Tatsuya Nakamoto

Size distribution measurement of nanometer-sized aerosol particles using dma under low-pressure conditions

Abstract A system for measuring nm-sized aerosol particles under low pressure conditions using a differential mobility analyzer (low pressure DMA, LPDMA) with a Faraday cup electrometer (FCE) as the detector is developed. The performance of the LPDMA is investigated experimentally using a tandem DMA technique. It is shown that LPDMA can be used to measure nm-sized particles (4–10 nm) under low-pressure conditions (60–760 Torr). The effect of Brownian diffusion on the performance of LPDMA is qualitatively discussed by comparing the results obtained using LPDMA with those of conventional and Vienna DMAs with dimensionless parameters. The equilibrium charge distribution of aerosol particles reached under low-pressure conditions is also evaluated by solving population balance equations for particle-ion collision. The LPDMA/FCE system is also applied to the measurement of nm-sized silver particles produced by physical vapor deposition (PVD) and TiO 2 particles produced by low pressure chemical vapor deposition (LPCVD)

Low-noise double-sided silicon strip detector for multiple-compton gamma-ray telescope

The Semiconductor Multiple-Compton Telescope (SMCT) is being developed to explore the gamma-ray universe in an energy band 0.1--20 MeV, which is not well covered by the present or near-future gamma-ray telescopes. The key feature of the SMCT is the high energy resolution that is crucial for high angular resolution and high background rejection capability. We have developed prototype modules for low noise Double-sided Silicon Strip Detector (DSSD) system to realize the SMCT. The geometry of the DSSD is optimized to achieve the lowest noise possible. New frontend LSI optimized for low noise operation is developed. We report on the design and test results of the prototype system. We have achieved an energy resolution of 1.3 keV (FWHM) for 60 keV and 122 keV at 0 degree C.

A prototype Si/CdTe Compton camera and the polarization measurement

A Compton camera is the most promising approach for gamma-ray detection in the energy region from several hundred kiloelectronvolts to megaelectronvolts, especially for application in high energy astrophysics. In order to obtain good angular resolution, semiconductor detectors such as silicon, germanium and cadmium telluride(CdTe) have several advantages over scintillation detectors, which have been used so far. Based on the recent advances of high resolution CdTe and silicon imaging detectors, we are working on a Si/CdTe Compton camera. We have developed 64-pixel CdTe detectors with a pixel size of 2 mm /spl times/ 2 mm and double- sided Si strip detectors(DSSDs) with a position resolution of 800 /spl mu/m. As a prototype Si/CdTe Compton camera, we use a DSSD as a scatterer and two CdTe pixel detectors as an absorber. In order to verify its performance, we irradiate the camera with 100% linearly polarized 170 keV /spl gamma/-rays and demonstrate the system works properly as a Compton camera. The resolution of the reconstructed scattering angle is 22/spl deg/(full-width at half-maximum). Measurement of polarization is also reported. The polarimetric modulation factor is obtained to be 43%, which is consistent with the prediction of Monte Carlo simulations.

Low-Noise Double-Sided Silicon Strip Detector for Soft Gamma-ray Compton Camera

A Semiconductor Multiple-Compton Telescope (SMCT) is expected to proceed a high-sensitivity soft gamma-ray observation in the energy range of 0.1-20 MeV. Double-sided silicon strip detector (DSSD) is one of key technologies for constructing SMCT, as well as the high-stopping semiconductor CdTe, because of its high energy resolution and high scattering efficiency. We have developed a low-noise system of DSSD and frontend LSI for SMCT, by optimizing geometrical structures of DSSD. We have thus obtained an energy resolution of 1.3 keV (FWHM) for 60 keV and 122 keV at -10°C in the multi-channel reading. Gamma-ray responses such as image flatness and charge splittings were found to be not problematic. We also demonstrated that our system achieved the good angular resolution close to the Doppler-broadening limit in the Compton imaging by two DSSDs.

Prototype of Compton camera using high resolution Si/CdTe detectors Si/CdTe Compton camera as a polarimeter

To bring a breakthrough in the observation of the gamma-ray universe, we are working on the development of Semiconductor Multi-Compton Telescope(SMCT). In the SMCT, all the energy, positional and timing resolution must be high to ensure high sensitivity. The imaging device based on the high resolution CdTe diode and Si, such as CdTe pixel detectors and Double-sided Si Strip Detectors (DSSDs), are promising candidates for the components of the SMCT. Here we report the results of a CdTe pixel detector connected with a low noise analog ASIC. We obtained an energy resolution of 2.5 keV(FWHM) at 122 keV, with a positional resolution of 2 mm. Performance of the first prototype Compton Camera using a DSSD and two CdTe pixel detectors is also described. We irradiated 100% linearly polarised 170 keV /spl gamma/-ray line to the system and obtained the polarimetric modulation factor of 43%.