Measurements have been made to assess the characteristics and origins of background events in microchannel plates (MCPs). An overall background rate of approximately 0.4 events cm/sup -3/-s/sup -1/ has been achieved consistently for MCPs that have been baked and scrubbed. The temperature and gain of the MCPs are found to have no significant effect on the background rate. Detection of 1.46-MeV gamma rays from the MCP glass confirms the presence of /sup 40/K, with a concentration of 0.0007%, in MCP glass. It is shown that beta decay from /sup 40/K is sufficient to cause the background rate and spectrum observed. Anticoincidence measurements indicate the background rate caused by cosmic ray interactions is small (>
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Siegmund et al. (1988) studied this question.