强脉冲X射线场中散射能谱获取方法

Scattered spectra detection method in high-intensity pulse radiation fields

通过对X射线与物质相互作用后产生的散射能谱的分析,可实现物质原子序数的提取,并可用于核材料等违禁品的探测。然而,高能X射线的特性对探测系统的屏蔽和时间响应提出了要求。该文提出了一种能够对脉冲X射线的散射能谱进行采集的实验方案:以LaBr3(Ce)晶体为X射线探测器来实现<100ns的散射光子分辨时间,以减少在5μs脉冲出束时间内的脉冲堆积问题;利用120MHz/14位的高采样率ADC(analog-digital converter)电路来采集前放电路的输出脉冲波形,并设计相应的离线算法将该波形数据重建为散射能谱;设计了合适的屏蔽结构,减少了来自加速器靶点的直接透射X射线和环境散射X射线对探测器的影响。利用该方案对11种具有不同原子序数的物质进行了测量,得到了它们的散射能谱,在511keV峰能量分辨率可达到5%左右。

The atomic number of materials can be extracted by analyzing the spectra of scattered photons produced after interactions with high energy X-rays, which can be used to detect contraband such as nuclear materials. However, the characteristics of high energy X-rays require extensive shielding and very fast detection systems. This paper introduces a scheme to acquire scattered X-ray spectra using LaBr3（Ce） detector to fast measure resolving time （〈100 ns） of scattered photons to alleviate pulse pileup problem in the 5 μs pulse. An analog digital convertor （ADC） with a sampling rate of 120 MHz and 14 bit resolution is used to digitize the signal waveform from the detector. An offline algorithm is used to reconstruct the scattered spectra. Shielding is used to reduce thenumber of photons transmitted from the accelerator scattered in the environment into the detector. Tests on 11 different materials give accurate results with high atomic number materials. The energy resolution is better than 5%@511 keV.