Tritium absorption and its effect on ceramic secondary electron multiplier

To find a means to avoid tritium contamination which affects secondary electron multipliers (SEM), the material used in a marked ceramic multiplier and the SEM itself were studied with respect to adsorption-desorption behavior and tritium removal. The tritium adsorbed on the material was desorbed to a large degree as tritiated water and to small extent as tritiated hydrocarbons. The desorption took place at to distinct adsorption/desorption sites. Effective removal from the material was achieved by heating in an inert gas flow at 500℃for 6 hours. However, heating in vacuo and/or in the presence of reactive gases (below 5x10-6 Torr) showed insufficient decontamination when Ceratron was used in the ultrahigh vacuum system. This is ascribed to re-adsorption of tritium accumulating on the cold parts of the vacuum system. On the other hand, the photon irradiation showed a substantial decrease in the noise level to its own background. The decontamination was not due to thermal effects, possibly arising from photodesorption and/or photocatalysis. The partial pressure of tritium could be measured with the Ceratron, while reducing the noise level by photon irradiation, with good reproducibility