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We sheared simulated-quartz gouges using a low-velocity rotary shear apparatus and evaluated the relationship between electron spin resonance (ESR) intensity and displacement quantitatively considering problems of contaminants. ESR intensity of E1’ centre increased while OHC and peroxy centre kept constant with the increasing displacement up to 1.4 m. Microstructural analysis showed grain size reduction and fracture of starting gouges; hence, the fracture can affect the change in ESR intensity. ESR measurements were also conducted for starting gouges with variable amounts of contaminants, and it was confirmed that the effect of contaminants on the change in ESR intensity was negligible. Moreover, we estimated the temperature rise by the frictional heating on the surface and between particles, and it was shown that the effect of frictional heating on ESR intensity was also negligible in our experimental condition. Therefore, we could clarify the relationship between ESR intensity and fracturing with various displacements separately from contaminants and frictional heating. The results imply that the zero-setting of ESR signals cannot occur by the fracture with low frictional heating at the shallow depth.

Rapid analysis of 90Sr in bone and tooth samples of cattle was achieved by inductively coupled plasma mass spectrometry (ICP-MS) coupled with mass-shift and solid-phase extraction techniques. The mass-shift technique with the O2 reaction mode of ICP-MS was applied to the mass shift of isobaric element 90Zr, effectively removing its interference. The solid-phase extraction technique using a Sr resin, which is a polymeric resin supported by 4,4′(5′)-bis-t-butylcyclohexano-18-crown-6, quantitatively separated 90Sr from the interfering matrix elements and isobars in the bone and tooth samples. The activity concentrations determined by ICP-MS were comparable with those determined by the conventional radiometric method. However, the limit of detection in the ICP-MS measurement of 0.1 g samples was lower than that in the radioactivity measurement. The analytical time of the ICP-MS method was shortened from 20 days to 11 h, compared with the radiometric method. Therefore, the ICP-MS method can be a rapid and useful procedure for determination of 90Sr in small bone and tooth samples taken from terrestrial animals.

Particles containing alpha (α) nuclides were identified from sediment in stagnant water in the torus room of the Fukushima Dai-ichi Nuclear Power Station(FDiNPS)’s Unit 2 reactor. We analyzed uranium (U), which is the main component of nuclear fuel, using scanning electron microscopy (SEM). Other α-nuclides (plutonium [Pu], americium [Am], and curium [Cm]) were detected by alpha track detection and the morphology of particles with α-nuclides were analyzed by SEM-energy dispersive X-Ray (EDX) analysis. Several uranium-bearing particles ranging from sub-µm to several µm in size were identified by SEM observation. These particles contained zirconium (Zr) and other elements which constituted fuel cladding and structural materials. The 235U/238U isotope ratio in the solid fractions that included U particles was consistent with what was found for the nuclear fuel in the Unit 2 reactor. This indicated that the U of similar fuel composition had made finer. The α-nuclide-containing particles identified by alpha track analysis were several tens to several hundred µm in size. The EDX spectra showed that these particles mainly comprised iron (Fe). Since the amount of α-nuclide material was very small, Pu, Am, and Cm were adsorbed on the Fe particles. This study clarifies that the major morphologies of U and other α-nuclides in the sediment of stagnant water in the torus room of FDiNPS’s Unit 2 reactor differed.

金沢大学理工研究域地球社会基盤学系, Single-domain magnetite particles exhibit minimum susceptibility along their elongation, resulting in so-called inverse fabric of the anisotropy of magnetic susceptibility (AMS). We report the discovery of inverse AMS fabrics from pelagic clay recovered by a ∼12m long piston core from the western North Pacific. A previous study identified fossil single-domain magnetite produced by magnetotactic bacteria (magnetofossils) as the dominant ferrimagnetic mineral in the sediment. The inverse AMS fabrics were found in a ∼2m zone. The ∼6 and ∼4m of sediment above and below this zone showed normal, horizontal AMS fabrics. Rock magnetic data and ferromagnetic resonance spectroscopy indicated that magnetofossils account for most of the mean susceptibility regardless of normal or inverse AMS. This was explained by the mixing models where the inverse fabric from magnetofossils is nearly balanced by the normal fabrics of terrigenous minerals. The corrected degree of AMS carried by magnetofossils in the sediment was estimated to be ∼1.01, which is comparable to that of typical pelagic sediment at shallow depth. On the other hand, terrigenous minerals in the sediment were estimated to have higher degree of anisotropy, possibly reflecting burial and subsequent erosion of >80m of sediment, which was also suggested by a subbottom acoustic stratigraphy. This suggests that inverse AMS fabrics due to magnetofossils may be widespread in pelagic clay without strong compaction. ©2019. American Geophysical Union. All Rights Reserved.

Electron spin resonance (ESR) dosimetry is one of the most powerful tools for radiation dose reconstruction. The detection limit of this technique using human teeth is reported to be 56 mGy or 67 mGy; however, the absorbed dose of Fukushima residents after the Fukushima Daiichi Nuclear Power Plant (FNPP) accident was estimated to be lower than this detection limit. Our aim is to assess the absorbed radiation dose of children in Fukushima Prefecture after the accident; therefore, it is important to estimate the detection limit for their teeth. The detection limit for enamel of deciduous teeth of Japanese children separated by the mechanical method is estimated to be 115.0 mGy. The density separation method can effectively separate enamel from third molars of Japanese people. As we have collected thousands of teeth from children in Fukushima, the present technique may be useful to examine their external absorbed dose after the FNPP accident.

The mechanisms of the seismic-electromagnetic phenomena (SEP) attracted as precursors of short-term earthquake forecast have been suggested, however, it is still incompletely understood. Among the possible mechanisms of the SEP is the surface charging mechanism related to the electron and hole trapping centers in quartz. Previous studies evaluated the plausibility of the mechanism from the surface charge density by the measurement of current or potential changes. On the other hand, only a few studies have evaluated the plausibility from the direct measurements of the trapping centers’ concentration.We have performed low-velocity friction experiments mimicking the fracture with low-frictional heating for simulated fault gouges (commercial natural quartz sands) at a normal stress of 1.0 MPa with displacements up to 1.4 m. In order to measure the concentration of the trapping centers in the simulated-fault gouges, we conducted electron spin resonance for the standard sample, TEMPOL (4-hydroxy-2,2,6,6-tetramethyl-piperidine-1-oxyl), and the gouges before and after friction. In recent decades, researchers also have obtained the concentrations of the trapping centers in the quartz damaged in the rock fracture experiments using ESR and a radical scavenger. From those concentrations with the measured or assumed surface areas, we calculated the surface charge density of the quartz and discussed the plausibility of the surface charging mechanism of the SEP.In our friction experiments, the E’ type centers were detected at g2 = 2.001 (e.g., E1’ center; ≡Si･, ES’ center; ≡Si･, Eα’ center; =Si:, where − is an electron pair, : is a lone pair, and ･ is an unpaired electron) in the ESR spectra of the simulated-quartz gouges and the trapping center increased by the fracture of low-velocity friction. Assuming that the trapping centers were produced on the grain surfaces by the fracture, the range of the increase in the surface charge density was (0.21–8.0) ×10-4 C/m2. The rock fracture experiments found the E1’ center, non-bridging oxygen hole center (NBOHC; ≡Si−O･), and peroxy center (≡Si−O−O･) in quartz. On the same assumption, the total surface charge density of those trapping centers and the density of the E1’ center or NBOHC were estimated as 2.7×10-1 and 5.0×10-2–3.94 C/m2, respectively.The surface charge density required for a corona discharge that can cause the SEP in the air over a flat plane is reported over 5.0×10-5 C/m2. The quantities calculated above are almost enough to induce a corona discharge. The surface charges can form the electric dipoles on the fault plane, inducing the electric and magnetic fields. Our experiment showed that the fracture by fault motions could produce the surface charges on the fault. It proves that the electromagnetic abnormalities by the fault motions may also be observed through the surface charging mechanism. Therefore, our study supports that the surface charging mechanism is plausible.

Radicals produced in crystalline L-alanine-3,3,3-d3 and L-alanine-d4 were observed by the electron spin resonance (ESR) technique during 1.5 keV soft X-ray irradiation. The spectral change from •CHCD3COOH to •CDCD3COOH by a hydrogen exchange reaction was directly observed in L-alanine-3,3,3-d3. The line width of the ESR spectra obtained by the soft X-ray irradiation was 1.5 times wider than that of hard X-rays from a previous report, meaning a higher density of radicals. The efficiency of the radical yield by the soft X-ray irradiation was 10−6 relative to that by γ-irradiation. The product formed by the radical recombination was observed by an LC/MS analysis. For the soft X-ray irradiation, many radicals will be lost by the efficient radical-radical recombination due to the higher density of the radicals, just as the high-LET irradiation by heavy ions. The result was the same as the yield of hydroxyl radicals in an aqueous solution that decreased with the decreasing photon energy from 1.25 MeV to 1.5 keV. We concluded that the high LET nature of the lower energy photons leads to the dense radical formation in the crystalline alanine powder.

Since the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, we have established an archive system of livestock and wild animals from the surrounding ex-evacuation zone. Wildlife within the alert zone have been exposed to low-dose-rate (LDR) radiation for a long continuous time. In this study, we analysed the morphological characteristics of the testes and in vitro fertilization (IVF) capacity of cryopreserved sperm of racoons from the ex-evacuation zone of the FDNPP accident. The radioactivity of caesium-137 (137 Cs) was measured by gamma-ray spectrometry, and the measured radioactivity concentration was 300-6,630 Bq/kg in the Fukushima raccoons. Notably, normal spermatogenesis was observed in the seminiferous tubules of the testes, with the germinal epithelium composed of a spermatogenic cell lineage with no evident ultrastructural alterations; freeze-thawing sperm penetration ability was confirmed using the interspecific zona pellucida-free mouse oocytes IVF assays. This study revealed that the chronic and LDR radiation exposure associated with the FDNPP accident had no adverse effect on the reproductive characteristics and functions of male raccoons.

Substantial amounts of radionuclides including strontium-90 (90Sr) were released by the Fukushima Daiichi Nuclear Power Plant (FNPP) accident. In the present study, we describe and discuss the presence of 90Sr in the ex-evacuation zone of the FNPP accident and its relationship with 90Sr activity concentration in the hard tissue of animals. We found that the activity concentration of 90Sr in the hard tissue exhibited a positive correlation with 90Sr pollution in their corresponding terrestrial and marine environments. Hard tissues, such as the teeth, bones, and otoliths, of animals and fishes could serve as useful tools in assessing 90Sr pollution in the environment during the period of the formation of those tissues.

90Sr specific activity in the teeth of young cattle that were abandoned in Kawauchi village and Okuma town located in the former evacuation areas of the Fukushima-Daiichi Nuclear Power Plant (FNPP) accident were measured. Additionally, specific activity in contaminated surface soils sampled from the same area was measured. (1) All cattle teeth examined were contaminated with 90Sr. The specific activity, however, varied depending on the developmental stage of the teeth during the FNPP accident; teeth that had started development before the accident exhibited comparatively lower values, while teeth developed mainly after the accident showed higher values. (2) Values of 90Sr-specific activity in teeth formed after the FNPP accident were higher than those of the bulk soil but similar to those in the exchangeable fraction (water and CH3COONH4 soluble fractions) of the soil. The findings suggest that 90Sr was incorporated into the teeth during the process of development, and that 90Sr in the soluble and/or leachable fractions of the soil might migrate into teeth and contribute to the amount of 90Sr in the teeth. Thus, the concentration of 90Sr in teeth formed after the FNPP accident might reflect the extent of 90Sr pollution in the environment.

Muon-catalyzed fusion (μCF) is a cyclic reaction where a negatively charged muon acts as a catalyst for nuclear fusion between hydrogen isotopes. The muon exists in the molecular orbital of the unifying nuclei during the nuclear fusion. The muon with the kinetic energy of the orbital is expected to leave after the nuclear fusion. This muon is called “recycling muon” because it finds the other fusion target nearby and starts the subsequent fusion reaction until the ends of its intrinsic lifetime. The recycling muon has valuable information about the nuclear reaction. In this study, we designed a setup to observe the recycling muons released from a solid hydrogen target using a newly developed charged particle transport method.

Recycling muon having approximately 10 keV kinetic energy produced in a muon catalysed fusion ( μ CF) cycle is expected to be a source of negative muon beam with high-spatial/time coherence. We report a time evolution calculation of μ CF cycle with a particular focus on the emission of recycling muons from a hydrogen film target. Rate equations for the μ CF reactions are solved using the 4th-order Runge-Kutta method. Considering a two-layer solid hydrogen film target composed of 1 mm hydrogen-deuterium layer and 2 µm deuterium-tritium layer, we have numerically simulated the time evolution of the muonic states and their populations in these layers. The muon atomic and molecular processes in the layers are solved simultaneously by introducing a probability of muonic deuterium atoms traveling between the layers via the Ramsauer-Townsend effect. The use of T 2 amplifies the recycling muon emission. A weak dependence of the emission fraction of the recycling muons on the T 2 concentration is predicted, which can be utilized to minimize the usage of tritium.

Positron annihilation lifetime measurements were performed on polyethylene films [low-density polyethylene and ultra-high molecular weight polyethylene (UHMWPE)] with a thickness of 15–2000 μm using a Na-22 positron source enclosed in a Kapton film. For thin films, some positrons will pass through the film and annihilate behind it. Using a single film in a commercial anti-coincidence system, by placing an annealed stainless steel (SUS304) cover behind the sample, it is possible to sufficiently measure the long-lifetime ortho-positronium (o-Ps) component even in thin films. Additionally, calculated intensities of the o-Ps component determined from the estimated film transmittance agreed well with the measured values. Furthermore, by applying this method to uniaxially stretched UHMWPE, we were able to observe structural changes owing to the stretching consistent with shorter measured o-Ps lifetime and increased o-Ps intensity.

The relationship between the CO2 radical intensity and the absorbed dose (dose response curve) of tooth enamel of Japanese macaque was observed by electron spin resonance and the detection limit of our system was estimated to be 33.5 mGy. Using the dose response curve, external exposure dose for seven wild Japanese macaques captured in Fukushima prefecture were examined. The results suggest that the external exposure dose for the wild Japanese macaques were ranged between 45 mGy and 300 mGy.

Nuclear Science and Engineering Directorate, Japan Atomic Energy Agency, Tokai, Ibaraki, 319-1195, Japan Institute of Applied Beam Science, Graduate School of Science and Engineering, Ibaraki University 4-12-1 Nakanarusawa, Hitachi, Ibaraki, 316-8511, Japan Center for the Advancement of Higher Education, Tohoku University 41 Kawauchi, Aoba-ku, Sendai, Miyagi, 980-8576, Japan Department of Chemistry, Graduate School of Science, Tohoku University, 6-3 Aoba, Aramaki Aoba-ku, Sendai, Miyagi, 980-8578, Japan

Pore entrance size of cage-like pores in mesoporous silica films is difficult to be determined by conventional techniques. A simple expedient is proposed by using positron annihilation lifetime spectroscopy (PALS) based on a slow positron beam. Because of the nature of positronium (Ps, the bound state of a positron and an electron) in mesoporous silica, almost no Ps annihilates in the smaller connecting channels of cages. By trimethylsilylation of the silica, an appreciable fraction of Ps can be trapped and annihilate in the channels, which renders the possibility to estimate the pore entrance size from Ps lifetime in it.

Micro-fabrication of poly(tetrafluoroethylene) (PTFE) was carried out using a high-energy heavy ion beam in the MeV region. PTFE was irradiated with various ions (6 MeV/u) under vacuum ( −4 Pa) at room temperature (298 K). The surface of the irradiated PTFE was observed by laser microscopy and a scanning electron microscope (SEM). Micro-scale fabrications of PTFE were successfully performed by direct ion beam etching. Under our experimental conditions the etching proceeded more effectively by heavy ion beams (larger than N 7+ ), compared with lower-energy ion beams (keV region). A larger atomic number ( Z ) of the irradiating ion induced higher etching rates in PTFE; the etching rate for Ne 10+ and Xe 54+ changed from 6.5×10 −13 to 2.0×10 −11 μm/(ion cm −2 ), respectively. As a result we suggest that due to their high electronic stopping powers, etching could be efficiently achieved using high-energy ion beams.

The physicochemical processes underlying the radiation sensitization of DNA by the K-shell photoabsorption of nitrogen and oxygen atoms are unclear. Accordingly, we evaluated electron paramagnetic resonance spectra of thin films of pyrimidine bases. By altering the substituents of the pyrimidine ring, we found a substituent effect on the yield of unpaired electrons induced by photoabsorption. The yield of the unpaired electrons of the DNA-base containing amino groups increased by the donation of electrons, and the yield of halogenated DNA-bases decreased by the withdrawal of electrons. These different physicochemical processes might affect DNA bases, leading to differences in DNA modification.

Ortho-positronium pick off annihilation lifetime gives the information of the microscopic free volume of polymers. Polyimide polymers such as Kapton are applied in many fields, but it was impossible to apply the positron lifetime method for free volume investigation because of no positronium formation. Here, we apply the idea of the free positron annihilation probability that is sum of the probability of annihilation by the positron and electrons on the molecular chain where the positron localized and that for the annihilation with the electrons on the neighboring molecular chains. The second term is probably affected by the free volume change. We have successfully shown the temperature dependence and the electron beam irradiation effect on the free volume change by observing the free positron annihilation lifetime for Kapton.

Mesoporous silica films on Si wafers were prepared via a sol-gel process using a triblock copolymer as the structural template. Spin-coated films were dried and subsequently subjected to Ar plasma treatments for decomposing the polymeric porogen. Mesopore formation in the silica film upon Ar plasma treatments was investigated by positron annihilation lifetime spectroscopy. In comparison with calcined silica film, much larger pores, more heterogeneous in size were found in silica film prepared with Ar plasma decomposition of the porogen.

Positron annihilation lifetime spectroscopy (PALS) has widely been used for probing open volume defects in various materials. PALS is in principle non-destructive, yet conventional PALS is not strictly non-destructive because cutting out of two specimens from the material is required. Recently we developed a novel method of PALS, which is potentially applicable to non-destructive, onsite material inspection. In order to explore the possibility of onsite monitoring of polymer degradation by this novel method of PALS, we studied variations of positron lifetime and mechanical properties of ultra high molecular weight polyethylene (UHMWPE) subjected to γ-irradiation. Correlations were found between the mechanical properties and ortho-positronium lifetimes, suggesting the feasibility of non-destructive, onsite monitoring of polymer degradation by PALS. The effect of γ-irradiation on positronium formation is discussed.

Purpose: To study the lifetime of the short-lived unpaired electron species induced in a calf thymus DNA film by soft X-rays in the energy regions around nitrogen and oxygen K-edge.Materials and methods: Dry calf thymus DNA films were measured by electron paramagnetic resonance (EPR) spectrometer during the monochromatic soft X-ray irradiation provided from a synchrotron accelerator (SPring-8, Super Photon ring-8 GeV). Two operation modes of SPring-8 with different electron bunch structures were used to explore dependence of EPR intensity on pulse interval of soft X-rays.Results: Observed EPR spectra did not show significant difference, in the spectral shape, intensity, g-factor and photon energy dependence, between the two bunch modes.Conclusions: The total yield of the unpaired electron species were estimated by assuming the exponential relaxation of the unpaired electrons with two different bunch modes of the synchrotron. The lifetime of the unpaired electron species is estimated to be in the r...

Here we determined the 90Sr concentrations in the teeth of cattle abandoned in the evacuation area of the Fukushima-Daiichi Nuclear Power Plant (FNPP) accident. 90Sr activity concentrations in the teeth varied from 6–831 mBq (g Ca)−1 and exhibited a positive relationship with the degree of radioactive contamination that the cattle experienced. Even within an individual animal, the specific activity of 90Sr (Bq (g Sr)−1) varied depending on the development stage of the teeth during the FNPP accident: teeth that were early in development exhibited high 90Sr specific activities, while teeth that were late in development exhibited low specific activities. These findings demonstrate that 90Sr is incorporated into the teeth during tooth development; thus, tooth 90Sr activity concentrations reflect environmental 90Sr levels during tooth formation. Assessment of 90Sr in teeth could provide useful information about internal exposure to 90Sr radiation and allow for the measurement of time-course changes in the degree of environmental 90Sr pollution.

The graded energy deposition of heavy ion beam irradiation to polymeric materials was utilized to synthesize a novel proton exchange membrane (PEM) with the graded density of sulfonic acid groups toward the thickness direction. Stacked Poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) films were irradiated by Xe54+ ion beam with the energy of 6 MeV/u under a vacuum condition. The induced trapped radicals by the irradiation were measured by electron spin resonance (ESR) spectroscopy. Irradiated films were grafted with styrene monomer and then sulfonated. X-ray photo-electron spectroscopy (XPS) spectra showed that the densities of sulfonic acid groups were controlled for injection “Surface” and transmit “Back” sides of the fabricated PEM. The membrane electrode assembly (MEA) fabricated by the function-graded PEM showed improved fuel cell performance in terms of voltage stability. It was expected that the function-graded PEM could control the graded concentration of sulfonic acid groups in PEM.

High linear energy transfer (LET) heavy ion beams were used to irradiate poly(tetrafluoroethylene-co-ethylene) (ETFE) under vacuum and in air. The irradiation effects in ETFE as a function of the depth were precisely evaluated by analyzing each of the films of the irradiated samples, which were made of stacked ETFE films. It was indicated that conjugated double bonds were generated by heavy ion beam irradiation, and their amounts showed the Bragg-curve-like distributions. Also, it was suggested that higher LET beams would induce radical formation in high density and longer conjugated C=C double bonds could be generated by the second-order reactions. Moreover, for samples irradiated in air, C=O was produced correlating to the yield of oxygen molecules diffusing from the sample surface.

Temperature dependence on S(t), positron age dependent shape parameter of annihilation gamma-rays, in water was observed. S(t) at the ortho-Ps pick off annihilation time region were higher at higher temperatures. It is indicating that there are more reactions of ortho-Ps at higher temperature. Hence it was successfully indicated that the longest lifetime, i.e. ortho-Ps component, on positron annihilation lifetime spectra for water could be shorter at higher temperatures. The radical reactions, such as PsOH formation or ortho-Ps oxidation by hydroxyl radicals, are spin dependent reactions. The geminate pair of ortho-Ps and hydroxyl radical in water can give spin dependent reaction and the enhancement of S(t) with certain time interval, i.e. quantum beats, were expected. It was observed even for water at 11°C. It is probably indicating the hyperfine coupling constants of hydroxyl radicals in water.

Surface morphology of bisphenol-A polycarbonate (BAPC) thin films, with thickness ranging from 30 to 1000 nm on silicon substrates was studied by atomic force microscopy. The films were prepared by spincasting from 1,2-dichloroethane solutions of 0.25–5.0 wt % BAPC. Even though longer annealing than 250 h was necessary for complete crystallization for bulk BAPC, high crystallinity was observed for 30 nm thick film after annealing at 200 °C for 48 h in vacuum. Positron annihilation lifetime spectroscopy measurements showed that the free volume hole size in 30 nm thick film was larger than that of bulk at 200 °C. Comparison of the BAPC concentration in the precursor solution with the overlap concentration suggests that the high crystallinity of the 30 nm BAPC film is due to less entangled chains caused by rapid removal of the solvent from the dilute solution. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010

Nanoimprint lithography has been applied to the manufacture of microlenses, antireflection films, and biochips because of its cost reduction advantage. Previously, we demonstrated a gas-permeable template derived from a thermal cross-linkable cellulose derivative with methacrylate (HPC-MOI) that eliminated defects due to the concentration of acetone gas between the template and the imprint material. In this study, we prepared a thermoset cellulose derivative with acrylate as the gas-permeable template (HPC-AOI). The results of Raman spectroscopy and indentation test confirmed that HPC-AOI had a very high cross-linking density when heated for 10 min. The micrographs and three-dimensional (3D) image of the 5 µm line and space pattern in the UV cross-linked material containing a volatile solvent showed that void defects were removed and edges were sharper when the HPC-AOI template was utilized.

6 MeV/u ion beams such as Si14+, Ar18+, Kr36+ and Xe54+ and 30 kV Ga+ focused ion beam (FIB) were irradiated to a chemically amplified deep-UV resist TDUR-P722 (Tokyo Ohka Kogyo) and electron beam (EB) resists ZEP520A and ZEP7000 (ZEON). Clear patterns were obtained on all resists for high energy ion beams, and it was confirmed that resist sensitivities were correlated with the energy deposition. In contrast, high flux FIB irradiation induced crosslinking reactions of resist polymers, and positive-negative inversion took place.

Ion-beam irradiation effects on polyimide, Kapton™, were studied with respect to optical and electronic properties. Stack films of Kapton™ (12.5 μm thick) were irradiated to various ion beams in air or vacuo at room temperature and subjected to ultraviolet–visible (UV–vis) spectroscopy, and change in absorbance and energy gap is discussed. The UV–vis absorption spectrum, which is assigned to the transition of electrons in benzene rings from π to π * orbital, upon He 2+ (6 MeV/u) irradiation in air, shifted towards longer wavelength direction for all cases, and the shift was more obvious for higher linear energy transfer (LET) ion beams. The energy gap of the transition was estimated, and the H + and He 2+ ion beams caused little change in the transition energy gap Eg , while the heavier ions such as C 6+ and Si 14+ caused more significant decrease. This decrease is assumed to the structural changes around benzene rings, and the infrared spectroscopy revealed breakage in imide groups next to benzene ring in the repeating unit of polyimide.

“Generalized modulus–ultimate elongation profile” was induced from the relationship between the modulus and the ultimate elongation of an elastomer that was quantitatively added crosslinking and scission. This profile can be used to evaluate the time-accelerated irradiation methods of ethylene-propylene-diene elastomer. The irradiation under low dose rate (0.33 kGy/h) at room temperature was the reference condition. The short-time irradiation condition was 4.2 kGy/h in 0.5 MPa oxygen at room temperature and 5.0 kGy/h in air at 70 °C. The former tended to bring about the higher ratio of scission than the reference condition; the latter tended to bring about the higher ratio of crosslinking.

Positrons have been used for material analysis not only because of their novel characteristics, such as an ability to detect open-volume type defects in materials, but also because interactions with solids differ from those of electrons in such processes as scattering and diffraction. Monoenergetic positron beams and microbeams were developed in the 1980s, and positron experiments have made progress in material analyses. In this article we review the fundamental technique of microbeam fabrication, especially using a magnetically-guided positron beam, its extension to various analytical methods, and expectations for future research.

Mesoporous silica films were synthesized via a sol–gel process under an acidic condition. Various amounts of triblock copolymer F38 were loaded to precursor sols as the pore generator. The evolution of the pores generated by porogen decomposition was investigated as a function of F38 loading by positron annihilation gamma-ray energy spectroscopy and positron annihilation lifetime spectroscopy based on slow positron beams. The threshold of pore percolation is found to be around 10 wt% of F38 loading by positron annihilation gamma-ray energy spectroscopy. Positron annihilation lifetime spectroscopy in the films show that the pore size increases from 1 nm to 3 nm with increasing F38 loading from 5 wt% to 30 wt%.

Doppler broadening of annihilation radiation (DBAR) and positron annihilation lifetime spectroscopy (PALS) have been successfully applied to the study of positronium (Ps)—forming amorphous solids such as polymers and silicon oxide in the bulk. Implementing depth selectivity to DBAR and PALS by combining them with variable-energy positron beams considerably broadens their applicability. Variation of incident positron energy over a wide range enables depth-profiling, whereas tuning of the beam energy enables the studies of surfaces, interfaces and thin films. In this paper, we discuss fundamentals and applications of energy variable DBAR and PALS for Ps—forming polymers and silicon oxide.

The high power terahertz (THz)-time domain spectroscopy (TDS) system has been designed based on S-band compact electron linac at Advanced Industrial Science and Technology (AIST). The THz pulse is expected to have the peak power of about 25 kW with frequency range 0.1–2 THz using the 40 MeV electron beam which has about 1 nC bunch charge with 300 fs bunch length (rms). The aptitude discussion of the EO sampling method with ZnTe crystal was accomplished to apply to our THz-TDS system. The preliminary experiment of the absorption measurements of P-PPV on the Si wafer has been successfully demonstrated using the 0.1 THz coherent synchrotron radiation (CSR) pulse and W-band rf detector. It is confirmed that the intense of the THz pulse is enough to perform the THz-TDS analysis of the sample on the Si wafer. In near future, the investigation of the un-researched materials will be started in the frequency range 0.1–2 THz with our high power THz-TDS system.

This paper describes the results on thermal and chemical analysis of polytetrafluoroethylene (PTFE) film stack after high-energy heavy ion beam irradiation under atmospheric fields at room temperature. After high-energy C6+ ion beam irradiation, the PTFE film stack was separated one by one, and then the various measurements such as differential scanning calorimetric (DSC) analysis and solid-state 19F magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy were performed to get information of the chemical reaction and structural change at the localized positions. By ion beam irradiation for PTFE at room temperature, it is suggested that the abnormal phenomena due to the change of morphology could be observed by DSC analysis. In the solid-state 19F-MAS-NMR spectroscopy of ion irradiated PTFE film including Bragg peak region, several new signals were observed besides the intense peak of –CF2– at −124 ppm. The detected new signals in ion irradiated PTFE should be due to the changed chemical structures. The signals, which are assigned, to the tertiary carbon group with branching site (Y-type crosslinking site), perfluoro-propylene site and chain end methyl site were directly detected, though it was under the oxidation condition. Thus, although it was under the oxidation condition, the branching or crosslinking reaction was taken place with the chain scission in the matrix. Moreover, the branched chain length would become short, compared with EB-crosslinked PTFE. Hence, it could be suggested that the irradiation of heavy ion beam induced large amounts of intermediate species, compared with EB or γ-ray irradiation, and then, those would be reacted with each other in the localized area. Especially, in region of the Bragg peak, the ion beam induced more large amounts of intermediate species than in the other region.

Porous materials have fascinated positron and positronium chemists for over decades. In the early 1970s it was already known that ortho -positronium ( o -Ps) exhibits characteristic long lifetimes in silica gels, porous glass and zeolites. Since then, our understanding of Ps formation, diffusion and annihilation has been drastically deepened. Ps is now well recognized as a powerful porosimetric and chemical probe to study the average pore size, pore size distribution, pore connectivity and surface properties of various porous materials including thin films. In this paper, developments of Ps chemistry in porous materials undertaken in the past some 40 yr are surveyed and problems to be addressed in future are briefly discussed.

Subnanoporosity was introduced into SiOCH-based thin films by mixing tetraethyl orthosilicate with hexamethyldisiloxane (HMDSO) in the plasma enhanced chemical vapor deposition process, and was evaluated by the variable-energy positron annihilation lifetime technique. It was found that with increasing the HMDSO fraction both porosity and pore size were enhanced, as evidenced by the decreased refractive index and increased ortho-positronium lifetime. The lifetimes from 2.0 to 6.8 ns suggested the tunable pore volumes within a range of 0.1–0.7 nm3.

Nanoporous polysiloxane films were fabricated by plasma polymerization of hexamethyldisiloxane mixed with cyclohexane under different conditions. The pores were generated through the elimination of carbonaceous aggregates (porogen) by annealing at 600 degrees C. Results of spectroscopic ellipsometry, Fourier transform infrared spectroscopy, and positron annihilation lifetime spectroscopy suggest that not only film porosity but also average pore size depends on the amount of the decomposable porogen. The pore size was controllable in a range between 0.6 and 1.0 nm in radius by proper selection of the substrate temperature and precursor composition.

The long-term oxidative degradation of chemical structures and the mechanical properties in different polyethylenes induced by ion-beam irradiation were investigated. They were measured along the ion trace when the samples were stored in the atmosphere for a very long time. The hydroperoxide group is very important in the degradation process. These degradation processes are attributed to the mobility of oxygen molecule due to the density and the crystallinity of polyethylene.

The radiation-induced oxidative degradation of polypropylene was studied. It is well known that the irradiated polymers react gradually with the air and decrease their mechanical properties for long-term storage. In this work, silicon oxide films were formed on polypropylene by sputtering to suppress the permeation of oxygen during the gamma-ray irradiation. Samples were stored in air for a long time and measured the chemical structure and the mechanical properties to obtain effects of the oxygen barrier coating. From the results, we found that such coatings have a good effect on suppressing the oxidative degradation for long-term storage.

The local reaction induced in the track for low-density polyethylene irradiated with ion-beam was investigated. The transformations of the chemical structure induced by irradiation are on trans-vinylene, end-vinyl, vinylidine and the cross-link. The different reaction processes are induced in the micro-region of the track. These processes depend on the stopping power. In the region of larger stopping power, the rate of the process, which produces the end-vinyl, increases and that of the trans-vinylene decreases. These results suggest that the main chain scission of the polyethylene can be induced by very large energy deposition in the micro-region.

The effect of gas barrier silica coatings on the tensile strength and elongation at break for gamma-irradiated 1 mm thick polypropylene was studied. The irradiation was carried out in air at a constant dose rate of 125 Gy·h-1 with a 60Co source and the silica coatings were formed by magnetron sputtering for a thickness up to 120 nm. The elongation at break for the sample without silica coatings was reduced at an irradiation time of 350 hours, whereas the reduction occurred at significantly longer times for the samples with silica coatings. This result shows that the gas barrier silica coating can improve the radiation resistance of a polymer as a result of suppressed radiation-induced oxidation.

The changes in the chemical structure and the mechanical properties of single-site polyethylene induced by ion-beam irradiation were investigated. The crystallinity of single-site polyethylene is very low, so the chemical structure and the mechanical properties are different from low density polyethylene. The LET effect of single-site polyethylene is more conspicuous than in low density polyethylene.

The distribution of the local transformations induced in a low density polyethylene irradiated with various ion-beams was observed by using micro-FT-IR system. The predominant transformations induced by irradiation are crosslinking, trans -vinylene, end-vinyl and vinylidine. The depth profile of the trans -vinylene resembles the Bragg curve, but that each of the end-vinyl and the vinylidine shows rather complicated profile. The irradiation effect of H + ions is similar to that of γ-rays, but on irradiation with the ions heavier than H + , the species induced are found to depend on the beam fluence and the stopping power of the ion.

気体透過バリアー膜を用いて酸素透過を抑制することにより, 高分子材料の耐放射線性向上を試みた。ポリプロピレンの両面にマグネトロンスパッタ法によりシリカ薄膜をコーティングした試料を作製し酸素透過測定を行った。シリカ膜厚100nm程度で酸素透過量が50cc・m-2・day-1から1cc・m-2・day-1程度まで減少し, シリカ薄膜が酸素透過バリアーとして有効であることが確かめられた。更に, シリカコーティングしたポリプロピレンとシリカコーティングを行っていないポリプロピレンを空気中で線量率125Gy・h-1で4000時間までγ線照射し, 酸化により生成したカルボニル基を顕微赤外吸収分光法により測定したところ, 未コーティング試料では試料表面付近が大きく酸化されたのに対し, シリカコーティング試料では酸化がほとんど見られず, シリカ薄膜により高分子の放射線酸化を抑制できることが確認された。