Charles Dubois Coryell
(photo courtesy of Endre Toth)

There is a great potential for use of supercritical (SC) solvents (in particular, SC-CO₂) for the extraction of unstable isotopes from nuclear waste. The main concern when handling solvents and reaction vessels after extraction of this waste is their level of radioactivity. When using supercritical solvents such as CO₂, in which UO₂ is extremely soluble, the temperature and pressure of the solvent can be adjusted quite easily to change its density (drastically!). High SC-CO₂ density thermalizes radioactive decay products (radiation) so that they do not reach the vessel walls (or the outside)

Using the MuSR technique at TRIUMF, Vancouver, BC, the positive muon was injected into supercritical carbon dioxide at varying densities. Its intra- track spur formation (the degree to which the muon ionizes the solvent (CO₂) and those high-energy electrons travel, thus forming radiation of their own) was closely studied using a MuSR Spectrometer.

Better understanding of  "spur formation" in supercritical CO₂ allows us to tune its temperature and pressure to the ideal levels for the safe use in UO₂ extraction.

Liquid scintillation counting (LSC) currently accounts for 71% of mixed radioactive, organic waste.  Development of an aqueous-based scintillation cocktail is desirable to reduce the amount of mixed waste produced. 
Polymerization of styrene-in-water microemulsions was used to entrap LSC fluor molecules, 2,5-diphenyloxazole (PPO) and p-bis(o-methylstyryl)-benzene (bis-MSB), in polystyrene nanoparticles to create an aqueous suspension.   These nanosuspensions were characterized using quasi-elastic light scattering and transmission electron microscopy and optimized with respect to PPO concentration, surfactant molecule(s), and styrene purification.  The nanosuspensions were used successfully to count various aqueous samples, including biological samples of digested blood and tissue.  Optimized nanosuspensions yielded counting efficiencies for ¹⁴C-acetic acid of up to 46% compared to commercially available LSC cocktail.

A short write-up about Gregory's research:

Online and Offline Gas-phase Chemistry of the Lighter Homologues of Rutherfordium

Gregory K. Pang  Mentors: Dr. Ch. Düllmann and Prof. H. Nitsche

Abstract: The gas phase chemistry of the group 4 elements (Zr, Hf) complexed with fluorinated β-diketones, specifically hexafluroacetylacetone (hfa) and trifluoroacetylacetone (tfa) was investigated. Two sets of experiments were performed: In the offline regime with macroamounts of stable isotopes, and in the online regime with short-lived isotopes (⁸⁵Zr, ^{158/162/165/169}Hf) produced in heavy-ion induced fusion reactions. These experiments were designed as a model study to prepare a future experiment with Rutherfordium (Rf, Z = 104). The offline studies comprised thermosublimatography experiments in a temperature gradient tube to investigate the thermochemistry of the Zr/Hf – hfa system. In the online regime, attention was paid to parameters that will be important in an experiment on a one-atom-at-a-time scale (in the case of Rf), namely maximum speed and yield. A maximum yield of ~90% for the 3.24 min. isotope ¹⁶⁹Hf was reached showing that the system is feasible for a Rf experiment. Successful application of this chemical system to a Rutherfordium experiment would result in the first transactinide compound with organic ligands.