[en] A bottle-like structure was discovered in etched tracks of fission fragments recorded in the gamma-ray-irradiated CR-39 track detector. The etched track has a relatively larger pit radius near the etched surface and has a smaller one in the deeper layer. This indicates that the supply of oxygen from the air should control the damage formation process

[en] Track registration properties in polymeric track detectors, including Poly(allyl diglycol carbonate), Bispenol A polycarbonate, Poly(ethylen terephtarate), and Polyimide, have been investigated by means of Fourie transform Infararede FT-IR spectrometry. Chemical criterion on the track formation threshold has been proposes, in stead of the conventional physical track registration models. (author)

[en] In this work, UV-visible spectral studies have been performed on irradiated CR-39 plastics detector by gamma-ray and light ions of proton (3.4 MeV), helium ion (5.1 MeV) and carbon ion (8.5 MeV). Based on the developed simple model for track accumulation process, the latent track radius of these light ions were assessed to be; 0.7 nm for proton, 1.1 nm for helium ion and 2.2 nm for carbon ion. The dependence of the track radius in nm on stopping power was found to be expressed by a following equation: r_t=0.157(dE/dx)^0.38, where dE/dx is in keV/μm. The normalized optical density of latent tracks to their range was found to be proportional to the stopping power. (author)

[en] In the present study, we assessed the response of the CR-39 detector to proton, deuteron and triton from their etch-pit growth curves obtained by multi-step etching technique and the difference among their track registration properties was discussed. In order to avoid incorrect evaluation due to the missing track effect, particle irradiation was performed at various incident energies. The response function, S(R), etch rate ratio, S, as a function of the residual range, R, was experimentally evaluated for all hydrogen isotopes by this method. In the next, we obtained another form of response functions of S(E), S(β) and S(LET₂₀₀), which were presented as functions of the particle energy, E, the particle velocity, β(=v/c), and the linear energy transfer in the case where the cut-off energy is 200 eV, LET₂₀₀, respectively. These information will be useful also in understanding the fundamentals of the latent track formation mechanism in the plastic track detectors. (J.P.N.)

[en] The thermal release behavior of helium implanted into copper at fluences ranging from 1x10²¹ to 1x10²³ ions/m² at 20 keV has been studied. The shape of the thermal release curves and the number of peaks strongly depended on the implantation fluences. Up to 1.5x10²² ions/m², the initiating temperature of helium release became lower with increasing fluences. Above fluences of 1.5x10²² ions/m², the amount of helium released at the lower temperature abruptly decreased and a porous surface structure appeared. The change in thermal release behavior at high fluences was qualitatively interpreted on the basis of the changes in helium permeability and surface erosion by sputtering. (orig.)

[en] The UN Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) 2016 White Paper published the results to deny the frequent occurrence of childhood thyroid cancer after the TEPCO Fukushima Daiichi nuclear accident. This paper picks up dubious descriptions in this report, and examines the logical framework of the discussions as a general review, and from the basic viewpoint of epidemiology as a specific issue. The relevant part of the 2016 White Paper was written in response to the submission of Prof. Tsuda's paper to Epidemiology magazine and the subsequent exchange of critical letters thereto, and the contents of the reply by Prof. Tsuda et al. were ignored. The UNSCEAR report debated on the basis of statistically unreliable figures by ignoring childhood thyroid cancer incidence at usual times. It compared the results with different diagnostic criteria, for instance, children in Korea and adults in Fukushima. The prevalence of childhood thyroid cancer in the areas where radiation exposure was relatively low, moderate, and high was compared, and the conclusion was that there was no tendency of dose response relationship. However, this relationship is visible when considering the elapsed time since the accident. In the Chernobyl nuclear accident, diseases increased a lot since the following year, so care should be taken in the future on the onset of illness in the youngest age group. (A.O.)

[en] The thermal release behavior of helium implanted into nickel with 20 keV He⁺ ions at fluences ranging from 1x10¹⁷ to 5x10¹⁷ ions/cm² has been studied. The number of helium release peaks increased and the temperature at which the release began became lower with increasing fluence. The surfaces of nickel samples heated after ion implantations were also examined. The release peaks were associated with distinct surface damage features such as holes and blisters. The release peak at high temperatures appeared to be controlled by the thermal vacancy absorption of bubbles. The release peaks at lower temperatures was attributable to the interbubble fracture associated with helium precipitation into bubbles. (orig.)

[en] A series of FT-IR spectrometric studies has been made on modified structure along ion tracks in PET, PC, PI and PADC. Systematic response studies were also performed on them as etched track detectors, paying a special attention on each detection thresholds. It has been confirmed that the three way junctions in PADC polymeric network are radiation tolerance, which have each methine group. (author)

[en] Thermal release behavior of helium implanted into silver with 20 keV He⁺ ions to fluences ranging from 5x10²⁰ to 5x10²¹ ions/m² has been studied. The number of release peaks increased and the initiating temperature for helium release became lower with increasing fluence. Above a fluence of 1.5x10²¹ ions/m², a significant release peak was observed around 550deg C independently of fluence. It was ascertained that the activation energy for helium release in this peak was equivalent to that for the silver self-diffusion. The helium releasing mechanism was discussed, comparing the results for silver to those for copper and nickel. (orig.)

[en] Simultaneous and discriminative measurement of the concentrations of radon and thoron in the indoor atmosphere was performed using a passive monitor with CR-39 track detector. Etch pits on a detector were discriminated with their sizes and shapes for alpha particle energies of 6.0 MeV(²¹⁸Po, ²¹²Bi), 7.7 MeV(²¹⁴Po) and 8.8 MeV(²¹²Po). Discriminating capability was enhanced by use of a degrader mounted on the detector. Etch pits were automatically classified for their sizes and shapes using a computer-aided counting system. Radon and thoron daughters were electrostatically collected onto the degrader surface in order to eliminate alpha particles impinged from the space near the detector surface with reduced energy. A cup for electrostatic collection was designed to prevent the alpha particles emitted from daughters attached on the cup wall and to obtain a flat distribution of daughters collected on the detector surface. The results of the application of this method to thoron-rich fields are described. (author)