Helium-3 is typically used in neutron detectors deployed at shipping ports to look for nuclear materials in cargo containers, in compliance with the U.S. Security and Accountability for Every Port Act. Unfortunately, helium-3 is rare and expensive.
Now, however, a group of Texas Tech University researchers led by Professors Hongxing Jiang and Jingyu Lin have developed an alternative material—hexagonal boron nitride semiconductor—for neutron detection. This material fulfills many key requirements for helium gas detector replacements and can serve as a low-cost alternative in the future.
The group proposed its concept to the Department of Homeland Security’s Domestic Nuclear Detection Office and received funding from its Academic Research Initiative program six years ago.
By using a 43-μm-thick hexagonal boron-10 enriched nitride layer, the group created a thermal neutron detector with 51.4% detection efficiency, which the researchers report is a record high for semiconductor thermal neutron detectors.
“Higher detection efficiency is anticipated by further increasing the material thickness and improving materials quality,” explained Professor Jiang, Nanophotonics Center and Electrical & Computer Engineering, Whitacre College of Engineering, Texas Tech University, as reported at Newswise.
“Our approach of using hexagonal boron nitride semiconductors for neutron detection centers on the fact that its boron-10 isotope has a very large interaction probability with thermal neutrons,” Jiang continued. “This makes it possible to create high-efficiency neutron detectors with relatively thin hexagonal boron nitride layers. And the very large energy bandgap of this semiconductor—6.5 eV— gives these detectors inherently low leakage current densities.”
Jiang added that compared with helium gas detectors, boron nitride technology improves the performance of neutron detectors in terms of efficiency, sensitivity, ruggedness, versatility, size, weight, can cost.
“Beyond special nuclear materials and weapons detection, solid-state neutron detectors also have medical, health, military, environment, and industrial applications,” he added. “The material also has applications in deep ultraviolet photonics and two-dimensional heterostructures. With the successful demonstration of high-efficiency neutron detectors, we expect it to perform well for other future applications.”
The team faced challenges developing hexagonal boron nitride with epitaxial layers of sufficient thickness. “It took our group six years to find ways to produce this new material with a sufficient thickness and crystalline quality for neutron detection,” Jiang noted.
Based on their experience working with III-nitride wide-bandgap semiconductors, the group knew at the outset that producing a material with high crystalline quality would be difficult.
“It’s surprising to us that the detector performs so well, despite the fact that there’s still a little room for improvement in terms of material quality,” he said.
The group’s next step is to demonstrate high-sensitivity of large-size detectors.
“These devices must be capable of detecting nuclear weapons from distances tens of meters away, which requires large-size detectors,” Jiang added. “There are technical challenges to overcome, but we’re working toward this goal.”
The group reported its work this week in a paper titled “Realization of highly efficient hexagonal boron nitride neutron detectors” published in Applied Physics Letters, from AIP Publishing.
