High amplitude events in microchannel plates

Measurements have been made to determine the characteristics of high-amplitude events in microchannel plates (MCPs). The background-pulse-amplitude spectrum is found to extend to >30x to MCP modal gain. The majority of the background events are initiated by ⁴⁰K beta decay in the MCP glass. However, up to 40% of the events are due to cosmic rays. Comparison of background pulse-amplitude spectra for horizontal and vertical MCP orientations suggests that the largest events are predominantly cosmic-ray-induced. Anticoincidence measurements confirm this result. A model describing the ⁴⁰K beta decay and cosmic-ray interactions in the MCP predicts spectra in accord with these observations. The response of MCPs subjected to simultaneous multiphoton input was also determined, showing that pulse amplitudes many times the modal gain are possible event though the response becomes nonlinear at high amplitudes