Takuji Atsumi

Soda-glass capillary plate gas detector

A new capillary plate (CP) has been developed for a hole-type micropattern gas detector. The plate consists of a bundle of fine soda-glass capillaries with a diameter of 100 /spl mu/m and a length of 1 mm. The electrodes on the surfaces of both ends of CP were coated with Inconel metal. The plate is similar to a conventional CP, except that the material used is not lead glass, but soda glass. The main advantages of the soda-glass CP compared to the lead-glass CP are a low surface resistivity and low background properties. The soda-glass CP gas detector was operated with a gas mixture of Ar(90%) + CH/sub 4/(8%) + TMA(2%) using 5.9 keV X-rays. Using the scintillation light emitted from the soda-glass CP, we successfully obtained the energy spectrum and accumulated image for the 5.9 keV X-rays. In this paper, we report on the characteristics of the new soda-glass CP and the background properties of both the soda-glass and lead-glass CPs. We also describe the outlook on the future development of an optical gas photomultiplier with the soda-glass CP.

Gain of a gas photomultiplier with CsI photocathode

A Gas PMT with the CsI photocathode was fabricated as a phototube of a glass vessel identical to a conventional vacuum PMT. A GEM and a Micromegas were installed in the phototube of the Gas PMT. The Gas PMT was operated with two different gas mixtures, Ar (90%) + CH4 (10%) and Ne (90%) + CF4 (10%), at the gas pressure of 1 atm. The gain of 105 was obtained for both the gas mixtures. It was found that the gain of the Gas PMT can be described using the Townsend ionization coefficient for the Micromegas. The imaging capability of the Ne gas mixture was checked by an optical imaging capillary (CP) gas detector, using X-ray beams. The image of an X-ray resolution chart indicates that the imaging resolution is determined by the diameter of the capillary, here 100 μm. The Ne gas mixture appropriate to the Gas PMT is well suited for a fine imaging detector.

Development of FOP-HARP imaging device

The high-gain avalanche rushing amorphous photoconductor (HARP) camera tube achieves ultrahigh-sensitivity by using the avalanche multiplication. The applications of this tube extend beyond broadcasting into other fields. It is attracting a great deal of attention especially for radiation diagnosis, such as synchrotron radiation microangiography, because it can obtain high-resolution and high-contrast images with a low dose of radiation. However, in the present system, a fluorescent screen and the photoconductive film of the HARP tube are connected optically by a lens-coupling method, and low light throughput remains a big problem. To improve the light throughput by using a fiber-coupling method, we applied a fiber-optic plate (FOP) to the substrate of a HARP tube. The FOP consists of three types of glass that have differing hardnesses and elastic coefficients that make it difficult to flatten the FOP surface enough to form the HARP film. We thus introduced a new mechanical polishing method and succeeded in realizing avalanche multiplication in the FOP-HARP tube. The results of shooting experiments by applying the FOP-HARP to the microangiography showed that a spatial resolution of over 20 line pairs/mm was obtained. Moreover, rat femoral arteries of 150-200 μm in diameter could be visualized as motion pictures with a one-fourth lower concentration of contrast material than that needed for ordinary microangiography. Another potential application of the FOP-HARP is an ultrahigh-sensitivity nearinfrared (NIR) image sensor made by fiber-coupling with an image intensifier (I.I.). The image sensor provides highquality images and should be a powerful tool for NIR imaging.

Soda glass capillary plate gas detector

A new capillary plate (CP) has been developed for a hole-type micropattern gas detector. The plate consists of a bundle of fine soda-glass capillaries with a diameter of 100 /spl mu/m and a length of 1 mm. The electrodes on the surfaces of both ends of CP were coated with Inconel metal. The plate is similar to a conventional CP, except that the material used is not lead glass, but soda glass. The main advantages of the soda-glass CP compared to the lead-glass CP are a low surface resistivity and low background properties. The soda-glass CP gas detector was operated with a gas mixture of Ar(90%) + CH/sub 4/(8%) + TMA(2%) using 5.9 keV X-rays. Using the scintillation light emitted from the soda-glass CP, we successfully obtained the energy spectrum and accumulated image for the 5.9 keV X-rays. In this paper, we report on the characteristics of the new soda-glass CP and the background properties of both the soda-glass and lead-glass CPs. We also describe the outlook on the future development of an optical gas photomultiplier with the soda-glass CP.

Visualization of microvessels by angiography using inverse-Compton scattering X-rays in animal models

The fundamental performance of microangiography has been evaluated using the S-band linac-based inverse-Compton scattering X-ray (iCSX) method to determine how many photons would be required to apply iCSX to human microangiography. ICSX is characterized by its quasi-monochromatic nature and small focus size which are fundamental requirements for microangiography. However, the current iCSX source does not have sufficient flux for microangiography in clinical settings. It was determined whether S-band compact linac-based iCSX can visualize small vessels of excised animal organs, and the amount of X-ray photons required for real time microangiography in clinical settings was estimated. The iCSX coupled with a high-gain avalanche rushing amorphous photoconductor camera could visualize a resolution chart with only a single iCSX pulse of ∼3 ps duration; the resolution was estimated to be ∼500 µm. The iCSX coupled with an X-ray cooled charge-coupled device image sensor camera visualized seventh-order vascular branches (80 µm in diameter) of a rabbit ear by accumulating the images for 5 and 30 min, corresponding to irradiation of 3000 and 18000 iCSX pulses, respectively. The S-band linac-based iCSX visualized microvessels by accumulating the images. An iCSX source with a photon number of 3.6 × 10(3)-5.4 × 10(4) times greater than that used in this study may enable visualizing microvessels of human fingertips even in clinical settings.

Optical Imaging Capillary Plate Gas Detector

A capillary plate (CP) gas detector with a CF4 gas mixture of argon and pure xenon has been successfully operated as a visible and near-infrared (NIR) scintillation proportional counter. Gas gains of up to 104 can be achieved using these gas mixtures. The scintillation light emitted during the generation of electron avalanches can be observed using a photomultiplier tube (PMT) and a compact optical imaging system which consists of a CP gas detector and a cooled charge-coupled device (CCD) camera coupled to lens optics. Using this optical imaging system, clearer images of X-rays have been obtained with the above gas mixtures. The successful operation using these gas mixtures has allowed us to realize a novel imaging device with a CP for medical imaging and gaseous PMTs sensitive to visible light.