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Radon Binding to Water-Soluble Cryptophane

Summary:

Collaboration on investigating the thermodynamics of radon binding with a new and novel class of cryptophane molecules is currently underway with researchers from the University of Pennsylvania (UPenn). 

Description:

In previous work, other noble gasses, e.g. xenon, were found to have a high affinity for this water-soluble cryptophane.  It exhibited better Xe binding (KA @ 3 x 104 M-1 at 310 K) than any previously described compound.  A similar result for radon would have significant metrological implications. Many radium (226Ra, 228Ra, etc.) and radon (220Rn, 222Rn, etc) assay procedures are conflicted because of the volatility of radon from solutions.  For example, this seriously restricts the ability to perform ion chamber measurements and gamma-ray spectrometry of sealed solution ampoules. A way to keep the radon bound in a solution would be a major breakthrough. The present cryptophane experiments, conducted at NIST with cryptophane syntheses from UPenn, were performed using a 226Ra-encapsulated generator as the source of 222Rn. The thermodynamic binding parameters would be extracted from differential measurements obtained by liquid scintillation counting of aliquots from reaction vessels. The first experiments, although yielding somewhat promising results, were not entirely successful because of experimental difficulties resulting from a radium breakthrough in the generator and the attendant ambiguities in data interpretation. A new series of experiments will be conducted shortly using a revised generator that has been constructed and with changes to the experimental design that has been incorporated into the protocol.