X-ray phase-sensitive microscope imaging with a grating interferometer: Theory and simulation

A general theoretical framework is presented to explain the formation of the phase signal in an x-ray microscope integrated with a grating interferometer, which simultaneously enables the high spatial resolution imaging and the improved image contrast. By using this theory, several key parameters of phase contrast imaging can be predicted, for instance, the fringe visibility and period, and the conversion condition from the differential phase imaging (DPI) to the phase difference imaging (PDI). Additionally, numerical simulations are performed with certain x-ray optical components and imaging geometry. Comparison with the available experimental measurement [Appl. Phys. Lett. 113 063105 (2018)] demonstrates the accuracy of this developed quantitative analysis method of x-ray phase-sensitive microscope imaging.     

A novel 2-dimensional cosmic ray position detector based on a CsI(Na) pixel array and an ICCD camera

A novel 2-D cosmic ray position detector has been built and studied. It is integrated from a CsI(Na) crystal pixel array, an optical fiber array, an image intensifier and an ICCD camera. The 2-D positions of one cosmic ray track is determined by the location of a fired CsI(Na) pixel. The scintillation light of these 1.0× 1.0 mm CsI(Na) pixels is delivered to the image intensifier through fibers. The light information is recorded in the ICCD camera in the form of images, from which the 2-D positions can be reconstructed. The background noise and cosmic ray images have been studied. The study shows that the cosmic ray detection efficiency can reach up to 11.4%, while the false accept rate is less than 1%.     

利用ICCD定位宇宙线来测量探测器时间分辨的方法研究

本研究采用双层150 mm×150 mm闪烁条阵列定位宇宙线的入射和出射位置. 阵列信号光使用波移光纤吸收传输,在ICCD相机前插入前置像增强器,使信号光延迟大于200 ns, 使ICCD可以由外部高速触发信号控制,有效记录随机触发事例.该宇宙线定位系统可以同时多点密集测量 通用探测器测试平台的时间分辨和闪烁光的渡越时间.该新方法与传统时间分辨测量方法相比提高了30倍以上 的效率.实验结果显示:时间探测器的时间分辨好于200 ps,满足通用探测器测试平台的设计要求.     

Attenuation length measurements of a liquid scintillator with LabVIEW and reliability evaluation of the device

An attenuation length measurement device was constructed using an oscilloscope and LabVIEW for signal acquisition and processing. The performance of the device has been tested in a variety of ways. The test results show that the set-up has a good stability and high precision (sigma/mean reached 0.4 percent). Besides, the accuracy of the measurement system will decrease by about 17 percent if a filter is used. The attenuation length of a gadolinium-loaded liquid scintillator (Gd-LS) was measured as 15.10±0.35 m where Gd-LS was heavily used in the Daya Bay Neutrino Experiment. In addition, one method based on the Beer-Lambert law was proposed to investigate the reliability of the measurement device, the R-square reached 0.9995. Moreover, three purification methods for Linear Alkyl Benzene (LAB) production were compared in the experiment.     

Performance study of a micro-pattern gas detector: leak microstructure

A micro-pattern gas detector named leak microstructure (LM) has been studied. A new chemical electrolytic technique is introduced to make perfect shaped LM needles with very sharp tips, and this method may be developed to make LM array detectors in batches. The experimental results are presented for both a single needle LM detector and a small LM array detector. The gas gain is up to 10⁵ by calculation from the waveform. Good gain stability and uniformity are achieved. The light emission from the needle tip is also measured in Ar/CF₄(95/5) gas mixture. The result shows a promising application for imaging.     

Experimental study of a THGEM detector with mini-rims

The gas gain and energy resolution of single and double THGEM detectors (5 cm×5 cm effective area) with mini-rims (rim less than 10 μm) were studied. The maximum gain was found to reach 5×10³ and 2×10⁵ for single and double THGEMs respectively, while the energy resolution for 5.9 keV X-rays varied from 18% to 28% for both single and double THGEM detectors of different hole sizes and thicknesses. Different combinations were also investigated of noble gases (argon, neon) mixed with a quantity of other gases (isobutane, methane) at atmospheric pressure.     

Performance of MPPC at low temperature

The performance of a MultiPixel Photon Counter (MPPC) from room to liquid nitrogen temperatures were studied. The gain, the noise rate and bias voltage of the MPPC as a function of temperature were obtained. The experimental results show that the MPPC can work at low temperatures. At nearly liquid nitrogen temperatures, the gain of the MPPC drops obviously to 35% and the bias voltage drops about 9 V compared with that at room temperature. The thermal noise rate from 10⁶ Hz/mm at room temperature drops abruptly to 0 Hz/mm at -100 ℃. The optimized operation point can be acquired by the experiment.     

Fast light of CsI（Na） crystals

The responses of different common alkali halide crystals to alpha-rays and gamma-rays are tested in this research. It is found that only CsI(Na) crystals have significantly different waveforms between alpha and gamma scintillations, while others do not exhibit this phenomena. The rise time of the fast light is about 5 ns and the decay time is 17±12 ns. It is suggested that the fast light of CsI(Na) crystals arises from the recombination of free electrons with self-trapped holes of the host crystal CsI. Self-absorption limits the emission of fast light of CsI(Tl) and NaI(Tl) crystals.