Pardo-Montero J, Gómez F
School of Cancer Studies, University of Liverpool, Liverpool, UK.
Phys Med Biol. 2009 Jun 21;54(12):3677-89. doi: 10.1088/0031-9155/54/12/005. Epub 2009 May 28.
An accurate computation of the collection efficiency due to recombination has a capital importance in order to perform high-precision dose measurements with ionization chambers. The two-voltage method, developed to compute charge collection efficiency in gas chambers, cannot be directly applied to liquid-filled ionization chambers (LICs) due to the ionized charge strong dependence on the collection electric field, which is caused by initial recombination. It is shown that in order to apply the two-voltage method to parallel-plate LICs it is necessary to introduce explicitly the slope of the ionization charge yield with respect to the polarization voltage applied in the chamber. A three-voltage method is also proposed to avoid the introduction of the slope parameter. That method allows decoupling initial and general recombination. It leads to a nonlinear system of equations which can be solved using numerical methods.
为了使用电离室进行高精度剂量测量，准确计算复合导致的收集效率至关重要。为计算气体室中的电荷收集效率而开发的双电压法，由于电离电荷对收集电场的强烈依赖性（这是由初始复合引起的），不能直接应用于充液电离室（LIC）。结果表明，为了将双电压法应用于平行板LIC，有必要明确引入电离电荷产率相对于施加在室中的极化电压的斜率。还提出了一种三电压法以避免引入斜率参数。该方法允许将初始复合和一般复合解耦。它导致一个非线性方程组，可以使用数值方法求解。
