Benjamin David Roach

Understanding biological responses to chronic low–dose rate gamma irradiation remains a key challenge in radiobiology because traditional exposure systems often limit throughput and experimental flexibility. We present the design, modeling, and validation of a 96-well plate platform integrating sealed 137Cs microsources that deliver variable low–dose rate gamma irradiation (targeted range 0.001–2 mGy/h) under uniform culture conditions. This system enables long-term, continuous exposure of cell cultures across a broad range of dose rates, which facilitates parallel investigation of radiation-induced DNA damage, stress signaling, and adaptive responses. Monte Carlo N-Particle (MCNP) simulations and calibrated film dosimetry confirmed differential dose delivery across wells (calculated and observed range 0.015–3 mGy/h), defined the current operating envelope, and revealed interwell and interplate crosstalk limitations of the platform while maintaining full compatibility with standard biological workflows. By allowing high-throughput, multi–dose rate studies within a single, self-contained platform, this approach advances experimental capabilities for probing dose rate–dependent biological mechanisms relevant to radiation protection, environmental exposure, and therapeutic research.

The U.S. Department of Energy's Office of Scientific and Technical Information

The U.S. Department of Energy's Office of Scientific and Technical Information

Conditions have been identified in which phenolic aldoximes and ketoximes of the types used in commercial solvent extraction processes can be doubly deprotonated and generate polynuclear Cu complexes with lower extractant:Cu molar ratios than those found in commercial operations. Electrospray mass spectrometry has provided an insight into the solution speciation in extraction experiments and has identified conditions to allow isolation and characterization of polynuclear Cu-complexes. Elevation of pH is effective in enhancing the formation of trinuclear complexes containing planar {Cu₃-μ₃-O}⁴⁺ or {Cu₃-μ₃-OH}⁵⁺ units. DFT calculations suggest that such trinuclear complexes are more stable than other polynuclear species. Solid structures of complexes formed by a salicylaldoxime with a piperidino substituent ortho to the phenolic OH group (L⁹H₂) contain two trinuclear units in a supramolecular assembly, {[Cu₃OH(L⁹H)₃(ClO₄)](ClO₄)} ₂, formed by H-bonding between the central {Cu₃-μ₃-OH}⁵⁺ units and oxygen atoms in the ligands of an adjacent complex. Whilst the lower ligand:Cu molar ratios provide more efficient Cu-loading in solvent extraction processes, the requirement to raise the pH of the aqueous phase to achieve this will make it impractical in most commercial operations because extraction will be accompanied by the precipitation (as oxyhydroxides) of Fe(III) which is present in significant quantities in feed solutions generated by acid leaching of most Cu ores.

This study demonstrates a method for determining the isotopic composition of low-level (sub-pg) plutonium (Pu) directly from a cotton swipe. Environmental sample (ES) swipes are routinely employed as a tool for monitoring activities in nuclear facilities. Traditional ES swipe analysis, as employed in nuclear safeguards, utilizes laborious ashing, digestion, and chemical separation procedures prior to mass spectrometric (MS) analysis. Here, an innovative sample introduction technique employing a microextraction probe to extract Pu directly from the swipe surface is described. The microextraction probe lowers onto the swipe surface, seals on a small area (8 mm²), and delivers solvent (2% HNO₃) to extract actinide material that may be present. The extracted analyte is subsequently directed into a sector field inductively coupled plasma (ICP)-MS for isotope ratio determination. This microextraction-ICP-MS method successfully determined the isotopic composition (²⁴⁰Pu/²³⁹Pu and ²⁴²Pu/²³⁹Pu) of three Pu certified reference materials (CRM 136, 137, and 138) that were deposited (1 pg) onto ES swipes. The percent relative difference from the certified value, uncorrected for instrumental fractionation, was 240Pu/²³⁹Pu ratio on all three CRMs and 242Pu/²³⁹Pu ratio on CRM 136 and 138. The percent relative standard deviation, an estimate of the sample-to-sample isotopic precision, was 240Pu/²³⁹Pu and 242Pu/²³⁹Pu. Method limits of detection were determined, based on measurements of an enriched ²⁴⁴Pu material, to be ∼7 fg. Additionally, a mixed uranium (U) and Pu deposition was made to determine the method's ability to simultaneously extract U and Pu and determine the isotopic composition of both analytes.

The U.S. Department of Energy's Office of Scientific and Technical Information