Quasi-simultaneous arrival (QSA) effects in secondary ion mass spectrometry can create mass-independent inaccuracies in isotope measurements when using electron multiplier detectors (EMs). The simple Poisson statistical model of QSA does not explain most experimental data. We present pulse-height distributions (PHDs) and time-series measurements to better study QSA. Our data show that PHDs and the distribution of multiple arrivals on the EM are not consistent with the Poisson model. Multiple arrivals are over-dispersed compared to Poisson and are closer to a negative binomial distribution. Through an emission–transmission–detection model we show that the QSA correction depends on the non-Poisson emission of multiple secondary ions, the secondary ion energy distribution, and other factors, making an analytical correction impractical. A standards-based correction for QSA is the best approach, and we show the proper way to calculate standards-normalized $\delta$ values to minimize the effect of QSA.

当使用电子倍增检测器（EMs）时，二次离子质谱法中的准同时到达（QSA）效应会在同位素测量中产生质量无关的误差。QSA的简单Poisson统计模型不能解释大多数实验数据。我们提出了脉冲高度分布（PHD）和时间序列测量，以更好地研究QSA。我们的数据表明，PHD和EM上多次到达的分布与Poisson模型不一致。与Poisson相比，多次到达的分布过于分散，并且更接近于负二项式分布。通过发射-发射-检测模型，我们表明QSA校正取决于多个次级离子的非泊松发射，次级离子能量分布和其他因素，因此进行分析校正是不切实际的。$\delta$ 值以最小化QSA的影响。