Positive ions produced by a 120eV electron impact on H2, He, CH4, N2, CO2, and Kr were detected with a microchannel plate (MCP), and the pulse-height distributions (PHDs) of the output signals were observed. As a result, the half width at half maximum (HWHM) of the region above the peak of the PHD was almost independent of the kind of ion. This finding demonstrates that the HWHM is due only to the amplification of the secondary electrons that emerged as a result of the collision of the ions with the surface of the MCP. The dependence of the peak position and the HWHM against the potential difference applied between the front and back of the MCP was also examined. It was found that the plots of the HWHM as a function of the potential difference applied to the MCP could be fitted by a linear line very well. A formula that can reproduce the observed PHDs is presented as a function of the potential applied to the MCP and the mass number. A relation of the mean peak height in the PHD to the potential applied to the MCP and the mass number is also presented.
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