Research on nonlinearity effect of secondary electron multiplier

The nonlinearity of secondary electron multiplier(SEM) of a thermal ionization mass spectrometer has been researched by using UTB-500 uranium isotope reference material and multi-collecting technique.The results show that the nonlinearity effect of SEM exists in the whole ion counting range,and there is an extreme point of the nonlinearity when the ion counting rate is about 20000cps.The deviation between measured value of the extreme point and the reference value of the reference sample can be up to 3%,and the nonlinearity obeys logarithm linearity law on both sides of extreme point.A kind of mathematics model of nonlinearity calibration has been put forward.Using this model,the nonlinearity of SEM of TIMS can be calibrated.