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Abstract: We studied the track response of CR-39 plastic nuclear track detectors (PNTD) for low (<6 MeV/n) and high (>100 MeV/n) energy heavy ions using the atomic force microscope (AFM). CR-39 PNTD was exposed to several heavy ion beams of different energy at HIMAC (Heavy Ion Medical Accelerator in Chiba). For AFM measurement, the amount of bulk etch was controlled to be ∼2 μm in order to avoid etching away of short range tracks. The response data obtained by AFM for ∼2 μm bulk etch was in good agreement with data obtained by the conventional optical microscope analysis for larger bulk etch. The response data from low energy beams (stopping near the surface) was also consistent with the data from high energy beams (penetrating the detector) as a function of REL (restricted energy loss) with the δ-ray cut off energy of ω 0 = 200 eV. We experimentally verified that REL (ω 0 = 200 eV) gives a universal function for wide energy range in CR-39 PNTD. This work has been done as part of a basic study in the measurement of secondary short range tracks produced by target fragmentation reactions in proton cancer therapy fields. [Copyright &y& Elsevier]

Abstract: The two-step etching method using PEW (Potassium hydroxide + Ethanol + Water) and NaOH solutions was applied to the control of the response of CR-39 plastic nuclear track detectors for the measurement of high LET (linear energy transfer) particles. CR-39 detectors were exposed to several heavy ion beams covering the LET∞H2O range of 30–750 keV/μm from HIMAC (Heavy Ion Medical Accelerator in Chiba) at NIRS (National Institute of Radiological Sciences), Japan. The detectors were pre-etched in PEW solutions with 3 different ethanol concentrations at the temperature of 70 °C for 30–60 min. Then, the detectors were post-etched in 7N NaOH solution at the same temperature for 4–28 h. We found that the response curves and the detection thresholds of the detectors smoothly shifted to higher LET regions as the ethanol concentration increases in PEW solution. [Copyright &y& Elsevier]

Abstract: We experimentally determined the suitable conditions of temperature and air pressure for measuring charge and mass compositions of heavy cosmic rays using CR-39 track detectors during long-duration, high-altitude balloon flights. The experiments were carried out utilizing Fe ion beams from Heavy Ion Medical Accelerator (HIMAC). Changes in the track registration sensitivity with temperature were studied at temperatures between 213 and 293K. The charge and mass shifts around Fe ions are possibly 0.11cu (charge unit) and 0.47amu (atomic mass unit) at the temperature deviation between 227 and 243K at balloon altitude. Decrease in track registration sensitivity as air pressure decreases has been observed between 13Pa and 27kPa. The charge and mass shifts around Fe ions are inferred to be 0.02cu and 0.09amu, respectively, when pressure varies between 20 and 27kPa. During balloon flight, air pressure drops below this; therefore, care must be taken to keep the temperature and air pressure of CR-39 detectors within acceptable limits. [Copyright &y& Elsevier]

Abstract: New optical system with an optical displacement sensor has been developed to measure the local thickness of CR-39 track detector. It can be applied to measure locally the thicknesses of whole detector area for making a map of the amount of bulk etch. The accuracy of the thicknesses measurement was found to be using CR-39 detector. This accuracy is one order of magnitude higher than that of conventional methods, such as the Micrometer method, and is comparable to that of track size measurement under the optical microscope. It will also greatly improve the charge and mass resolutions of CR-39 detector that we can apply to measure galactic cosmic rays (GCRs) nuclei, especially the trans-iron nuclei in GCRs. [Copyright &y& Elsevier]

Abstract: The radial core size of tracks in CR-39 plastics has been determined for several heavy ions, O (8.6MeV), Ne (18.8MeV), Si (27MeV), Ar (35MeV) and Fe (80MeV), by AFM and UV methods. In the AFM method, the core radii were assessed from the growth behavior of minute etch pits within 1min of etching. These were derived from each intersection of the extrapolated line, fitted to each growth curve of etch pit radius. With the UV method, changes in the UV–visible spectra of CR-39 with fluence were obtained. Then the critical fluence where the track overlapping became statistically significant was determined for each ion. Based on the track overlapping model, the track core radius was calculated. Both methods were found to give results concordant with each other for these heavy ions. [Copyright &y& Elsevier]

Abstract: We verified the angular dependence of track registration sensitivity for four types of CR-39 plastic nuclear track detectors using heavy ion beams. These detectors have been launched with several types of luminescence detectors on the Russian segment of the International Space Station (ISS) to intercompare passive radiation dosimeter components from several institutions. CR-39 detectors were irradiated by several kinds of heavy ions with several hundred MeV/n. All the etched tracks were analyzed using a high-speed microscope (HSP-1000) with ellipse fitting software (PitFit). Reduction of sensitivity was observed near the region of the critical angle. Corrections were made using an empirical method based on the known structure of the galactic cosmic ray spectrum. [Copyright &y& Elsevier]

Abstract: We verified that the two-step etching method of the combination of pre-etching with PEW (Potassium hydroxide+Ethanol+Water) solution and post-etching with NaOH solution makes drastic improvement of charge resolution for high Z/β particles (Z: nuclear charge, β: velocity) in CR-39 nuclear track detectors. Detectors were exposed to several heavy ions from Ne to Kr with the energies of <500MeV/n at HIMAC (Heavy Ion Medical Accelerator in Chiba). The optimum etching conditions were determined to be a pre-etching of PEW solution with concentration of 60wt% of ethanol for 40min and a post-etching of 7N NaOH for 12h. This resulted in a charge resolution for Kr (Z/β ∼60) of 0.18c.u. (charge units). The Z/β detection threshold was increased as a function of ethanol concentration in PEW pre-etching solutions. We found that the two-step etching method would be useful technique for the precise charge identification by a single track measurement. The 60wt% ethanol concentration in PEW would be adequate selection for the purpose of trans-iron nuclei measurement discriminating abundant light nuclei in galactic cosmic rays. [Copyright &y& Elsevier]

Abstract: It is necessary to accumulate the 10B atoms selectively to the tumor cells for effective Boron Neutron Capture Therapy (BNCT). In order to achieve an accurate measurement of 10B accumulations in the biological samples, we employed a technique of neutron capture autoradiography (NCAR) of sliced samples of tumor tissues using CR-39 plastic track detectors. The CR-39 track detectors attached with the biological samples were exposed to thermal neutrons in the thermal column of the JRR3 of Japan Atomic Energy Agency (JAEA). We obtained quantitative NCAR images of the samples for VX-2 tumor in rabbit liver after injection of 10BSH entrapped water-in-oil-in-water (WOW) emulsion by intra-arterial injection via proper hepatic artery. The 10B accumulations and distributions in VX-2 tumor and normal liver of rabbit were investigated by means of alpha-track density measurements. In this study, we showed the selective accumulation of 10B atoms in the VX-2 tumor by intra-arterial injection of 10B entrapped WOW emulsion until 3 days after injection by using digitized NCAR images (i.e. alpha-track mapping). [Copyright &y& Elsevier]

Highlights: [•] Dose reduction effect for space radiation by water shielding material was verified. [•] Absorbed dose and dose equivalent were evaluated with passive dosimeters. [•] Observed dose reduction rate was found to be 37±7% in dose equivalent. [•] It will effectively reduce the annual dose for space crews and long-term mission. [ABSTRACT FROM AUTHOR]

Highlights: [•] The angular and transverse momentum distributions of all PFs do not evidently depend on target size. [•] Mean value and width of angular distribution decrease with increasing of PF charge for the same target. [•] The averaged transverse momentum decreases with the increase of the charge of PF. [•] The temperature parameter of PF emission source decreases with the increase of the size of PF. [Copyright &y& Elsevier]

Abstract: The total charge changing and partial projectile fragment production cross sections of 471 A MeV 56Fe on C, Al and CH2 targets are investigated using CR-39 plastic nuclear track detector. It is found that the total charge changing cross sections are consistent with the prediction from Bradt–Peters semi-empirical formula. The partial cross sections for projectile fragment production agree with the results from other experiments and show a significant enhancement for the fragments with even-Z. Finally, the partial cross sections of fragments with charge 5 ≤ Z ≤ 9 are firstly investigated in present paper. [Copyright &y& Elsevier]

Abstract: Measurements of fragment emission angles for 57 and 93 MeV/nucleon 12C and 95 MeV/nucleon 16O projectiles in graphite, Plexiglas and polyethylene targets were performed using trajectory tracing technique with CR-39 detectors. The results were compared with calculations with the fragment emission angle model (FRANG). The angular resolution of the measurements was achieved to be <0.1°. The measured fragment emission angles imply that the generally accepted straight-ahead approximation of fragment emissions in nuclear collisions is oversimplified as the fragments are clearly emitted at different angles related to the primary particles. The calculated values were in agreement with the experimental ones within the margin of a few degrees for most of the examined projectile-target systems. However, some discrepancies were observed. Thus a new calculation was performed with a modified version of the model M-FRANG. For both FRANG and M-FRANG, chai-square values were calculated to test the degree of agreement with our measurements. It was confirmed that the M-FRANG showed better agreement despite its simplicity, and it was established it can be successfully used in several applications, including simple and fast test of more complicated 3D particle and heavy ion transport codes. [Copyright &y& Elsevier]

Abstract: A new method to trace heavy ion trajectories in a stack consisting of interleaved CR-39 plastic nuclear track detectors and target material layers was developed and tested for use in the measurement of projectile charge changing cross-sections of heavy ion fragmentation reactions. A high speed imaging microscope with sophisticated track analysis software was utilized to extract the charge information from multiple ion tracks belonging to a single fragmentation event. The systematic error of trajectory tracing was verified for the measurement system. In order to verify the validity of system, the projectile total charge changing cross-sections for Fe ions on carbon target was estimated and compared with previous experiments at initial beam energy of 1GeV/n. The result is in good agreement with results obtained by other investigators. This method allows precise and fast measurement of the projectile charge changing cross-section with higher statistics on a level compatible to that of silicon spectrometer measurements. [Copyright &y& Elsevier]

Abstract: Mixtures of allyl diglycol carbonate (CR-39) and diallyl phthalate (DAP) were cast into resin plates under same polymerizing conditions. The copolymer plates were irradiated with many kinds of ions at the medium energy beam irradiation room or biological irradiation room of National Institute of Radiological Sciences (NIRS)-Heavy Ion Medical Accelerator in Chiba (HIMAC). After etching in an aqueous solution of KOH, whether enlarged ion tracks exist or not was determined by using an optical microscope. It was found that every plate has a characteristic value in LET as threshold for track formation. The threshold increases with the concentration of DAP. It has been shown that the threshold is adjustable by changing the ratio of CR-39 and DAP. It is expected that the copolymers can be used for the discrimination of heavy ions in cosmic rays. [Copyright &y& Elsevier]

Abstract: The total charge-changing cross sections and the partial cross sections for the production of projectile fragment are measured in the interactions of 388A MeV 20Ne with aluminum, carbon and polyethylene targets sandwiched with CR-39 plastic nuclear track detectors. The measured total charge-changing cross sections are compared with the prediction using Bradt–Peters semi-empirical formula, and NUCFRG2 and PHITS models. It is shown that the measured experimental results are in good agreement with theoretical model predictions. The partial cross sections for projectile fragment production are consistent with other experimental results at same and nearly the same energies except for fragment with charge Z =5. The partial cross sections of fragment with charge Z =5 from C and Al targets are smaller than other experimental results, and the result from H target is greater than that of other experiments, which can be explained by the limitation of detection efficiency of CR-39. Finally, it is clearly seen that the partial cross sections for projectile fragment production show obvious odd–even effects. [Copyright &y& Elsevier]

Abstract: As a feasibility study, gas chromatography–mass spectrometry (GC–MS) and matrix-assisted laser desorption ionization–mass spectrometry (MALDI–MS) have been applied to analyze etch products of CR-39 plastic (one of the most frequently used solid states nuclear track detector) for the understanding of track formation and etching mechanisms by heavy ion irradiation. The etch products of irradiated CR-39 dissolved in sodium hydroxide solution (NaOH) contain radiation-induced fragments. For the GC–MS analysis, we found peaks of diethylene glycol (DEG) and a small but a definitive peak of ethylene glycol (EG) in the etch products from CR-39 irradiated by 60MeVN ion beams. The etch products of unirradiated CR-39 showed a clear peak of DEG, but no other significant peaks were found. DEG is known to be released from the CR-39 molecule as a fragment by alkaline hydrolysis reaction of the polymer. We postulate that EG was formed as a result of the breaking of the ether bond (C–O–C) of the DEG part of the CR-39 polymer by the irradiation. The mass distribution of polyallylalcohol was obtained from the etch products from irradiated and unirradiated CR-39 samples by MALDI–MS analysis. Polyallylalcohol, with the repeating mass interval of m/z =58Da (dalton) between m/z =800 and 3500, was expected to be produced from CR-39 by alkaline hydrolysis. We used IAA as a matrix to assist the ionization of organic analyte in MALDI–MS analysis and found that peaks from IAA covered mass spectrum in the lower m/z region making difficult to identify CR-39 fragment peaks which were also be seen in the same region. The mass spectrometry analysis using GC–MS and MALDI–MS will be powerful tools to investigate the radiation-induced polymeric fragments and helping to understand the track formation mechanism in CR-39 by heavy ions. [Copyright &y& Elsevier]

Abstract: Total charge-changing cross sections and cross sections for the production of projectile-like fragments were determined for fragmentation reactions induced by 370MeV/n 20Ne ions in water and lucite, and 490MeV/n 24Mg ions in polyethylene, carbon and aluminum targets sandwiched with CR-39 plastic nuclear track detectors. An automated microscope system and a track-to-track matching algorithm were used to count and recognize the primary and secondary particles. The measured cross sections were then compared with published cross sections and predictions of different models. Two models and the three-dimensional Monte Carlo Particle Heavy Ion Transport Code System (PHITS) were used to calculate total charge-changing cross sections. Both models agreed within a few percent for the system 24Mg+CH2, however a deviation up to 20% was observed for the systems 20Ne+H2O and C5H8O2, when using one of the models. For all the studied systems, PHITS systematically underestimated the total charge-changing cross section. It was also found that the partial fragmentation cross sections for 24Mg+CH2 measured in present and earlier works deviated up to 20% for Z =6–11. Measured cross sections for the production of fragments (Z =4–9) for 20Ne+H2O and C5H8O2 were compared with predictions of three different semi-empirical models and JQMD which is used in the PHITS code. The calculated cross sections differed from the measured data by 10–90% depending on which fragment and charge was studied, and which model was used. [Copyright &y& Elsevier]

Abstract: The development of SPICE (single-particle irradiation system to cell), a microbeam irradiation system, has been completed at the National Institute of Radiological Sciences (NIRS). The beam size has been improved to approximately 5μm in diameter, and the cell targeting system can irradiate up to 400–500 cells per minute. Two cell dishes have been specially designed: one a Si3N4 plate (2.5mm×2.5mm area with 1μm thickness) supported by a 7.5mm×7.5mm frame of 200μm thickness, and the other a Mylar film stretched by pressing with a metal ring. Both dish types may be placed on a voice coil stage equipped on the cell targeting system, which includes a fluorescent microscope and a CCD camera for capturing cell images. This microscope system captures images of dyed cell nuclei, computes the location coordinates of individual cells, and synchronizes this with the voice coil motor stage and single-particle irradiation system consisting of a scintillation counter and a beam deflector. Irradiation of selected cells with a programmable number of protons is now automatable. We employed the simultaneous detection method for visualizing the position of mammalian cells and proton traversal through CR-39 to determine whether the targeted cells are actually irradiated. An immuno-assay was also performed against γ-H2AX, to confirm the induction of DNA double-strand breaks in the target cells. [Copyright &y& Elsevier]

Abstract: We have developed an automated scanning system for handling a large number of nuclear track etched detectors (NTEDs). The system consists of a magazine station for sample storage, a robotic sample loader, a high-speed wide-area digital imaging microscope device (modified HSP-1000) and PitFit software for analyzing etch pits. We investigated the performance of the system using CR-39 plastic NTED samples exposed to high-energy heavy ions and fast neutrons. When applying the system to fast neutron dosimetry, the typical scanning speed was about 100 samples/day with a scan area of 4cm2/sample. The neutron doses obtained from a fully automatic measurement agreed closely with those from a semi-automatic measurement. These results indicate the feasibility of fully automatic scanning of CR-39 personal neutron dosimeters. The system is also expected to be applicable to future large-scale experiments using CR-39 plastic and BP-1 glass NTEDs for observing ultraheavy galactic cosmic rays with high mass resolution. [Copyright &y& Elsevier]

Abstract: In radiation cancer therapies using energetic charged particles such as proton/heavy-ion therapy and boron neutron capture therapy (BNCT), studies on radiation-induced biological response at cellular level are important because the radiation damage from energetic charged particles is highly localized along their paths and the radiation sensitivity is quite different in each cellular organelle. In such studies the information on the position of charged particle impact in biological cells is necessary. A novel method for high-resolution nuclear track mapping in detailed cellular histology has been developed. In this technique, biological specimens mounted on CR-39 plates are exposed to energetic charged particles. The irradiated samples are exposed to UV, and then etched for a short time. Both etch pits of nuclear tracks and relief for transmission UV image of the specimen can be observed on the CR-39 surface with an atomic force microscope (AFM) at about 100nm resolution. [Copyright &y& Elsevier]

The radial size of track cores in CR-39 plastics for several types of ions has been determined by two different methods. First, atomic force microscope observations were performed on the irradiated CR-39 subsequent to the slight chemical etchings. The track core radii for C, O, Ne and Xe ions evaluated from the intersections of the extrapolated lines, fitted to each growth curve of etch pit radius, were found to be in the range between 2.8 and 4.1 nm, independent of the ion species. Second, UV–visible spectra of the irradiated CR-39 were obtained at various fluences. Based on a track overlapping model, the track core radii are evaluated for H, He, C and O ions. Their core radii were almost proportional to the cube root of the stopping power. The results from the two different measurements are in good agreement with each other. [Copyright &y& Elsevier]

Soft X-ray microscopy using CR-39 plastic track detectors was demonstrated with an atomic force microscope (AFM) readout for the first time. A transmission X-ray image of the biological cells was recorded on the CR-39 surface, and revealed as relief after etching process. The resolution of the X-ray imaging is expected to be 100 nm or less, therefore imaging of biological cells is possible at an intracellular structure level. Using this technique, the high resolution image of both biological cells and charged particle tracks can be obtained simultaneously on a CR-39 with the AFM. In boron neutron capture therapy, this new technique provides the information on the distribution of boron compounds and radiation dose by charged particles mapping inside a cell. [Copyright &y& Elsevier]

Abstract: In order to identify the chemical modification along nuclear tracks in CR-39 detectors, we have made a series of FT-IR measurements for thin CR-39 plastic films irradiated by Fe ions. The films were reduced in the thickness by long time chemical etchings down to from as-received CR-39 sheets of thick. It enabled us to obtain unsaturated IR spectra. The samples were exposed to 147MeV Fe ions at HIMAC in air. Amount of loss of carbonated ester bonds due to the exposure was assessed from the changes in the absorbance of and bonds with Fe fluence. The assessed G-value for destroying carbonate ester bonds was found to be about 10 (scission/100eV). [Copyright &y& Elsevier]

Abstract: Observation of trans-iron nuclei in galactic cosmic rays () requires a high performance cosmic ray detector telescope with a large exposure area because of their extremely low fluxes. A solid-state track detector such as CR-39 has the advantage of easy extension of exposure area, but it is necessary to raise the detection threshold in order to suppress background tracks produced by galactic cosmic rays with . The track registration sensitivity and detection threshold for heavy ions with various were verified by using track detectors of copolymers of CR-39 and DAP (diallyl phthalate) with various DAP concentration. We found that it is possible to control the detection threshold of copolymers by changing DAP concentration. In order to detect heavy ions with , the optimum DAP concentration was found to be approximately 50%. [Copyright &y& Elsevier]