Studies on the Discrimination Effect of Secondary Electron Multiplier (SEM) for MAT261 Thermal Ionization Mass Spectrometry and the Establishment of Count Mode of SEM

Mass discrimination effect and ions intensity-dependent discrimination effect of secondary electron multiplier (SEM) in analog mode for MAT261 thermal ionization mass spectrometry (TIMS) were carried out. Mass discrimination factor were determined accurately and the measurement conditions under which ions intensity-dependent discrimination effect could be ignored were obtained. Moreover, the count mode of SEM was established for accurate measurement of weak signal. Comparison with the two modes， which were finished using standard solution of plutonium. The results from analog mode corrected by mass discrimination effect and directly from count mode of SEM respectively agree well with the nominal value. It means that accurate analysis of weak signal can be achieved using the established count mode of SEM.