Search

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.

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.

In this paper, a waveband-shift-free optical phase conjugator based on difference-frequency generation (DFG-OPC) that enables broadband operation is proposed and theoretically investigated. First, the principle of phase-conjugated (PC) wave generation with the DFG-OPC is mathematically described. Using a Sagnac loop interferometer with a χ(2) optical nonlinear material and two dispersive elements (DEs), a PC wave with the same wavelength as a signal can be generated. Subsequently, the required DE length difference for the PC wave generation is theoretically calculated. The calculation results indicate the minimal DE length difference is 20.0 μm, and this is because the DFG-OPC enables broadband operation. Second, the wavelength characteristics of the DFG-OPC are investigated through numerical simulation. The operation bandwidth of the DFG-OPC depends on the DE length difference, and an operating bandwidth of the DFG-OPC of 54.5 nm can be achieved when the DE length difference is less than 0.01 m. Finally, the influence of the splitting ratio of an optical 3-dB coupler in the DFG-OPC is numerically studied. The results indicate that tolerance of the optical coupler splitting ratio is equal to or less than ±6% for the DFG-OPC.

M-ary modulated signals interleaved with amplified reference light is proposed and numerically investigated. The proposed method improves chromatic dispersion tolerance, and transmittable distance of 10-Gbuad interleaved 16QAM signals is extended by 2.46 times compared to the conventional systems.

Direction sensitivity could provide robust evidence for the direct detection of weakly interacting massive particles constituting dark matter. However, the sensitivity of this method remains low due to the radioactive backgrounds. The purpose of this study is to develop a low-background detector as a two-dimensional imaging device for a gaseous time projection chamber. In direction-sensitive dark matter experiments (e.g. NEWAGE), α -rays emitted from the detector components often create substantial radioactive backgrounds. Based on the study of the background of NEWAGE, a new detector “low- α μ -PIC” is developed. The produced μ -PIC performs well as a gas detector and the α -ray emission rate from the μ -PIC reduced by a factor of 100.

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.

We developed in-line PSA for the simultaneous amplification of wavelength-multiplexed and polarization-multiplexed QAM signals. We achieved >20-dB gain and a 12-nm bandwidth for 16-channel PDM-16QAM signals with an inherent PSA characteristic of a 5.1-dB SNR advantage.

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.

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 propose digital compensation method of quadrature imbalance for M-ary modulated signals interleaved with reference light. Error vector magnitude of 10-Gbaud interleaved QPSK signals with Quadrature imbalance is improved by 18.8 % under 18-dB SNR condition.

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.

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.

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.

A new-concept time projection chamber (TPC) using a commercial resistive sheet, sheet-resistor micro-TPC (SRμ-TPC), has been developed and its performance measured. SRμ-TPC has the potential to create a more uniform electric field than conventional TPCs with resistor chains owing to its continuous sheet resistivity, and its production would be easier than that of conventional TPCs. The material used in this study, Achilles-Vynilas, was found to be thin, transparent, and have low radioactivity. A performance test with cosmic muons showed very promising results, including the demonstration of good tracking performance. This type of TPC field cage can offer an alternative for the widely used conventional field cages.

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.

A new scenario is presented for the cause of magnetospheric relativistic electron decreases (REDs) and potential effects in the atmosphere and on climate. High density solar wind heliospheric plasmasheet (HPS) events impinge onto the magnetosphere, compressing it along with remnant noon-sector outer-zone magnetospheric ~10-100 keV protons. The betatron accelerated protons generate coherent EMIC waves through a temperature anisotropy (T┴/T|| > 1) instability. The waves in turn interact with relativistic electrons and cause the rapid loss of these particles to a small region of the atmosphere. A peak total energy deposition of ~3 x 1020 ergs is derived for the precipitating electrons. Maximum energy deposition and creation of electron-ion pairs at 30-50 km and at

ND-PSA with a pump light recovered by an OPLL circuit is experimentally demonstrated for the first time. The ND-PSA with recovered pump amplifies 20-Gbit/s QPSK-PCTWs and results in 19.1-dB Q-factor even though optical phase noise is loaded to the input PCTWs.

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.

Noise characteristics of non-degenerate optical parametric phase sensitive amplifiers are theoretically investigated using numerical simulation. Quantum properties of noise are taken into account by adding random amplitude to signal as vacuum noise. Amplitude noise suppression owing to gain saturation and its mitigation due to distributed loss in a gain medium are shown.

ND-PSA repeaters using recovered pump generated from PCTWs is proposed. Calculations show proposed repeaters enables over 76-span transmission of 20-Gbit/s QPSK PCTWs, and phase-synchronization using sum frequency light from BPSK PCTWs is experimentally demonstrated.

Optical phase-locking among 5-Gbit/s BPSK phase-conjugated twin waves and a free-funning pump is experimentally demonstrated. A sum-frequency and second harmonic generation assisted OPLL circuit compensates error signals between the PCTWs and the pump successfully.

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.

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。

Compensating for intercarrier nonlinear distortion allows launching higher power into the transmission fiber and it leads to an increase in the transmission distance. Numerical calculations show that the launch power is increased by 10 dB and the maximum transmission distance is more than tripled, when the optical repeater spacing of 80 km, dispersion-shifted fiber, and signal format of 10 Gb/s nonreturn-to-zero are assumed. It is experimentally demonstrated that waveform distortion due to the four-wave mixing (FWM) among different carriers in wavelength-division multiplexing (WDM) becomes deterministic by phase-locking optical carriers and that FWM distortion can be compensated at 5 Gb/s with three-channel condition by employing DSP at the transmitter or receiver.

In this paper, we show the influence of intrachannel crosstalk in an optical switch network. The intrachannel crosstalk is mainly due to a signal that is not sufficiently blocked by the optical switch. The signal has a broadband spectrum and causes coherent crosstalk at the optical switching node. We investigate analytically the relationship between the channel isolation of the optical switching node that the optical switch network comprises and the crosstalk penalty due to the broadband signal. We confirm experimentally that the relationship is suited to the optical switch network that emulates an optical cross-connect system. We also show experimentally that it is important to use the optical switch with a high channel isolation level in the entire range of the signal bandwidth in order to suppress the impairment due to the crosstalk. We confirm that in a 50-GHz spaced system, a 44-Gb/s return-to-zero differential quadrature phase-shift-keying signal is sufficiently transmitted without a crosstalk penalty through 24 optical switching nodes, comprising wavelength selective filters with a high channel isolation level in the entire range of the signal bandwidth.

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.

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 ...

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 report on the development of a large Compton camera with the full reconstruction of the Compton process based on a prototype. This camera consists of two kinds of detectors. One is a gaseous time projection chamber (micro-TPC) for measuring the energy and the track of a Compton recoil electron. The micro-TPC is based on a μ -PIC and a GEM, which are micro-pattern gas detectors (MPGDs). The size of the micro-TPC was 10 cm × 10 cm × 8 cm in the case of the prototype, and we enlarged it to 23 cm × 28 cm × 15 cm . The other detector part is a NaI (Tl) Anger camera for measuring the scattered gamma-ray. With these informations, we can completely reconstruct a Compton event, and determine the direction of the incident gamma-ray, event by event. We succeeded in reconstructing events of incident 662 keV gamma-rays. The measured angular resolutions of the “angular resolution measure” (ARM) and the “scatter plane deviation” (SPD) were 9 . 3 ∘ and 158 ∘ (FWHM), respectively.

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.

A Micro Pixel Chamber, called “ μ -PIC”, is a gaseous 2D imaging detector with a fine pixel electrode based on the Printed Circuit Board technology, and we developed it for the X/gamma-ray imaging and the tracking of the charged particles [A. Ochi, et al., Nucl. Instr. and Meth. A 478 (2002) 196; T. Nagayoshi, et al., Nucl. Instr. and Meth. A 525 (2004) 20.]. The previous μ -PIC has a fine position resolution, a high gas gain, a good gas gain uniformity and the stable operation. Although the detection area of the previous μ -PIC ( ∼ 10 × 10 cm 2 ) is not large enough for a variety of the application, for example an MeV gamma-ray Compton camera [T. Tanimori, et al., New Astron. Rev. 48 (2004) 263.] and dark matter search [T. Tanimori, et al., Phys. Lett. B 578 (2004) 241.]. Therefore, we developed a new μ -PIC having a ∼ 30 × 30 cm 2 detection area. The structure and the pitch of the electrode are same as those of the previous μ -PIC. There are 768 × 768 pixels in the whole area. This μ -PIC (TOSHIBA SN041129-1) is operated with a stable gas gain of ∼ 3500 and a maximum gain of ∼ 7000 at the center region, and the variety of the gain was 16.7% RMS. An X-ray image of the whole area was also taken by the irradiation of the X-rays from 109Cd (22 keV) to the whole detection area.

We numerically investigated influence of chromatic dispersion on an optical transmission of 16 quadrature amplitude modulation (QAM) signals interleaved with reference light. Simulation results showed that values of dispersion tolerance, satisfying 3-dB eye opening penalty, of 5-, 10-, and 20-Gbaud interleaved 16QAM were 630-, 156-, and 38-ps/nm, respectively.

For MeV gamma-ray astronomy, we have developed an electron-tracking Compton camera (ETCC) as a MeV gamma-ray telescope capable of rejecting the radiation background and attaining the high sensitivity of near 1 mCrab in space. Our ETCC comprises a gaseous time-projection chamber (TPC) with a micro pattern gas detector for tracking recoil electrons and a position-sensitive scintillation camera for detecting scattered gamma rays. After the success of a first balloon experiment in 2006 with a small ETCC (using a 10$\times$10$\times$15 cm$^3$ TPC) for measuring diffuse cosmic and atmospheric sub-MeV gamma rays (Sub-MeV gamma-ray Imaging Loaded-on-balloon Experiment I; SMILE-I), a (30 cm)$^{3}$ medium-sized ETCC was developed to measure MeV gamma-ray spectra from celestial sources, such as the Crab Nebula, with single-day balloon flights (SMILE-II). To achieve this goal, a 100-times-larger detection area compared with that of SMILE-I is required without changing the weight or power consumption of the detector system. In addition, the event rate is also expected to dramatically increase during observation. Here, we describe both the concept and the performance of the new data-acquisition system with this (30 cm)$^{3}$ ETCC to manage 100 times more data while satisfying the severe restrictions regarding the weight and power consumption imposed by a balloon-borne observation. In particular, to improve the detection efficiency of the fine tracks in the TPC from $\sim$10\% to $\sim$100\%, we introduce a new data-handling algorithm in the TPC. Therefore, for efficient management of such large amounts of data, we developed a data-acquisition system with parallel data flow., 11 pages, 24 figures

Photon imaging for MeV gammas has serious difficulties due to huge backgrounds and unclearness in images, which are originated from incompleteness in determining the physical parameters of Compton scattering in detection, e.g., lack of the directional information of the recoil electrons. The recent major mission/instrument in the MeV band, Compton Gamma Ray Observatory/COMPTEL, which was Compton Camera (CC), detected mere $\sim30$ persistent sources. It is in stark contrast with $\sim$2000 sources in the GeV band. Here we report the performance of an Electron-Tracking Compton Camera (ETCC), and prove that it has a good potential to break through this stagnation in MeV gamma-ray astronomy. The ETCC provides all the parameters of Compton-scattering by measuring 3-D recoil electron tracks; then the Scatter Plane Deviation (SPD) lost in CCs is recovered. The energy loss rate (dE/dx), which CCs cannot measure, is also obtained, and is found to be indeed helpful to reduce the background under conditions similar to space. Accordingly the significance in gamma detection is improved severalfold. On the other hand, SPD is essential to determine the point-spread function (PSF) quantitatively. The SPD resolution is improved close to the theoretical limit for multiple scattering of recoil electrons. With such a well-determined PSF, we demonstrate for the first time that it is possible to provide reliable sensitivity in Compton imaging without utilizing an optimization algorithm. As such, this study highlights the fundamental weak-points of CCs. In contrast we demonstrate the possibility of ETCC reaching the sensitivity below $1\times10^{-12}$ erg cm$^{-2}$ s$^{-1}$ at 1 MeV., 19 pages, 12 figures, Accepted to the Astrophysical Journal

An electron-tracking Compton camera (ETCC) is a detector that can determine the arrival direction and energy of incident sub-MeV/MeV gamma-ray events on an event-by-event basis. It is a hybrid detector consisting of a gaseous time projection chamber (TPC), that is the Compton-scattering target and the tracker of recoil electrons, and a position-sensitive scintillation camera that absorbs of the scattered gamma rays, to measure gamma rays in the environment from contaminated soil. To measure of environmental gamma rays from soil contaminated with radioactive cesium (Cs), we developed a portable battery-powered ETCC system with a compact readout circuit and data-acquisition system for the SMILE-II experiment. We checked the gamma-ray imaging ability and ETCC performance in the laboratory by using several gamma-ray point sources. The performance test indicates that the field of view (FoV) of the detector is about 1$\;$sr and that the detection efficiency and angular resolution for 662$\;$keV gamma rays from the center of the FoV is $(9.31 \pm 0.95) \times 10^{^-5}$ and $5.9^{\circ} \pm 0.6^{\circ}$, respectively. Furthermore, the ETCC can detect 0.15$\;\mu\rm{Sv/h}$ from a $^{137}$Cs gamma-ray source with a significance of 5$\sigma$ in 13 min in the laboratory. In this paper, we report the specifications of the ETCC and the results of the performance tests. Furthermore, we discuss its potential use for environmental gamma-ray measurements., Comment: 10 pages, 7 figures, proceeding of the 10th International Conference on Position Sensitive Detectors (PSD10)