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Summary
Collaboration on investigating the thermodynamics of radon binding with a new and novel class of cryptophane molecules was completed with researchers from the University of Pennsylvania (UPenn).
Description
In collaboration with the University of Pennsylvania, a 222Rn emanation sources, similar to the NIST 222Rn emanation standard (SRM 4968, NIST, 1996) was found to have a unique and novel application in a radon-in-water generator for the determination of the binding affinity of radon to a cryptophane molecular host. In previous work, other noble gases, e.g. xenon, were found to have a high affinity for this water-soluble crytophane. It exhibited better Xe binding (KA = 42,000 ± 2,000 L· mol-1 at 293 K) than any previously described compound. A novel experimental design was developed. This involved performing the reactions at femtomole levels, developing exacting gravimetric sampling methods and making precise 222Rn assays by liquid scintillation counting. The 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 were extracted from differential measurements obtained by liquid scintillation counting of aliquots from reaction vessels. A cryptophane-radon association constant was determined to be KA = 49,000 ± 12,000 L· mol-1 at 293 K, which was the first measurement of radon binding to a molecular host. 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. The use of cryptophane as a binding agent may keep radon in solution making ion chamber and gamma spectrometry measurements of radium solutions more accurate and reliable. Two publications were completed as a result of this research:
Notice of Online Archive: This project ended in 2011 and thus this page is no longer being updated and remains online for informational and historical purposes only. The information is accurate as of February 2021. For questions about page contents, please contact Ronald Collé.