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Neutron imaging is a pivotal non-destructive testing technique for scientific and industrial fields. This report summarizes the progress of neutron imaging detector research in China Spallation Neutron Source (CSNS), focusing on four major directions: high spatial resolution, energy- resolved, large field of view (FOV), and compact imaging detectors.
To meet the demand for micron-scale resolution, a high spatial resolution detector was developed. It utilized a custom-made, ultra-thin (5 μm) scintillator screen based on isotopically enriched ¹⁵⁷Gd₂O₂S:Tb (GOS), coupled with a high-magnification lens and a scientific CCD camera. This system achieved a remarkable spatial resolution of 6.6 μm at the Energy-Resolved Neutron Imaging Instrument (ERNI) of CSNS. The detector represents a significant leap in imaging capability at CSNS, enabling advanced non-destructive investigations at the micron-scale. In parallel, to enhance GOS scintillator performance of the light output and intrinsic spatial resolution, GOS transparent ceramics and hexagonal boron nitride (hBN) scintillator were developed. A 50 μm thick GOS ceramic achieved a resolution of 12 μm and the thinnest thickness reached 20 μm with a spatial resolution better than 15 μm. The poorer spatial resolution of the thinner scintillator is mainly due to the quality of the scintillator and further improvements are expected from the optimization of the GOS manufacturing process. The hBN scintillator with a thickness of 20 μm has achieved a spatial resolution of 25 μm, and higher spatial resolution will be achieved as the transparency of the scintillator is further enhanced.
Energy-resolved imaging, crucial for analyzing material morphology, residual stress, and texture, is efficiently realized on pulsed sources via the time-of-flight (TOF) method, necessitating detectors with high temporal resolution. We adopted a new detector scheme, which achieved energy-resolved neutron imaging by introducing a high-time-resolution camera and coupling it with a scintillator. Based on this design, an energy-resolved detector was developed by utilizing the TPX3Cam camera，which utilizes the Timepix3 chip to enable single-photon detection and nanosecond-scale time-stamping. This detector achieved a spatial resolution of ~20 μm and a neutron wavelength resolution better than 0.16% with a maximum FOV of 100×100 mm². To overcome the limitations of Timepix3, a next generation detector was built using the independently developed high speed time-resolved camera based on the Timepix4 chip, which offers superior time resolution (200 ps), a larger sensor (512×448 pixels, ~6.94 cm² imaging area), and a faster readout speed (163.8 Gbps) with a maximum count rate of 2.5 Ghits/s. Preliminary tests show a spatial resolution of 25 μm and a wavelength resolution of 0.43%. Furthermore, a large-area Gas Electron Multiplier (GEM) detector with a 200×200 mm² effective area was developed for large sample energy-resolved imaging, achieving a spatial resolution of 1.80 mm and a wavelength resolution of 0.3%.
For large samples such as aircraft engine blades and batteries, a large field neutron imaging detector was developed by coupling a large-area ⁶LiF/ZnS scintillator with a large-format CCD camera. Using a 2048×2048 pixels camera (15 μm pixel size), an imaging FOV of 210×220 mm² with a resolution better than 120 μm was achieved. Employing a larger camera with 4096×4096 pixels improved the resolution to 75 μm while maintaining the same FOV. Additionally, to support the rapid diagnosis of the neutron beam and the samples, a compact imaging detector was developed with a FOV of 100×100 mm² and a resolution of 122 μm.
These detectors have been successfully deployed at ERNI and Engineering Materials Diffractometer (EMD) of CSNS. By advancing detector capabilities across spatial, temporal, and field-of-view dimensions, our work provides comprehensive imaging tools for materials science and industrial applications and has supported numerous user experiments. In the future, we will focus on pushing the spatial resolution of micro-scale imaging detectors to further limits by fabricating higher-quality scintillators, and developing large area, high spatial resolution, high energy-resolved imaging detectors based on Timepix4.