Case a , field and track parallel

With no electron-attaching impurities present, the electrons give rise to a current given as 

Nq is the number of electron/ion pairs, and tj denotes the drift time. The collected charge as a function of time, Q(t), is then obtained as 

The charge measured due to electrons is one half of the total charge deposited by the ionizing particle. The other half is transferred by the positive ions which are not detected by the charge-sensitive amplifier. Equation 119 describes a parabola with its apex at t. When impurities are present, the electron current is given as 

X is the lifetime of the electrons with respect to attachment. The collected charge becomes 

With the introduction of the dimensionless quantities t/tj and x/t, Equation 123 becomes 

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