Resolution analysis of thermal neutron radiography based on accelerator-driven compact neutron source

Owing to the immobility of traditional reactors and spallation neutron sources,the demand for compact thermal neutron radiography(CTNR)based on accelerator neutron sources has rapidly increased in industrial applications.Recently,thermal neutron radiography experiments based on a D-T neutron generator performed by Hefei Institutes of Physical Science indicated a significant resolution deviation between the experimental results and the values calculated using the traditional resolution model.The experimental result was up to 23%lower than the calculated result,which hinders the achievement of the design goal of a compact neutron radiography system.A GEANT4 Monte Carlo code was developed to simulate the CTNR process,aiming to identify the key factors leading to resolution deviation.The effects of a low collimation ratio and high-energy neutrons were analyzed based on the neutron beam environment of the CTNR system.The results showed that the deviation was primarily caused by geometric distortion at low collimation ratios and radiation noise induced by highenergy neutrons.Additionally,the theoretical model was modified by considering the imaging position and radiation noise factors.The modified theoretical model was in good agreement with the experimental results,and the maximum deviation was reduced to 4.22%.This can be useful for the high-precision design of CTNR systems.

Thin-film approximate point scattered function and its application to neutron radiography

A simpler and improved utility approximate point scattered function for thin-film converters currently used in neutron photographic devices is proposed as a correction method to produce clearer,more realistic images.The validity of the model was demonstrated through a simulation experiment.Based on the results,an error analysis was carried out,certain corrections were made to the original model,and the final model achieved a very low relative error in the simulation experiment.The model can also be optimized for quantitative neutron photographic analysis using iterative algorithms to obtain realistic neutron photographic images more quickly.At the end of the article,the model is extended to consider the case of energy spectrum hardening by introducing a temperature correction parameter.

The review and prospect of neutron radiography in China

Neutron radiography is one of radiography non-destructive testing.It is a valuable complementary of X and γ rays radiography.The present status and history of neutron radiography in China was described briefly,facilities of neutron radiography and their development were introduced in this paper.

Neutron Radiography System Collimator Design via Monte Carlo Calculation

Neutron radiography uses the unique interaction probabilities of neutrons to create images of materials. This imaging technique is non-destructive. MCNP Monte Carlo Code has been used to design an optimized neutron radiography system that utilizes 241Am-Be neutron source. Many different arrangements have been simulated to obtain a neutron flux with higher amplitude and more uniform distribution in the collimator outlet, next to image plane. In the final arrangement the specifications of neutron filter, Gamma-ray shield and beam collimator has been determined. Simulations has been carried out for a 5Ci 241Am-Be neutron source. In this case 43.8 n/cm2s thermal neutron flux has been achieved at a distance of 35 cm from neutron source.

Corrections on energy spectrum and scatterings for fast neutron radiography at NECTAR facility

Distortions caused by the neutron spectrum and scattered neutrons are major problems in fast neutron radiography and should be considered for improving the image quality. This paper puts emphasis on the removal of these image distortions and deviations for fast neutron radiography performed at the NECTAR facility of the research reactor FRM-II in Technische Universit/it Mfinchen （TUM）, Germany. The NECTAR energy spectrum is analyzed and established to modify the influence caused by the neutron spectrum, and the Point Scattered Function （PSeF） simulated by the Monte-Carlo program MCNPX is used to evaluate scattering effects from the object and improve image quality. Good analysis results prove the sound effects of the above two corrections.

Numerical study of point spread function of a fast neutron radiography system based on scintillating-fiber array

For a scintillating-fiber array fast-neutron radiography system,a point-spread-function computing model was introduced,and the simulation code was developed. The results of calculation show that fast-neutron radiographs vary with the size of fast neutron sources,the size of fiber cross-section and the imaging geometry. The results suggest that the following qualifications are helpful for a good point spread function: The cross-section of scintillating fibers not greater than 200 μm×200 μm,the size of neutron source as small as a few millimeters,the distance between the source and the scintillating fiber array greater than 1 m,and inspected samples placed as close as possible to the array. The results give suggestions not only to experiment considerations but also to the estimation of spatial resolution for a specific system.

An empirical formula for scattered neutron components in fast neutron radiography

Scattering neutrons are one of the key factors that may affect the images of fast neutron radiography. In this paper, a mathematical model for scattered neutrons is developed on a cylinder sample, and an empirical formula for scattered neutrons is obtained. According to the results given by Monte Carlo methods, the parameters in the empirical formula are obtained with curve fitting, which confirms the logicality of the empirical formula. The curve-fitted parameters of common materials such as 6 LiD are given.

STUDY ON MODERATORS OF SMALL－SIZE NEUTRON RADIOGRAPHY INSTALLATIONS WITH NEUTRON TUBE AS SOURCE

Calculation of moderator analogues for 14 MeV neutrons as source were made at a IBM/PC AT computer using TAMAKER-ANISN program and 46 groups (25 neutron groups, 21 photon groups) UW cross section data. The intensifying effect of lead and natural uranium for moderating 14 MeV neutrons is confirmed. Adopting proper structure of the moderator, the intensifying factor M (times) may be larger than 3. Using lead and natural uranium in sub-critical assemblies (or call boosters),with 14 MeV neutrons as source, with the same dimension as that of above, the intensifying effect is also condrmed. With a proper structure of sub-critical assembly,the intensifying factor M may be close to or eved larger than (1 - k)-1 where k isthe effective multiplication factor.

Neutron collimator design of neutron radiography based on the BNCT facility

For the research of CCD neutron radiography, a neutron collimator was designed based on the exit of thermal neutron of the Boron Neutron Capture Therapy（BNCT） reactor. Based on the Geant4 simulations, the preliminary choice of the size of the collimator was determined. The materials were selected according to the literature data. Then, a collimator was constructed and tested on site. The results of experiment and simulation show that the thermal neutron flux at the end of the neutron collimator is greater than 1.0×10^6n/cm^2/s, the maximum collimation ratio（L/D） is 58, the Cd-ratio（Mn） is 160 and the diameter of collimator end is 10 cm. This neutron collimator is considered to be applicable for neutron radiography.

Neutron Radiography of Space Pyrotechnics

The research work, facilities, and results of NDT testing of space pyrotechnics in China using Neutron Radiography (NR) at the Tsinghua University swimming-pool reactor are introduced in this paper. The image quality (NR) approached the standard of ASTM E 545-86 level I. NR experimental research of typical and possible defects was performed along with a theoretical analysis. The feasibility of using NR NDT (non-destructive testing) for space pyrotechnics was proven experimentally. Space detonating cord is tested with Neutron Radiography. The detonating cord with artificial explosive charge defects as a reference is put into every neutron radiography film. Slagging of the lead cladding and explosive charge inhomogeneity are discovered.

Multi-distortion suppression for neutron radiographic images based on generative adversarial network

Neutron radiography is a crucial nondestructive testing technology widely used in the aerospace,military,and nuclear industries.However,because of the physical limitations of neutron sources and collimators,the resulting neutron radiographic images inevitably exhibit multiple distortions,including noise,geometric unsharpness,and white spots.Furthermore,these distortions are particularly significant in compact neutron radiography systems with low neutron fluxes.Therefore,in this study,we devised a multi-distortion suppression network that employs a modified generative adversarial network to improve the quality of degraded neutron radiographic images.Real neutron radiographic image datasets with various types and levels of distortion were built for the first time as multi-distortion suppression datasets.Thereafter,the coordinate attention mechanism was incorporated into the backbone network to augment the capability of the proposed network to learn the abstract relationship between ideally clear and degraded images.Extensive experiments were performed;the results show that the proposed method can effectively suppress multiple distortions in real neutron radiographic images and achieve state-of-theart perceptual visual quality,thus demonstrating its application potential in neutron radiography.

Neutron imaging at Peking University

Neutron imaging techniques were investigated at Peking University based on a 4.5 MV Van de Graaff accelerator.The thermal neutron radiography,fast neutron radiography and fast neutron resonance radiography were tested.The low neutron flux limits the image quality.A new radio frequency quadrupole (RFQ) accelerator based on neutron source with a yield of 1 012 n/s is being set up.

Detector development at the Back-n white neutron source

Purpose Back-n is a white neutron beamline at China spallation neutron source,which was established in the year of 2018.It is a powerful facility for nuclear data measurement,neutron detector calibration,and radiation effect research.Method A series of detectors were built for different experiments,including beam monitoring,beam profile measurement,neutron induced secondaries(fission fragments,light charged particles and gamma)cross section measurement,and neutron resonance radiography,etc.A common digitization electronics and a cluster-based DAQ were developed for these detector systems.Most detectors have been employed at Back-n and serviced for experiments from the beginning of the beamline running.Results and conclusion As an overview of detectors of Back-n,the details of the detector design and the experiment performing are described in this paper.Some developing systems,e.g.,MTPC and B-MCP,are also included.