Gyozo Toda

Hot Isostatic Pressed Gd2O2S:Pr, Ce, F Translucent Scintillator Ceramics for X-Ray Computed Tomography Detectors

Translucent scintillator ceramics of Gd2O2S:Pr, Ce, F were fabricated using a hot isostatic pressing (HIP) technique. The optical transmission is about 60% of the incident light and the X-ray stopping power is also quite high. Owing to the enhancement of these properties by the HIP densification process, the highest light output from a 1 mm thick specimen combined with a silicon photodiode, when excited by 120 kV X-rays, has reached 1.8 times that of CdWO4 single crystals. The present ceramics are very promising candidates for scintillator materials in X-ray computed tomography (CT) detector applications.

Optical fiber drawing method with gas flow controlling system

A method for reducing the diameter variation of optical fibers during fiber drawing is described. The method is based on the control of gas flow and drawing speed. Rapid fluctuations in diameter are suppressed by adjusting the gas flow rate, and slower ones are controlled by changing the drawing speed. The efficiency of this method has been tested by applying stepwise disturbance of +or-63% in preform feeding speed. Fluctuations of fiber diameter are controlled within +or-1 mu m despite the forced disturbance. By applying this method to high-speed drawing (30 m/min), a high-tensile-strength fiber, with diameter fluctuations within +or-1 mu m and transmission losses near the 0.85- mu m wavelength region of approximately 3 dB/km, is achieved. >

Effects of the lapped surface layers on the dielectric properties of ferroelectric ceramics

The effects of lapped surface layers on the dielectric properties of Ba‐ and Sr‐modified lead titanate and lead zirconate ferroelectric ceramics are examined. Specimens with lapped surfaces show anomalous dielectric behaviors, namely, smaller dielectric constant, higher Curie temperature, smaller dielectric loss (below Curie point), and smaller remanent polarization than those of specimens whose surface layers are removed by chemical etching. This may be ascribed to the existence of a lapped surface layer, which seems to be a (0.1–2)‐μm‐thick nonferroelectric layer of small dielectric constant with a two‐dimensional tensile stress of 5–15 kbars. The thinness of the layer results in a large capacitance on the order of 0.5 μF/cm2. The above model for lapped surface layer, especially involving the two‐dimensional tensile stress, explains well the anomalous dielectric behaviors measured in this paper.