuclides (e.g. 226Ra standards), which can introduce problems in certain cases.
The objective of this work is to fill this gap by developing a laboratory system for 222Rn-in-water standardization. We designed and constructed a dedicated instrumentation, which allows 100% transfer of 222Rn from the primary 222Rn standard (defined solid angle method, DSA), mixing of the transferred radon with water and preparation of radon-in-water samples with traceable radon activity concentration. The system allows preparing GS and LSC radon-in-water samples thus enabling the establishment of a traceability chain to the DSA standard.
The concept of the system is based on the cryogenic transfer of 222Rn from the DSA standard to water under controlled conditions, homogenization of 222Rn in water and 222Rn-loss-free simultaneous preparation of up to six 100 ml samples for GS and up to ten 10 ml samples for LSC. During the first repeatability tests, we obtained a relative standard deviation of 0.25% on the activity concentration of the 10 LSC samples prepared. We also achieved qualitative transfer of the water to LSC cocktail with 0.25% relative standard deviation of the mass of water transferred to the LSC samples, which was evaluated by repetitive sampling tests with radon-free water. A good agreement between the calculated activity concentration (based on the DSA activity and volume measurements) and the GS and LSC sample measurements is obtained within the estimated uncertainties. The results of the proof-of-concept experiments show that we can produce 222Rn-in-water with standard uncertainty of the activity concentration better than 1% and traceable GS and LSC sources with similar standard relative uncertainty.
We will discuss the concept and design of the system, its performance in pilot tests and the obtained results. We will also address the new possibilities of this system for radon metrology, especially the possibility to compare three different 222Rn measurement techniques: DSA, LSC and GS.
