Abstract
The authors have developed a new type of channel electron multipliers (CEM's) which are made of the caramic semiconductors of barium titanate family or zinc oxide-titanium oxide family. The ceramic CEM's have a gain of 108 at the applied voltage of 3∼4kV, and have a typical value of resistance 109Ω. The CEM's of barium titanate family have positive resistivity-temperature characteristics unlike those of the conventional type using a semiconductor thin film on the inner wall of a glass tube. This ensures a protection against a “thermal run away” and the selection of the value of resistance of tube materials is not unduly limited.
It was also expected that the ceramic CEM's were durable and stable both mechanically and chemically. Experiments using mainly those of barium titanate family were performed to clarify the upper limit of the operation temperature and the allowable baking condition. The ceramic CEM's used in the experiment were able to work at temperature above about 250°C, whereas a decrease of gain took place when the CEM's of a conventional type were operated at temperatures above about 150°C. The baking condition allowable for the ceramic CEM's was higher in temperature and longer in time than those for the conventional CEM's.
The initial value of electron gain of 108 fell to 107 after the accumulated counts of 109, somewhat less than 1010 counts for the conventional CEM's. However, the ceramic CEM's exhibited an almost constant gain over the first 108 counts followed by an irregular gain decrease, while in the case of the conventional CEM's the gain exhibited a linear decrease during the operation. The CEM's which suffered a gain fatigue during the life test completely recovered their initial gain following a reexposure to the atmosphere. They are also sensitive to ions and soft X-rays. Besides the characteristics mentioned above, the ceramic CEM's have an advantage that they can be manufactured easily and economically. In the industrial applications, the CEM's may be used as a β-ray detector or a photomultiplier in a vacuum sealed structure. In this case, more reliable performance can be expected for the ceremic CEM's than for the conventional CEM's because the CEM's allow a higher temperature for baking during the sealing process.
