Development of novel ion detector that combines a microchannel plate with an avalanche diode

摘要

Detector gain saturation is a well-known issue with the chevron microchannel plate (MCP) detector configured with two MCPs, which is widely used in the time-of-flight (TOF) mass spectrometer. In these detectors, high-intensity signals saturate the gain stages, thus reducing the magnitude of subsequent signals. To solve this issue, we developed a new detector that combines an MCP with an avalanche diode. Gain saturation was evaluated by measuring the percent of signal intensity loss of the second significant ion peak on the TOF spectrum using xenon isotopes, and then verified by argon spiked with nitrogen as a model sample. The signal intensity ratio of ~(132)Xe/~(129)Xe on the chevron MCP and the new detector named 'MIGHTION' was 0.31 and 0.94 using the ion counting result as the reference, which corresponds to 69 % signal suppression for the chevron MCP, but only an 8% difference for MIGHTION. By using trace-level argon spiked with nitrogen, the argon intensity change was monitored by alternately switching the nitrogen sample on and off with the ion gate. The intense nitrogen peak did not suppress the argon intensity peak, which appears 1.17 μs later. The nitrogen peak intensity was about 240 times larger compared to argon, and the peak voltage was 3.25 V with a 50·Ω load.