Frequency gradient analysis (FGA) neutron-gamma pulse shape discrimination (PSD) based on Fourier transform has proved to be an effective method for discrimination between two types of pulses by simply constructing a discrimination parameter by subtracting the amplitude of the 1st frequency component from the 0th frequency component. However, the discrimination parameter constructed by the above method could not meet the requirements at some lower sample rates, and the dark noise caused using optoelectronic devices such as miniaturized SiPMs array further erodes the difference between the two frequency components. This paper proposes a new discrimination parameter construction method based on FGA for neutron-gamma discrimination, which is referred as mFGA (modified FGA). This discrimination parameter uses the 0th frequency component and other frequency components to enhance the discrimination performance. A neutron detector module consisting of a 25.4 mm× 25.4 mm× 50.8 mm NaI:Tl,⁶Li (NaIL) scintillator and an array of 8 × 8 SiPMs was established to verify the method of mFGA. The module measured a ²⁵²Cf neutron source under three shielding conditions: no shield, 5 cm high-density polyethylene (HDPE), and 10 cm lead brick. The proposed mFGA method was used to calculate the figure of merit (FoM) under each shielding condition and compared to the traditional frequency gradient method (FGA) and the traditional charge comparison method (CCM). The results show that the discrimination performance with the mFGA method is significantly improved. Taking the HDPE shielding group as an example, the performances of the three methods are FoM-FGA =1.14, FoM-mFGA =2.75, FoM-CCM =0.92. At the same time, with the increase of energy, due to the neutron gamma pulse becoming similar, and the discrimination performance of FGA and CCM decrease significantly. The discrimination performance of the mFGA method is relatively stable in all energy regions. Therefore, the proposed method is superior to the traditional FGA of the 0th frequency minus the 1st frequency and has a good application prospect for neutron-gamma discrimination with detectors of poor signal quality.

中文翻译：

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基于 SiPM 的 NaIL 闪烁体探测器的频域脉冲形状辨别优化

基于傅里叶变换的频率梯度分析（FGA）中子-伽玛脉冲形状辨别（PSD）已被证明是辨别两类脉冲的有效方法，只需从中子-伽玛脉冲形状中减去第一个频率分量的幅度即可构造辨别参数。第 0 频率分量。然而，上述方法构建的辨别参数在某些较低采样率下无法满足要求，并且使用小型化SiPM阵列等光电器件引起的暗噪声进一步侵蚀了两个频率分量之间的差异。本文提出了一种基于FGA的新的中子-伽玛判别参数构造方法，称为mFGA（modified FGA）。该辨别参数使用第0频率分量和其他频率分量来增强辨别性能。建立了由25.4 mm×25.4 mm×50.8 mm NaI:Tl、 ⁶ Li (NaIL)闪烁体和8×8 SiPM阵列组成的中子探测器模块来验证mFGA方法。该模块在三种屏蔽条件下测量了²⁵² Cf 中子源：无屏蔽、5 厘米高密度聚乙烯 (HDPE) 和 10 厘米铅砖。所提出的 mFGA 方法用于计算每种屏蔽条件下的品质因数 (FoM)，并与传统频率梯度法 (FGA) 和传统电荷比较法 (CCM) 进行比较。结果表明，mFGA 方法的判别性能显着提高。以HDPE屏蔽组为例，三种方法的性能分别为FoM-FGA=1.14、FoM-mFGA=2.75、FoM-CCM=0.92。同时，随着能量的增加，由于中子伽马脉冲变得相似，FGA和CCM的辨别性能显着下降。 mFGA方法的判别性能在所有能量区域都相对稳定。因此，该方法优于传统的第0频率减去第1频率的FGA，对于信号质量较差的探测器的中子伽马鉴别具有良好的应用前景。