基于碎片云运动模型的缓发γ射线电离大气蒙特卡罗模拟

Monte Carlo simulation of delayedγ-rays ionizing the atmosphere based on debris motion model

高空核爆炸碎片云释放出的缓发γ射线在高空非均匀大气的输运过程中电离大气,使得电离层中电子数密度剧增,进而影响途经电离层的无线电通信链路。为了准确描述随时空演化的缓发γ射线源电离大气过程,首先建立高空核爆炸碎片云运动演化的流体力学模型,然后根据碎片云参数建立缓发γ射线分层等效体源模型,最后采用蒙特卡罗方法模拟缓发γ射线在高空大气中输运并电离大气的过程。针对碎片云形状时空演化特性,采用辐射源分层抽样的方法得到缓发γ射线初始位置;针对大气密度随高度指数衰减的特性,采用质量厚度抽样方法简化模型、提升效率。结果表明:碎片云形状对缓发γ射线电离大气的范围和强度存在明显影响。兆吨级高空核爆炸缓发γ射线电离大气范围可达千公里以上。当爆高不变而当量增加时,碎片云高度和水平半径增大,缓发γ射线电离大气范围和强度增大。保持当量不变而增加爆高时,碎片云高度和水平半径增大,缓发γ射线电离大气范围增大,但强度有所降低。

[Background]In the aftermath of a high-altitude nuclear explosion,the delayedγ-rays emanating from the debris undergo a complex ionization process while traversing the non-uniform high-altitude atmosphere.This process results in a significant augmentation of the electron number density in the ionosphere,thereby affecting radio communication links traversing the ionosphere.[Purpose]This study aims to develop a comprehensive modeling and simulation framework that accurately captures the temporal and spatial evolution of delayedγ-ray sources and their corresponding atmospheric ionization effects.[Methods]Firstly,a hydrodynamic model was established to simulate the debris motion resulting from a high-altitude nuclear explosion.Subsequently,a hierarchical equivalent model of delayedγ-ray sources was formulated based on the debris parameters.Then,the Monte Carlo method was utilized to simulate the ionization effect of these delayedγ-rays in the non-uniform high-altitude atmosphere.Finally,given the dynamic evolution of the debris shape,a stratified sampling approach was employed to determine the initial positions of the delayedγ-rays.Various conditions such as 4 Mt equivalent explosion at a height of 40 km,4 Mt equivalent at a height of 80 km,100 kt equivalent at a height of 40 km,and 100 kt equivalent at a height of 80 km,the fragment cloud was evenly divided into 10 layers according to their respective proportions.MCATNP code was used to calculate the distribution of electron production rates formed by the ionization of the atmosphere by delayedγ-rays generated by the debris different times after the explosion.Furthermore,considering the exponential decay of atmospheric density with height,the mass thickness sampling method was adopted to simplify the computational model.[Results&Conclusions]The results indicate that the ionization intensity and range of delayedγ-rays are significantly influenced by the debris shape.In the case of a megaton-level high-altitude nuclear explosion,the ionization range of delayedγ-rays can extend to over a thousand kilometers.Specifically,with a constant explosion height,an increase in the equivalent yield leads to an augmentation in the debris height and horizontal radius,thereby enhancing the ionization range and intensity.Conversely,when the burst height is increased while maintaining a constant equivalent yield,the debris height and horizontal radius increase,leading to an expansion in the ionization range but a reduction in ionization intensity.