Some fundamental studies on the application of a continuous channel electron multiplier (channeltron) for monitoring gaseous tritium present in an evacuated vessel at low pressures below 10-4Torr were carried out. The results showed that at the tritium pressures lower than 10-6Torr the tritium counting rate measured by the channeltron increased linearly, in practice, with increasing tritium pressure, as was expected by assuming that the interactions between β-particle emitted from tritium and the vessel wall and gaseous molecules during the migration of β-particle to the channeltron can be ignored. However, in the range of pressures over 10-5Torr the measured tritium counting rate was found to be getting smaller than the expected with increase in tritium pressure. This is presumably due to the absorption and scattering of β-particles by gaseous tritium.
This paper proposes scintillation cameras which can handle input pulse rates beyond 1 Mcps with negligible loss of spatial resolution and energy resolution at low pulse rates. The cameras are based on the “variable sampling-time technique”, in which phototube current pulses are first shortened in width and then selectively integrated by gated integrators followed by sample-and-hold circuits. The period of integration before sampling is not fixed but shortened by the arrival of the following pulse to keep a high pulse-pair time resolution. An approximate expression for the count rate characteristics has been derived, and its validity was confirmed by Monte Carlo simulation. The result indicates that the maximum observed count rate will reach 420-520 kcps with an energy window fraction of 0.5 for typical design parameters.
Porcelain teeth, some of which contain uranium compounds for aesthetic purpose, have been widely used in dental clinics. Hazardous effects due to uranium radiation have been suggested by recent publications. In the previous study, the authors reported the uranium content of porcelain teeth and radiation dose by it. In this study, using the fission track method, the authors examined spatial distribution of uranium in dental porcelain teeth (4 brands) which were marketed in Japan. From each sample of porcelain tooth, a 1-mm-thick specimen was sliced, and uranium content was measured at every 0.19 mm from labial side to lingual side for making a uranium distribution chart. Higher uranium concentration was found in Trubyte Bioblend porcelain teeth (USA) and they showed almost uniform distribution of uranium, while those of the Japanese three brands indicated, in most case, comparatively lower concentration and found to be non-uniform distributions. Range of uranium concentration in these brands were N.D.-5.2 ppm (Shofu-Ace), N.D.-342 ppm (Shofu-Real), N.D.-47 ppm (G.C. Livdent) and N.D, -235 ppm (Trubyte Bioblend), respectively.
Brain scan with99mTc-labelled macroaggregated albumin (MAA brain scan) and computed tomography studies (CT) were performed on 78 patients with intracranial diseases.99mTc-MAA was injected into right and left carotid artery respectively, at the different time. And then diagnostic evaluation of both techniques were investigated. The MAA brain scan was useful for the detection of ischemic lesion in the early stage after onset of cerebral infarction. It was shown in 29.5% that partial field of anterior cerebral artery was injected through the contralateral artery. In these cases, the MAA brain scan was also useful. In the cases of hemorrhagic lesions, however, the CT was more useful than MAA brain scan. Therefore, the both techniques helped each other in the diagnosis of intracranial diseases.