Simon Pimblott

Reactions of Cr(ii) and Cr(iii) with the primary radiolytic transient species (solvated electron and Cl₂˙⁻) in molten eutectic LiCl–KCl were characterized, including the reactivity of their products.

Acetohydroxamic acid (AHA) has been proposed for inclusion in advanced, single‐cycle, used nuclear fuel reprocessing solvent systems for the reduction and complexation of plutonium and neptunium ions. For this application, a detailed description of the fundamental degradation of AHA in dilute aqueous nitric acid is required. To this end, we present a comprehensive, multiscale computer model for the coupled radiolytic and hydrolytic degradation of AHA in aqueous sodium nitrate and nitric acid solutions. Rate coefficients for the reactions of AHA and hydroxylamine (HA) with the oxidizing nitrate radical were measured for the first time using electron pulse radiolysis and used as inputs for the kinetic model. The computer model results are validated by comparison to experimental data from steady‐state gamma ray irradiations, for which the agreement is excellent. The presented model accurately predicts the yields of the major degradation products of AHA: acetic acid, HA, nitrous oxide, and molecular hydrogen.

Acetohydroxamic acid (AHA) has been proposed for inclusion in advanced, single‐cycle, used nuclear fuel reprocessing solvent systems for the reduction and complexation of plutonium and neptunium ions. For this application, a detailed description of the fundamental degradation of AHA in dilute aqueous nitric acid is required. To this end, we present a comprehensive, multiscale computer model for the coupled radiolytic and hydrolytic degradation of AHA in aqueous sodium nitrate and nitric acid solutions. Rate coefficients for the reactions of AHA and hydroxylamine (HA) with the oxidizing nitrate radical were measured for the first time using electron pulse radiolysis and used as inputs for the kinetic model. The computer model results are validated by comparison to experimental data from steady‐state gamma ray irradiations, for which the agreement is excellent. The presented model accurately predicts the yields of the major degradation products of AHA: acetic acid, HA, nitrous oxide, and molecular hydrogen.

A comprehensive multiscale model determines the fundamental reaction mechanisms of the radical-induced degradation of acetohydroxamic acid in acidic aqueous solutions.

Primary radiolytic species such as the solvated electron (e_s^–) and Cl₂^•– are key to predicting radiation effects on the long-term behavior of molten salt reactor fuel.

Primary radiolytic species such as the solvated electron (e_s^–) and Cl₂^•– are key to predicting radiation effects on the long-term behavior of molten salt reactor fuel.

Room temperature post-irradiation measurements of diffuse reflectance and EPR spectroscopies were made to characterize the long-lived radiation-induced species formed upon gamma irradiation (up to 100 kGy) of solid KCl, MgCl₂, and ZnCl₂ salts.

Room temperature post-irradiation measurements of diffuse reflectance and EPR spectroscopies were made to characterize the long-lived radiation-induced species formed upon gamma irradiation (up to 100 kGy) of solid KCl, MgCl₂, and ZnCl₂ salts.

This article describes the radiation facilities and associated sample preparation, management, and analysis equipment currently in place at the Dalton Cumbrian Facility, a facility which opened in 2011 to support the UK’s nuclear industry. Examples of measurements performed using these facilities are presented to illustrate their versatility and the breadth of research they make possible. Results are presented from research which furthers our understanding of radiation damage to polymeric materials, radiolytic yield of gaseous products in situations relevant to nuclear materials, radiation chemistry in light water reactor cooling systems, material chemistry relevant to immobilization of nuclear waste, and radiation-induced corrosion of fuel cladding elements. Applications of radiation chemistry relevant to health care are also described. Research concerning the mechanisms of radioprotection by dietary carotenoids is reported. An ongoing open-labware project to develop a suite of modular sample handling components suited to radiation research is described, as is the development of a new neutron source able to provide directional beams of neutrons.

To facilitate the development of molten salt reactor technologies, a fundamental understanding of the physical and chemical properties of molten salts under the combined conditions of high temperature and intense radiation fields is necessary. Optical spectroscopic (UV–Vis–near IR) and electrochemical techniques are powerful analytical tools to probe molecular structure, speciation, thermodynamics, and kinetics of solution dynamics. Here, we report the design and fabrication of three custom-made apparatus: (i) a multi-port spectroelectrochemical furnace equipped with optical spectroscopic and electrochemical instrumentation, (ii) a high-temperature cell holder for time-resolved optical detection of radiolytic transients in molten salts, and (iii) a miniaturized spectroscopy furnace for the investigation of steady-state electron beam effects on molten salt speciation and composition by optical spectroscopy. Initial results obtained with the spectroelectrochemical furnace (i) and high-temperature cell holder (ii) are reported.

A computational Monte Carlo simulation approach for modeling the thermalization of low‐energy electrons is presented. The simulation methods rely on, and use, experimentally based cross sections for elastic and inelastic collisions. To demonstrate the different simulation options, average numbers of interactions and the range of low‐energy electrons with initial energies ranging from 1 to 20 eV are calculated for density normalized gaseous water. Experimental gas‐phase cross sections for (subexcitation) electrons of energies in the range of 1–20 eV were taken from the compilation of Hayashi. The ballistic collision‐by‐collision simulations provide information on the intricacies of the thermalization processes not available experimentally. © 2018 Wiley Periodicals, Inc.

Evaluating the radiation stability of mineral phases is a vital research challenge when assessing the performance of the materials employed in a Geological Disposal Facility for radioactive waste. This report outlines the setup and methodology for efficiently allowing the determination of the dose dependence of damage to a mineral from a single ion irradiated sample. The technique has been deployed using the Dalton Cumbrian Facility’s 5 MV tandem pelletron to irradiate a suite of minerals with a controlled α-particle (4He2+) beam. Such minerals are proxies for near-field clay based buffer material surrounding radioactive canisters, as well as the sorbent components of the host rock.

Evaluating the radiation stability of mineral phases is a vital research challenge when assessing the performance of the materials employed in a Geological Disposal Facility for radioactive waste. This report outlines the setup and methodology for efficiently allowing the determination of the dose dependence of damage to a mineral from a single ion irradiated sample. The technique has been deployed using the Dalton Cumbrian Facility’s 5 MV tandem pelletron to irradiate a suite of minerals with a controlled α-particle (4He2+) beam. Such minerals are proxies for near-field clay based buffer material surrounding radioactive canisters, as well as the sorbent components of the host rock.

Microbial communities have the potential to control the biogeochemical fate of some radionuclides in contaminated land scenarios or in the vicinity of a geological repository for radioactive waste. However, there have been few studies of ionizing radiation effects on microbial communities in sediment systems. Here, acetate and lactate amended sediment microcosms irradiated with gamma radiation at 0.5 or 30 Gy h ⁻¹ for 8 weeks all displayed NO ₃ ⁻ and Fe(III) reduction, although the rate of Fe(III) reduction was decreased in 30-Gy h ⁻¹ treatments. These systems were dominated by fermentation processes. Pyrosequencing indicated that the 30-Gy h ⁻¹ treatment resulted in a community dominated by two Clostridial species. In systems containing no added electron donor, irradiation at either dose rate did not restrict NO ₃ ⁻ , Fe(III), or SO ₄ ²⁻ reduction. Rather, Fe(III) reduction was stimulated in the 0.5-Gy h ⁻¹ -treated systems. In irradiated systems, there was a relative increase in the proportion of bacteria capable of Fe(III) reduction, with Geothrix fermentans and Geobacter sp. identified in the 0.5-Gy h ⁻¹ and 30-Gy h ⁻¹ treatments, respectively. These results indicate that biogeochemical processes will likely not be restricted by dose rates in such environments, and electron accepting processes may even be stimulated by radiation.

Combined microfocus XAS and XRD analysis of α-particle radiation damage haloes around thorium-containing monazite in Fe-rich biotite reveals changes in both short- and long-range order. The total α-particles flux derived from the Th and U in the monazite over 1.8 Ga was 0.022 α particles per atomic component of the monazite and this caused increasing amounts of structural damage as the monazite emitter is approached. Short-range order disruption revealed by Fe K-edge EXAFS is manifest by a high variability in Fe–Fe bond lengths and a marked decrease in coordination number. XANES examination of the Fe K-edge shows a decrease in energy of the main absorption by up to 1 eV, revealing reduction of the Fe³⁺ components of the biotite by interaction with the ₂⁴He²⁺, the result of low and thermal energy electrons produced by the cascade of electron collisions. Changes in d spacings in the XRD patterns reveal the development of polycrystallinity and new domains of damaged biotite structure with evidence of displaced atoms due to ionization interactions and nuclear collisions. The damage in biotite is considered to have been facilitated by destruction of OH groups by radiolysis and the development of Frenkel pairs causing an increase in the trioctahedral layer distances and contraction within the trioctahedral layers. The large amount of radiation damage close to the monazite can be explained by examining the electronic stopping flux.

The dissociation energetics in the phenol+⋯Ar2(2π) cluster ion have been investigated using photoionization efficiency and mass analyzed threshold ionization spectroscopy. The appearance energies for the loss of one and two Ar atoms are determined as ∼210 and ∼1115 cm−1, respectively. The difference between the appearance energy for the first Ar ligand in phenol+⋯Ar2(2π) and the dissociation energy of the phenol+⋯Ar(π) dimer (535 cm−1) is explained by the isomerization of one π-bound Ar ligand to the OH binding site (H-bond) upon ionization. The energy difference between phenol+⋯Ar2(2π) and phenol+⋯Ar2(H/π) could also be estimated to be around 325 cm−1, which corresponds roughly to the difference of the binding energy of a π-bound and H-bound Ar ligands. The binding energy of the H-bound Ar atom in phenol+⋯Ar2(H/π) is derived to be ∼905 cm−1.

The cooling water of nuclear reactors undergoes radiolytic decomposition induced by gamma, fast electron, and neutron radiation in the core. To model the process, recombination reaction rates and radiolytic yields for the water radical fragments need to be measured at high temperature and pressure. Yields for the action of neutron radiation are particularly hard to determine independently because of the beta/gamma field also present in any reactor. In this paper we report the design of an apparatus intended to measure neutron radiolysis yields as a function of temperature and pressure. A new methodology for separation of neutron and beta/gamma radiolysis yields in a mixed radiation field is proposed and demonstrated.

Muonium formation in liquid hexane is examined by computer simulation. In track-end competition between muonium formation and cation–electron recombination, the muon is found to react with electrons from a significant part of the track end, corresponding to an energy attenuation of several tens of keV and a length of several microns. This muonium formation extends to microseconds following muon implantation. Delayed muonium formation leads to a much smaller amplitude of the muonium asymmetry than for prompt muonium formation during slowing down of the muon, and in this way may account for the missing polarization in transverse magnetic field experiments. If reaction of muons with electrons from their radiolysis tracks contributes to the experimentally observed muonium yield, the muon must thermalize between 60 and 150 nm from the last ionization of the track to reproduce the amplitudes of the muon and muonium asymmetries. For the smallest distance, 60 nm, the experimentally observed muonium asymmetry results from delayed muonium only. As the muon thermalization distance increases, prompt muonium formation also contributes, so that at 150 nm the observed asymmetry is almost entirely due to prompt muonium formation.

Recently we presented [Chem. Phys. Lett. 142, 385 (1987)] a method for calculating the diffusion-controlled geminate escape probability of an ion pair in an anisotropic medium. The escape probability depends on both the length and the direction of the initial interion vector, and is reducible to a function of two dimensionless variables describing the overall anisotropy of the medium. In this paper the treatment is extended to include an initial distribution of interion distances and an external field. Inclusion of a field increases the number of independently variable parameters to five: two to describe the anisotropy of the medium and three to describe the intensity and direction of the applied field. It is shown that the effects of including anisotropy are not negligible for the typical case of anthracene and that the slope-to-intercept ratio of the field-dependent escape probability for a spherically averaged distribution depends on the direction of the applied field.