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Multi-MeV high-purity proton acceleration by using a hydrogen cluster target irradiated with repetitive, relativistic intensity laser pulses has been demonstrated. Statistical analysis of hundreds of data sets highlights the existence of markedly high energy protons produced from the laser-irradiated clusters with micron-scale diameters. The spatial distribution of the accelerated protons is found to be anisotropic, where the higher energy protons are preferentially accelerated along the laser propagation direction due to the relativistic effect. These features are supported by three-dimensional (3D) particle-in-cell (PIC) simulations, which show that directional, higher energy protons are generated via the anisotropic ambipolar expansion of the micron-scale clusters. The number of protons accelerating along the laser propagation direction is found to be as high as 1.6 ±0.3 × 10⁹/MeV/sr/shot with an energy of 2.8 ±1.9 MeV, indicating that laser-driven proton acceleration using the micron-scale hydrogen clusters is promising as a compact, repetitive, multi-MeV high-purity proton source for various applications.

We evaluate the track segment yield G′ of typical water radiolysis products (eaq−, ·OH and H2O2) under heavy ions (He, C and Fe ions) using a Monte Carlo simulation code in the Geant4-DNA. Furthermore, we reproduce experimental results of ·OH of He and C ions around the Bragg peak energies (< 6 MeV/u). In the relatively high energy region (e.g., > 10 MeV/u), the simulation results using Geant4-DNA have agreed with experimental results. However, the G-values of water radiolysis species have not been properly evaluated around the Bragg peak energies, at which high ionizing density can be expected. Around the Bragg peak energy, dense continuous secondary products are generated, so that it is necessary to simulate the radical–radical reaction more accurately. To do so, we added the role of secondary products formed by irradiation. Consequently, our simulation results are in good agreement with experimental results and previous simulations not only in the high-energy region but also around the Bragg peak. Several future issues are also discussed regarding the roles of fragmentation and multi-ionization to realize more realistic simulations.

In this article, two etched track detector methods for measuring short-range particles are presented and compared. The primary method employs observations of the evolution of the track geometry in intermittent etching, with the use of the appropriate track scanning procedures. The alternative method requires one-step etching and a specific analysis of the track parameters. Both methods proved to be effective in identifying target nuclear fragments amongst a high background from primary cosmic radiation. Additionally, the linear energy transfer (LET) spectrum of the target nuclear fragments, obtained onboard the International Space Station, was found to be consistent with the results from high-energy proton beams in ground-based experiments.

Radiation cancer therapy with ultra-high dose rate exposure, so called FLASH radiotherapy, appears to reduce normal tissue damage without compromising tumor response. The aim of this study was to clarify whether FLASH exposure of proton beam would be effective in reducing the DNA strand break induction. We applied a simple model system, pBR322 plasmid DNA in aqueous 1× TE solution, where DNA single strand breaks (SSBs) and double strand breaks (DSBs) can be precisely quantified by gel electrophoresis. Plasmid DNA were exposed to 27.5 MeV protons in the conventional dose rate of 0.05 Gy/s (CONV) and ultra-high dose rate of 40 Gy/s (FLASH). With both dose rate, the kinetics of the SSB and DSB induction were proportional to absorbed dose. The SSB induction of FLASH was significantly less than CONV, which were 8.79 ± 0.14 (10-3 SSB per Gy per molecule) and 10.8 ± 0.68 (10-3 SSB per Gy per molecule), respectively. The DSB induction of FLASH was also slightly less than CONV, but difference was not significant. Altogether, 30 MeV proton beam at 40 Gy/s reduced SSB and not DSB, thus its effect may not be significant in reducing lethal DNA damage that become apparent in acute radiation effect.

In this study, we represent the track response data of poly (allyl diglycol carbonate) (PADC) using the number of interactions with the stopping medium induced by secondary electrons. The Number of Interactions induced by Secondary Electrons (NISE) is calculated using a Monte Carlo simulation code in Geant4-DNA. The description of the track response data given by NISE is improved compared with those proposed previously based on the stopping power and Radial Electron Fluence around Ion Tracks (REFIT). We also simulate the removal cross sections of the carbonate ester bond in PADC irradiated with protons and heavy ions (He, C, and Fe) based on the NISE. A radiation-oxidation kinetics model is combined with the estimation obtained in the present study. Discrepancies are found between the experimental results and our present simulation even after applying the radiation-oxidation kinetics model in the low stopping power region (<10 eV). Our results demonstrate that the interactions among electrons lying within the low-energy region (<7.4 eV) and the energy dependence of the yields due to bond breaks are crucial for obtaining more accurate estimation.

The lunar surface is directly and continuously exposed to Galactic Cosmic ray (GCR) particles and Solar energetic particles (SEPs) due to the lack of atmosphere and lunar magnetic field. These charged particles interact with the lunar surface materials producing secondary radiations such as neutrons and gamma rays. In a departure from precise GCR and SEP data, we estimated the effective dose equivalent at the lunar surface and in a lunar lava tube in this paper by using PHITS, a Monte Carlo simulation tool. The effective dose equivalent due to GCR particles at the lunar surface reached 416.0 mSv yr−1 and that due to SEPs reached 2190 mSv/event. On the other hand, the vertical hole of the lava tube provides significant radiation protection. The exposure by GCR particles at the bottom of the vertical hole with a depth of 43 m was found to be below 30 mSv yr−1 while inside a horizontal lava tube, the value was less than 1 mSv yr−1 which is the reference value for human exposure on the Earth. We expect that the lunar holes will be useful components in the practical design of a lunar base to reduce radiation risk and to expand mission terms.

FLASH radiotherapy appears to kill off tumor cells while sparing healthy tissues, by irradiation at ultra high dose rate (>40 Gy s−1). The present study aims to clarify the mechanism of the sparing effect by proton irradiation under the FLASH conditions from a viewpoint of radiation chemistry. To do so, we evaluate radiation chemical yields (G values) of 7-hydroxy-coumarin-3-carboxylic acid (7OH–C3CA), which is produced by water radiolysis using coumarin-3-carboxylic acid (C3CA) solution as a radical scavenger of hydroxyl radicals. We shoot 27.5 MeV protons in the dose rate ranging from 0.05 to 160 Gy s−1. The recombination process of hydroxyl radicals produced is followed by varying the concentration of C3CA from 0.2 to 20 mM, which corresponds to the scavenging time scale from 7.1 to 714 ns. The G value of 7OH–C3CA produced decreases with increasing dose rate on the same scavenging time scale. Additionally, the trend of the relative G value normalized at a scavenging time scale of 100 ns, where radical–radical reaction subsides, is consistent in the examined dose rate range. This finding implies that G values of 7OH–C3CA produced reduce with increasing dose rate due to the oxygen depletion. We experimentally present that the sparing effect for healthy tissues would be seen even with a proton beam under the FLASH conditions due to the depletion of oxygen.

Ion track detection technology providing dosimetric quantity of linear energy transfer (LET) under submicron spatial resolution is capable of not only single cellular dosimetry (micrometer scale) but also autoradiographic dosimetry in tissues (centimeter scale). Plastic nuclear track detector (PNTD) and fluorescent nuclear track detector (FNTD) are applicable for microdosimetric study in targeted radionuclide therapy with high LET alpha particles and auger electrons. We have demonstrated co-visualization of human gastric cancer cells (NCI-N87) bound with 211At-labeled trastuzumab antibodies against HER2 antigens and alpha particle tracks emitted from each cell using CR-39 PNTD. This method provides the binding efficiency of 211At-agent on the targeted cells and single cellular dose. The autoradiographic dosimetry with tissues sliced from mice carrying metastatic cancer in the livers injected with 211At-agent provides the dose concentration in specific tumours localized in the tissue. In situ single cellular dosimetry is available with Al2O3:C,Mg FNTD under the confocal microscopy. Co-visualization of ion tracks and DNA double strand break regions in a single cell has been demonstrated with FNTD where cells were cultured. Single cellular dosimetry with live cells will be applicable for investigating biological response. A confocal microscopy of FNTD traces fluorescent signals as a function of detector depth. Fluorescent signals due to auger electrons emitted from 64Cu reagent mounted on the detector has been discriminated from associated beta rays and photons by their range difference. We present a possibility of single cellular dosimetry with ion track detection technology for targeted radionuclide therapy., IAEA Technical Meeting on Imaging Using Ionizing Radiation to Address Biological Challenges

IAEA Technical Meeting on Imaging Using Ionizing Radiation to Address Biological Challenges

In this paper we report about the demonstration of the nuclear track imaging capabilities of Ag-activated phosphate glass. A 375 nm laser and confocal laser scanning microscopy (CLSM) were respectively used for track excitation and detection. Specifically, the blue and orange radiophotoluminescent (RPL) tracks and dose distributions observed after irradiation with soft X-rays, gamma rays and heavy charged particles (HCPs) are examined. In addition, the origins of the reductions in RPL efficiency for high-dose X-ray irradiation and for irradiation with HCPs with high linear energy transfer (LET) values are investigated via a CLSM and a conventional fluorescent reader and discussed. © 2017 Elsevier B.V., Embargo Period 12 months

A possible mechanism for the formation of the source composition of cosmic rays is proposed by taking into account the condensation process occurring in the interstellar space. This process may have produced the overabundance of heavy and ultra heavy nuclei in the source composition as compared with the chemical composition of the sun. Since the chemical composition of galactic cosmic ray source is similar to that of meteorite as classified as C2, that of galactic cosmic rays was compared with that of silicon carbide of presolar grains. It is found that both the iron isotope ratios and chemical composition of ultra heavy cosmic rays are similar to those in presolar grains. The chemical composition of presolar grains and meteorites may give a clue to search for the birth place of cosmic rays in the interstellar space.

We report the activities on the working group 'High Energy Cosmic Ray Observation'. We have been developing the CALET (Calorimetric Electron Telescope) instrument on-board the Japanese Experiment Module/Exposed Facility, JEM/EF, of the ISS (International Space Station). We are successfully developing the instruments, and carried out a balloon flight of the proto-type in 2006. The working group hosted two meetings in Japan and two international meetings in US and China to subscribe for the AO of JEM/EF missions by JAXA.