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 应用科技  2018, Vol. 45 Issue (6): 80-85  DOI: 10.11991/yykj.201803003 0

### 引用本文

WU Bing, SONG Yushou, XIE Zhaoyang. Monte Carlo simulation on the attenuation length features of the plastic scintillator[J]. Applied Science and Technology, 2018, 45(6), 80-85. DOI: 10.11991/yykj.201803003.

### 文章历史

Monte Carlo simulation on the attenuation length features of the plastic scintillator
WU Bing, SONG Yushou, XIE Zhaoyang
Fundamental Science on Nuclear Safety and Simulation Technology Laboratory, Harbin Engineering University, Harbin 150001, China
Abstract: The optical attenuation of the plastic scintillator is usually used for positioning and correcting the intensity of signal, and the cognition on the attenuation law is related to the measurement precision of some physical quantity. By Monte Carlo method, the influencing factor and influencing mode of the attenuation length of plastic scintillator was researched systematically. Combining with the control variable method, four types of influencing factors of the optical surface type, cross-sectional area, reflective material and surface roughness of the plastic scintillator were simulated and analyzed one by one, and the tendency of attenuation length changing with the factor was obtained. Then, using the novel interval subdivision method, the plastic scintillator was divided into several equidistant intervals according to the distance. The distribution characteristics of the attenuation length in each interval were compared, and the general law of the attenuation length in the interval subdivision method was summarized. The results show that polished back painted polygon has the best light collection efficiency under the same other conditions, and the attenuation length decreases with the increase of cross-sectional area, reflectance of the reflecting material, and surface roughness. At the same time, the attenuation length varies continuously in the direction of the scintillator interval, and the attenuation law is not a simple exponential law, it is the attenuation law of a compound type. This simulation study has a high reference value for the experimental design of plastic scintillator detectors.
Keywords: plastic scintillator    attenuation length    Monte Carlo    control variable method    interval subdivision method    optical surface type    cross-sectional area    surface roughness

1 模型与方法

1.1 建立模型

1.1.1 表格的规范化

1.1.2 闪烁体光学模块

1）在单一介质中的传播。首先在physicslist中添加吸收和瑞利散射2个类；其次在探测器构建程序中设定闪烁体对其中所产生的光的衰减长度。

2）在不同介质界面上的传播。首先在physicslist中添加边界过程；其次在探测器构建程序中建立光学边界，即选用UNIFIED模型。

1）polished：如图2(a)，以此为界面的2种介质表面均十分光滑，光在界面上的反射、折射满足菲涅尔定律。该表面要求用户在探测器构建时定义2种光介质的折射率。

2）polishedfrontpainted：如图2(b)，加入反射材料后，光子在这样的表面上以一定的几率发生镜面反射，其余部分被反射层吸收。在用户探测器构建程序中除了要给定介质I的折射率外，还要定义反射层的吸收几率。

3）polishedbackpainted：如图2(c)，光吸收层与介质I之间不是紧密接触而存在其他介质材料III。在I和III之间光传输遵守菲涅耳定律，在III和反射材料之间的行为与图2(b)相同。要使用此光学界面，在图2(b)的基础参数上，还要给定介质I与吸收层之间夹层的折射律。

4）ground：如图2(d)，界面是粗糙材料，这种粗糙在UNIFIED模型中通过小面元来实现。这些小面元的法线方向符合高斯分布，同时其法线分布的σ值就反映该面的粗糙程度。

5）groundfrontpainted：如图2(e)所示，类似于图2(b)，光在界面上以反射率给定的几率发生理想型的完全漫反射，其余部分被吸收。

6）groundbackpainted：如图2(f)所示，类似于图2(c)，只是光在从介质I向III入射，发生图2(d)界面的行为。

1.1.3 电子学信号处理模块

 ${T_{{\rm{anode}}}} = {T_{{\rm{cathode}}}} + {T_{{\rm{trans}}}}$

 ${V_i}(t) = \frac{{G{C_e}}}{{{C_c}}}\frac{{{t^2}{{\rm{e}}^{ - {t^2}}}/{\tau ^2}}}{{\int {{t^2}{{\rm{e}}^{ - {t^2}}}/{\tau ^2}{\rm{d}}t} }}$

1.2 数据分析拟合

 $N(x) = {N_0}{e^{ - x/\lambda }}$

2 模拟结果与讨论

2.1 光学面类型

2.2 截面积

2.3 反射系数

2.4 表面粗糙度

2.5 细分区间法模拟