The Role of Transient Radiation-Induced Non-Equilibrium Actinide Species in Solution
Invited seminar on "The Role of Transient Radiation-Induced Non-Equilibrium Actinide Species in Solution."
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
SEARCH · Search NASA
Results for “Pulse Electron Radiolysis”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Elucidating the Radiation-Induced Redox Chemistry of Plutonium Under Used Nuclear Fuel Reprocessing Conditions
Plutonium plays a critical role in the development of sustainable nuclear fuel cycles, and yet, our fundamental understanding of this element’s inherent radiation-induced redox chemistry and associated impacts on nuclear fuel cycle technologies is limited. Unanticipated changes in oxidation state distribution can influence the speciation and transport of plutonium in a given process. Control of these parameters is especially important for used nuclear fuel reprocessing technologies, wherein the separation and recovery of plutonium is typically achieved by the selective formation, maintenance, and complexation of specific oxidation states. Furthermore, plutonium’s inherent radiation-induced redox chemistry has the capacity to influence the radiolytic behavior of its complexes, the longevity of which are critical in the design of efficient and cost-effective advanced reprocessing technologies. These radiation-induced processes are unavoidable under fuel cycle conditions owing to the inherency of ionizing radiation fields to the decay of plutonium’s isotopes and to the various other radioisotopes generated by nuclear fission and neutron-capture process and the subsequent radioactive decay of their products. As such, mechanistically understanding the response of plutonium’s multiple oxidation states to multi-component ionizing radiation fields is essential for predicting the behavior of this critical element under used nuclear fuel reprocessing conditions. Here, through a combination of time-resolved (electron pulse) and steady-state (alpha and gamma) irradiation experiments complemented by quantitative, multiscale modeling calculations, we present advances in our understanding of radiation-induced plutonium redox chemistry!
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Backend Nuclear Fuel Cycle Radiation Chemistry
Given global commitments to significantly increase nuclear energy capacity, it is now more important than ever to develop efficient used nuclear fuel management strategies to improve resource utilization, energy security, and waste minimization. Here, an overview of nuclear energy, backend fuel cycle challenges, and advances in used nuclear fuel reprocessing radiation chemistry will be presented. More specifically, the use of electron pulse irradiation techniques to explore radiation-induced reaction mechanisms in actinide containing solutions and solvent systems.
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
Thrust 2 Radiation Induced Actinide Reaction Kinetics in Molten Iodide Chloride Salts Mixtures
Slide deck for research highlight summaries for Thrust 2.
38 - RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCL↗
Assessing the Impact of Molecular Architecture on the Radiation Durability of Diglycolamide Minor Actinide Extractants
NS&T Highlight Slide
37 - INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL C↗
Electrons and Their Multiple Kinetic Fates in an Ionic Liquid
Ionic liquids (ILs) for electrochemical, nuclear, and solar energy applications operate under harsh conditions, where electrons and transient radical species can form. This communication discusses why anions such as bis(trifluoromethylsulfonyl)imide (Tf 2 N − ) are reduced at the electron-rich electrode whereas in laser photoionization or pulse radiolysis studies, where electrons are ejected from species in the bulk, we often detect long-lived electrons in cavities that interact with IL cations instead. This work argues that bulk excess electrons generated photolytically or radiolytically follow kinetically favored pathways. As such, cavity electrons may not be the most energetically favorable states, but when they form, and they do form, they are kinetically stable. Reduction reactions of anions or electron localization in cavities and subsequent reactions are all expected outcomes. Here we focus on a pyrrolidinium-based IL of the dicyanamide (N(CN) 2 − ) anion because of its large electrochemical window and very low viscosity, which are ideal for energy applications.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Electron Transfer Theory Elucidates the Hidden Role Played by Triethylamine and Triethanolamine during Photocatalysis
Triethylamine (TEA) and triethanolamine (TEOA) are renowned, in part, for their ability to reductively quench excited states by outer-sphere electron transfer with vast and still growing applications as sacrificial electron donors for photocatalytic systems. Upon amine oxidation, the resulting TEA •+ and TEOA •+ radical cations undergo proton transfer (or hydrogen atom transfer), resulting in the formation of a chemical reductant that has an α-carbon centered radical adjacent to the nitrogen center (TEA • and TEOA • ). In this contribution, we have electrochemically and spectroscopically characterized a set of electron acceptors which, upon accepting an electron, are a series of photocatalysts, [ReCl(R 1 R 2 -bpy)(CO) 3 ] •– , where R 1 and R 2 are electron-donating and electron-withdrawing groups in the 4,4′- and 5,5′-positions on the bipyridyl ligand. Here, we substantiated the formation of the electron donors, TE(O)A • , by spin trapping electron paramagnetic resonance spectroscopy, where TE(O)A • reacts with 2,4,6-tri-tert-butylnitrosobenzene to generate N-centered and O-centered radical adducts. Having established the chemical behaviors of the electron acceptors and donors individually, the electron transfer rate constants were determined across a 1.43 V range in driving force. The redox potential of TEA • was benchmarked to within ±80 mV on an absolute scale in V vs Fc + /Fc in CH 3 CN by using an empirical rate vs free-energy correlation, electron transfer theory, and density functional theory calculations. The equilibrium potentials for TEA • and TEOA • were determined to be −1.98 V and −1.76 V, respectively. Based on the kinetic and thermochemical analysis presented for TEA • and TEOA • , these transient radicals can be broadly considered strong homogeneous chemical reductants within the wider context of photoredox potentials. Thus, this work clarifies a frequently unnoticed secondary function for these sacrificial electron donors during photocatalysis and rationalizes the possibility of a one-photon/two-electron conversion process that is dependent on the free-energy exchange between TE(O)A • and photocatalysts.
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
An analytical approach to evaluation of space radiation effects on materials for long-life missions
An analytical model was developed which quantifies effects on organic composite matrix materials of high energy electrons and of UV as well as interactions between the two radiations. Literature data on polyethylene were used to construct a degradation kinetics scheme corresponding to an Earth orbit at L=3. Analysis of the model showed that steady state concentrations of radicals put limits on accelerated test conditions. These conclusions were validated by an experimental study on polymethylmethacrylate using UV laser excitation. Relationships for balancing electron and UV radiations to equal acceleration factors are derived. Pulse radiolysis using an electron-beam along with time-resolved spectroscopy is shown to be able to separate primary form secondary reactions. Implications of these reactions to changes in engineering material properties are indicated. The use of mechanistic studies is discussed in the context of general test strategies for evaluating materials for space applications.
Moacanin, J.↗
Coupling Pulse Radiolysis with Nanosecond Time-Resolved Step-Scan Fourier Transform Infrared Spectroscopy: Broadband Mid-Infrared Detection of Radiolytically Generated Transients
We describe the first implementation of broadband, nanosecond time-resolved step-scan Fourier transform infrared (S 2 -FT-IR) spectroscopy at a pulse radiolysis facility. This new technique allows the rapid acquisition of nano- to microsecond time-resolved infrared (TRIR) spectra of transient species generated by pulse radiolysis of liquid samples at a pulsed electron accelerator. Wide regions of the mid-infrared can be probed in a single experiment, which often takes < 20–30 min to complete. It is therefore a powerful method for rapidly locating the IR absorptions of short-lived, radiation-induced species in solution, and for directly monitoring their subsequent reactions. Time-resolved step-scan FT-IR detection for pulse radiolysis thus complements our existing narrowband quantum cascade laser-based pulse radiolysis-TRIR detection system, which is more suitable for acquiring single-shot kinetics and narrowband TRIR spectra on small-volume samples and in strongly absorbing solvents, such as water. We have demonstrated the application of time-resolved step-scan FT-IR spectroscopy to pulse radiolysis by probing the metal carbonyl and organic carbonyl vibrations of the one-electron-reduced forms of two Re-based CO 2 reduction catalysts in acetonitrile solution. Transient IR absorption bands with amplitudes on the order of 1 × 10 −3 are easily detected on the sub-microsecond timescale using electron pulses as short as 250 ns.
(S2-FT-IR)↗
Steric and Lewis Basicity Influence of the Second Coordination Sphere on Electrocatalytic CO 2 Reduction by Manganese Bipyridyl Complexes
This study aims to provide a greater insight into the balance between steric (bpy vs (Ph) 2 bpy vs mes 2 bpy ligands) and Lewis basic ((Ph) 2 bpy vs (MeOPh) 2 bpy vs (MeSPh) 2 bpy ligands) influence on the efficiencies of the protonation-first vs reduction-first CO 2 reduction mechanisms with [Mn I (R 2 bpy)(CO) 3 (CH 3 CN)] + precatalysts, and on their respective transition-state geometries/energies for rate-determining C–OH bond cleavage toward CO evolution. The presence of only modest steric bulk at the 6,6'-diphenyl-2,2'-bipyridyl ((Ph) 2 bpy) ligand has here allowed unique insight into the mechanism of catalyst activation and CO 2 binding by navigating a perfect medium between the nonsterically encumbered bpy-based and the highly sterically encumbered mes2bpy-based precatalysts. Cyclic voltammetry conducted in CO 2 -saturated electrolyte for the (Ph) 2 bpy-based precatalyst [2-CH 3 CN] + confirms that CO 2 binding occurs at the two-electron-reduced activated catalyst [2] – in the absence of an excess proton source, in contrast to prior assumptions that all manganese catalysts require a strong acid for CO 2 binding. This observation is supported by computed free energies of the parent–child reaction for [Mn–Mn] o dimer formation, where increased steric hindrance relative to the bpy-based precatalyst correlates with favorable CO 2 binding. A critical balance must be adhered to, however, as the absence of steric bulk in the bpy-based precatalyst [1-CH 3 CN] + maintains a lower overpotential than [2-CH 3 CN] + at the protonation-first pathway with comparable kinetic performance, whereas an ~2-fold greater TOF max is observed at its reduction-first pathway with an almost identical overpotential as [2-CH 3 CN] + . Notably, excessive steric bulk in the mes2bpy-based precatalyst [3-CH 3 CN] + results in increased activation free energies of the C–OH bond cleavage transition states for both the protonation-first and the reduction-first pathways relative to both [1-CH 3 CN] + and [2-CH 3 CN] + . In fact, [3-CH 3 CN] + requires a 1 V window beyond its onset potential to reach its peak catalytic current, which is in contrast to the narrower (<0.30 V) potential response window of the remaining catalysts here studied. Furthermore, voltammetry recorded under 1 atm of CO 2 with 2.8 M (5%) H 2 O establishes [2-CH 3 CN] + to have the lowest overpotential (η = 0.75 V) in the series here studied, attributed to its ability to lie “on the fence” when providing sufficient steric bulk to hinder (but not prevent) [Mn–Mn] o dimerization, while simultaneously having a limited steric impact on the free energy of activation for the rate-determining C–OH bond cleavage transition state. While the methoxyphenyl bpy-based precatalyst [4-CH 3 CN] + possesses an increased steric presence relative to [2-CH 3 CN] + , this is offset by its capacity to stabilize the C–OH bond cleavage transition states of both the protonation-first and the reduction-first pathways by facilitating second coordination sphere H-bonding stabilization.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Vibrational Spectroscopy Reveals Effects of Electron Push–Pull and Solvent Polarity on Electron Delocalization in Radical Anions of Donor–Acceptor Compounds
Herein, the nature of excess electrons has been studied in donor–acceptor (D–A) compounds based on substituted triarylamines and a nitrile-functionalized fluorene, by changing the substituents on the triarylamines and also the solvent polarity. We observed that both electron push-pull capability at the distant location in the amine donor unit and solvation in solvents of varying polarity significantly affect the nitrile $ν(C≡N)$ vibrations of the fluorene acceptor unit in radical anions of these D–A compounds. Quantum calculations show that the push-pull capability translates the position of an excess electron while keeping its width relatively constant. On the other hand, solvation changes both, making an electron more compact in polar media. The current study points to the idea that solvation plays a more significant role in controlling the nature of excess electrons, while synthetic modification that influences electron push-pull capability enables further tuning.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Solvated Electron in Acetonitrile: Radiation Yield, Absorption Spectrum, and Equilibrium between Cavity- and Solvent-Localized States
The equilibrium between a solvent cavity-localized electron, ecav-, and a dimeric solvent anion, (CH 3 CN)$_{2}^{•-}$, which are the two lowest energy states of the solvated electron in acetonitrile, has been investigated by pulse radiolysis at 233-353 K. The enthalpy and entropy for the e$_{cav}^{-}$ to (CH 3 CN)$_{2}^{•-}$ conversion amount to -11.2 ± 0.3 kcal/mol and -39.3 ± 1.2 cal/(mol K), corresponding to a 0.44 ± 0.35 equilibrium constant at 25 °C. The radiation yield of the solvated electron has been quantified using a Co(II) macrocycle that scavenges electrons with a 1.55 × 10 11 M -1 s -1 rate constant. The apparent yield increases without saturation over the attainable scavenger concentration range, reaching 2.8 per 100 eV; this value represents the lower limit for the acetonitrile ionization yield in pulse radiolysis. The apparent molar absorption coefficient of (20.8 ± 1.5) × 10 3 M -1 cm -1 at 1450 nm and 20 °C for the solvated electron and individual vis-near-infrared (NIR) absorption spectra of e$_{cav}^{-}$ and (CH 3 CN)$_{2}^{•-}$ are derived from the data. Variances with previous reports are thoroughly discussed. All together, these results resolve several controversies concerning the solvated electron properties in acetonitrile and furnish requisite data for quantitative pulse radiolysis investigations in this commonly used solvent.
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
Reactivity of Zn + aq in high-temperature water radiolysis
For this work, reactivity of transients involving Zn + in high-temperature water radiolysis has been studied in the temperature range of 25–300 °C. The reduced monovalent zinc species were generated from an electron transfer process between the hydrated electron and Zn 2+ ions using pulse radiolysis. The Zn + species can subsequently be oxidized by the radiolytically-produced oxidizing species: ˙OH, H 2 O 2 and ˙H. We find that the absorption of monovalent zinc is very sensitive to the pH of the medium. An absorption maximum at 306–311 nm is most pronounced at pH 7 and the signal then decreases in acidic media where the reducing electrons are competitively captured by protons. At pH values higher than 7, hydroxo-forms of Zn 2+ are created and the maximum of the absorption signal begins to shift to the red spectral region. We find that the optical spectrum of Zn + aq cannot be fully explained in terms of a charge-transfer to solvent (CTTS) process, which was previously proposed. Reaction rates of most of the recombination reactions investigated follow the empirical Arrhenius relationship at temperatures up to 200 °C and have been determined at higher temperatures for the first time. A bimolecular disproportionation reaction of Zn + aq is not observed under the conditions investigated.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Multiscale Evaluation of Acetohydroxamic Acid (AHA) Radiolysis Under Used Nuclear Fuel Reprocessing Solvent System Conditions
Acetohydroxamic acid (AHA) has been proposed as an alternative agent for the selective separation of plutonium and neptunium from co-extracted uranium during the reprocessing of used nuclear fuel. However, the fundamental radiolytic behavior of this molecule under envisioned process conditions – i.e., acidic biphasic solvent systems – is not sufficiently understood to support process applications. Here we present a systematic irradiation study (steady-state gamma and time-resolved pulsed electron) into the radiolytic integrity of AHA and formation of degradation products in aqueous nitric acid (HNO3) solutions (0.2 M) in presence and absence of an organic phase, comprising current (tri-butyl phosphate - TBP) and future (N,N-di-(2-ethylhexyl)butyramide - DEHBA and di-2-ethylhexylisobutyramide - DEHiBA) reprocessing ligands dissolved in n-dodecane diluent. Experimental data are complimented by predictive multiscale model calculations for the elucidation of underpinning mechanisms.
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
Selective Reduction of Carbon Dioxide in Water Using [M(bpy2+)(CO)3(I)]2+ (M = Mn, Re) Electrocatalysts with Pendent Cations
Manganese(I) carbonyl complexes are promising electrocatalysts for CO2 reduction, yet their application in homogeneous aqueous media remains limited by poor solubility and selectivity. Here, we report water-soluble Mn(I) and Re(I) complexes fac-[M(bpy2+)(CO)3X]2+ (X = I or Cl), featuring bipyridine ligands functionalized with -Ph-CH2-(NMe3)+ cationic ammonium groups that integrate water solubility with secondary-sphere stabilization. In bicarbonate buffer at pH 6.8, the Mn catalyst is completely selective for CO production at a low overpotential (η = 0.3 V), operating by a protonation-first mechanism with observed rates of ~10 s−1. Pulse radiolysis reveals that the one-electron reduced Mn species undergoes dimerization in the absence of CO2 but uniquely reacts competitively with CO2 through an initial pre-equilibrium followed by fast formation of a dinuclear CO2-bridged species (ΔGo = −12.4 kcal mol−1). At a higher 0.6 V over-potential, a faster reduction-first pathway (~100 s−1) is available upon reduction of the metallo-carboxylic acid intermediate, Mn-CO2H2+; however, this regime is functionally limited by the formation of a resistive, noncatalytic film on the electrode surface. Comparison to the analo-gous water-soluble Re catalyst (kobs = 440 s−1, η = 0.6 V) highlights the distinct mechanistic ad-vantages of earth-abundant Mn in low-potential catalysis. These results demonstrate how cati-onic second-sphere design enables selective, homogeneous CO2 reduction in water while reveal-ing competing radical and electrode-mediated processes that govern catalytic performance.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Sub-picosecond Production of Solute Radical Cations in Tetrahydrofuran after Radiolysis
Ultrafast hole transfer from solvent radical cations produced by radiolysis with ~10 ps, 9 MeV electron pulses to solutes was investigated in tetrahydrofuran (THF). Because of rapid fragmentation of initially produced THF +• , solute radical cations are not expected and have not previously been reported. Using 9,9-Dihexyl-2,7-dibromofluorene (Br 2 F) at 5 to 1000 mM, Br 2 F +• was observed with radiation chemical yields up to G = 2.23 / 100 eV absorbed. While more than half of this was the result of direct solute ionization, the results highlight the importance of capture of holes from THF +• prior to solvation and fragmentation. The observed data show a time-resolution limited (15 ps) rise in transient absorption of Br 2 F +• , identical in form to reports of pre-solvated or dry electron capture in water and a few organic liquids, including THF. The results were thus interpreted with a similar formalism, finding C 37 = 1.7 M, the concentration at which 37% of holes escape capture. The yield of solvent hole capture can be accounted for by the formation of solvent holes adjacent to solute molecules reacting faster than they can fragment, however mechanisms such as delocalized holes or rapid hopping may play a role. Finally, low temperature results find over two times more capture, supporting the speculation that if THF +• was longer lived, the yield of capture in under 15 ps would have been at least 2x larger at 1 M Br 2 F, possibly capturing nearly all available holes from the solvent.
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
Influence of metal ion complexation on the radiolytic longevity of butyramide extractants under direct dissolution conditions
The direct dissolution of volox-treated used nuclear fuel (UNF) into an organic solution—comprised of diluent and specialized extractants—poses a promising alternative to the traditional liquid-liquid solvent extraction approach to reprocessing UNF. However, moving to direct dissolution removes the presence of a concentrated nitric acid aqueous phase, which has been shown to significantly influence the radiolytic longevity of extractants in liquid-liquid solvent extraction flowsheets. With this in mind, and given the limited knowledge of radiation effects under direct dissolution conditions, we present a time-resolved and dose accumulation study on the impact of direct dissolution conditions on the radiolytic longevity of two candidate butyramide extractants—N,N-di-(2-ethylhexyl) butyramide (DEHBA) and N,N-di-(2-ethylhexyl)isobutyramide (DEHiBA)—in pre-equilibrated n-dodecane solvent in the presence and absence of process relevant metal ions, uranium and rhenium. Rhenium, and by extension technetium, extraction had little impact (=10%) on the overall radiolytic stability of these ligands, despite observed increases in chemical kinetic reactivity (>2×) of the corresponding complexes with the n-dodecane radical cation. Uranium-loading on the other hand, significantly improved the lifetime of both ligands (>30%) under gamma irradiation, with a greater stabilization observed for DEHBA over DEHiBA. This draft manuscript has been prepared in fulfillment of NTRD-MRWFD-2024 M3FT-24IN030101115.
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
Ionic Liquids under Radiation and the Dimer Radical Dicyanamide Anion
Ionic liquids (ILs) used in solar, electrochemical, nuclear, or even space exploration applications will necessarily be exposed to conditions in which electron detachment may occur and transient charge-depleted radical species may form. In a recent article (J. Am. Chem. Soc. 2025, 147, 23395–23398), we studied the different possible kinetic fates of an excess electron in the popular 1-butyl-1-methylpyrrolidinium dicyanamide IL but did not address the nature of electron-deficient transient radical species these leaving electrons produce, the so-called holes. Using pulse radiolysis measurements and first-principles calculations in the bulk and gas phases to interpret these, we show that the most likely hole species in this IL is a dimer radical anion that, somewhat surprisingly, has similar spectral features to the excess electron, including a broad near-infrared absorption band.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗