Measurements of the rate of evaporation of caesium from the tri-alkali photocathode in an alkali-free environment

A Langmuir ion gauge has been used to measure the rate of evaporation of caesium from a tri-alkali photocathode transferred from its activation cell into high vacuum. The variation with temperature has been studied over the range 22-40 °C, and a value obtained for the latent heat of evaporation. The loss of caesium was found to be relatively slow at room temperature, about 5 × 104 atoms cm−2 s−1, and it is concluded that the photocathode is stable in an alkali-free environment.