Absorbed doses are heterogeneously distributed in microscopic scales such as DNA and cell nucleus. In order to clarify the influence of the microscopic dose heterogeneity on radiation effects, the probability density of microscopic doses should be evaluated. This report briefly reviews the concept of microscopic dose heterogeneity, and summarizes the features and applications of our developed model for calculating their probability density.
Dosimetry systems whose principle or design are base on radiation chemistry, so-called chemical dosimetry systems, are applied to absorbed dose measurements in radiation processing and radiomedical diagonostic treatment. Such dosimetry systems are overviewed assosiating with their useful roll for quality control/quality assurance, related international standards for their standardization, and so on.
The basic processes in solid-state radiation detectors, with main emphasis on their influence on energy resolution, are overviewed. We discuss the statistics of the number of electron–hole pairs, scintillation light yield dependent on the incident energy of γ rays, and the energy transfer process in scintillators that have dopants as luminescence centers. These processes are discussed in relation with the initial processes in radiation chemistry.
To understand the mechanisms of radiation biological effects, modeling and simulation studies are important. In particular, simulation approach is powerful tool to evaluate certain assumptions of mechanisms and the relationship among experimental results in different levels of biological systems. This article summarizes our approach to evaluate radiation action on DNA and cells by combination of knowledge in radiation physics, chemistry and biology. It contains theoretical approach to estimate physico-chemical process of DNA damage induction. Outline of the mathematical model for dynamics of DNA damage and cellular response is also presented.
Due to the extremely high viscosity of ionic liquid at low temperatures, solvation dynamics around excess electrons are quite slow. Therefore, it is possible to measure reactivity of dry electron and its absorption spectra though these measurements are quite difficult uner room temperature condition.
Radiation effects on the mixtures of inorganic oxides and water have been investigated for understanding radiation chemistry in solid–liquid systems. A number of studies revealed that energy deposition on solid phase stimulates reactions at the interface. This energy/charge transfer has been demonstrated by experiments to affect early stage of the radiolysis. However, the interfacial reactions subsequent to the energy/charge transfer require further studies. Here, we will see gaps between the basic understanding on the early stage and radiation effects connected to applications, taking zeolite/water and uranium oxide/water interfaces for examples. In the zeolite/water mixtures, the amount of hydrogen production is generally higher than that expected from the water content in the mixtures. The increases in hydrogen are interpreted by the concept of energy/charge transfer, but not quantitatively explained. The interfacial reactions on uranium oxides have an impact on the corrosion of nuclear fuel in contact with water, especially at the grain boundaries. However, the reactions are still unknown except for hydrogen peroxide and oxygen. Understanding of the interfacial reactions subsequent to the energy/charge transfer would bridge these gaps and enable to predict the radiation effects in applications.
Insoluble inorganic compound, extractant, and enzyme were immobilized into the graft-chain phase formed onto a commercially available 6-nylon fiber by radiation-induced graft polymerization and subsequent chemical modifications. Insoluble cobalt ferrocyanide-impregnated fiber has removed radioactive caesium ions from water contaminated with radionuclides at TEPCO Fukushima Dai-ichi Nuclear Power Plant. Additionally, HDEHP-impregnated and urease-immobilized fibers were applicable to the recovery of rare-earth ions such as Nd and Dy in an acidic medium and the hydrolysis of urea in water, respectively.
History of the lithography for high volume manufacturing of semiconductor devices based on ionizing radiation, the contribution of radiation chemistry to the lithography, and the big expectation of radiation chemistry in the development of the future lithography are introduced.
The dissolution characteristics of a chemically amplified electron beam (EB) resist composed of partially tert-butoxycarbonyl group (tBOC) protected poly(p-vinylphenol)(PVP), a dissolution inhibitor, and an acid generator were investigated. The resist sensitivity was improved with decreasing tBOC ratio of the matrix resin. As the tBOC ratio increased, the resolution of the resist was better. SEM observation of the pattern profile was carried out to investigate the sensitivity and the resolution of the resist. The optimum tBOC ratio was 23.8％. As dissolution inhibitors, hydroquinone protected by a tert-butoxycarbonyl group(B-HQ) and isophthalic acid protected by a tert-butyl group(B-IP) are used. Dissolution inhibitors (B-HQ and B-IP) become dissolution promoters (HQ and IP) after exposure. The dissolution rate of the resist consisting of B-IP was faster than that of B-HQ in the exposed area. Pka of IP is smaller than that of HQ, and the acidity of IP is higher than that of HQ. Therefore IP enhances the solubility of the matrix resin in the alkaline developer. We evaluated the dependence of sensitivity of the resist upon acid generators. Triphenylsulfonium triflate, Diphenyliodonium triflate, Triphenylsulfonium antimonate, and Diphenyliodonium antimonate were used. When iodonium ion was used as cation, the sensitivity of the resist was better. When antimonate ion as anion was used, the sensitivity of the resist was better.
We investigated the chemical structure of positive-tone novolak photoresists into which B, P, and As ions were implanted with doses of 5×1012 to 5×1015 atoms/cm2. The thickness of the surface-hardened layer of ion-implanted photoresists increased in the order As–P–B. The energy supplied from the ions to the photoresist concentrated on the surface side in the increasing order of B–P–As. The photoresists are exhibitting carbonization and/or cross-linkage attributable to the decrease in OH, CH, and O1s and the increase in C=C, C1s, and π-conjugated systems.
Radiation chemical processes has established a presence in polymerica materials processing due to their advantageous fabrication capability with uniform chemical reactions induced, size-controllability, etc. Meanwhile, there is a long history of the concept and technology of controlling the shape of polymer materials in nanometer scales. Pioneering works were reported in the middle of the 20th century, where the change of physical properties induced by radiation-induced chemical reactions was studied based on the molecular size and shape of polymers.
“Long chains” in polymers that can variously change their conformations dominantly determine the characteristics and advantages of polymer materials such as mechanical property, thermal stability, solubility and processability, and so on. Therefore, their statistical and quantitative analyses of polymer chains have been demonstrated. Since the radius of gyration for a polymer chain is in the range of several nanometers, it has been a more suitable target than a small molecule to characterize its conformation and size. Due to such nanometer-scale sizes, controlling the morphology and functions is directly linked to the development of functional nanomaterials. On the other hand, it is easy to imagine the difficulty in fabricating polymers into nanomaterials with a size of several to tens of nanometers. In this article, a part of our studies on the novel nano-fabrication techniques is introduced, utilizing polymerization, degradation, and cross-linking reactions induced by irradiations.
A positron is an antiparticle of an electron. A positron injected into solids or liquids annihilates with one of the electrons. The mean lifetime of positron annihilation in the materials is from about 100 picoseconds to several nanoseconds. The mass energy of the electron and the positron is emitted as two γ-rays in most cases. The energy of the annihilation γ-ray can provide the information on the state of the electron and the positron just before the annihilation. Positronium (Ps; a bound state of an electron and a positron) formation time is usually about one picosecond and can probe reactions occurred up to picosecond. Furthermore, it is also possible to discuss the reactions of spur species occurred at nanosecond time region by reactions of long-lived triplet Ps. Here, the methods and the studies related to radiation chemistry are introduced to start new challenges by the positron annihilation methods for radiation chemistry researches.
With rapid advances being made in radiotherapy treatment, three-dimensional (3D) dose measurement techniques of great precision are required more than ever before. It is expected that 3D gel dosimeters will satisfy clinical needs for an effective detector that can measure the complex 3D dose distributions. They are devices that utilize the radiation-induced chemical reactions of radiosensitive (radiochromic) molecules or ions in a gel to store information about radiation dose. The 3D absorbed dose distribution can be deduced from the resulting product distribution using several imaging modalities, such as MRI, X-ray and optical CTs. In this article, the fundamental characteristics and an application of 3D gel dosimeters are reviewed.
Water radiolysis becomes a significant factor in explosive hydrogen generation and degradation of structural materials in decommissioning and waste management after nuclear severe accident such as loss of coolant accident (LOCA). Seawater used as coolant in Fukushima Dai-ichi Nuclear Power Plant (1F) Accident made the phenomena complicated. Advanced studies on water radiolysis for the 1F accident were described briefly in terms of seawater salts, coexistence of solids and engineering conditions.
Since the ionizing radiation for agriculture has been utilized as a tool of cultivar improvement, a lot of plants having new characters were created by heavy ion-beams. While food irradiation is realized for many purpose among many countries, only sprouting inhibition of potatoes is permitted in Japan. Several detection methods of irradiated foods were developed to confirm the food labeling. Novel methods are also done in progress for detecting various kinds of irradiated foods.
Ionizing radiation plays an important role to produce large organic molecules such as long linear molecules and PAH (Poly-Aromatic Hydrocarbons) molecules as well as small molecules like hydrogen in interstellar circumstances. A brief overview of chemical reactions and chemical evolution in space is described. Some of the important open issues that are related to chemical evolutions in the origin of life are also reviewed.