Ken'ichi Tsuchiya

First underground results with NEWAGE-0.3a direction-sensitive dark matter detector

Abstract A direction-sensitive dark matter search experiment at Kamioka underground laboratory with the NEWAGE-0.3a detector was performed. The NEWAGE-0.3a detector is a gaseous micro-time-projection chamber filled with CF4 gas at 152 Torr. The fiducial volume and target mass are 20 × 25 × 31 cm 3 and 0.0115 kg, respectively. With an exposure of 0.524 kg days, improved spin-dependent weakly interacting massive particle (WIMP)-proton cross section limits by a direction-sensitive method were achieved including a new record of 5400 pb for 150 GeV / c 2 WIMPs. We studied the remaining background and found that ambient γ-rays contributed about one-fifth of the remaining background and radioactive contaminants inside the gas chamber contributed the rest.

Direction-sensitive dark matter search results in a surface laboratory

Abstract We developed a three-dimensional gaseous tracking device and performed a direction-sensitive dark matter search in a surface laboratory. By using 150 Torr carbon-tetrafluoride (CF 4 ) gas, we obtained a sky map drawn with the recoil directions of the carbon and fluorine nuclei, and set the first limit on the spin-dependent WIMP (Weakly Interacting Massive Particles)-proton cross section by a direction-sensitive method. Thus, we showed that a WIMP-search experiment with a gaseous tracking device can actually set limits. Furthermore, we demonstrated that this method will potentially play a certain role in revealing the nature of dark matter when a low-background large-volume detector is developed.

Performance of the micro-PIC gaseous area detector in small-angle X-ray scattering experiments

The application of a two-dimensional photon-counting detector based on a micro-pixel gas chamber (micro-PIC) to high-resolution small-angle X-ray scattering (SAXS), and its performance, are reported. The micro-PIC is a micro-pattern gaseous detector fabricated by printed circuit board technology. This article describes the performance of the micro-PIC in SAXS experiments at SPring-8. A dynamic range of >10(5) was obtained for X-ray scattering from a polystyrene sphere solution. A maximum counting rate of up to 5 MHz was observed with good linearity and without saturation. For a diffraction pattern of collagen, weak peaks were observed in the high-angle region in one accumulation of photons.

Observation of diffuse gamma-ray with Electron-Tracking Compton imaging camera loaded on balloon

We have developed an electron tracking Compton camera (ETCC) as an MeV gamma-ray telescope in the next generation. Our detector consists of a gaseous time projection chamber and a position sensitive scintillation camera. In order to evaluate the performance of this detector, we constructed a flight model detector as a balloon experiment for the observation of diffuse cosmic gamma rays and atmospheric gamma rays. The balloon launched on September 1 in 2006. The balloon reached to 35 km at altitude, and the level flight continued during 4.0 hours. We succeeded in the detection of about 200 downward gamma rays in the energy range of 100 keV-1 MeV during the 3.5 hours level flight (live time 3.0 hours). The detected photon number was consistent to the simulated one. Also, we measured the dependence of the gamma-ray flux on the zenith angle between 0deg and 90deg. Here we report on the detailed performance of the ETCC in this flight.

Development of a gamma camera based on an 8×8 array of LaBr 3 (Ce) scintillator pixels coupled to a 64-channel multi-anode PMT

We have developed a gamma camera based on an array of LaBr3(Ce) scintillator pixels coupled to a multi-anode photomultiplier tube (MAPMT). It consisted of an 8times8 array of LaBr3(Ce) pixels with a size of 5.8times5.8times15 mm3 and a 64-channel MAPMT (Hamamatsu flat-panel H8500) with an effective area of 49times49 mm2. The pixels of the LaBr3(Ce) array were made from two LaBr3(Ce) monolithic crystals with a diameter of 38 mm and a height of 38 mm, which had energy resolutions of 4.33plusmn0.02% at 356 keV and 3.25plusmn0.01% at 662 keV. They were assembled into the array with a reflector between pixels, and sealed hermetically by our own technique. The pitch of the LaBr3(Ce) pixels, 6.1 mm, was determined to be the same as that of the anodes. The thickness of pixels was 15 mm to have moderate detection efficiency for sub-MeV/MeV gamma rays. We evaluated the performance as follows. At first, in order to remove the effect of the gain variance among anodes of the MAPMT, the array was coupled to a single-anode PMT, and collimated gamma rays from isotopes were irradiated to one pixel in the array. The energy resolutions (FWHM) were 5.4 (average) plusmn1.0 (RMS) % at 356 keV and 4.5plusmn1.0 % at 662 keV. Next, in order to obtain a gamma-ray image of 64 pixels by readout of only four channels, we used a resistor-chain readout system in the charge division method. In flood field irradiation of gamma rays, each pixel was clearly resolved. The energy resolutions (FWHM) of 64 pixels were 8.6plusmn1.0% at 356 keV and 5.8plusmn0.9 % at 662 keV. The averages were represented by (5.8plusmn0.7) (E/662 keV)-052 plusmn 0.02 % at energies from 122 keV to 835 keV.

The Performance of the Micro Time Projection Chamber Based on /spl mu/-PIC

We have been developing a micro-TPC (mu-TPC) based on a micro pixel chamber (mu-PIC) with a real-time readout system. The mu-PIC has micro-pixel electrodes with a pitch of 400 mum in an area of 10times10 cm2. The mu-TPC has high performances for tracking charged particles and measuring their energy deposition so that there are various developing applications such as an advanced Compton camera, a neutron detector, a dark matter search detector and so on. A prototype model of the mu-TPC with a size of 10times10times8 cm with an Ar-based gas mixture was developed and its performance was evaluated. Furthermore a flight model of the mu-TPC for a balloon experiment was developed with a size of 10times10times15 cm with a Xe-based gas mixture. We carried out a balloon-borne experiment in September, 2006. The operation of mu-TPC at an altitude of 30 km was successful without any trouble and any damage.

Compton imaging Camera using an Electron-Tracking gaseous TPC and a scintillation camera

We are developing an Electron-Tracking Compton imaging Camera (ETCC) based on a gaseous Time Projection Chamber (TPC) and a scintillation camera. The ETCC detects the energy and the direction of the incident gamma ray using the information of the recoil electron and the scattered gamma ray. We have developed the ETCC with a detection volume of 23 × 28 × 30 cm3 which consists of the 23 × 28 × 30 cm3 gaseous TPC and 30 × 30 cm2 GSO(Ce) scintillation camera. And we obtained the gamma-ray image and investigated the performances of the ETCC. The Angular Resolution Measure (ARM) and the Scatter Plane Deviation (SPD) are 6.1 degree and 64.5 degree (HWHM) at 662keV, respectively, and the energy resolution is 18.0%(FWHM) at 662keV.

An Electron-Tracking Compton imaging camera based on a gaseous TPC and a scintillation camera

We are developing an electron-tracking Compton imaging camera (ETCC) based on a gaseous time projection chamber (TPC) and a scintillation camera. The ETCC detects the energy and the direction of the incident gamma ray using the information of the recoil electron and the scattered gamma ray. We have developed the ETCC with a detection volume of 23 times 28 times 15 cm3 which consists of the 23 times 28 times 15 cm3 gaseous TPC and 30 times 30 cm2 GSO(Ce) scintillation camera. We obtained the gamma-ray image and investigated the performances of the ETCC. The angular resolution measure (ARM) and the scatter plane deviation (SPD) are 6.1 degree and 64.5 degree (HWHM) at 662 keV, respectively, and the energy resolution is 18.0% (FWHM) at 662 keV.

Low-power wide-dynamic-range readout system for a 64-channel multi-anode PMT of a scintillation gamma camera

We have developed a low-power wide-dynamic-range readout system for a 64-channel multi-anode photomultiplier (PMT) of a scintillation gamma camera. Each anode is individually read with the system that contains discrete devices of amplifiers, comparators, sample-hold ADCs, and FPGAs. The size of the system which is designed for a two-dimensional array of Hamamatsu flat panel PMT H8500 is 5×5×14 cm3. The input dynamic range is variable by replacing the feedback capacitor of the preamplifier (e.g., 700 pC and 4000 pC for GSO(Ce) and LaBr3(Ce) crystals, respectively). The serialized ADC data are sent to a VME sequence module. The total power consumption is 1.6 W per 64 channels. With this system we have developed a gamma camera using an 8×8 array of GSO(Ce) pixels with a pixel size of 6×6×13 mm3 coupled to an H8500, and obtained flood-field irradiation images at energies from 30 keV to 1.3 MeV. The energy resolution was 10.8±0.4% (FWHM) at 662 keV. In addition, we used the readout system for an 8×8 array of LaBr3(Ce) pixels with a pixel size of 6×6×15 mm3 and obtained a flood-field irradiation image at 662 keV.

Visualization of Aged Fingerprints with an Ultraviolet Laser

Detection of aged fingerprints is difficult because they can degrade over time with exposure to light, moisture, and temperature. In this study, aging fingerprints were visualized by time‐resolved spectroscopy with an ultraviolet‐pulsed laser. Fingerprints were prepared on glass slides and paper and then stored under three lighting conditions and two humidity conditions for up to a year. The fluorescence intensities of the fingerprints decreased with time. Samples were stored in the dark degraded less than in sunlight or under a fluorescent lamp. Samples were stored under low humidity degraded less than under moderate humidity. As the storage period increased, a fluorescence emission peak appeared that was at a longer wavelength than the peak visible in earlier spectra. This peak was used for visualization of an aged fingerprint over time. An image of the fingerprint was not initially visible, but an image appeared as the time since deposition of the fingerprint increased.