A novel neutron imaging material

Neutron radiography, as a unique nondestructive testing technology, has irreplaceable value in fields such as materials science, advanced manufacturing, nuclear science, and biomedicine due to its high sensitivity to light elements and strong penetration capability through heavy metals. One of the core components of this technology lies in the neutron imaging material that can convert neutron signals into visible light. Currently, neutron imaging predominantly relies on ⁶LiF/ZnS composite materials. Their function is based on blending the non-luminescent neutron converter ⁶LiF (the thermal neutron capture cross-section of ⁶Li is 973 barns) with the phosphor ZnS. However, this material suffers from several drawbacks, including low detection efficiency, poor spatial resolution, and long decay times.

The isotope ¹⁰B stands out as a promising neutron conversion nuclide due to its high thermal neutron capture cross-section (3840 barns), excellent chemical stability, and low cost. Nevertheless, boron compounds inherently lack efficient luminescent capabilities and still depend on combination with external phosphors for functionality. Therefore, a key scientific challenge lies in overcoming the limitations of traditional composite structures by developing a pure boron compound imaging material that integrates both high neutron capture efficiency and high intrinsic luminescence efficiency.

Recently, the research team led by Wei Zheng from Sun Yat-sen University, in collaboration with the team of Jianrong Zhou from the China Spallation Neutron Source, has reported a novel pure boron compound neutron imaging material—nano-polycrystalline hexagonal boron nitride (NPhBN)—in the journal PhotoniX.

Zheng's team employed a high-temperature rapid chemical vapor deposition technique to fabricate large-area (8 inch) and uniform hexagonal boron nitride film with a nano-polycrystalline structure. This structure confines charge carriers at the nanoscale, significantly enhancing the defect luminescence efficiency, and achieving a photoluminescence quantum yield of 42.5% for the material. Therefore, this work achieves the functional integration of neutron capture and luminescence within a single boron compound. Zhou's team systematically evaluated the neutron response time, spatial resolution, and imaging quality of NPhBN. Concurrently, the teams led by Linfeng He from the China Institute of Atomic Energy and Jie Chen from the China Spallation Neutron Source provided important support for the relevant tests. NPhBN exhibits an ultrafast neutron response time of 14.6 ns and a high spatial resolution of 30 μm. The neutron radiography system built with this material successfully achieved high-contrast imaging on the complex cooling channels inside a turbine blade of an aircraft engine, as well as the distribution of organic matter within a copper-shell lighter.

This work not only overcomes the inherent limitations of the conventional ⁶LiF/ZnS approach from both principle and material perspectives, but also comprehensively demonstrates an innovative pathway covering material design, fabrication, and system integration. It provides a key material and a feasible solution for developing next-generation high-performance neutron imaging technology.