Ambiguities in the grid-inefficiency correction for Frisch-Grid Ionization Chambers
Ambiguities in the grid-inefficiency correction for Frisch-Grid Ionization Chambers
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DOI：
10.1016/j.nima.2011.01.088
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发表时间：
2012-05
影响因子：
1.4
通讯作者：
A. Al-Adili;F. Hambsch;R. Bencardino;S. Oberstedt;S. Pomp
中科院分区：
文献类型：
--
作者：
A. Al-Adili;F. Hambsch;R. Bencardino;S. Oberstedt;S. Pomp
在过去的20年里，带有弗里希栅的电离室已经非常成功地应用于中子诱发裂变碎片的研究。它们是耐辐射的，并且可以很容易地适应实验条件。使用弗里希栅格的优点在于从阳极板上感应的电荷中去除角度依赖性。然而，由于屏蔽电荷的栅极效率低下（GI），阳极信号仍然略微依赖于角度。然而，对GI的校正对于确定电离粒子的正确能量是必不可少的。GI校正可以达到阳极信号的百分之几。目前，文献中提到了两种相互矛盾的校正方法。第一种方法将信号的角度相关部分与信号脉冲高度相加;第二种方法从后者中减去前者。利用双Frisch栅电离室（TFGIC）对~（252）Cf源自发裂变碎片（FF）进行了加性和减性探测。在同一腔室侧分别使用具有不同线间距（分别为1和2 mm）的两个平行线栅。所有其他实验条件不变。2 mm网格的GI是1 mm网格的两倍多。在GI校正之前和之后，比较两次测量中阳极上的感应电荷。GI校正前，2 mm网格导致的脉冲高度分布低于1 mm网格。在将两个GI校正应用于两个测量之后，仅添加剂方法导致相同的网格独立脉冲高度分布。相反，减法校正的应用导致不一致的、依赖于网格的结果。计算结果还表明，两种修正方法对235 U（nth，f）的FF质量分布的影响可以忽略不计。
Ionization chambers with Frisch grids have been very successfully applied to neutron-induced fission-fragment studies during the past 20 years. They are radiation resistant and can be easily adapted to the experimental conditions. The use of Frisch grids has the advantage to remove the angular dependency from the charge induced on the anode plate. However, due to the Grid Inefficiency (GI) in shielding the charges, the anode signal remains slightly angular dependent. The correction for the GI is, however, essential to determine the correct energy of the ionizing particles. GI corrections can amount to a few percent of the anode signal. Presently, two contradicting correction methods are mentioned in literature. The first method adding the angular-dependent part of the signal to the signal pulse height; the second method subtracting the former from the latter. Both additive and subtractive approaches were investigated in an experiment where a Twin Frisch-Grid Ionization Chamber (TFGIC) was employed to detect the spontaneous fission fragments (FF) emitted by a252Cf source. Two parallel-wire grids with different wire spacing (1 and 2mm, respectively), were used individually, in the same chamber side. All the other experimental conditions were unchanged. The 2mm grid featured more than double the GI of the 1mm grid. The induced charge on the anode in both measurements was compared, before and after GI correction. Before GI correction, the 2mm grid resulted in a lower pulse-height distribution than the 1mm grid. After applying both GI corrections to both measurements only the additive approach led to identical grid independent pulse-height distributions. The application of the subtractive correction on the contrary led to inconsistent, grid-dependent results. It is also shown that the impact of either of the correction methods is negligible on the FF mass distributions of235U(nth, f).