The effect of free-electron collection on the recombination correction to ionization measurements of pulsed radiation
The effect of free-electron collection on the recombination correction to ionization measurements of pulsed radiation
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DOI：
10.1088/0031-9155/41/5/005
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发表时间：
1996-05-01
影响因子：
3.5
通讯作者：
Balk, OA
中科院分区：
文献类型：
--
作者：
Boag, JW;Hochhauser, E;Balk, OA
讨论了暴露于脉冲辐射的小型剂量测定电离室中电荷收集过程的三种模型。所有三个模型都允许电荷转移中存在自由电子成分，以略有不同的方式将其合并到模型中，并将所得的收集效率公式与临床剂量测定中通常满足的变量范围进行比较。介绍了平面平行电离室和 Baldwin-Farmer 0.6 cm(3) 电离室的自由电子分数的测量结果。在正常工作电压下，小室中自由电子的比例通常很高，但很明显，如果针对纯离子传导计算的 f 值允许进行一些改进，则显然这只能导致收集效率的提高。因此，在低脉冲剂量下以效率 f = 0.9950 收集离子的室中 50% 的自由电子分数将将该效率提高至仅 0.9982。相同的腔室，在相同的工作电压下，因此在相同的自由电子分数下，如果暴露于更大的脉冲剂量，单独计算离子的效率为 0.9531，则真实效率将为 0.9830，这是一个很大的变化。
Three models of the charge collection process in small dosimetric ionization chambers exposed to pulsed radiation are discussed. All three models allow for the presence of a free-electron component in the charge transfer, incorporating this into the model in slightly different ways, and the resulting collection efficiency formulae are compared over the range of variables normally met within clinical dosimetry. Measurements of the free-electron fraction for plane-parallel ionization chambers and for a Baldwin-Farmer 0.6 cm(3) chamber are presented. The proportion of free electrons at the normal operating voltage is often high in small chambers but it is obvious that this can only lead to an increase in collection efficiency if the f-value calculated for purely ionic conduction allows for some improvement. Thus, a 50% free-electron fraction in a chamber which collects ions with efficiency f = 0.9950 at low pulse doses will increase this efficiency to only 0.9982. The same chamber, at the same operating voltage, and therefore the same free-electron fraction, if exposed to larger pulse doses, yielding an efficiency of 0.9531 as calculated for ions alone, would have a true efficiency of 0.9830-a large change.