2.7.1.1 - Enrichment in Organic Cocktail
Introduction
We recommend touse organic cocktails for the enrichment of Radon because of the high distribution coefficient of more than 15 for Radon gas e.g. in toluene [Möbius Ramamonjisoa et al. 1998], see also [Möbius et al. 1999], [Haaslahti et al. 2000] and [Möbius 2002]. The method makes use of absorption of Radon from about 5 L air. The air is sucked with a laboratory or hand pump through an impinger or diffuser into a glass vial, containing 50 mL organic cocktail like BetaPlate Scint as extracting agent. The LS measurement is done by α/β-discrimination after equilibration between Radon and its progenies.
The extraction cell for the enrichment of Radon in an organic cocktail is shown in figure 37. More details can be found in "LSC-Handbuch 2008" [Möbius und Möbius 2008].
Figure 37: Rn extraction cell
Materials and Equipment
Organic cocktail (e.g. BetaPlate Scint)
Pump
Extraction cell
Procedure
50 mL BetaPlate Scint cocktail are added into the extraction cell (fig. 37).
For Radon enrichment, the air is pumped for 20 min (ca. 1 L/min) through the diffuser.
20 mL of the Radon containing cocktail are transferred into a counting vial and measured after 3 h storage time by α/β-PSD.
Evaluation
As we have shown earlier [Möbius and Möbius 2008] a saturation activity will be reached after about 10 minutes sampling time. The saturation activity is practically independent on the temperature of the scintillation cocktail and on its volume within a range of 20 and 80 mL.
Our experimental arrangement has been recalibrated with the commercially available AlphaGuard Equipment (Genitron Instr.). One α-signal per minute for a Radon concentration of 45 Bq/m3 in equilibrium with progenies could be found with BetaPlate Scint at 20°C and 0.5 L/minute of air. With the HIDEX Triathler equipment, this corresponds to a minimum detectable activity of 15 Bq/m3 with 0.02 counts/min background in the α-channel, 95% counting efficiency for α-nuclides using a 20 mL glass vial and 1 h counting time. This value is sufficient for the measurement of Radon both, in dwellings and outdoors. The method is simple, fast and reproducible.
With the measurement of an additional glass fiber filter mounted before the extraction cell, the state of equilibrium between Radon and progenies can be estimated.
The filter is moistened after air filtration with BetaPlate Scint and mounted onto the outer wall of a 20 mL glass vial (see also chapter 2.4.4., swipe assay measurements).
Results and a comparison with active carbon canisters are described elsewhere [Zafimanjato 2007].
Detection limit (MDA): 15 Bq/m3
Total analysis uncertainty: 15 %
Haaslahti J., Aalto, J. and Oikari, T. 2000: The determination of low levels of Radon and Radium in water by a portable single PM-tube liquid scintillation counter with pulse shape discrimination electronics; Application Note, Hidex Oy, Turku, Finland
Möbius Ramamonjisoa T. L., Frenzel E. and Möbius S. 1998: Becquerels Stein; Strahlenschutzpraxis 4 (1998) 53-56
Möbius T.L., Frenzel E., Haaslahti J., Kamolchote K. and Möbius S. 1999: LSC as powerful and fast tool for in-situ measurement of natural radionuclides in water; 45th Conference on Bioassay, Analytical and Environmental Radiochemistry BAER'99, Gaithersburg 18-22 October 1999
Möbius S. 2002: Fast methods for field analysis of natural radionuclides - new approaches; in: S. Möbius et al. „LSC2001 Advances in Liquid Scintillation Spectrometry”, pp 235-246, Radiocarbon 2002, Tucson
Möbius S. and Möbius T. L. 2008: LSC-Handbuch, DGFS e.V. und Forschungszentrum Karlsruhe GmbH, Karlsruhe 2008
Zafimanjato L. 2007: Etude du comportement et détection du Radon dans les échantillons de l’environnement par la technique des scintillations – Application au Radium. Doctorat du Troisième Cycle ; Institut National des Sciences et Techniques Nucléaires, Antananarivo 2007, Madagascar
