Applied Radiation Chemistry: Theory, Methods and Applications

Introduction

Radiation chemistry deals with chemical processes initiated by the interaction of high-energy photons (X-rays) or charged particles (electrons, protons, alpha or heavy ions) with matter. Such radiation results in the ionization of the medium, and hence is called ionizing radiation [1]. As ionizing radiation produces highly reactive chemical species, radiation techniques enable one to unravel complex mechanisms initiated by short-lived radicals and offer a wide range of technological applications. Since the first application on an industrial scale over 60 years ago, radiation technologies have been proven to be reliable, efficient, versatile, economical and environmentally friendly. Major high-volume application fields include sterilization and polymer processing, but new directions leading to products of high added value are being currently developed. New experimental and simulation tools make it possible to obtain a more detailed insight into the physical and chemical phenomena underlying these developments. Understanding radiation chemistry is also essential for the sustainable development of the nuclear power industry, in particular, for the processing of nuclear fuel, handling radioactive waste and maintaining the integrity of materials in currently operating nuclear power reactors. Fast progress and continuously rising interest in technologies involving the interactions of ionizing radiation with matter encouraged us to collate the latest research on current and emerging applications of radiation chemistry in this Special Issue of Applied Sciences.

This Special Issue on Applied Radiation Chemistry: Theory, Methods and Applications includes 3 reviews and 11 original articles authored by researchers from America, Asia and Europe. These papers cover the following subjects: applications of ionizing radiation in nanotechnology, green processing and product design, radiation synthesis and processing of advanced polymeric and non-polymeric materials, radiation chemistry applications in nuclear power engineering, radiation technologies for water purification and new irradiation equipment and facilities. More details about the published papers are outlined below.

A review by the Frederick Currell’s group described the radiation facilities and equipment at the Dalton Cumbrian Facility, opened to support the UK’s nuclear industry [2]. Examples of measurements performed using these facilities were also presented by the authors to illustrate the importance of radiation research for the nuclear power industry, material chemistry and healthcare. The following three papers focused on the challenges and problems related to the nuclear power industry and engineering. A. Gasiorowski from the Lodz University of Technology and co-workers synthesized the phosphate glass samples doped with Tb₂O₃ for usage in thermoluminescence dosimetry (TDL) in high-activity nuclear waste disposals [3]. The investigated dosimetric system is reusable and the dosimeter reading requires only a basic TL reader without any modifications. The second paper authored by B. Pastina from Posiva Oy and J. A. LaVerne from the University of Notre Dame dealt with the problem of the fractional radionuclide release rate from the UO₂ matrix, which is essential for the assessment of the long-term safety of the direct disposal of spent nuclear fuel in deep geologic repositories [4]. The authors emphasized that the commonly used value of 10⁻⁷ radionuclide per year is overestimated, so they proposed a more reliable assessment, including the processes at the fuel/water interface, which keep the spent fuel surface in a reduced state. The third paper by D. Swiatla-Wojcik from the Lodz University of Technology was a simulation study addressing the development of effective methods to control and minimize the corrosive environment associated with the radiolysis of a coolant in light-water nuclear power reactors [5]. The simulation indicated the synergic effect of H₂ gas and base, added to the coolant, on the diminishment of the steady-state concentration of harmful oxidants (O₂ and H₂O₂).

A review authored by A. Bojanowska-Czajka from the Institute of Nuclear Chemistry and Technology concerned the application of ionizing radiation to the removal of biodegradable organic pollutants after conventional wastewater treatment [6]. The author focused on the radiation-assisted degradation of endocrine disruptors that are extremely dangerous for living organisms, even at low concentrations. The use of electron beam (EB) for wastewater treatment was also a subject of the original paper by U. Gryczka and co-workers from the same institution [7]. Based on the experiments and Monte Carlo simulation of the dose distribution, the authors proposed solutions that can minimize the size and the cost of the shielding construction in EB installations.

Product design and further synthesis and material processing in order to obtain advanced functional materials using radiation technologies were covered by four publications. O. Güven from the Hacettepe University reviewed the applications of ionizing radiation to nano-scale grafting, and to the synthesis and modification of various nanomaterials, including carbon-based, metal-based and polymer-based nanomaterials [8]. The author described the methods and highlighted their importance. The radiation-induced synthesis of nano-sized polymeric materials, such as nanogels, was the subject of the paper by M. Matusiak and co-workers from the Lodz University of Technology [9]. The authors explored the dependence of the crosslinking mechanism of poly(acrylic acid) on pH, that is one of the main factors controlling inter- and intra-molecular recombination of polyion macroradicals in aqueous solution. The radiation synthesis of nanogels is advantageous over conventional, chemical synthesis methods, especially for medical applications. The development of pH-sensitive delivery systems was addressed by C. Yu and collaborators from Peking University, who showed that the γ-radiation-initiated polymerization of cyclic ethers in aqueous solution led to the pH-controlled formation of microspheres or micelles [10]. Such microcapsules may be used in drug delivery systems or in the oil extraction industry.

One of the key applications of radiation technology is the processing of polymeric materials and composites in order to render them new, unique features. G. Ranoux et al. from Université de Reims Champagne Ardenne proved that the radiation-induced curing of epoxy-aromatic resins is less sophisticated and less time consuming than the conventional thermal curing and produces high-performance composites of an enhanced durability [11].

The application of ionizing radiation to the processing of nature-derived materials was the subject of four papers [12,13,14,15]. J. Du and co-workers from the Hubei University of Science and Technology and Huazhong Universities of Science and Technology developed a method of bamboo sawdust modification through the radiation-induced grafting of glycidyl methacrylate and further ring-opening reactions with amine-containing compounds. They evidenced that phosphates absorption by the product may be enhanced by amines modifications [12]. Compared to conventional synthesis, the radiation method reduced the synthesis time from tens of hours to several minutes. The paper by M. Al-Sheikhly’s group from the University of Maryland raised the problem of food packaging subject to radiation disinfection [13]. The authors showed that the radiation-induced modification of biodegradable poly(lactic acid) film used for food packaging did not change the gas permeability property, and the degradation of polymer chains could accelerate the decomposition of composted packaging. The processing of natural polymers with ionizing radiation was also explored by A. Hiroki and M. Taguchi from the National Institutes for Quantum and Radiological Science and Technology. They used a radiation crosslinking technique to synthesize biodegradable cellulose derivative-based hydrogels for soft contact lenses [14]. Multicomponent hydrogels have an excellent transparency and possess mechanical properties adequate to the proposed application. The paper by R. A. Wach and collaborators from the Lodz University of Technology and the Università degli Studi di Palermo described the results of the radiation-induced crosslinking of polysaccharides modified with hydroxypropyl and carboxymethyl functional groups to produce dual stimuli-responsive hydrogels [15]. The authors demonstrated that the extent of water uptake can be easily tuned by the composition and the radiation dose, and further controlled by the pH and temperature of the aqueous environment.

This Special Issue provides an insight into the recent developments and current trends in applications of radiation chemistry in various fields, including medicine and pharmacology, environment protection, material engineering and the nuclear power industry. The versatility of materials synthesized or modified without the use of harmful additives allows radiation technologies to be environmentally friendly and contributes to sustainable development.