Silica gels and porous glasses thermally treated at various temperatures were examined for use as an adsorbent to separate tritiated water (HTO) with an adsorption method. The HTO was adsorbed much stronger than H2O. A high partition coefficient of 1.38 was observed for the thermally treated silica gel at 1100°C in vacuo. From the measurement of IR spectra, isolated silanol groups were formed on the thermally treated silica gel surface. We can conclude that there is a large mass effect for the concentration of tritiated water on the thermally treated silica gels because hydroxyl groups or water molecules adsorbed on them are difficult to form hydrogen bonds with each other.
It is necessary to know the incident direction of gamma rays to search for the position of radioactive materials or contamination remotely. In order to meet this demand, a new gamma ray detector, which positively raises directional sensitivity against incoming gamma rays, has been developed. This detector is composed of three kinds of different scintillators and a photomultiplier tube. The types of scintillators are NaI (Tl), CsI (Tl), and BGO. The section shape of each scintillator is sectorial of 120 degrees. The one cylindrical scintillator is made by optically connecting three sectorial scintillators. Gamma rays penetrate along a straight path through each scintillator of the detector, and the length of each path is dependent on the incident direction. Therefore the probability of photoelectric effect in each scintillator is changed, according to an incident direction of gamma rays. As a result, the gamma ray counts of three peaks observed in a spectrum obtained by a multi-channel analyzer have dependency with the direction. The response curve of each scintillator with respect to a peak count and an incident direction was made by experiments using a gamma ray source of137Cs. It has been recognized that these response curves have sensitivity in the total range from 0 to 360 degrees. Therefore the proposed detector has the possibility that the direction can be identified.
We developed a radiation automatic measurement system using magnetic levitated electrode ionization chamber, and we measured the background throughout the long term. As the result, we confirmed that this measuring system was supersensitive, and it had high reliability in long-term measurement. As the result of measuring γ-ray of KCl by using this measuring system, we could measure the dose of lowlevel radiation supersensitively that we could not measure by the past ionization chamber. We estimated the detectable limit of this system with the ionization current of about 2.3×10-17A (2.4nGy/h in the absorbed dose rate) in 1 hour measurement. This measuring system is useful as an area monitor for the space dose rate measurement.