Search

MeV gamma-rays provide a unique window for the direct measurement of line emissions from radioisotopes, but observations have made little significant progress since COMPTEL on board the Compton Gamma-ray Observatory (CGRO). To observe celestial objects in this band, we are developing an electron-tracking Compton camera (ETCC) that realizes both bijective imaging spectroscopy and efficient background reduction gleaned from the recoil-electron track information. The energy spectrum of the observation target can then be obtained by a simple ON–OFF method using a correctly defined point-spread function on the celestial sphere. The performance of celestial object observations was validated on the second balloon SMILE-2+ , on which an ETCC with a gaseous electron tracker was installed that had a volume of 30 × 30 × 30 cm3. Gamma-rays from the Crab Nebula were detected with a significance of 4.0σ in the energy range 0.15–2.1 MeV with a live time of 5.1 hr, as expected before launch. Additionally, the light curve clarified an enhancement of gamma-ray events generated in the Galactic center region, indicating that a significant proportion of the final remaining events are cosmic gamma-rays. Independently, the observed intensity and time variation were consistent with the prelaunch estimates except in the Galactic center region. The estimates were based on the total background of extragalactic diffuse, atmospheric, and instrumental gamma-rays after accounting for the variations in the atmospheric depth and rigidity during the level flight. The Crab results and light curve strongly support our understanding of both the detection sensitivity and the background in real observations. This work promises significant advances in MeV gamma-ray astronomy.

HiZ-GUNDAM is a future satellite mission which will lead the time-domain astronomy and the multi-messenger astronomy through observations of high-energy transient phenomena. A mission concept of HiZ-GUNDAM was approved by ISAS/JAXA, and it is one of the future satellite candidates of JAXA’s medium-class mission. We are in pre-phase A (before pre-project) and elaborating the mission concept, mission/system requirements for the launch in the late 2020s. The main themes of HiZ-GUNDAM mission are (1) exploration of the early universe with high-redshift gamma-ray bursts, and (2) contribution to the multi-messenger astronomy. HiZ-GUNDAM has two kinds of mission payload. The wide field X-ray monitors consist of Lobster Eye optics array and focal imaging sensor, and monitor ~1 steradian field of view in 0.5 – 4 keV energy range. The near infrared telescope has an aperture size 30 cm in diameter, and simultaneously observes four wavelength bands between 0.5 – 2.5 μm. In this paper, we introduce the mission overview of HiZ-GUNDAM.

MeV gamma-ray astronomy in an energy range of hundreds of keV to tens of MeV is a unique window for observing nucleosynthesis, however this field has not opened up until recently because of imaging difficulties. Thus, we are developing an electron-tracking Compton camera (ETCC), which consists of a gaseous electron tracker and pixel scintillator arrays, as a next generation MeV gamma-ray telescope. Because the ETCC detects all parameters after Compton scattering, we can determine the momentum of incident gamma-rays with powerful background rejection. This ETCC has confirmed low-noise and high-sensitivity observations at high altitude through Sub-MeV gamma-ray Imaging Loaded-on-balloon Experiment I (SMILE-I) in 2006 and SMILE-2+ in 2018. Therefore, we are planning scientific observations using an ETCC with an effective area of ∼10 cm2 for 0.3 MeV, a spatial resolution of ≤10 degrees for 0.5 MeV, and a field of view of 3 sr as the next step (SMILE-3). In this paper, we present the design of the SMILE-3 ETCC and its expected observations.

We investigate the feasibility of an Electron Tracking Compton Camera (ETCC) for an imaging in a clinical situation. The ETCC is an emergence technology which can trace the track of Compton recoiled electrons. This makes possible to reconstruct images with fewer detected events compared with a conventional Compton camera. The ETCC was originally developed for astronomical purposes. In this study, we applied the ETCC in a clinical situation, especially for imaging of an At-211 therapy. This is because the At-211 has a high therapeutic efficiency and provides considerable recent research interest. In order to investigate the feasibility of the ETCC, we performed a simulation with a point source of At-211 in a water sphere with a radius of 10 cm. We found that the ETCC system can reconstruct the images with only about 1000 events. In addition, we improved the spatial resolution of the reconstructed image using a bootstrapping method. The spatial resolution was good enough to resolve a large tumor. These results suggest that the ETCC system can be used for an imaging in At-211 radiation therapy.

The first directional dark matter search with three-dimensional tracking with head–tail sensitivity (3D-vector tracking analysis) was performed with a gaseous three-dimensional tracking detector, or the NEWAGE-0.3b’ detector. The search was carried out from 2013 July to 2017 August (Run14 to Run18) at the Kamioka underground laboratory. The total livetime is 434.85 d, corresponding to an exposure of 4.51 kg$\>$d. A 90 % confidence level upper limit on spin-dependent WIMP-proton cross-section of $4.3\times10^{2}$ pb for WIMPs with the mass of 150 GeV$\>c^{-2}$ is obtained.

The electron tracking Compton camera (ETCC) system proposed by Tanimori, et al. (2006) facilitates reconstruction of three-dimensional distribution of radioisotopes without a mechanical collimator. This system has been developed for observations in astronomy, but it applicable to the imaging in nuclear medicine as well. The ETCC uses the information obtained by Compton scattered photons and recoiled electrons, which are generated in the process of Compton scattering. Without the information of the recoiled electron, the source position is localized only on a cone whose apex angle corresponds to the Compton scattering angle. However, as the ETCC can measure the energy and direction of the recoiled electron, the source position is fundamentally determined uniquely at a line on the cone surface. The quality of an ETCC image is affected by the uncertainly in the measurement of the energy of a scattered photon and that of a direction and energy of a recoiled electron. The former is affected by the Compton angle (Angular resolution: ARM) and the latter is affected by the dispersion on the cone with a Compton angle (Angular resolution: SPD). The paper studied the effect of the ARM and SPD on the reconstructed image. To evaluate the effect of the angular resolutions ARM and SPD, we assumed three detector geometries using one to three ETCCs. We assumed that the ETCC was composed of a CF4 gas detector with the size of 20 × 20 × 20 cm3 and NaI detector with the size of 20 × 20 cm2. The targeted gamma rays were 300 keV (Ga-67), 511 keV (PET) and 4438 keV (Carbon therapy). The phantom used water in sphere with a diameter of 3 cm. We transported photons with GEANT4 Monte Carlo code, and image reconstruction was performed with a list mode ML-EM algorithm. The results of simulations showed that the blurring of an image was improved with more than two detectors and the quality of images was better when we used high energy gamma rays.

Micro pixel chambers (μ-PICs), which are a type of the micro-pattern gas chambers, are usually manufactured using the printed-circuit-board (PCB) technology. However, recent application projects have begun to require higher gas gains and finer position resolution than those obtainable with current μ-PICs. It is difficult to improve the electrode structure to achieve these improvements because PCB technology limits the precision of electrode fabrication and the thickness of the substrate. We have therefore adopted micro-electro-mechanical-systems (MEMS) technology and developed the first prototype of a through-glass-via (TGV) μ-PIC. This prototype TGV μ-PIC worked well, achieving a maximum gain of approximately 20,000 and an energy resolution of 20.6% (FWHM) at 5.9 keV over the whole 5 × 5 cm2 detection area.

Recently, there appears lots of papers on the possibility of light Dark Matter (DM) in MeV and sub-GeV scale. Until now, only INTEGRAL and COMPTEL provided experimental data of 511keV of galactic center, and two spectra of Galactic Diffuse MeV gammas (GDMG) and COMPTEL provided the Cosmic Background MeV gammas (CBMG) for wide sky for indirect detection of light DMs. However except 511keV, those spectra for diffuse gammas included large statistical and systematic errors in spite of 10 years observation, since both two instruments suffered from severe background radiation in space. In 2018 April, we (SMILE-project in Comic-ray Group of Kyoto University) have observed MeV gamma rays for whole southern sky by Electron Tracking Compton Camera (ETCC) using JAXA balloon at Australia during one-day. (SMILE2+ Project) By measuring all parameters of Compton scattering in every gamma, ETCC has achieved for the first time to obtain the complete direction of MeV gammas as same as optical telescopes, and also to distinguish signal gammas from huge background gammas in space clearly. In this observation, ETCC with a large Field of View of 3sr observed MeV gammas from 3/5 of all sky including galactic centre, a half disk, crab, and most of CBMG By reconstructing the Compton process, we successfully obtained pure comic gammas by reducing background by more 2 orders, which is clearly certificated by the clear enhancement of detected gamma flux with ˜30% during galactic center passing through the Field of View, which is consistent with the ratio of CBMG and GDMG. Now 511keV gammas GDMG are preliminarily detected with ˜5 and >10σ respectively around Galactic Centre. Also we have obtained near 105events of CBMG in with quite low background of only a few 10% in total CBMG events. Thus we obtained good data for both with high statistics and very low systematics even one day observation.

NEWAGE is a direction-sensitive direct dark matter search experiment with a three-dimensional gaseous tracking detector (μ-TPC). Our goals are detection of the dark matter - nucleus scattering signal and the investigation of kinematics of the dark matter in the Galaxy. A dark matter search experiment with the NEWAGE-0.3b’ detector was performed from Jul. 2013 to Aug. 2016 (RUN14 to Run17). The total live time is 230.16 days which is about 8 times larger than that of our previous measurement. In the analysis, the event selection was improved and the background was reduced to about 1/3 at 50 keV. This work is important to investigate the properties of the dark matter in the Galaxy in the future dark matter research.

A new active target named MAIKo (Mu-PIC based Active target for Inverse Kinematics$_{\circ}$) has been developed at Kyoto University and Research Center for Nuclear Physics (RCNP), Osaka University. MAIKo is suited for missing-mass spectroscopy of unstable nuclei at forward scattering angles in inverse kinematics. MAIKo consists of a time projection chamber (TPC), which incorporates a micro-pixel chamber ($\mu$-PIC) as the electron multiplication and collection system. In MAIKo, the medium gas also plays the role of a reaction target, thus allowing detection of low-energy recoil particles with high position resolution. The MAIKo TPC was commissioned with He(93%)+iso-C$_{4}$H$_{10}$(7%) and He(93%)+CO$_{2}$(7%) mixture gasses at 430 hPa. The gas gain and the angular resolution of MAIKo were evaluated with an alpha source and a $^{4}$He beam at 56 MeV. The TPC was stably operated up to 1000-kcps beam intensity. A tracking algorithm using the Hough transform method has been developed to analyze scattering events. An angular resolution of 1.3$^{\circ}$ was achieved for scattered $^{4}$He particles., Comment: 13 pages, 17 figures

To establish imaging spectroscopy of cosmic gamma-rays from a few hundreds of keV to a few tens MeV, we developed an electron-tracking Compton camera (ETCC). The ETCC consists of a time projection chamber (TPC) and pixelated scintillator arrays (PSAs). The ETCC is superior to conventional gamma-ray imaging detectors of this energy band in that the arrival direction of an incident gamma-ray is firmly determined at one point and realizes high noise rejection efficiency. We performed a campaign to demonstrate the gamma-ray imaging performance of the ETCC at balloon altitude via the sub-MeV gamma-ray imaging loaded-on-balloon experiment 2+ (SMILE-2+). The balloon was launched on April 7, 2018, at 6:26 ACST (UTC +9:30) from Alice Springs, Australia. We performed a level flight for 26 hours at an altitude of 39.6 km. The main observation targets were the Galactic Center region and the Crab Nebula and we succeeded in observing them without any critical problems. The configuration of the flight model ETCC and the housekeeping data are described in detail.

Micro pixel chambers (μ-PIC) are gaseous two-dimensional imaging detectors originally manufactured using printed circuit board (PCB) technology. They are used in MeV gamma-ray astronomy, medicalimaging, neutron imaging, the search for dark matter, and dose monitoring. The position resolution of the present μ-PIC is approximately 120 μm (RMS), however some applications require a fine position resolution of less than 100 μm. To this end, we have started to develop a μ-PIC based on micro electro mechanical system (MEMS) technology, which provides better manufacturing accuracy than PCB technology. Our simulation predicted the gains of MEMS μ-PICs to be twice those of PCB μ-PICs at the same anode voltage. We manufactured two MEMS μ-PICs and tested them to study their behavior. In these experiments, we successfully operated the fabricatedMEMS μ-PICs and we achieved a maximum gain of approximately 7×103 and collected their energy spectra under irradiation of X-rays from 55Fe. However, the measured gains of the MEMS μ-PICs were less than half of the values predicted in the simulations. We postulated that the gains of the MEMS μ-PICs are diminished by the effect of the silicon used as a semiconducting substrate.

Energy-resolved neutron imaging at a pulsed source utilizes the energy-dependent neutron transmission measured via time-of-flight to extract quantitative information about the internal microstructure of an object. At the RADEN instrument at J-PARC in Japan, we use cutting-edge detectors employing micro-pattern detectors or fast Li-glass scintillators and fast, all-digital data acquisition to perform such measurements, while continuing their development toward better utilization of the intense neutron source. In particular, for the Micro-Pixel Chamber based Neutron Imaging Detector ({\mu}NID), a micro-pattern detector with a 400 {\mu}m pitch and employing 3He for neutron conversion, we have successfully improved the spatial resolution from 200 to 100 {\mu}m, increased the detection efficiency from 18 to 26% for thermal neutrons, and increased the maximum count rate from 0.4 to 1 Mcps. We are also testing a new readout element with a 215 {\mu}m pitch for further improved spatial resolution, and a {\mu}NID with boron-based neutron converter for increased rate performance., Comment: 8 pages, 5 figures; accepted to Proceedings of International Conference on Neutron Optics 2017, Nara, Japan (JPS Conference Proceedings)

NEWAGE is a direction-sensitive WIMP search experiment using micro pixel chamber. After our first underground measurement at Kamioka in 2009, we constructed a new detector, which was designed to have a twice larger target volume with low background material, a lowered threshold of 50 keV, an improved data acquisition system. In 2013, dark matter search in Kamioka underground laboratory was performed. We have succeeded to lower the background level by about one order of magnitude., 13th International Conference on Topics in Astroparticle and Underground

We obtain the transmission image of a commercial lithium ion (Li-ion) battery using a pulsed neutron beam at the beamline 09 of the Materials and Life Science Experimental Facility at the Japan Proton Accelerator Research Complex. The purpose of this study is to improve the performance of the Li-ion battery by nondestructive observation of its charging and discharging. The transmission images for three charge states (3.2 V, 3.7 V, and 4.2 V) reveal differences between these three states, which we attribute to electrolyte migration. The transmission spectra show Bragg edges originating from the electrodes, current collectors, and battery vessel. Although the battery as a whole has the expected relation between the charge accumulation and the quantity of lithium amounts in the positive and negative electrodes, a portion of the battery deviates from this relation, which may imply a position dependent charging in the battery.

For MeV gamma-ray astronomy, We have developed an electron-tracking Compton camera (ETCC) as a next generation satellite telescope. Our detector consists of a Comptonscattering target and a scattered gamma-ray absorber. The target is a gaseous Time Projection Chamber (TPC), which uses $\mu $ PIC as the 2-dimensional readout detector, and the absorber is position sensitive scintillation arrays (PSAs). We developed a prototype ETCC and certificated its performance in a groundbased experiment. The prototype ETCC had a sharp PSF of 15° included 50%, 662 keV) at the ARM of 5° and the SPD of 100°. We plan to update the prototype ETCC and observe the electronpositron annihilation line of the galactic center in Australia in early 2018 (SMILE-II +). In the data acquisition (DAQ) system of the prototype ETCC, the dead time is estimated to be $\sim 20$ % at the trigger rate of $\sim 100$ Hz in a balloon observation, and the prototype ETCC can work. The SMILE-II + ETCC can also work at the balloon altitude. On the other hand, in the future observation with the ETCC, that has a larger effective area than the effective area of SMILE-II + ETCC, the DAQ rate is expected to be $\sim~1$ kHz. The dead time gets saturation due to sending data via VME bus and common start system in PSA. To overcome the two problem, we develop a new TPC readout board and a PSA readout unit. We create a test model ETCC which have the new TPC readout boards and the new PSA readout units. Although the dead time is $\sim 20$ % at 30 Hz with a small ETCC in the prototype DAQ system, the dead time is $\sim 20$ % at 2 kHz in the new system.

Energy-resolved neutron imaging at a pulsed source utilizes the energy-dependent neutron transmission, measured via time-of-flight, to extract quantitative information on the internal microstructure of an object in situ. These techniques, however, are currently limited by the count-rate capability of available imaging detector systems, resulting in long measurement times and reduced spatial resolution. At RADEN, we are building on our previous detector development work to provide nearly three times improvement in rate performance of our micro-pixel chamber based neutron imaging detector $(_{\mu }$ NID) by changing from 3 He to a boron-based neutron converter and optimizing the shape for a much reduced event size and maximized detection efficiency. We are also designing a new micro-pattern readout element with an additional readout axis to facilitate clean event separation under high-rate conditions. Proof-of-principle testing at RADEN of the $_{\mu }$ NID with a flat, $1.2{\mu }m$ thick $^{10}B$ conversion layer confirmed a spatial resolution of 0.45 to 0.5 mm and indicated an improvement in rate capacity up to 22 Mcps or more. Once the boron converter is optimized for detection efficiency, this detector will help to unlock the full potential of these energyresolved neutron imaging techniques at pulsed sources.

Negative-ion time projection chambers(TPCs) have been studied for low-rate and high-resolution applications such as dark matter search experiments. Recently, a full volume fiducialization in a self-triggering TPC was realized. This innovative technology demonstrated a significant reduction in the background with MWPC-TPCs. We studied negative-ion TPC using the μ-PIC+GEM system and obtained sufficient gas gain with CS2 gas and SF6 gas at low pressures. We expect an improvement in detector sensitivity and angular resolution with better electronics.

Purpose: Conventional gamma‐ray detector, PET and SPECT, have the limitation of energy and field of view. These limitations are major problems of studying for a new medical imaging. Therefore, we have developed the new imaging detector which is an electron‐tracking Compton camera (ETCC). Methods: A reconstruction method of Compton camera (CC) is using the physics principle. Because of using physics principle, CC can have a wide energy dynamic range and wide field of view. Conventional CC, however, cannot catch Compton recoil electron tracks, and this is one of the reasons of low imaging power. We have developed a time projection chamber (TPC) using micro pixel chamber (μPIC) as the new detector for ETCC. The μPIC is 2‐dimensional gaseous detector and this position resolution is less than 400 μm. Using this detector, ETCC can get electron tracks which are generated from Compton scattering. In this paper, we show the prototype ETCC performance and imaging results. Results: ETCC achieved a wide energy dynamic range (200–1300keV) and wide field of view (3 steradian). Also we succeeded in imaging new imaging reagents using mice as follows; (1) F‐18‐FDG (511 keV) and I‐131‐MIBG (364 keV) simultaneous imaging for double clinical tracer imaging, (2) Zn‐65‐ porphyrin (1116 keV) imaging for high energy gamma‐ray imaging and, (3) imaging of some minerals (Mn‐54, Zn‐65) in mice and so on. And we succeeded in 3‐D imaging which has imaged only one direction using one head camera.Conclusions: We have developed the ETCC for new medical imaging device and succeeded in imaging the some imaging reagents. We started to develop the new ETCC which can image the mouse within 30 min. Thus, this detector has the possibility of new medical imaging.

X-ray and gamma-ray polarimetry is a promising tool to study the geometry and the magnetic configuration of various celestial objects, such as binary black holes or gamma-ray bursts (GRBs). However, statistically significant polarizations have been detected in few of the brightest objects. Even though future polarimeters using X-ray telescopes are expected to observe weak persistent sources, there are no effective approaches to survey transient and serendipitous sources with a wide field of view (FoV). Here we present an electron-tracking Compton camera (ETCC) as a highly-sensitive gamma-ray imaging polarimeter. The ETCC provides powerful background rejection and a high modulation factor over a FoV of up to 2$\pi$ sr thanks to its excellent imaging based on a well-defined point spread function. Importantly, we demonstrated for the first time the stability of the modulation factor under realistic conditions of off-axis incidence and huge backgrounds using the SPring-8 polarized X-ray beam. The measured modulation factor of the ETCC was 0.65 $\pm$ 0.01 at 150 keV for an off-axis incidence with an oblique angle of 30$^\circ$ and was not degraded compared to the 0.58 $\pm$ 0.02 at 130 keV for on-axis incidence. These measured results are consistent with the simulation results. Consequently, we found that the satellite-ETCC proposed in Tanimori et al. (2015) would provide all-sky surveys of weak persistent sources of 13 mCrab with 10% polarization for a 10$^{7}$ s exposure and over 20 GRBs down to a $6\times10^{-6}$ erg cm$^{-2}$ fluence and 10% polarization during a one-year observation., Comment: 22 pages, 19 figures, 1 table, accepted for publication in ApJ

An all-sky monitor with nuclear imaging spectroscopy is a promising tool for the systematic study of supernova explosions. In particular, progenitor scenarios of type-Ia supernovae, which are not yet well understood, can be resolved using light curves in the nuclear gamma-ray band. Here we report an expected result of an all-sky monitor with imaging spectroscopy using electron-tracking Compton camera, which will enable us to observe nuclear gamma-ray lines from type-Ia supernovae., Comment: 4 pages, 2 figures, Proceedings of the 14th International Symposium on Nuclei in the Cosmos (NIC-XIV)

NEWAGE is a direction-sensitive direct dark matter search experiment. NEWAGE uses a micro time-projection chamber with a detection volume of $\rm 31 \times 31 \times 41 cm^3$, which is read by a macro-petterned gaseous detectors, $\rm \mu$-PIC. Underground measurements with the current detector, NEWAGE-0.3b’, have been performed since 2013. After the first direction-sensitive limits drived from 31.6 live-days of NEWAGE-0.3b' data were published, measurements were continued and the preliminary results from an addtional 170 days of results are reported here. In order to improve the sensitivity, low $\alpha$-particle emission $\rm \mu-PICs$ are being developed. Studies on negative-ion gases are also on-going. These recent activities that aim to improve the sensitivity are also presented here.

Since the discovery of nuclear gamma-rays, its imaging has been limited to pseudo imaging, such as Compton Camera (CC) and coded mask. Pseudo imaging does not keep physical information (intensity, or brightness in Optics) along a ray, and thus is capable of no more than qualitative imaging of bright objects. To attain quantitative imaging, cameras that realize geometrical optics is essential, which would be, for nuclear MeV gammas, only possible via complete reconstruction of the Compton process. Recently we have revealed that "Electron Tracking Compton Camera" (ETCC) provides a well-defined Point Spread Function (PSF). The information of an incoming gamma is kept along a ray with the PSF and that is equivalent to geometrical optics. Here we present an imaging-spectroscopic measurement with the ETCC. Our results highlight the intrinsic difficulty with CCs in performing accurate imaging, and show that the ETCC surmounts this problem. The imaging capability also helps the ETCC suppress the noise level dramatically by ~3 orders of magnitude without a shielding structure. Furthermore, full reconstruction of Compton process with the ETCC provides spectra free of Compton edges. These results mark the first proper imaging of nuclear gammas based on the genuine geometrical optics., 放射線発見以来初の幾何光学に基づくガンマ線画像化法を発見・実用化 : ガンマ線完全可視化により放射線利用の安全評価が正確に. 京都大学プレスリリース. 2017-02-14.

Time-of-flight Positron emission tomography (TOF-PET) is one of the next-generation medical imaging methods, which requires scintillators with a very short decay time. However, the shortest scintillation decay times are typically 20–30 ns, and these values are not sufficient for TOF-PET. Cherenkov counters are used in high energy physics and they are expected to be applied in medical imaging due to their short decay time. Here, high-refractive index materials are necessary for Cherenkov radiators to reach a high light output. We measured refractive indices of Gd3Ga5O12 (GGG), Y3Ga5O12 (YGG) and Lu3Ga5O12 (LuGG) crystals grown by a micro-pulling-down ( μ - PD ) method. The GGG, YGG and LuGG crystals were found to have refractive indices of ~ 2.5 , ~ 2.3 and ~ 2.3 at 400 nm, respectively. Then we grew a 40 mm diameter GGG crystal by the Czochralski method, and the emission decay times of the GGG crystals irradiated with muons and gamma rays were 10 ± 1 ns and 10 ± 2 ns , respectively, using a photomultiplier tube (Hamamatsu R6231-100). Cherenkov light of the GGG crystal could be observed for the gamma-ray irradiation.

Imaging of $^{95m}$Tc radioisotope was conducted using an electron tracking-Compton camera (ETCC). $^{95m}$Tc emits 204, 582, and 835 keV $\gamma$ rays, and was produced in the $^{95}$Mo(p,n)$^{95m}$Tc reaction with a $^{95}$Mo-enriched target. The recycling of the $^{95}$Mo-enriched molybdenum trioxide was investigated, and the recycled yield of $^{95}$Mo was achieved to be 70\% - 90\%. The images were obtained with each of the three $\gamma$ rays. Results showed that the spatial resolution increases with increasing $\gamma$-ray energy, and suggested that the ETCC with high-energy $\gamma$-ray emitters such as $^{95m}$Tc is useful for the medical imaging of deep tissue and organs in the human body., 電子飛跡検出型コンプトンカメラ(ETCC)を用いて放射性同位元素$^{95m}$Tcの画像撮像を実施した。$^{95m}$Tcは、204, 582, 835keVの3本の$\gamma$線を放出し、濃縮同位体$^{95}$Moを用いて$^{95}$Mo(p,n)$^{95m}$Tc反応で合成される。濃縮$^{95}$Mo同位体三酸化物の再利用について実験を実施し、再生率70$\sim$90\%を達成した。画像は3本の$\gamma$線それぞれを用いて解析し取得した。その結果、$\gamma$線エネルギーが高いほど空間分解能が向上することが判り、$^{95m}$Tcのような高エネルギー$\gamma$線放出核を利用することで、ETCCが人体の深部の組織や器官の医療画像撮像に有効であることを示唆する結果を得た。

We have developed a prototype time-resolved neutron imaging detector employing the micro-pixel chamber (muPIC), a micro-pattern gaseous detector, coupled with a field programmable gate array-based data acquisition system for applications in neutron radiography at high-intensity neutron sources. The prototype system, with an active area of 10cm x 10cm and operated at a gas pressure of 2 atm, measures both the energy deposition (via time-over-threshold) and 3-dimensional track of each neutron-induced event, allowing the reconstruction of the neutron interaction point with improved accuracy. Using a simple position reconstruction algorithm, a spatial resolution of 349 +/- 36 microns was achieved, with further improvement expected. The detailed tracking allows strong rejection of background gamma-rays, resulting in an effective gamma sensitivity of 10^-12 or less, coupled with stable, robust neutron identification. The detector also features a time resolution of 0.6 microseconds., 10 pages, 13 figures; accepted for publication in NIMA

We have developed a prototype time-resolved neutron imaging detector employing a micro-pattern gaseous detector known as the micro-pixel chamber ({\mu}PIC) coupled with a field-programmable-gate-array-based data acquisition system. Our detector system combines 100{\mu}m-level spatial and sub-{\mu}s time resolutions with a low gamma sensitivity of less than 10^-12 and high data rates, making it well suited for applications in neutron radiography at high-intensity, pulsed neutron sources. In the present paper, we introduce the detector system and present several test measurements performed at NOBORU (BL10), J-PARC to demonstrate the capabilities of our prototype. We also discuss future improvements to the spatial resolution and rate performance.

We have developed an Electron Tracking Compton Camera (ETCC), which provides a well-defined Point Spread Function (PSF) by reconstructing a direction of each gamma as a point and realizes simultaneous measurement of brightness and spectrum of MeV gamma-rays for the first time. Here, we present the results of our on-site pilot gamma-imaging-spectroscopy with ETCC at three contaminated locations in the vicinity of the Fukushima Daiichi Nuclear Power Plants in Japan in 2014. The obtained distribution of brightness (or emissivity) with remote-sensing observations is unambiguously converted into the dose distribution. We confirm that the dose distribution is consistent with the one taken by conventional mapping measurements with a dosimeter physically placed at each grid point. Furthermore, its imaging spectroscopy, boosted by Compton-edge-free spectra, reveals complex radioactive features in a quantitative manner around each individual target point in the background-dominated environment. Notably, we successfully identify a "micro hot spot" of residual caesium contamination even in an already decontaminated area. These results show that the ETCC performs exactly as the geometrical optics predicts, demonstrates its versatility in the field radiation measurement, and reveals potentials for application in many fields, including the nuclear industry, medical field, and astronomy., 放射線発見以来初の幾何光学に基づくガンマ線画像化法を発見・実用化 : ガンマ線完全可視化により放射線利用の安全評価が正確に. 京都大学プレスリリース. 2017-02-14.

The Energy-Resolved Neutron Imaging System RADEN, located at the J-PARC Materials and Life Science Experimental Facility in Japan, is the world's first dedicated high-intensity, short-pulsed neutron imaging beam line. To carry out energy-resolved neutron imging at RADEN, we use cutting-edge detector systems employing micropattern detectors and data acquisition systems based on Field Programmable Gate Arrays to provide the necessary sub-μs time resolution, high counting rates, and event-by-event background rejection. One such detector, the Micro Pixel Chamber-based Neutron Imaging Detector (μNID), provides a spatial resolution of 120 μm (s), time resolution of 0.6 μs, 18% detection efficiency for thermal neutrons, and effective gamma sensitivity of less than 10−12. We have recently increased the rate capacity of the μNID from 600 kcps to more than 8 Mcps via an upgrade of the readout electronics and the introduction of a new gas mixture optimized for higher count rate, better spatial resolution, and higher detection efficiency. We are also developing new detection elements with strip pitches of 280 μm and 215 μm, down from 400 μm, with a corresponding improvement in the spatial resolution expected. Here, we present the progress of the ongoing development of the μNID, including the results of recent on-beam tests performed at RADEN.

The field of MeV gamma-ray astronomy has not opened up until recently owing to imaging difficulties. Compton telescopes and coded-aperture imaging cameras are used as conventional MeV gamma-ray telescopes; however their observations are obstructed by huge background, leading to uncertainty of the point spread function (PSF). Conventional MeV gamma-ray telescopes imaging utilize optimizing algorithms such as the ML-EM method, making it difficult to define the correct PSF, which is the uncertainty of a gamma-ray image on the celestial sphere. Recently, we have defined and evaluated the PSF of an electron-tracking Compton camera (ETCC) and a conventional Compton telescope, and thereby obtained an important result: The PSF strongly depends on the precision of the recoil direction of electron (scatter plane deviation, SPD) and is not equal to the angular resolution measure (ARM). Now, we are constructing a 30 cm-cubic ETCC for a second balloon experiment, Sub-MeV gamma ray Imaging Loaded-on-balloon Experiment: SMILE-II. The current ETCC has an effective area of ~1 cm2 at 300 keV, a PSF of ~10° at FWHM for 662 keV, and a large field of view of ~3 sr. We will upgrade this ETCC to have an effective area of several cm2 and a PSF of ~5° using a CF4-based gas. Using the upgraded ETCC, our observation plan for SMILE-II is to map of the electron-positron annihilation line and the 1.8 MeV line from 26Al. In this paper, we will report on the current performance of the ETCC and on our observation plan.

The measurement of the direction of WIMP-induced nuclear recoils is a compelling but technologically challenging strategy to provide an unambiguous signature of the detection of Galactic dark matter. Most directional detectors aim to reconstruct the dark-matter-induced nuclear recoil tracks, either in gas or solid targets. The main challenge with directional detection is the need for high spatial resolution over large volumes, which puts strong requirements on the readout technologies. In this paper we review the various detector readout technologies used by directional detectors. In particular, we summarize the challenges, advantages and drawbacks of each approach, and discuss future prospects for these technologies., Comment: 58 pages, 26 figures, accepted by Physics Reports

We have successfully refined the position resolution of a two-dimensional X-ray photon-counting detector based on the micro-pixel gas chamber (μ-PIC) by measuring the charge distribution of an X-ray interaction without the use of analog-to-digital converters (ADCs). By updating the logic of the Field Programmable Gate Arrays (FPGAs) included in the data acquisition system, we were able to acquire the pulse widths, or time-above-threshold of the μ-PIC signals, by measuring both the leading and trailing edges of the digital signals. By using the measured widths to estimate the peak of the charge distribution, the position resolution of our detector was improved to σ=93.3±2.8μm from a value of σ=229.5±6.8μm found using the FPGA logic of the previous system. This represents an improvement of nearly 60%.

It is an on-going challenge to verify the proton range in situ during proton therapy. Since the protons stop in target tissue, measurement of gamma-rays emitted either promptly from nuclear de-excitation or in pair from positron annihilation is the feasible method to monitor the proton range in-vivo. Using the technique of gamma collimation, we empirically demonstrated that the proton range and prompt gamma distribution are well correlated in the therapy energy range, and that measuring prompt gammas is a viable method for the clinical application. However, this collimation technique appears not to be applicable to passively scattered proton beams. The device chosen for gamma imaging in 2D is an electron tracking Compton camera, which images single-emission photons employing a gas chamber to induce Compton scattering. Images of prompt gammas were attained at the proton beam energy of 140 MeV. Measurements showed that gamma image in the energy range of 800–2000 keV provides a better match with the proton range compared to the image by lower energy gammas.

In order to develop novel vacuum ultra violet (VUV) emitting scintillators, we grew Nd 0.5%, Tm 0.5%, and Er 0.5% doped LuF 3 scintillators by the μ-pulling down method, because LuF 3 has a very wide band gap and Nd 3+ , Tm 3+ , and Er 3+ luminescence centers show fast and intense 5d–4f emission in VUV region. Transmittance and X-ray induced radioluminescence were studied in these three samples using our original spectrometer made by Bunkou-Keiki company. In the VUV region, transmittance of 20–60% was achieved for all the samples. The emission peaks appeared at approximately 180, 165, and 164 nm for Nd 3+ , Tm 3+ , and Er 3+ doped LuF 3 , respectively. Using PMT R8778 (Hamamatsu), we measured their light yields under 241 Am α-ray excitation. Compared with Nd:LaF 3 scintillator, which has 33 photoelectrons/5.5 MeV α, Nd:LuF 3 and Tm:LuF 3 showed 900±90 and 170±20 ph/5.5 MeV-α, respectively. Only for the Nd doped one, we can detect 137 Cs 662 keV γ-ray photoabsorption peak and the light yield of 1200±120 ph/MeV was measured. We also investigated their decay time profiles by picosecond pulse X-ray equipped streak camera, and the main decay component of Nd:LuF 3 turned out to be 7.63 ns.

We have developed an Electron-Tracking Compton Camera (ETCC) for medical imaging and MeV gamma-ray astronomy. The ETCC consists of a gaseous Time Projection Chamber ( μ -TPC) and pixel scintillator arrays. To improve the detection efficiency, we have optimized the gas mixture in the μ -TPC and operated the ETCC at high pressure. Basic characteristics such as the gas gain, drift velocity, energy resolution, and position resolution of the μ -TPC were examined, and using this optimization, both the efficiency and the angular resolution of the ETCC were measured. We achieved a steady gas gain of ∼ 20 , 000 in Ar/CF4/isoC4H10 (54:40:6) at 1.4 atm. The diffusion constant in Ar/CF4/isoC4H10 (54:40:6) at 1.4 atm was ∼ 2 times better than in Ar/C2H6 (90:10) at 1 atm. The efficiency in Ar/CF4/isoC4H10 (54:40:6) at 1.4 atm was also ∼ 2 times higher than in Ar/C2H6 (90:10) at 1 atm.

We have evaluated the possibility of the Electron-Tracking Compton Camera (ETCC) to simultaneously operate as a pair-creation camera. The ETCC consists of a gaseous micro-time projection chamber (micro-TPC) and a scintillation camera. Several prototypes of the camera were developed and their performance was studied. Because the micro-TPC can detect a large number of hit points along one charged particle track, has a good position resolution of about 0.2 mm, and uses the filling gas as the scattering material, the influence of multiple scattering is small. This makes the micro-TPC well-suited to detecting pair-creation events. We have examined the performance of a camera of size 10×10×15 cm3, using the pair-creation mode in the energy range of 10–100 MeV. Using this camera, we performed a proof-of-principle experiment with laser inverse Compton gamma rays at the National Institute of Advanced Industrial Science and Technology (AIST), and we succeeded in tracking electron–positron pairs and in reconstructing 10 and 20 MeV gamma rays. In this paper, we report the fundamental performance of the gamma-ray camera with pair-creation mode.

With the development of the Compton camera which can realize high position resolution, technetium isotopes emitting high energy gamma-rays are required. In this study, Technetium-95m which emits some gamma rays with higher than 200 keV was produced by the 95Mo(p,n)95mTc reaction. Image of gamma-rays from 95mTc was taken by a Compton gamma-ray camera.

In order to develop novel scintillating materials, we grew 0.5 mol%, 1 mol%, and 3 mol% Nd-doped LuLiF4 scintillators by the micro-pulling down method, because LuLiF4 has a very wide band gap and Nd3+ shows fast and intense 5d-4f emission as a luminescence center. The transmittance and emission peaks were examined in these three samples by using our original spectrometer made by Bunkou-Keiki Company. At wavelengths longer than 180 nm, approximately 60-80% transmittance with three absorption peaks around 140, 160 and 175 nm and emission peak at approximately 180 nm were observed for all the crystals. Light yields and decay time constants of the samples irradiated by 241Am γ-ray were measured using photomultiplier tubes R8778 (Hamamatsu). The light yield of the 1 mol% doped LuLiF4 was 700 photons/5.5MeV α that is much greater than that of Nd:LaF3 scintillator (100 photons/5.5MeV α). As for decay time profiles, the main component of Nd:LuLiF4 was 12 ns in the case of α-ray irradiation. 137Cs 662 keV γ-ray photoabsorption peak was detected in 1 mol% doped LuLiF4 only, and the light yield was 300 ph/MeV.

We have developed a LaBr3:Ce scintillator array consisting of 8 × 8 pixels with a size of 5.8 mm×5.8 mm×15.0 mm, which serves as an absorber of scattered gamma rays with energies from 0.1 to 1 MeV in a Compton camera. The pixels were cut from two pieces of LaBr3:Ce crystal with a diameter of 38 mm and a length of 38 mm with full width at half-maximum (FWHM) energy resolutions of 4.1 ± 0.1% and 3.0 ± 0.1% at 356 and 662 keV, respectively, measured with a single anode photomultiplier tube (PMT). The crystal had the following volumetric uniformities: light outputs with a difference of 0.5% (standard deviation: SD) and energy resolutions with that of 2% (SD) at 356 keV. In contrast, for each pixel in the array, the average and SD FWHM energy resolutions over 64 pixels, measured with a single-anode PMT and a collimator, were 5.8 ± 0.9% at 356 keV. The array was then coupled to a 64-channel multi-anode PMT (Hamamatsu H8500), the anode pitch of which was the same as the LaBr3:Ce pixel pitch of 6.1 mm. When the 64 anodes were read out from four channels in a resistor chain by the charge division method, the FWHM energy resolution of all 64 pixels was 7.0 ± 0.5% at 662 keV, whereas that of the inner 6×6 pixels was 5.8 ± 0.4% at 662 keV. In addition, we measured a Gd2SiO5:Ce (GSO:Ce) scintillator array consisting of 8×8 pixels with a size of 5.9 mm×5.9 mm×13.0 mm to compare its performance with that of the LaBr3:Ce array. The FWHM energy resolution of all 64 GSO:Ce pixels was 10.8 ± 0.3% at 662 keV. With these energy resolutions, FWHM angular resolutions of the Compton camera using the LaBr3:Ce and GSO:Ce arrays are expected to be 4.6° and 5.3°, respectively, at 662 keV.

A gas-based neutron detection system with individual readout method and comprising a micro-pixel detector head was constructed, and preliminary experiments were conducted under neutrons irradiation. The detection system also consisted of a micro-pixel detector head, a gas chamber that had feedthrough lines of 541 channels, amplifier-shaper-discriminator boards, position encoders with field programmable gate arrays, and a device capable of fast data acquisition. The micro-pixel detector head exhibited a fast response time, and the full width at half maximum of the response time was 160 ns. Its gas gain was about 50 at an anode-cathode voltage of 560 V and a gas pressure of 0.5 MPa (0.45 MPa for He and 0.05 MPa for CF 4 ). Signal pulse peaks of neutrons could be identified and their output voltages at an anode and a cathode were 2.4 and 5.3 mV, respectively; on the other hand, the output voltage of all the anodes was 105 mV. The neutron detection system could easily distinguish neutron signals from the background noise, and the gas gain of the micro-pixel detector head did not changed.

NEWAGE-0.3a is a prototype direction-sensitive dark matter search detector. We measured its response to electron tracks and nuclear tracks while focusing on the tracking performances in an underground laboratory. It showed a gamma-ray rejection power of 8.1 ± 1.9 × 10 −6 at 100 keV α.e.(alpha-equivalent) and an energy resolutions of 45% at 6 MeV α.e. The absolute nuclear efficiency was 80% at 100 keV α.e. and the nuclear directional-dependent efficiency was also measured. The three-dimensional angular resolution for the nuclear track was 46 ± 3° in the energy range from 100 keV α.e. to 400 keV α.e.

As next-generation MeV gamma-ray telescope, we have developed an electron-tracking Compton camera (ETCC) that consists of a gaseous tracker and an absorber. The ETCC obtains the energy and direction of both a scattered gamma ray and a recoil electron, and determines both the energy and direction of an incident gamma ray, photon by photon. Furthermore, this camera features powerful background rejection based on Compton-scattering kinematics. To prepare for future spacecraft loading, we planned the balloon experiment, “Sub-MeV gamma-ray Imaging Loaded-on-balloon Experiment” (SMILE). As the first step in SMILE, we demonstrated gamma-ray detection using our camera by observing diffuse cosmic gamma rays and secondary gamma rays generated by collisions between high-energy cosmic rays and nuclei in the air. On September 1, 2006, our detector was loaded on a balloon and launched from Sanriku Balloon Center, ISAS/JAXA. The balloon realized level flight at an altitude of about 35 km during a live time of 3.0 h. We ...

In 2004, we searched for very high energy (VHE) gamma-ray emission from the Galactic Plane using the CANGAROO-III stereoscopic observation system. Two different longitude regions (l = −19°.5 and l = +13°.0) on the Galactic Plane were observed during July and August 2004. We analyzed events that triggered three telescopes aiming to measure the diffuse emission component. No significant signal associated with the Galactic Plane was found from either of the regions. Assuming that the gamma-ray spectrum is described by a single power-law for energies ranging between a few GeV and TeV, lower limits of the power-law spectral indices were found to be 2.2 for both of the regions with a 99.9% confidence level. This result is consistent with the other VHE measurements and constrains a hypothesis in which a very hard (∼2.0) cosmic ray electron spectrum was introduced to explain the EGRET GeV anomaly.

We have studied the performance of a readout system with ASIC chips for a gamma-ray camera based on a 64-channel multi-anode PSPMT (Hamamatsu flat-panel H8500) coupled to a GSO(Ce) scintillator array. The GSO array consists of 8×8 pixels of 6×6×13 mm 3 with the same pixel pitch as the anode of the H8500. This camera is intended to serve as an absorber of an electron tracking Compton gamma-ray camera that measures gamma rays up to ∼1 MeV. Because we need a readout system with low power consumption for a balloon-borne experiment, we adopted a 32-channel ASIC chip, IDEAS VA32_HDR11, which has one of the widest dynamic range among commercial chips. However, in the case of using a GSO(Ce) crystal and the H8500, the dynamic range of VA32_HDR11 is narrow, and therefore the H8500 has to be operated with a low gain of about 10 5 . If the H8500 is operated with a low gain, the camera has a narrow incident-energy dynamic range from 100 to 700 keV, and a bad energy resolution of 13.0% (FWHM) at 662 keV. We have therefore developed an attenuator board in order to operate the H8500 with the typical gain of 10 6 , which can measure up to ∼1 MeV gamma ray. The board makes the variation of the anode gain uniform and widens the dynamic range of the H8500. The system using the new attenuator board has a good uniformity of min:max∼1:1.6, an incident-energy dynamic range from 30 to 900 keV, a position resolution of less than 6 mm, and a typical energy resolution of 10.6% (FWHM) at 662 keV with a low power consumption of about 1.7 W/64ch.

We developed an analog-readout system for a pixel-readout micro-pixel chamber (µ-PIC) to be used as an astronomical X-ray polarimeter, and demonstrated that the sensitivity of the new system reached up to that predicted by a simulation. A pixel-readout µ-PIC is a micro-pattern gaseous detector with a fine position resolution and good stability at sufficient gain operation, and is suited for astronomical X-ray polarimetry. However, as shown by Katagiri et al. (2007), the sensitivity to X-ray polarization was found to be statistically lower by a significant amount than that expected from the simulation of Ueno et al. [Nucl. Instrum. Methods Phys. Res., Sect. A 525 (2004) 28] because of the readout system and background produced by the scattering of the X-ray beam in air. We therefore developed a new readout system and carried out a beam test with aluminum tubes that reduced the background. As a result, we demonstrated that for collimated beams, the modulation factors, which are indicators of the sensitivity to X-ray polarization, were 0.24±0.08 at 8 keV and 0.18±0.07 at 15 keV in a neon-based gas mixture, and 0.18±0.04 at 15 keV in an argon-based mixture. These values are consistent with those predicted by the simulation within errors.

We have developed the Electron Tracking Compton Camera (ETCC) with reconstructing the 3-D tracks of the scattered electron in Compton process for both sub-MeV and MeV gamma rays. By measuring both the directions and energies of not only the recoil gamma ray but also the scattered electron, the direction of the incident gamma ray is determined for each individual photon. Furthermore, a residual measured angle between the recoil electron and scattered gamma ray is quite powerful for the kinematical background rejection. For the 3-D tracking of the electrons, the Micro Time Projection Chamber (μ-TPC) was developed using a new type of the micro pattern gas detector. The ETCC consists of this μ-TPC (10×10×8 cm3) and the 6×6×13 mm3 GSO crystal pixel arrays with a flat panel photo-multiplier surrounding the μ-TPC for detecting recoil gamma rays. The ETCC provided the angular resolution of 6.6° (FWHM) at 364 keV of 131I. A mobile ETCC for medical imaging, which is fabricated in a 1 m cubic box, has been operated since October 2005. Here, we present the imaging results for the line sources and the phantom of human thyroid gland using 364 keV gamma rays of 131I.