Texas Tech University researchers have devised a new way to help prevent the smuggling of nuclear weapons by developing a material—hexagonal boron nitride semiconductors—to detect the neutron signals that identify the presence of substances used in the manufacture of nuclear devices.

The U.S. Security and Accountability for Every Port Act mandates that all overseas cargo containers be scanned for possible nuclear materials or weapons. Helium-3 gas is currently used within detectors deployed in ports for this purpose.

However, while helium-3 gas works well for neutron detection, it is extremely rare. Demand for helium-3 gas detectors has nearly depleted the supply, most of which was generated during the period of intensive nuclear weapons production in the second half of the 20th century.

Texas Tech professors Hongxing Jiang and Jingyu Lin report that their development of hexagonal boron nitride semiconductors for neutron detection fulfills many key requirements for helium gas detector replacements—and can serve as a low-cost alternative in the future.

U.S. federal regulations require that all foreign cargo containers be scanned for nuclear materials or weapons. Image credit: Pixabay.By using a 43-micron-thick hexagonal boron-10-enriched nitride layer, the group created a thermal neutron detector with 51.4% detection efficiency—a record high for semiconductor thermal neutron detectors. They anticipate the potential for developing even higher detection efficiency by increasing the material thickness and improving material quality.

“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,” says Jiang. “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 says the boron nitride technology improves the performance of neutron detectors in terms of their efficiency, sensitivity, ruggedness, compactness, weight and expense.

The main innovation behind this new type of neutron detector was developing hexagonal boron nitride with epitaxial layers of sufficient thickness—which previously didn’t exist.

Now that the group has solved the problem of producing hexagonal boron nitride with sufficient thickness and crystalline quality to enable the demonstration of neutron detectors with high efficiency, the next step is to develop high sensitivity in large-size detectors.