涂硼正比计数管感应电流信号模拟及脉冲宽度分析研究

Simulating Induced Current Signal of Boron-coating Proportional Counter and Study of Pulse Width Analysis

涂硼正比计数管的感应电流脉冲宽度会造成脉冲堆积,降低计数准确度。通过Garfield++仿真中子场中涂硼正比计数管不同偏置电压和不同空间位置电子离子对的感应电流信号,研究偏置电压和电子离子对空间位置分布对感应电流脉冲宽度的影响。结果表明:在纯中子场中,正比计数管感应电流信号在低偏置电压下主要由电子漂移贡献,在1 100 V以上高偏置电压下,主要由离子漂移贡献;入射粒子在灵敏区运动时长对感应电流脉冲宽度无影响;初电离电子离子对空间位置分布形成电子径向距差异,初始电离中不同径向距的电子的漂移时长之间最大差值和脉冲展宽高度一致,表明初始电离中的电子漂移时长差异是引起感应电流脉冲宽度增大的来源。研究结果表明:正比计数管对中子的感应电流脉冲宽度主要由离子漂移过程的时长和初始电离中不同空间位置的电子间最大漂移时长差构成。

The induced current pulse width of the boron-coating proportional counter is able to cause pulse piling up and degrade the counting accuracy. Meanwhile, the pulse broadening of the induced current pulse decreases the magnitude of the induced current pulse, reducing the ability of discrimination and counting for pulse. After an ion passes proportional counter, there will be a series of electron ion pairs with a spatial position distribution following the track of the projectile ion. For finding the factors affecting the width of induced current pulse, in pure neutron field the current signals induced by electron ion pairs in different spatial positions under different bias voltages were simulated through Garfield++, to study the influence of bias voltage and spatial position distribution of electron ion pairs on the induced current pulse width. The induced current pulse and its pulse width under bias voltages are obtained by changing the bias voltages in simulation. Because the spatial position distribution of original ion pairs forms the radial distance difference of electrons, the induced current pulse and its pulse width with the condition of radial distance difference of electrons can be obtained through changing the spatial position distribution of original ion pairs. After simulating the results show that in pure neutron field the induced current signal is mainly contributed by electron drifting under low bias voltage, and is mainly contributed by ion drifting under high bias voltage above 1 100 V. The traveling time of projectile particles is about several ns in sensitive area, so it has no effect on the induced current pulse width. The maximum difference value among the drifting duration of electrons with different radial distances in original ion pairs is highly consistent with the pulse broadening, indicating that the drifting duration difference among electrons in original ion pairs is the source of the increasing of induced current pulse width. The study result shows that the induced current pulse width of proportional counter to neutron mainly consists of the duration of ion drifting process, that is, intrinsic pulse width, and the maximum difference among drifting duration of electrons with different spatial positions in original ion pairs. The designing and manufacturing proportional counter should be optimized specially to degrade the influence of the spatial position distribution of original ion pairs on the induced current pulse width. When applying proportional counter, the influence that the spatial position distribution of original ion pairs generated by the projectile ions with different tracks is on the induced current pulse width and magnitude should be considered into the output of proportional counter.