A void fraction measuring system has been developed, which is composed of a small californium-252 neutron source, a moderating type neutron detector and a data acquisition system. The system is used for on-line measurement of void fraction in an oil tube. To reduce the background count in neutron measurement, optimum condition were examined for the thickness of moderator around a BF3counter and shields surrounding a void measuring portion. Calibration of the void fraction measurement was carried out by using powder simulation material in a stationary state. The effectiveness of the system was verified by means of the comparison between the present method and the oil sampling one. Finally the system was applied to the automatic transmission (AT) placed on a chassis dynamometer test bench and the performance of the defoamant of AT fluid was successfully evaluated.
SPECT reconstruction is commonly performed using 360°or 180°projection data. However, it is also possible to reconstruct SPECT images using other projection data arcs. The purpose of this study was to characterize images obtained by limiting the projection data to 270°by discarding the projection views with severe attenuation (Fig. 1) . A series of phantom studies was performed with and without plastic chambers simulating perfusion defects using201Tl and99mTc. Images using 270°, 360°, and 180°projection arcs were identically reconstructed from the same data. In the absence of plastic chambers, intraslice uniformity in a given slice was assessed by computing the coefficient of variation (CV) of average counts in 8 ROIs within the slice. Interslice uniformity was assessed by computing the CV of average counts in five short axial slices. With plastic chambers in place, the variability in defect contrasts was assessed by computing the CV of defect contrasts in 4 chambers, located on the anterior, lateral, inferoposterior, and septal walls. The intraslice uniformity of the 270°images were considerably inferior to those of the 360°and 180° images. The interslice uniformity was highest in the 360°images, and lowest in the 180°images. The variation in defect contrasts in the 270°image was higher than those of the other two images. The 270°images showed a high defect contrast in the septum and high counts in the anterior and anteroseptal wall. Because a large variation in defect contrasts within a segment might result in false positive or negative in diagnosis, 270°imaging is not recommended over 360°or 180°imaging.
The dispersal rates of125I defined here as a dispersed activity in Bq per hour divided by the total activity contained in a solution, and the collection efficiency of dispersed125I by charcoal cartridges were measured under the various pH conditions in the solution. The values of dispersal rate observed under working conditions in common biochemical procedures were (3.74±1.19) ×10-4 (h-1), (4.27±1.90) ×10-4 (h-1) and (6.31±2.05) ×10-4 (h-1) for alkaline, neutral and acidic conditions of the solution, respectively. And those values obtained by the evaporation of solution to dryness were elevated more than 100 to 1000 times independent of pH of the solution. Under the case of common biochemical procedures, nearly 90% of the dispersed125I was trapped on the 1st charcoal cartridge which was inserted between dispersal part and exhaust part. No125I was detected in the following 2nd and 3rd charcoal cartridges.
A proportional counter has been designed to detect soft X-rays in energy-dispersive X-ray fluorescence (EDXRF) analysis of elements having a medium atomic number. The counter consists of a 25 mm diameter cylindrical cathode with an entrance window of a thin Mylar film and a 50μm diameter anode wire, it was filled with PR gas at 1 atm using by a gas flow system. The maximum gas multiplication of the counter is over 4×104at 2000 V of the applied voltage and the energy resolution for X-ray is between 17% and 35% in the energy range between 5.9 ke V and 1.5 ke V. The counter exceeds PIN photo-diode Si detector (AMPTEK's type XR-100) in detection efficiency under 15 keV of the X-ray energy.