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The nuclear charge pickup cross sections of 40Ar on polyethylene(CH2), carbon, aluminum, copper and lead targets at the highest energy of 495 MeV/n were measured using CR-39 nuclear track detector. The cross sections for H were calculated from those measured on C and CH2 targets. The dependence of charge pickup cross section on target mass was studied, it was found that the nuclear charge pickup cross section exhibits a linear dependence on the target mass.

The nuclear charge pickup cross sections of 40Ar on polyethylene(CH2), carbon, aluminum, copper and lead targets at the highest energy of 495 MeV/n were measured using CR-39 nuclear track detector. The cross sections for H were calculated from those measured on C and CH2 targets. The dependence of charge pickup cross section on target mass was studied, it was found that the nuclear charge pickup cross section exhibits a linear dependence on the target mass.

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, 27.5 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.

Radiation dosimetry was carried out at the exposure facility (EF) and the pressurized module (PM) of the Japanese Kibo module installed in the International Space Station as one study on environmental monitoring for the Tanpopo mission. Three exposure panels and three references including biological and organic samples and luminescence dosimeters were launched to obtain data for different exposure durations during 3 years from May 2015 to July 2018. The dosimeters were equipped with additional shielding materials (0.55, 2.95, and 6.23 g/cm2 mass thickness). The relative dose variation, as a function of shielding mass thickness, was observed and compared with Monte Carlo simulations with respect to galactic cosmic rays (GCRs) and typical solar energetic particles (SEPs). The mean annual dose rates were DEF = 231 ± 5 mGy/year at the EF and DPM = 82 ± 1 mGy/year at the PM during the 3 years. The PM is well shielded, and the GCR simulation indicated that the measured mean dose reduction ratio inside the module (DPM/DEF = 0.35) required ∼26 g/cm2 additional shielding mass thickness. Observed points of the dose reduction tendency could be explained by the energy ranges of protons (10–100 MeV), where the protons passed through, or were absorbed in, the shielding materials of different mass thickness that surrounded dosimeters.

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.

Energetic ion beam experiments with major space radiation elements, 1H, 4He, 16O, 28Si and 56Fe, have been conducted to investigate the radiation shielding properties of composite materials. These materials are expected to be used for parts and fixtures of space vehicles due to both their mechanical strength and their space radiation shielding capabilities. Low Z materials containing hydrogen are effective for shielding protons and heavy ions due to their high stopping power and large fragmentation cross section per unit mass. The stopping power of the composite materials used in this work is intermediate between that of aluminum and polyethylene, which are typical structural and shielding materials used in space. The total charge-changing cross sections per unit mass, σUM, of the composite materials are 1.3–1.8 times larger than that of aluminum. By replacing conventional aluminum used for spacecraft with commercially available composite (carbon fiber / polyether ether ketone), it is expected that the shielding effect is increased by ~17%. The utilization of composite materials will help mitigate the space radiation hazard on future deep space missions.

A new Open-Source dosemeter, SPACEDOS, has been developed for measurements of cosmic radiation on board spacecraft and small satellites. Its main advantages are that it is small and lightweight with low power consumption. It can be adjusted for specific applications, e.g. used in pressurized cabins of spacecraft or in vacuum environments in CubeSats or larger satellites. The open-source design enables better portability and reproduction of the results than other similar detectors. The detector has already successfully performed measurements on board the International Space Station. The obtained results are discussed and compared with those measured with thermoluminescent detectors located in the same position as SPACEDOS.

It has been observed that healthy tissues are spared at ultra-high dose rate (UHDR:40 Gy/s), so called FLASH effect. To elucidate the mechanism of FLASH effect, we evaluate changes in radiation chemical yield (G value) of 7-hydroxy-coumarin-3-carboxylic acid (7OH-C3CA), which is formed by the reaction of hydroxyl radicals with coumarin-3-carboxylic acid (C3CA), under carbon ions (140 MeV/u) and protons (27.5 and 55 MeV) in a wide-dose-rate range up to 100 Gy/s. The relative G value, which is the G value at each dose rate normalized by that at the conventional dose (CONV: 0.1 Gy/s), 140 MeV/u carbon-ion beam is almost equivalent to 27.5 and 55 MeV proton beams. This finding implies that UHDR irradiations using carbon-ion beams have a potential to spare healthy tissues. Furthermore, we evaluate the G value of 7OH-C3CA under the de-oxygenated condition to investigate roles of oxygen to the generation of 7OH-C3CA effect. The G value of 7OH-C3CA under the de-oxygenated condition is lower than that under the oxygenated condition. The G value of 7OH-C3CA under the de-oxygenated condition is higher than those under UHDR irradiations. By direct measurements of the oxygen concentration during 55 MeV proton irradiations, the oxygen concentration drops by 0.1%/Gy, which is independent of the dose rate. When the oxygen concentration directly affects to yields of 7OH-C3CA, the rate of decrease in the oxygen concentration may be correlated with that of decrease in the G value of 7OH-C3CA. However, the reduction rate of G value under UHDR is significantly higher than the oxygen consumption. This finding implied that the influence of the reaction between water radiolysis species formed by neighborhood tracks could be strongly related to the mechanisms of UHDR effect.

固体線量計は、普段我々が放射線を取り扱う管理区域内での作業時に義務付けられている、個人被ばく線量測定に用いられるごく身近なものである。放射線が通った飛跡を記録するプラスチック飛跡検出器（CR-39）と放射線量に応じた蛍光を呈するルミネッセンス線量計（熱蛍光TL、光刺激ルミネッセンスOSL、ラジオフォトルミネッセンスRPLを基本原理）を組み合わせた個人線量計が一般的に用いられている。近年、放射線が通った跡を蛍光飛跡として記録する蛍光飛跡検出器（FNTD：Fluorescent Nuclear Track Detector）1 の開発研究が進んでいる。FNTDは化学処理を要さず光学測定のみで、あらゆる種類の放射線の線量評価が可能である。これは現在のCR-39とルミネッセンス線量計の組み合わせ手法に置き換わるものと期待されている。FNTDは、法令上の個人被ばく線量測定だけでなく、放射線治療場や宇宙環境などの複雑な放射線混成場での活用や、生物学・医学に資する応用研究に広がっている。本稿では固体線量計の中でも比較的新しいFNTDについて紹介する。

蛍光飛跡検出器（FNTD：Fluorescent Nuclear Track Detector）は，何らの化学的処理を要さず光学測定系のみで，放射線の飛跡をイメージングし，被ばく線量を定量評価することができる．近年ではFNTD を活用した生物学や医学などへの応用研究が盛んに進められている．本稿では次世代の個人被ばく線量計として期待されているだけでなく，さまざまな応用の可能性を秘めているFNTD の現状と展望について紹介する．

We have been studying the effectiveness of direct action, which induces clustered DNA damage leading to cell killing, relative to indirect action. Here a new criterion Direct Ation-Based Biological Effectiveness (DABBLE) is proposed to understand the contribution of direct action for cell killing induced by C ions. DABBLE is defined as the ratio of direct action to indirect action. To derive this ratio, we describe survival curves of mammalian cells as a function of the number of OH radicals produced 1 ps and 100 ns after irradiation, instead of the absorbed dose. By comparing values on the vertical axis of the survival curves at a certain number of OH radicals produced, we successfully discriminate the contribution of direct action induced by C ions from that of indirect action. DABBLE increases monotonically with increasing linear energy transfer (LET) up to 140 keV/μm and then drops, when the survival curves are described by the number of OH radicals 1 ps after irradiation. The trend of DABBLE is in agreement with that of relative biological effectiveness (RBE) of indirect action. In comparison, the value of DABBLE increases monotonically with LET, when the survival curves are described by the number of OH radicals 100 ns after irradiation. This finding implies that the effectiveness of C ion therapy for cancer depends on the contribution of direct action and we can follow the contribution of direct action over time in the chemical phase.

A liver metastasis from a primary gastric cancer (LMGC) is relatively common and results in an extremely poor prognosis due to a lack of effective therapeutics. We here demonstrate in a clinically relevant mouse model that an α-particle radioimmunotherapy approach with 211At-labeled trastuzumab has efficacy against LMGCs that are positive for human epidermal growth factor receptor 2 (HER2). Methods:211At was produced in a cyclotron via a 209Bi (α,2n) 211At reaction. 211At-trastuzumab was subsequently generated using a single-step labeling method. NCI-N87 cells (HER2-positive human gastric cancer cells) carrying a luciferase gene were intrasplenically transplanted into severe combined immunodeficiency mice to generate an HER2-positive LMGC model. A biodistribution study was then conducted through the intravenous injection of 211At-trastuzumab (1 MBq) into these LMGC xenograft mice. In parallel with this experimental therapy, phosphate-buffered saline, intact trastuzumab, or 211At-nonspecific human IgG (1 MBq) was injected into control groups. The therapeutic efficacy was evaluated by monitoring tumor changes by chemiluminescence imaging. Body weights, white blood cell counts, and serum markers of tissue damage were monitored at regular intervals. Microdosimetry using a CR-39 plastic detector was also performed. Results: The biodistribution analysis revealed an increased uptake of 211At-trastuzumab in the metastasized tumors that reached approximately 12% of the injected dose per gram of tissue (%ID/g) at 24 h. In contrast, its uptake to the surrounding liver was about 4 %ID/g. The LMGCs in the mouse model reduced dramatically at 1 wk after the single systemic injection of 211At-trastuzumab. No recurrences were observed in 6 of 8 mice treated with this single injection, and their survival time was significantly prolonged compared with the control groups, including the animals treated with 211At-nonspecific antibodies. No severe toxicities or abnormalities in terms of body weight, white blood cell number, liver function, or kidney parameters were observed in the 211At-trastuzumab group. Microdosimetric studies further revealed that 211At-trastuzumab had been delivered at an 11.5-fold higher dose to the LMGC lesions than to the normal liver. Conclusion: α-radioimmunotherapy with 211At-trastuzumab has considerable potential as an effective and safe therapeutic option for LMGC.

The paper describes the features of operation and testing of Russian dosimeters made on the basis of PIPS detectors for assessing radiation environment in space flights and for mixed radiation fields. Preliminary results of testing with high-energy protons and heavy ions are considered. Experimental results were verified by German M-42 silicone dosimeter. M-42 dosimeter model has been already proven credible for aviation and space flight dosimetry.

A liver metastasis from a primary gastric cancer (LMGC) is relatively common and results in an extremely poor prognosis due to a lack of effective therapeutics. We here demonstrate in a clinically-relevant mouse model that an α-radioimmunotherapy (α-RIT) approach with astatine-211-labeled-trastuzumab (211At-trastuzumab) has efficacy against LMGCs that are positive for human epidermal growth factor receptor 2 (HER2). Methods: 211At was produced in a cyclotron via a 209Bi (α, 2n) 211At reaction. 211At-trastuzumab was subsequently generated using a single-step labelling method. NCI-N87 cells (HER2-positive human GC cells) carrying a luciferase gene were intrasplenically transplanted into severe combined immunodeficiency mice to generate a HER2-positive LMGC model. A bio-distribution study was then conducted through the intravenous injection of 211At-trastuzumab (1 MBq) into these LMGC xenograft mice. In parallel with this experimental therapy, PBS, intact trastuzumab or 211At-non-specific human IgG (1MBq) were injected into control groups. The therapeutic efficacy was evaluated by monitoring tumor changes by chemiluminescence imaging. Monitoring of body weights, white blood cell counts, and serum markers of tissue damage were conducted at regular intervals. Microdosimetry using a CR39 plastic detector was also performed. Results: The biodistribution analysis revealed an increased uptake of 211At-trastuzumab in the metastasized tumors that reached approximately 12% of the injected dose per gram of tissue (%ID/g) at 24 hours. In contrast, its uptake to the surrounding liver was about 4%ID/g. The LMGCs in the mouse model reduced dramatically at 1 week after the single systemic injection of 211At-trastuzumab. No recurrences were observed in six of eight mice treated with this single injection and their survival time was significantly prolonged compared to the control groups, including the animals treated with 211At-non-specific antibodies. No severe toxicities or abnormalities in terms of body weight, white blood cell number, liver function, or kidney parameters were observed in the 211At-trastuzumab group. Microdosimetric studies further revealed that 211At-trastuzumab had been delivered at an 11.5- fold higher dose to the LMGC lesions compared to the normal liver. Conclusion: α-RIT with 211At-trastuzumab has considerable potential as an effective and safe therapeutic option for LMGC.

After the development of chirped pulse amplification by G. Mouro, laser ion acceleration has attracted a lot of interest for various fields of research, such as high energy density physics, nuclear physics, and fast ignition scheme in inertial confinement fusion. Recent theoretical and numerical investigations predict generation of sub-GeV to GeV energy ions. However, it is difficult to discriminate GeV-scale ions into different mass and energies using conventional diagnostic instruments (e.g. Thomson parabola spectrometer, solid state nuclear track detector). We have developed a novel diagnostic system based on particle counting analysis (PCA), which is generally used in nuclear physics experiments. The diagnosis provides a mass-dependent ion spectrum based on time-of-flight and pulse-height analysis of single particle events. With a novel arrangement of multiple scintillators with different ion stopping powers, PCA offers potential advantages over commonly used diagnostics in terms of coverage solid angle, detection efficiency, and real-time analysis for GeV-scale ions. The basic detector setup was tested using the Heavy Ion Medical Accelerator in Chiba (HIMAC) in Japan. Our system shows its ability to resolve protons, B^5+, C^6+, and O^8+ ion beams with energy range of 60-430 MeV/u. We also discuss an advanced detector design using multi-layered scintillator pixel array coupled with avalanche photodiodes, which allows angularly-resolved analysis and makes PCA more practical diagnostic technique in laser-driven particle acceleration experiments., High Temperature Plasma Diagnostics Conference 2022

ペタワットクラスの高強度レーザーと水素クラスターターゲットを用いたレーザー駆動陽子線加速では、衝撃波加速をベースとした数百MeV級の準単色陽子線発生が示唆されている。本研究では、その実証実験のために原子核乾板と散乱体を交互に積層したEmulsion cloud chamber(ECC)を用いたレーザー加速陽子線計測器開発を行った。計測データ解析にサポートベクトル回帰を利用することで、厚さ2 cmのコンパクトなECC内での多重クーロン散乱量から300 MeVまでの陽子線のエネルギーをΔE/E = 10%の精度で測定可能であることを示した。, 第34回固体飛跡検出器研究会

高強度レーザーを用いたイオン加速手法は、粒子線がん治療やRI製造、原子核物理実験などへの応用が検討されている。このためには、加速された粒子の正確で精度のよいエネルギー測定が必須である。本研究では、FNTDの高強度レーザーを用いて加速された陽子線のエネルギー計測への適用可能性を検討した。FNTD内に記録された陽子線の飛跡を共焦点顕微鏡の焦点深度を変えながら観察した。得られた飛跡の長さから、陽子線のエネルギーを決定することに成功した。, 第34回固体飛跡検出器研究会

ラジオフォトルミネッセンス（RPL）を原理とした線量計として知られる銀活性リン酸塩ガラスを用いて、蛍光イオントラック計測に関する特性を評価した。HIMACにおいて照射した重粒子線の蛍光イオントラックを共焦点顕微鏡により測定した。LET（線エネルギー付与）の下限は5 keV/µm（水換算）程度であり、閾値型の高LET粒子検出器として動作する可能性があり、例えば宇宙放射線計測への応用が考えられる。, 第34回固体飛跡検出器研究会

蛍光飛跡検出器（FNTD）は、高い感度と優れた電荷分解能を有する受動型の固体飛跡検出器である。FNTDの応用分野は広がる一方で、素子間での感度の差異（着色効果と呼ぶ）が課題として指摘されている。本研究では、着色が異なるFNTDを用意し、α線照射を行うことで着色効果の補正方法を検討した。着色効果の補正により、着色の異なる素子であっても応答特性の統一的な記述が可能となる。詳細は発表で述べる。, 第34回固体飛跡検出器研究会

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.

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.

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.

Geant4 Monte Carlo simulations were carried out to investigate the possible shielding materials of aluminum, polyethylene, hydrides, complex hydrides and composite materials for radiation protection in spacecraft by considering two physical parameters, stopping power and fragmentation cross section. The dose reduction with shielding materials was investigated for Fe ions with energies of 500 MeV/n, 1 GeV/n and 2 GeV/n which are around the peak of the GCR energy spectrum. Fe ions easily stop in materials such as polyethylene and hydrides as opposed to materials such as aluminum and complex hydrides including high Z metals with contain little or no hydrogen. Attenuation of the primary particles in the shielding and fragmentation into more lightly charged and therefore more penetrating secondary particles are competing factors: attenuation acts to reduce the dose behind shielding while fragmentation increases it. Among hydrogenous materials, 6Li10BH4 was one of the more effective shielding materials as a function of mass providing a 20% greater dose reduction compared to polyethylene. Composite materials such as carbon fiber reinforced plastic and SiC composite plastic offer 1.9 times the dose reduction compared to aluminum as well as high mechanical strength. Composite materials have been found to be promising for spacecraft shielding, where both mass and volume are constrained.

We investigated the optimum etching condition for potassium hydroxide-ethanol–water solution (PEW) to detect only alpha and 7Li particles from 10B(n, α)7Li reactions registered in a CR-39 plastic nuclear track detector. The background recoil protons, which are induced by fast neutrons with energies of

We investigated the optimum etching condition for potassium hydroxide-ethanol–water solution (PEW) to detect only alpha and 7Li particles from 10B(n, α)7Li reactions registered in a CR-39 plastic nuclear track detector. The background recoil protons, which are induced by fast neutrons with energies of

We have developed a measurement method for laser-accelerated multi-hundred-MeV-class protons using an emulsion cloud chamber (ECC), which consists of a stack of nuclear emulsion films and scatterer plates. Based on multiple Coulomb scattering (MCS) theory depending on the incident energy of protons, we have constructed a regression model to inversely estimate the incident energy by means of support vector regression (SVR) with a radial basis function. The prediction accuracy was approximately 10% (standard deviation) for protons with energies up to 0.3 GeV in a 25 layer ECC with 0.5 mm thick tungsten plates, corresponding to a 2 cm thick compact detector.

Plasmid DNA is commonly used as a simpler substitute for a cell in studies of early effects of ionizing radiation because it allows to determine yields of primary DNA lesions. Experimental studies often employ plasmids of different lengths, in different concentrations in the aqueous solution. Influence of these parameters on the heavy-ion induced yields of primary DNA damage has been studied, using plasmids pUC19 (2686 bp), pBR322 (4361 bp) and pKLAC2 (9107 bp) in 10 and 50 ng/μl concentration. Results demonstrate the impact of plasmid length, while no significant difference was observed between the two concentrations. The uncertainty of the results is discussed.

We aim to determine the detection threshold of Kapton as an Etched Track Detector irradiated with 345 MeV/u U ion, as well as other several heavy ions of Al, Si, Ar, Kr and Xe. The heavier ions are found to have higher detection threshold in the stopping power. At the same stopping power, the track registration sensitivity decreases with increasing the nuclear charge of ions. U ion has the lowest sensitivity as S = 0.04 at the detection threshold of 3400 keV/μm. We have updated the conventional radial dose distribution theory using a relatively new experimentally supported formula for the effective charge up to U ion. The local doses at a track radius of 0.8 nm, which is half of the length of a repeat unit of Kapton, is useful to understand the relation between the sensitivity of heavy ions and the stopping power at each detection threshold.

宇宙における有人活動の場は、現在の国際宇宙ステーション（ISS）から月へと展開しつつある。また民間人の宇宙旅行も現実化しつつある。人類の宇宙進出は拡大の一途をたどっているとともに、我々に大変身近なものになってきている。宇宙は我々が暮らしている地球上と比べてはるかに多くの被ばくを受ける環境である。宇宙放射線と呼ばれる放射線は、陽子から鉄に至る様々な荷電粒子で構成されており地球上のそれとは大きく異なる。特にヘリウムより重い重粒子線は大きな線エネルギー付与（LET）を持つので、人体に大きな影響を及ぼす。更に宇宙放射線が宇宙機の構造体や人体等の構成元素と衝突して中性子等の様々な二次粒子が発生する。宇宙放射線の線量当量を求めるためには、個々の重粒子線のLETを実測する必要がある。標準的な線量評価法として、固体飛跡検出器とルミネッセンス線量計を組み合わせた受動型線量計がISS内で利用されている。宇宙放射線の遮へい方法として物質中で減衰させる方法が考えられる。その遮へい性能を決定する物理量は阻止能と二次粒子生成断面積である。前者は物質の質量と電荷の比に比例するので水素を多く含むような物質が減衰させやすい。後者は宇宙放射線の原子核を物質中で核破砕させ、LETの小さい粒子に変換し線量を低減するもので、材料の平均質量が小さいほど断面積は大きくなり破砕しやすい。この指標に基づくと、従来の宇宙機材料であるアルミニウムよりも、炭素や炭化ケイ素を含む複合材料が適していると考えられる。本発表ではISSで現在までに得られている宇宙放射線計測の観測結果と新たな遮へい材料を用いた防護技術の開発の取り組みについて紹介する。, 日本量子医科学会第1回学術大会

1980年代にレーザーに応用されたチャープパルス増幅法(Gérard A. Mourou ,2018 年ノーベル物理学賞)を皮切りとした近年のレーザー技術の発展は目覚ましく, 国内 では最高強度1PW出力のJ-KAREN-Pレーザが稼働しており,海外では10PW出力のEL-NPが 現在建設中である. このような超高強度レ ーザーをターゲット物質に照射することで, 物質は瞬時にイオン化し,加速される.現在,相対論的イオン,特にGeV級の高エネ ルギーを持つイオンの加速原理に関する研究が行われている.しかし,既存の計測技術 である固体飛跡検出器やトムソンパラボラ計測器を用いて, GeV領域にまで加速され たイオンを計測することは困難である.我々は,宇宙線計測や加速器などの核物理 研究の領域では普遍的に用いられているシンチレーション検出器を用いた単一粒子計数法に基づくイオン計測に着目し,これを レーザー粒子加速実験に応用するための計測器開発を行っている., 第38回 プラズマ・核融合学会 年会

Laser plasma proton acceleration, where it was recently reported that near-100-MeV proton acceleration was demonstrated, offers the potential to realize a compact and cost-effective accelerator in the future. Because it can generate an extreme electric field that is over six orders of magnitude higher than that of a conventional radio-frequency accelerator apparatus. To understand the underlying physics of the acceleration process and increase maximum proton energy, precise measurement of both the energy spectrum and the two-dimensional distribution is required. Against this background, we have developed a new measurement method for laser-accelerated sub-GeV-class protons using the nuclear emulsion. Based on the Multiple Coulomb Scattering (MCS) method in an Emulsion Cloud Chamber (ECC), which is a stack of nuclear emulsion films and scatterer plates, the incident energies were inversely evaluated by the scattering angle. The proof-of-principle experiment has been conducted with the Heavy-Ion Medical Accelerator in Chiba (HIMAC) to verify that the ECC is able to identify sub-GeV protons with the MCS method. Combined with a technique of machine learning, a new measurement method has been developed to obtain an energy spectrum of laser-accelerated sub-GeV protons by the ECC with the MCS method., ICMaSS2021

The laser-driven ion acceleration has been one of the most active areas of research during the last decade, because the accelerated ion beams have unique properties such as ultrashort duration, high brilliance, and low emittance. It has a potential to develop energy saving compact particle accelerators. In such situation, characterization of laser-accelerated ions in both space and energy domains are one of the most critical issues to understand the physics of laser-driven ion acceleration process. To characterize the laser-accelerated ions, we have applied CR-39 etched type track detectors and nuclear emulsion as the passive detectors. Several methods have been developed to measure two dimensional ion distributions and energy spectrum using the passive detectors. In addition, micro channel plate with phosphor screen integrate in Thomson parabola spectrometer to obtain the shot-by-shot energy spectrum of laser-accelerated ions. The recent results of the measurements using the active and passive ion detectors will be discussed in the presentation., ICMaSS2021

【はじめに】 標的アイソトープ治療は播種性のがんに対する有効な治療法として知られている。特にオージェ電子はLETが高く、飛程が短いことから正常組織への影響を抑えながら高い治療効果が見込める。オージェ電子放出核種の中でも、Cu-64はオージェ電子に加えて陽電子も放出するため、治療と診断を同時におこなう（セラノスティクス）ことが可能である。そのため、標的アイソトープ治療に使用する核種の中でも大きな注目を集めているが、オージェ電子の線量評価手法が確立されておらず、他の放射線がん治療法との効果の比較が困難であることが課題の1つである。本研究では、極めて高い感度を持つ蛍光飛跡検出器（FNTD）を使用し、オージェ電子の線量評価手法の確立に取り組んだ。 【結果と考察】 実験はFNTD上にCu-64標識した塩化銅水溶液を滴下して行った。液滴内でオージェ電子の飛程が終端を迎えてしまう事を避けるために、塩化銅水溶液滴下後にカバーガラスを被せ、液滴の厚みを可能な限り薄くした。滴下より約1ヵ月経過後、共焦点顕微鏡を用いてFNTD内に記録された飛跡の情報を読みだした。 【図1】に蛍光強度と深さの関係を示す。共焦点顕微鏡の焦点深度を調整することで、オージェ電子及び競合過程で放出されるベータ粒子（β線及び陽電子）の減衰過程を追跡することが可能である。FNTDの表面付近ではオージェ電子の寄与による高い蛍光強度が確認できる。その後の蛍光はベータ粒子の寄与によるものだと考えられる。ベータ粒子の蛍光強度の深さ依存性を外挿することで、ベータ粒子の寄与とオージェ電子の寄与を切り分けて評価することに成功した。その結果、Cu-64の線源付近ではオージェ電子の寄与とベータ粒子のそれが約1：1であることを明らかにした。オージェ電子の線量を正確に評価するためには、FNTDの蛍光強度のエネルギー依存性およびFNTDの着色効果を明らかにする必要がある。発表では最近の取り組みについても述べる。, 第2回標的アイソトープ治療線量評価研究会