Establishment of Imaging Spectroscopy of Nuclear Gamma-Rays based on Geometrical Optics.

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.

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.

Development of micro-PIC as a time-resolved X-ray area detector.

The application of a two-dimensional micro-pixel gas chamber (micro-PIC) to X-ray diffraction studies, and its performance, are reported. micro-PIC has a 10 cm x 10 cm detection area, and a fast-readout system for real-time X-ray imaging has been developed. Using the timing of each incoming X-ray measured by micro-PIC, continuous rotation photograph measurements were carried out for a 400 microm-diameter spherical organic crystal of Ylid (C(11)H(10)O(2)S), and then diffraction spots were successfully obtained within 2theta of 49 degrees. As a result, good internal agreement factors of 3.7% and 7.0% were confirmed among each of the symmetrically equivalent reflections for exposure times of 3700 s and 98 s, respectively.