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In this study, we focused on the fact that the color information of an image has a significant effect on the emotion recalled, and we created a dataset with discrete and continuous emotion labels for color and grayscale image pairs, which are not present in existing emotion image datasets. As a result of the analysis of the continuous-valued emotion labels, we found that the color images evoked a wider range of positive and negative emotions. We also conducted experiments to transform the color of the image to the target emotion using the emotion label and the image as input and succeeded in changing the color of the entire image according to the input emotion value. Another experiment is conducted to convert the emotion category and we confirmed that the image was generated in such a way that the evoked emotion was changed compared to the original image.

Varestraint test is one of the most-used methods to evaluate weld solidification cracking susceptibility. However, the standard about the detailed test method and the evaluation method has not been ...

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.

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.

The noise property of a phase-sensitive amplifier using an optical phase-locked pump was evaluated. An average NF of 1. 7-dB at a 23.2-dB gain was achieved within an input power range of −31 to −21 dBm.

Wavelength-conversion free optical phase conjugator (OPC) based on difference frequency generation is proposed. Numerical results show the proposed OPC enables over 60-nm wideband operation.

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.

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.

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.

We present a platform on all-programmable SoC for micro autonomous robots for probing, exploring, rescuing, etc. Contrast to challenges for auto drive cars having relatively rich power supply and high-performance computing platform, our challenge is to develop technologies for autonomous robots with tight restrictions on size, weight, and energy consumption. We utilize all-programmable SoCs for the purpose and develop a system including camera interface, image processing, recognition, action planning, and motor control. The key techniques are to optimize the dataflow between software (and main memory) and hardware for efficiency and to adopt a standard stream interface in hardware modules for productivity. The system can be utilized as a common platform for micro autonomous robots. The system is implemented as a robot car named ZybotR2-Z2 and achieves 3 to 37 frame/sec image recognition and car control with single Zynq-7020 device.

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.

Carrier extraction with a two-branch configuration for pump phase-locking to polarized PDM-PCTWs signals is proposed and experimentally demonstrated. Carrier extraction from circular polarized 20-Gbit/s PDM-BPSK-PCTWs is achieved by sum-frequency generation and a right circular polarizing.

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.

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

Heterodyne optical phase-locked loop assisted by sum-frequency and second-harmonic generation for non-degenerate phase-sensitive optical amplifier repeaters is proposed. Experiment of offset pump phase-locking to 5-Gbit/s BPSK phase-conjugated twin waves is successfully achieved by our method.

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.

Pump phase-locking method dependence of non-degenerate phase-sensitive optical amplifier (ND-PSA) repeaters on phase-conjugated twin waves transmission is investigated. Simulation results show ND-PSAs with an optical phase-locked loop method can extend a transmission distance compared to the case of an optical injection locking method in dispersion compensated links.

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.

In this paper, an optical phase-locked loop assisted by sum-frequency and second-harmonic generation (SS-OPLL) for frequency nondegenerate optical parametric phase-sensitive amplifier repeaters is experimentally demonstrated. First, theoretical derivations show that carrier extraction from phase-conjugated twin waves (PCTWs) and reference light generation are achieved by sum-frequency generation; therefore, the SS-OPLL circuit enables optical phase locking between PCTWs and a pump wave by a simple architecture based on a balanced OPLL. Then, optical phase locking between 20-Gbit/s quadrature phase-shift keying PCTWs and an individual pump source is experimentally demonstrated. Experimental results indicate that phase errors were reduced during the SS-OPLL operation.

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.

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 address emerging threats to the security of photonic networks as these networks become heterogeneous being opened to the upper layers, other operators, and end users. We review the potential threats, mainly loss of the confidentiality of user data transmitted through optical fibers and disturbances of network control, both of which could seriously damage the entire network. We then propose a novel conceptual model of a secure photonic network by introducing a quantum key distribution (QKD) network to its legacy structure. Secure keys generated by the QKD network are managed by key management agents (KMAs) and used to encrypt not only user data but also control signals. The KMAs cooperate with the generalized multiprotocol label-switching controller for secure path provisioning and drive photonic and modern crypto engines in appropriate combinations. Finally, we present a roadmap of a deployment scenario, starting from niche applications such as mission critical and business applications and the next. Digital cinema distribution through a photonic network is presented as an example of a niche application.

著者人数: 20名, Accepted: 2011-05-04, 資料番号: SA1003239000

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.