Radiation chemistry and the nuclear fuel cycle

A global collaboration is currently developing solvent extraction separations for the nuclear fuel cycle of the future. The goal is to recover fissionable material for recycle, mitigate proliferation concerns, and mitigate the environmental impact of nuclear waste disposal. Relying on selective metal complexing agents, the radiation stability of these solvent extraction ligands will determine the efficiency and recycle lifetime of any solvent intended for use in this high-radiation environment. This paper reviews work at the Idaho National Laboratory regarding the radiation chemistry of nuclear solvent extraction ligands, with particular emphasis on the reactions of nitrogen-centered radicals.     

Radiation hydrolysate of tuna cooking juice with enhanced antioxidant properties

Tuna protein hydrolysates are of increasing interest because of their potential application as a source of bioactive peptides. Large amounts of tuna cooking juice with proteins and extracts are produced during the process of tuna canning, and these cooking juice wastes cause environmental problems. Therefore, in this study, cooking juice proteins were hydrolyzed by irradiation for their utilization as functional additives. The degree of hydrolysis of tuna cooking juice protein increased from 0% to 15.1% at the absorbed doses of 50 kGy. To investigate the antioxidant activity of the hydrolysate, it was performed the ferric reducing antioxidant power (FRAP) assay, and the lipid peroxidation inhibitory and superoxide radical scavenging activities were measured. The FRAP values increased from 1470 μM to 1930 μM and IC₅₀ on superoxide anion was decreased from 3.91 μg/mL to 1.29 μg/mL at 50 kGy. All of the antioxidant activities were increased in the hydrolysate, suggesting that radiation hydrolysis, which is a simple process that does not require an additive catalysts or an inactivation step, is a promising method for food and environmental industries.     

Progress of diffraction enhanced imaging at the Beijing Synchrotron Radiation Facility

A simple framework that allows a new general diffraction enhanced imaging (DEI) equation to be derived is presented. This latter equation may explain all open problems associated with the equation introduced by Chapman and those not explained by the first DEI equation, such as the noise background due to the small-angle scattering reflected by the analyzer. Combing the DEI equation with computed tomography (CT) theory, we propose a new DEI–CT formula that explains qualitatively the contour contrast caused by extinction of the refraction. Two formulae with a new method to extract the refraction angle are also introduced. Within this new theoretical framework the three components of the gradient of the refractive index can be reconstructed.     

Gold immunochromatographic strips for enhanced detection of Avian influenza and Newcastle disease viruses

A new technique that uses gold immunochromatographic strips enhances the detection sensitivity by inducing the clustering of additional gold nanoparticles (AuNPs) around the immunogold particles immobilized on nitrocellulose strips. The additional AuNPs provide an intense signal that can be detected by the naked eye. The AuNPs were synthesized and conjugated to monoclonal antibodies using self-assembly. Other antibodies were immobilized in a defined detection zone on the nitrocellulose membrane. The detection principle is based on a “sandwich” immunoreaction, where gold-labeled antibodies serve as signal vehicles. To improve the sensitivity of the strips, we use a mixture of 1% HAuCl₄ and 10 mmol L⁻¹ NH₂OH·HCl to “enlarge” the gold nanoparticles. The detecting limits of Avian influenza virus (AIV) and Newcastle disease virus (NDV) are significantly increased. Compared with commercial test strips, this method is 100-fold more sensitive. This method is easy to perform and can be carried out on-site in test laboratories.     

Radiation vulcanization of NR/SBR composite enhanced with different polyfunctional monomers

The effect of different polyfunctional monomers (PFMs) as enhancing agents on the properties of natural rubber/styrene-butadiene rubber blend reinforced with 40 (phr) part per hundred part of rubber, by weight of HAF carbon black and vulcanized with gamma irradiation was investigated. The coagents N,N’ methylene diacrylamide (MDA), trimethylol propane-trimethacrylate (TMPTMA) and trimethylol-methane tetraacrylate (TMMTA) were used at a constant content of 5 phr. The physico-chemical properties such as tensile strength, tensile modulus at 100 % elongation, elongation at break, gel fraction and swelling number were studied. The results indicated that the properties are greatly improved by PFMs at lower doses. TMMTA as coagent is more effective than TMPTMA and MDA.     

Radiation chemistry of aqueous iodine systems under nuclear reactor accident conditions

Radiation-chemical behavior of cesium iodide solutions was investigated using a once-through flow system in relation to the behavior of radioactive iodine under the condition of nuclear reactor accidents. It was found that several factors such as initial concentration of CsI, pH and O₂ concentration have a large influence on the oxidation-reduction reactions in the radiolysis of the iodide solutions. A pulse radiolysis technique was applied to this system to obtain clearer understanding of the radiolysis mechanism, and the rate constants were measured with the several important reactions involved.     

Radiation crosslinking of poly(vinyl chloride) enhanced by a tetrafunctional coagent

Irradiations were carried out with mixtures of poly(vinyl chloride) and a solvent capable of preventing the polymer from discoloration, such as tetrahydrofuran or cyclohexanone, both in the absence and in the presence of a tetrafunctional monomer (ethyleneglycol dimethacrylate) acting as a coagent for enhanced crosslinking. Comparison of the results enabled formulation of a reaction scheme based on an early depletion of the free coagent molecules via polymerization. In the early stages, the PVC macromolecules, whenever dissociated into free radicals, initiate a chain addition of coagent molecules resulting in the formation of complex macromolecules with a number of pendant CC groups. All the latter macromolecules, because of their high susceptibility to radical attack, grow rapidly and eventually become part of the gel portion. In the late stages, radical addition to pendant CC groups in the gel network still occurs effectively but the addition steps are very few and there may be only one such step before radical deactivation. Hence, there is small consumption of double bonds; further, the PVC macromolecules, once homolytically dissociated, are directly incorporated into the gel. An interesting consequence is that no crosslinked macromolecules remain in the sol portion. The influence of the solvent is discussed.     

Radiation measurements and radioecological aspects of fallout from the Fukushima nuclear accident

Fallout from the Fukushima Nuclear Accident has been monitored for about 1 month in Thessaloniki, Northern Greece. Three different radionuclides, one short-lived, one relatively long-lived and one long-lived fission product were identified in air, precipitation, soil, grass and milk samples. The ¹³¹I, ¹³⁷Cs and ¹³⁴Cs activity concentrations in air reached 497, 145 and 126 μBq m⁻³, respectively on 4 April, 2011. The external exposure dose rate to humans of the order of 14.4 pSv per day due to ¹³⁷Cs deposited on the ground was very small compared to the normal background level. The accumulated dose equivalent to the adult thyroid from inhaled ¹³¹I varied from 0.4 to 3.5 nSv per day was insignificant and there was not any problem for the Greek population and no preventive measures were needed to be provided against the nuclear accident according to the Greek Atomic Energy Commission, the official agent of the Greek Government. Some special radioecological aspects in the air-grass-cow-milk-man pathway for ¹³¹I were particularly studied.     

Radiation protection relevant to nuclear chemistry in the light of recent international recommendations

The paper discusses the requirements for radiation protection in nuclear chemistry which are related to the recent recommendations of the International Commission on Radiological Protection. These recommendations have been incorporated into the updated International Basic Safety Standards issued by the International Atomic Energy Agency as well as into new relevant Directives of the European Union based on which the legislation of the EU Member States has to be updated. The new international requirements are aimed at the further improvement of strict control of radiation sources, their safety and security as well as the minimization of exposure to workers and members of the public. It would be appropriate for the nuclear chemistry community to become familiar with the changes in radiation protection so that it would be easier for nuclear chemists to adopt new requirements in their everyday practical work.     

Simultaneous acquisition of multi-nuclei enhanced NMR/MRI by solution-state dynamic nuclear polarization

Dynamic nuclear polarization (DNP) has become a very important hyperpolarization method because it can dramatically increase the sensitivity of nuclear magnetic resonance (NMR) of various molecules. Liquid-state DNP based on Overhauser effect is capable of directly enhancing polarization of all kinds of nuclei in the system. The combination of simultaneous Overhauser multi-nuclei enhancements with the multi-nuclei parallel acquisitions provides a variety of important applications in both MR spectroscopy (MRS) and image (MRI). Here we present two simple illustrative examples for simultaneously enhanced multi-nuclear spectra and images to demonstrate the principle and superiority. We have observed very large simultaneous DNP enhancements for different nuclei, such as ¹H and ²³Na, ¹H and ³¹P, ¹⁹F and ³¹P, especially for the first time to report sodium ion enhancement in liquid. We have also obtained the simultaneous images of ¹⁹H and ³¹P, ¹⁹F and ³¹P at low field by solution-state DNP for the first time.     

Davies electron-nuclear double resonance revisited: enhanced sensitivity and nuclear spin relaxation

Over the past 50 years, electron-nuclear double resonance (ENDOR) has become a fairly ubiquitous spectroscopic technique, allowing the study of spin transitions for nuclei which are coupled to electron spins. However, the low spin number sensitivity of the technique continues to pose serious limitations. Here we demonstrate that signal intensity in a pulsed Davies ENDOR experiment depends strongly on the nuclear relaxation time T(1n), and can be severely reduced for long T(1n). We suggest a development of the original Davies ENDOR sequence that overcomes this limitation, thus offering dramatically enhanced signal intensity and spectral resolution. Finally, we observe that the sensitivity of the original Davies method to T(1n) can be exploited to measure nuclear relaxation, as we demonstrate for phosphorous donors in silicon and for endohedral fullerenes N@C(60) in CS(2).     

A new model for Overhauser enhanced nuclear magnetic resonance using nitroxide radicals

Nitroxide free radicals are the most commonly used source for dynamic nuclear polarization (DNP) enhanced nuclear magnetic resonance (NMR) experiments and are also exclusively employed as spin labels for electron spin resonance (ESR) spectroscopy of diamagnetic molecules and materials. Nitroxide free radicals have been shown to have strong dipolar coupling to (1)H in water, and thus result in large DNP enhancement of (1)H NMR signal via the well known Overhauser effect. The fundamental parameter in a DNP experiment is the coupling factor, since it ultimately determines the maximum NMR signal enhancements which can be achieved. Despite their widespread use, measurements of the coupling factor of nitroxide free radicals have been inconsistent, and current models have failed to successfully explain our experimental data. We found that the inconsistency in determining the coupling factor arises from not taking into account the characteristics of the ESR transitions, which are split into three (or two) lines due to the hyperfine coupling of the electron to the (14)N nuclei (or (15)N) of the nitric oxide radical. Both intermolecular Heisenberg spin exchange interactions as well as intramolecular nitrogen nuclear spin relaxation mix the three (or two) ESR transitions. However, neither effect has been taken into account in any experimental studies on utilizing or quantifying the Overhauser driven DNP effects. The expected effect of Heisenberg spin exchange on Overhauser enhancements has already been theoretically predicted and observed by Bates and Drozdoski [J. Chem. Phys. 67, 4038 (1977)]. Here, we present a new model for quantifying Overhauser enhancements through nitroxide free radicals that includes both effects on mixing the ESR hyperfine states. This model predicts the maximum saturation factor to be considerably higher by the effect of nitrogen nuclear spin relaxation. Because intramolecular nitrogen spin relaxation is independent of the nitroxide concentration, this effect is still significant at low radical concentrations where electron spin exchange is negligible. This implies that the only correct way to determine the coupling factor of nitroxide free radicals is to measure the maximum enhancement at different concentrations and extrapolate the results to infinite concentration. We verify our model with a series of DNP experimental studies on (1)H NMR signal enhancement of water by means of (14)N as well as (15)N isotope enriched nitroxide radicals.     

Semi-quantitative trace analysis of nuclear fast red by surface enhanced resonance Raman scattering

The dye nuclear fast red has been detected and determined semi-quantitatively by means of surface enhanced resonance Raman scattering (SERRS) and surface enhanced Raman scattering (SERS), using laser exciting wavelengths of 514.5 and 632.8 nm, respectively, by employing a citrate-reduced silver colloid. A good linear correlation is observed for the dependence of the intensities of the SERRS bands at 989 cm⁻¹ (R=0.9897) and 1278 cm⁻¹ (R=0.9872) on dye concentration over the range 10⁻⁹ to 10⁻⁷ M, when using an exciting wavelength of 514.5 nm. At dye concentrations above 10⁻⁷ M, the concentration dependence of the SERRS signals is non-linear. This is almost certainly due to the coverage of the colloidal silver particles being in excess of a full monolayer of the dye. A linear correlation is also observed for the dependence of the intensities of the SERS bands at 989 cm⁻¹ (R=0.9739) and 1278 cm⁻¹ (R=0.9838) on the dye concentration over the range 10⁻⁸ to 10⁻⁶ M when using an exciting wavelength of 632.8 nm. Strong fluorescence prevented collection of resonance Raman scattering (RRS) spectra from powdered samples or aqueous solutions of the dye using an exciting wavelength of 514.5 nm, but weak bands were observed in the spectra obtained from both powdered and aqueous samples of the dye using an exciting wavelength of 632.8 nm. A study of the pH dependence of SERRS/SERS and UV–VIS absorption spectra revealed the presence of different ionisation states of the dye. The limits of detection for nuclear fast red by SERRS (514.5 nm), SERS (632.8 nm) and visible spectroscopy (535 nm) are 9, 89 and 1000 ng ml⁻¹, respectively.     

Radiation durability of aluminophosphate glass prepared for the stable storage of high-level nuclear wastes

⁵⁷Fe Mössbauer spectra of 30CaO·15Al₂O₃·5Fe₂O₃·25PbO·25P₂O₅ glass consist of two quadrupole doublets due to distorted Fe(III)O₆ and Fe(II)O₆ octahedra. Mössbauer spectra of the aluminophosphate glass irradiated with⁶⁰Co γ-rays (≈5·10⁴Gy) were essentially the same as those of non-irradiated glass. Mössbauer spectra of γ-ray irradiated aluminophosphate glass, containing 10 stable isotopes (Sr, Y, Zr, Nb, Mo, Ba, La, Ce, Pr, and Nd) as the simulated nuclear waste, were also the same as those of non-irradiated glass. These results indicate that the aluminophosphate glass containing iron and lead has high radiation-durability, in addition to high heat resistivity and high water resistivity.     

Fluorescent and colorimetric immunoassay of nuclear matrix protein 22 enhanced by porous Pd nanoparticles

A new modified ELISA enhanced by porous Pd nanoparticles for colorimetric and fluorescence dual-modal immunoassay of nuclear matrix protein 22 has been demonstrated. Benefited from different signalreadout and independent signal amplified mechanism, the improved ELISA will afford more reliable detection performance, which can bring high promising for clinical diagnosis.