Matthew J. O'HAra

This report summarizes the development and demonstration of thorium-228/radium-224/radon-220 (228Th/224Ra/220Rn) and radium-224/radon-220 (224Ra/220Rn) emanation-based generator for producing high-purity 212Pb in a form suitable for targeted alpha therapy applications. The project was motivated by limitations of conventional wet-column 224Ra/212Pb generators, including the possibility of 224Ra breakthrough and the need for post-elution chemical processing prior to biomolecule labeling. In contrast, the approach described here uses gas-phase transport of 220Rn away from a 228Th or 224Ra-bearing source, followed by spatially separated decay to 212Pb and aqueous recovery of the product into a radiolabeling-compatible buffer solution. The work addressed the five original Specific Objectives, while accounting for the later revised scope in which no tasks were eliminated, but several activities were reduced in scale. The team identified practical 220Rn emanation source configurations based on a suite of commercially available resins and specific carrier gas conditions. The project also evaluated multiple Rn collection strategies, including organic solvent capture, cryogenic deposition, organic nanocage media (CC3), and closed-loop decay chamber concepts. These studies established the basis for a simplified generator approach in which 220Rn is transported from the source and 212Pb is subsequently recovered from the collection region in small aqueous volumes. A major outcome of the report is the demonstration that the generator can produce 212Pb with high yields, purity, and chelation performance. The decay chamber concept enabled recovery of most chamber-deposited 212Pb into ammonium acetate or sodium acetate buffers. Generator testing used both 228Th and 224Ra emanation sources; the highest-activity generator testing reached approximately 18.7 mCi, exceeding the revised 10–15 mCi activity target. In these evaluations, 212Pb recovery into sodium and ammonium acetate was typically near 90% of the decay chamber activity, with overall product yields (considering 220Rn emanation fraction and 212Pb collection fraction) reaching approximately 82% under the best conditions. Product purity was likewise strong: decay-based measurements showed no detectable 228Th or 224Ra contamination in selected high-activity product fractions, with calculated 212Pb product decontamination factors greater than 108. Results also demonstrate that the recovered 212Pb product is chemically useful, not merely radionuclidically pure. When 212Pb was collected directly into ammonium acetate containing the TCMC (DOTAM) chelator, essentially quantitative complexation was observed, with 99.8–100.0% bound and 99.3–99.7% bound when assessed by an instant thin layer chromatography (iTLC) and aminopropyl (NH2) cartridge method, respectively. These results indicate that the product matrix did not contain a bindable-metal inventory sufficient to inhibit TCMC labeling under the evaluated conditions. We also demonstrated that radiolabeling onto TCMC chelator can happen concurrently with 212Pb stripping with acetate salt solutions – thereby reducing 212Pb collection and labeling to a single step. Overall, the report shows that the revised project objectives were met: the team developed an automated, high-yield 228Th/212Pb and 224Ra/212Pb generator concept capable of producing high-purity, label-ready 212Pb while substantially reducing the risk of parent-isotope breakthrough and opportunities for metals contamination. Finally, the project trained future radiochemists by embedding students and Research Associates directly into the full development cycle of the generator system. Participants gained hands-on experience in alpha-emitting radionuclide handling, source preparation, gas-phase 220Rn transport, generator assembly, automated fluidic operation, radiometric counting, decay correction, yield calculations, radionuclidic purity assessment, contamination control, and radiol

The near real-time detection of airborne particles-of-interest is needed for avoiding current/future threats. The incorporation of imprinted particles into a micelle-based electrochemical cell produced a signal when brought into contact with particle analytes (such as SARS-COV-2), previously imprinted onto the structure. Nanoamp scales of signals were generated from what may’ve been individual virus-micelle interactions. The system showed selectivity when tested against similar size and morphology particles. The technology was compatible with airborne aerosol sampling techniques. Overall, the application of imprinted micelle technology could provide near real-time detection methods to a host of possible analytes of interest in the field.

The aim of work this year has been to investigate the role of alpha (a)-radiation and hydrogen (H2) on the corrosion of uranium oxide (UO2) using a microfluidic device. The microfluidic device, termed the Particle-Attached Microfluidic Electrochemical Cell, (PAMEC), enables monitoring of the UO2 electrochemical corrosion potential (Ecorr) under different environments, including de-aerated conditions and in the presence of dissolved H2. The Si3N4 window allows us to study morphological and chemical changes under an electron microscope. We have previously demonstrated that the PAMEC matches the results from bulk electrochemical tests with UO2 [1]. We used the high specific activity uranium (U) isotope, 233U, (t1/2 = 160,000 years) incorporated into UO2, to generate a localized a-field. The objective of the experiments were to mimic the radiation environment that would be experience at the surface of aged spent nuclear fuel (SNF) during long-term geologic disposal under anoxic conditions. Wittman et al. [2] predicted that in the presence of a pure a-radiation field and under H2 conditions, the concentration of the radiolytic oxidant H2O2 would be suppressed or even eliminated. In a UO2 corrosion experiment this would be exhibited through a lowering of the measured UO2 corrosion potential compared to identical conditions inmore » the absence of dissolved H2. We found that the predictions of Wittman and co-workers were supported and that the corrosion potential of the 233U-doped UO2 in solution lowered with presence of H2 gas and increased in the absence of H2, when under anoxic conditions. The PAMEC experiments indicate that H2O2 has been eliminated in a solution sparged with H2 while exposed to an a-radiation field. The corrosion potential of the a-doped 233U(10%)- 238UO2 in a solution sparged with Ar/H2 matched the corrosion potential of 238UO2 in solution sparged with air. This clearly demonstrated that the H2O2 had been eliminated and that the only oxidant present was O2 in this system in complete agreement with the modeling results of Wittman et al. These results point to the need to improve the Fuel Matrix Degradation (FMD) Process Model training data set that is being used in the FMD surrogate model that is being developed for the repository program. The incorporation of realistic radiation chemistry will improve the scientific basis for the FMD Model. « less

This procedure covers the determination of the percent 14C in biogenic gasoline, jet fuel, and diesel range hydrocarbons prepared from distillation of hydrotreated pyrolysis oils and blended with fossil derived hydrocarbons (e.g. fossil diesel, gasoline, jet, or toluene). Either an internal 14C standard or a color quench curve is used to correct for potential signal quenching effects. Recent publications provide some background of direct LSC methods used for determination of biogenic fuel content [1,2].

Data demonstrates large variance in the volatilization temperatures of MoO₂ (likely as MoF₆) vs. UO₂ (as UF₆). This forms the basis of a gas-phase separation of ⁹⁹Mo from U.

Cyclotron-produced astatine-211 (²¹¹At) shows tremendous promise in targeted alpha therapy (TAT) applications due to its attractive half-life and its 100% α-emission from nearly simultaneous branched alpha decay. Astatine-211 is produced by alpha beam bombardment of naturally monoisotopic bismuth metal (²⁰⁹Bi) via the (α, 2n) reaction. In order to isolate the small mass of²¹¹At (specific activity = 76 GBq·µg⁻¹) from several grams of acid-dissolved Bi metal, a manual milliliter-scale solvent extraction process using diisopropyl ether (DIPE) is routinely performed at the University of Washington. As this process is complex and time consuming, we have developed a fluidic workstation that can perform the method autonomously. The workstation employs two pumps to concurrently deliver the aqueous and organic phases to a mixing tee and in-line phase mixer. The mixed phases are routed to a phase settling reservoir, where they gravity settle. Finally, each respective phase is withdrawn into its respective pump. However, development of a phase boundary sensor, placed in tandem with the phase settling reservoir, was necessary to communicate to the system when withdrawal of the denser aqueous phase was complete (i.e., the intersection of the two phases was located). The development and optimization of the autonomous solvent extraction system is described, and the²¹¹At yields from several ~1.1 GBq-level²¹¹At processing runs are reported.