Michiaki Takahashi

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.

Performance of 8

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.

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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.

8 Pixel LaBr

We have developed an electron-tracking Compton camera (ETCC) for new medical imaging device. Conventional gamma camera, PET and SPECT, have the problem of energy limitation. This problem is one of the major problems for this study. However, our ETCC has a wide energy dynamic range (200–1300 keV). Also ETCC have the wide field of view because ETCC does not need a collimator and does not need to catch two gamma rays which produced by the annihilation process. In this paper, we show the results of imaging result of the 3-D which have imaged only one direction using one head camera. And we have developed the two-head ETCC. Two-head ETCC have a good efficiency and spatial resolution.

_{3}

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.

:Ce and Gd

We have developed an electron-tracking Compton camera (ETCC) for new imaging reagents study. Energy limitation of gamma camera is major problem for this study. However, our ETCC has a wide energy dynamic range (200-1300 keV). In this paper, we show the results of imaging reagent study 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) middle size animal imaging (rabbit). Also we studied the improvement for the camera system.

_{2}

We have developed a sub-MeV and MeV gamma-ray imaging Compton camera for use in gamma-ray astronomy; it consists of a gaseous time-projection chamber (TPC) to convert the Compton scattering events and a scintillator array to absorb photons. The TPC measures the energy and three-dimensional tracks of Compton-recoil electrons, while the pixel scintillator arrays measure the energy and positions of scattered gamma rays. Therefore, our camera can reconstruct the incident gamma rays, event by event, over a wide field of view of approximately 3 str. We are now developing a Compton camera for a balloon-borne experiment.