Hydrogen-reduced lead glass of channel electron multipliers is comparatively resistant to the repeated aeration of the vacuum chamber. Nevertheless, it must be considered that glass has the characteristic of binding moisture from the environment in the form of water vapor from the air moisture (hygroscopy). Over a longer period of time, this leads to a decrease in gain and therefore to a reduction of the lifetime.

For this reason, we deliver the electron multipliers in a sealed bag, which contains a dry bag. We recommend opening the package first when the detector is actually required and to store the detector and dry bag in a resealable PE bag after inspection. This allows the detector to be stored for approximately 1 year. If technically possible, optimal storage of the detectors would be in a nitrogen or argon atmosphere or vacuum.

The bound water and other desorbed molecules lead to a reduction in the work function so that the CEM gain is very high. In the clean-up phase during the burn-in-procedure, CEMs, which have been stored for a longer period of time, pass through a deep valley of the gain until they reach a stable plateau again. This occurs after recommissioning and should be considered when setting the applied voltage and the discriminator threshold.

Fig. 3 shows the burn-in plot of a CEM type KBL1010 measured after having been sealed in the dry bag for 2.5 years. Please note that the gain is not within the specification for a new CEM.