To meet the application demand for simultaneous structure inspection and elemental analysis, research on neutron imaging-driven prompt gamma activation analysis instrument is of great significance. Relying on the China Mianyang Research Reactor, the China Academy of Engineering Physics proposed the physical design of the PGAA -NT apparatus, carried out Monte Carlo simulations, signal commissioning and experimental tests, and successfully established an experimental facility that couples PGAA with neutron imaging. In terms of characterisation, the beam parameters, background features, Compton-suppression performance, wide-energy-range detection efficiency, and imaging spatial resolution of the instrument were accurately measured. The instrument exhibits the low background (full spectrum <200 cps at 1.5 x 108 ncm-2s-1), high energy resolution (2 keV at 1.332 MeV), high imaging spatial resolution ( <10 m) and millimetre-scale activated analysis volume. It provides a neutron measurement platform that combines three-dimensional structure detection with position-sensitive elemental analysis. This instrument fills the gap in China's PGAA-NT field, with performance reaching the international advanced level.

Neutron imaging inevitably suffers from image degradation such as image information loss and image blurring. Many experimental methods and device optimization schemes have been proposed to further improve the resolution of neutron imaging, this often sacrifices time resolution or incurs high retrofitting costs. This study proposes a flexible and effective super-resolution method based on neutron imaging experiment and deep learning algorithm. In the experiment, a large number of neutron images were measured using the reactor neutron imaging facility. The experiment measured multiple samples under various conditions to ensure that the network has good generalization ability. In the network structure, a more complex image super-resolution generative adversarial network was introduced. In the network, residual module, skip technology and dense connection were used to enhance the interaction performance of multi-scale feature information. More high-frequency details were reconstructed by introducing perceptual loss instead of pixel loss. The perceptual loss was calculated by extracting deep features of the image through an independent VGG network. Finally, the model was verified through real neutron imaging, with clarity, richness of information, spatial resolution, and subjective visual effect as the evaluation metrics. The results show that this method can achieve higher quality super-resolution reconstruction. The super-resolution image has better definition, greater information recovery, and improved spatial resolution level. The deep learning super-resolution method can express the intrinsic laws of neutron images, and reduce the optical blur caused by the imaging device acting as a frequency filter.

Neutron capture event imaging is a novel technique that has the potential to substantially enhance the resolution of existing imaging systems.This study provides a measurement method for neutron capture event distribution along with multiple reconstruction methods for super-resolution imaging.The proposed technology reduces the point-spread function of an imaging system through single-neutron detection and event reconstruction,thereby significantly improving imaging resolution.A single-neutron detection experiment was conducted using a highly practical and efficient 6 LiF-ZnS scintillation screen of a cold neutron imaging device in the research reactor.In milliseconds of exposure time,a large number of weak light clusters and their distribution in the scintillation screen were recorded frame by frame,to complete single-neutron detection.Several reconstruction algorithms were proposed for the calculations.The location of neutron capture was calculated using several processing methods such as noise removal,filtering,spot segmentation,contour analysis,and local positioning.The proposed algorithm achieved a higher imaging resolution and faster reconstruction speed,and single-neutron super-resolution imaging was realized by combining single-neutron detection experiments and reconstruction calculations.The results show that the resolution of the 100 μm thick 6 LiF-ZnS scintillation screen can be improved from 125 to 40 microns.This indicates that the proposed single-neutron detection and calculation method is effective and can significantly improve imaging resolution.

Taking advantage of the special reaction principle between neutrons and elements, the neutron imaging method is better suited to testing the structure and the defects of light materials that are covered by heavy materials. In contrast to thermal or cold neutron imaging, the fast neutrons are best suited to testing the large samples composed of various materials. Fission neutrons emitted from the reactor are more stable than those from other neutron sources. Based on the beamline for thermal neutron imaging at China Mianyang Research Reactor (CMRR), a combination of filters could increase the proportion of the fission neutrons. Various fission neutron collimators were calculated, designed and measured. The flux of fission neutrons was close to 3 x 105 cm-2 s- 1, when the collimation ratio was about 172. A fission neutron imaging system was built as well. The field of view (FOV) was as large as 400 mm x 400 mm, and the experimental spatial resolution was better than 0.5 mm. The fission neutron tomography was tested. The reconstruction results were comparable to the tomography performed in NECTAR at FRM-II. In addition, a serial time acquisition method was applied in the tomography to reduce the white noise. The ART reconstruction method may improve the quality of the reconstruction images.

Nuclear energy is a vital source of clean energy that will continue to play an essential role in global energy production for future generations. Nuclear fuel rods are core components of nuclear power plants, and their safe utilization is paramount. Due to its inherent high radioactivity, indirect neutron radiography (INR) is currently the only viable technology for irradiated nuclear fuel rods in the field of energy production. This study explores the experimental technique of indirect neutron computed tomography (INCT) for radioactive samples. This project includes the development of indium and dysprosium conversion screens of different thicknesses and conducts resolution tests to assess their performance. Moreover, pressurized water reactor (PWR) dummy nuclear fuel rods have been fabricated by self-developing substitute materials for cores and outsourcing of mechanical processing. Experimental research on the INR is performed using the developed dummy nuclear fuel rods. The sparse reconstruction technique is used to reconstruct the INR results of 120 pairs of dummy nuclear fuel rods at different angles, achieving a resolution of 0.8 mm for defect detection using INCT.

High-resolution neutron radiography provides novel and stirring opportunities to investigate the structures of light elements encased by heavy elements. For this study, a series of Gd2O2S:Tb, F particles were prepared using a high-temperature solid phase method and then used as a scintillation screen. Upon reaching 293 nm excitation, a bright green emission originated from the Tb3+ luminescence center. The level of F doping affected the fluorescence intensity. When the F doping level was 8 mol%, the fluorescence intensity was at its highest. The absolute quantum yield of the synthesized particles reached as high as 77.21%. Gd2O2S:Tb, F particles were applied to the scintillation screen, showing a resolution on the neutron radiograph as high as 12 μm. These results suggest that the highly efficient Gd2O2S:Tb, F particles are promising scintillators for the purposes of cold neutron radiography.

The measurement of the neutron field relative distribution can significantly improve the accuracy of PGNAA, and can broaden the scope of PGNAA toward large samples. For this purpose, according to the properties and characteristics of neutron tomography, a new method to calculate the neutron field relative distribution inside the objects based on neutron tomography has been proposed. PGNAA technique combined with neutron field relative distribution was used to calculate element content as verification method. The results show that the PGNAA measurement accuracy for large samples was significantly improved, which proves that the measurement method of the neutron field relative distribution is accurate and reliable.

BackgroundNeutron radiography (NR) is an important nondestructive testing method. NR is particularly useful for detection of light materials in medium and large heavy samples. Especially, the fast neutrons can penetrate the heavy materials and reveal the structure of the light materials. Compared to accelerator neutron sources, the fission neutrons elicited from a reactor are stable and of high quality. The fission neutron imaging is a useful complementary testing technology, especially for industrial applications that require high throughput and large-scale testing.PurposeThis study aims to investigate the super field of view neutron imaging by fission neutrons elicited from research reactor.MethodsBased on theoretical analysis and Monte-Carlo simulation, one filter combination was employed to improve the proportion of fission neutrons in the thermal neutron beamline at China Mianyang Research Reactor (CMRR). A fission neutron imaging system was constructed by employing a large field fast neutron fluorescent screen, short focus distance lens, and scientific charge coupled device (CCD) camera. Finally, some samples were tested using fission neutron tomography.ResultsThe fission neutron flux reaches up to 3×105 cm-2·s-1 when the L/D ratio is about 260. The field of view of NR is up to 400 mm×400 mm with resolution was better than 0.5 mm. Using super field of view method, samples less than 600 mm can be tested with this new system.ConclusionsCombination of theoretical calculation and experimental methods, fission neutron imaging can be improved to overcome some of the limitations of traditional neutron radiography techniques, and meet the needs of large sample detection in the future.

为适应CMRR冷中子成像装置配备双晶体单色器的需求,采用MC方法计算了主选择波长中子及其二次谐波中子在成像位置处不同厚度高定向热解石墨的强度,通过它们相对强度变化确定了高定向热解石墨的厚度.确定厚度后,模拟计算了成像位置的单色中子注量率、波长分辨率、有效视场及其均匀性,通过本研究为CMRR冷中子单色中子成像装置研制提供了设计参考.

A novel non-destructive testing scanning system based on a large-size line array fast neutron detector and compact D-T neutron source has been constructed. The scanning range is up to 1000 mm, and the resolution is better than 1 mm. The fast neutron detection subsystem consists of a polypropylene zinc sulfide scintillator embedded with wavelength-shifting fibers, coupled with a light lens and a scientific CCD camera. With a new rotating tritium target, the lifetime of the compact D-T neutron source could achieve ten hours. The experimental results indicate that the scanning method based on line array fast neutron detector and D-T neutron source is feasible and enables the detection of slits on the order of 0.5 mm in width. Fast neutron tomography has been realized by this detection system too.

Cold neutron has a strong ability to penetrate metal materials and identify light elements, making it an ideal nondestructive testing technique for detecting cracks, bubbles, or other defects in metals. However, the low imaging resolution and detection efficiency of scintillators limit the application of cold neutron technology in imaging. The particle size and luminescence properties of scintillator materials have an important influence on the spatial resolution and detection efficiency of cold neutron radiography. Here, we report a series of NaF-doped Gd2O2S:Tb3+ (NaF-d-GOS:Tb) scintillators with adjustable particle size, which were prepared through a two-step method of solution precipitation followed by solid-phase vulcanization calcination. It was found that the NaF-d-GOS:Tb scintillators showed the highest quantum yield, reaching up to 62.94%. They were applied to fabricating cold neutron ultrathin screens. The resolution can reach 12 mu m in the cold neutron imaging system. These NaF-d-GOS:Tb scintillators with excellent fluorescence facilitate the development of nondestructive testing techniques based on cold neutron imaging.

The use of scintillation glass fiber array in the reported cold neutron imaging detector can suppress lateral spreading of the scintillation light effectively and achieve a high spatial resolution while maintaining high detection efficiency. Theoretical analysis and experiments were combined to investigate influencing factors on the spatial resolution, the imaging contrast, the signal-to-noise ratio (SNR), and the detection efficiency with a cold neutron imaging detector made of new gadolinium scintillation glass fiber array and an infinity corrected optical readout system. The experiments were carried out on the Cold Neutron Radiography Facility at China Academy of Engineering Physics (CAEP). The cold neutron imaging detector made of 0.3-mm-thick Tb3+/Ce3+ co-doped Gd2O3 scintillation glass fiber array with a fiber diameter of 6 mm achieved a spatial resolution of 28.8 lp/mm (17.4 $\mu \text{m}$ ), an SNR of 28.6:1, and a cold neutron detection efficiency of 31.6%, i.e., a cold neutron absorption efficiency of 81.0%.

A moveable multi-use neutron imaging facility was constructed based on a compact accelerator D-T neutron source, for use in thermal and fast neutron radiography and tomography. Experiments were carried out to investigate the imaging quality for different standard samples. The smallest width of a slit that can be tested by digitized thermal neutron radiography was found to be 0.06 mm, while the smallest diameter of holes tested by digitized fast neutron radiography was 0.5 mm. A gadolinium wire of 0.2 mm in diameter within a multi-material structure was reconstructed clearly with thermal neutron tomography, and holes in a light material were reconstructed with fast neutron tomography.

The artifacts of radial edges are obvious shortcoming of external CT image. In order to suppress the artifacts of the radial edge of external CT images the weighted directional total variation (WDTV) algorithm is used to calculate the local directional differences along the radial and tangential directions, and two weighted parameters are introduced to carry out the weighted sum of these two local directional differences. The WDTV algorithm can better describe the sparsity of external CT image gradient magnitude and effectively improve the quality of reconstructed image. In order to meet the needs of high-noise neutron external CT inspection, different total variation (TV) minimization constraints are applied in certain angle ranges near the radial and tangential directions under the framework of WDTV reconstruction model. In the improved WDTV algorithm, TV minimization plays a more obvious role and has stronger performance of suppressing radial edge artifacts and anti-noise. The results of computer simulation and gear cold neutron experiment show that the improved WDTV reconstruction model can suppress the noise of reconstructed images more effectively and improve the quality of reconstructed images.

BaFBr:Eu2+ with narrow size distribution and good dispersion is fabricated via a precipitation method. After annealing, it shows excellent optical properties.

Polarimetric neutron tomography provides a powerful tool for direct visualization of magnetic fields in the bulk of matter. However, the measurable field strength has been severely restricted because neutron spin precession angles have to be limited below π due to the phase wrapping problem. In this article we show that in most cases the spin precession limit can be extended by identifying and correcting discontinuities in the sinograms. We present an improved method so that Algebraic reconstruction technique can be applied in the precession interval [π,2π] to improve the reconstruction quality. Robustness of this method against device parameters and statistical noise has been studied through numerical simulation, some unexpected influence have been found and discussed.

高能中子照相技术因其超强的样品透视能力而成为射线无损检测技术近年来研究的热点,转换屏是中子照相装置的一种关键部件.目前耦合科学级中子数字相机系统用到的高能中子照相转换屏主要有塑料闪烁体、光纤阵列、压制荧光屏和光纤转换屏等,其性能差异很大,需进行性能测试以确定不同转换屏的应用特点或场景.本文针对传统中子照相转换屏探测效率的定义问题,在物理原理基础上对其定义进行了修正,通过实验方法对各类转换屏的高能中子探测效率、空间分辨力等性能指标进行了测试.结合实验系统参数对转换屏绝对效率进行了反推计算,结果表明:压制荧光屏和光纤转换屏分别具有最高的空间分辨率和探测效率.

分析了快中子照相图像的主要噪声特点和传统NL-means滤波算法的不足,提出了一种改进的适用于快中子照相特点的Nl-means图像滤波算法.实验结果表明,改进之后的算法不仅可以有效滤除快中子照相图像中的大量白疵点,而且有效的保护了图像中的边缘与细节信息,可为快中子照相图像的进一步处理提供参考.

Limitations of fast neutron radiography include low detection efficiency and poor spatial resolution. D-T neutron radiography is one compact fast neutron radiography method. Based on D-T associated alpha particle method and coded source imaging method, we indicate one new method to improve resolution of D-T neutron radiography. This method could get distribution of D-T neutrons by detecting alpha particles. Without real coded mask, the D-T radiography structure is considered as coded source imaging of fast neutrons. With reconstruction method, the real object could be reconstructed from projections. One prospect setup of D-T associated alpha neutron source has been carried out with Monte-Carlo simulation. The projection images of two different situations are collected and reconstruction results show that it's possible to improve image quality of D-T neutron radiography.

快中子照相技术因其超强的样品透视能力而成为射线无损检测技术近年来研究的热点,转换屏是中子照相装置的关键部件.光纤转换屏是一种新型的快中子照相转换屏,较大程度兼顾了光纤阵列的高探测效率和荧光屏的高成像质量,具有很好的应用前景.本文以D-T加速器为中子源,用ZnS和环氧树脂以及光纤研制了快中子照相光纤转换屏,耦合科学级CCD数字成像系统,进行了快中子数字照相技术研究,获取了不同光纤排列方式的光纤转换屏积分曝光图像,同时测量了快中子荧光屏和塑料闪烁体等其他快中子照相用转换屏的发光效率,实验结果表明,光纤转换屏的发光效率高于其他类型转换屏的.