WCOE RESEARCHERS FIND ALTERNATIVE FOR NUCLEAR WEAPON DETECTION
Adopted from AIP Media Line: https://publishing.aip.org/publishing/journal-highlights/hexagonal-boron-nitride-semiconductors-enable-cost-effective-detection
HEXAGONAL BORON NITRIDE SEMICONDUCTORS ENABLE COST-EFFECTIVE DETECTION OF NEUTRON
SIGNALS
Texas Tech University researchers demonstrate hexagonal boron nitride semiconductors
as a cost-effective alternative for inspecting overseas cargo containers entering
U.S. ports.
AIP News Release — WASHINGTON, D.C., August 16, 2016 -- One of the most critical issues the United
States faces today is preventing terrorists from smuggling nuclear weapons into its
ports. To this end, the U.S. Security and Accountability for Every Port Act mandates
that all overseas cargo containers be scanned for possible nuclear materials or weapons.
Detecting neutron signals is an effective method to identify nuclear weapons and special
nuclear materials. Helium-3 gas is used within detectors deployed in ports for this
purpose.
The catch? While helium-3 gas works well for neutron detection, it's extremely rare
on Earth. Intense demand for helium-3 gas detectors has nearly depleted the supply,
most of which was generated during the period of nuclear weapons production during
the past 50 years. It isn't easy to reproduce, and the scarcity of helium-3 gas has
caused its cost to skyrocket recently -- making it impossible to deploy enough neutron
detectors to fulfill the requirement to scan all incoming overseas cargo containers.
Helium-4 is a more abundant form of helium gas, which is much less expensive, but
can't be used for neutron detection because it doesn't interact with neutrons.
A group of Texas Tech University researchers led by Professors Hongxing Jiang and
Jingyu Lin report this week in Applied Physics Letters, from AIP Publishing, that
they have developed an alternative material -- hexagonal boron nitride semiconductors
-- 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's concept was first proposed 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-micron-thick hexagonal boron-10 enriched nitride layer, the group created
a thermal neutron detector with 51.4 percent detection efficiency, which 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.
"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."
The key significance of the group's work? This is a completely new material and technology
that offers many advantages.
"Compared to helium gas detectors, boron nitride technology improves the performance
of neutron detectors in terms of efficiency, sensitivity, ruggedness, versatile form
factor, compactness, lightweight, no pressurization ... and it's inexpensive," Jiang
said.
This means that the material has the potential to revolutionize neutron detector technologies.
"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 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.
"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.
One of the most important impacts of the group's work is that "this new material and
its potential should begin to be recognized by the semiconductor materials and radiation
detection communities," Jiang added.
Now that the group has solved the problem of producing hexagonal boron nitride with
sufficient thickness, as well as crystalline quality to enable the demonstration of
neutron detectors with high efficiency, the 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 article, "Realization of highly efficient hexagonal boron nitride neutron detectors," is authored by A. Maity, T.C. Doan, J. Li, J.Y. Lin and H.X. Jiang. http://scitation.aip.org/content/aip/journal/apl/109/7/10.1063/1.4960522
ABOUT THE JOURNAL
Applied Physics Letters features concise, rapid reports on significant new findings
in applied physics. The journal covers new experimental and theoretical research on
applications of physics phenomena related to all branches of science, engineering,
and modern technology. See http://apl.aip.org
Hongxing Jiang, Ph.D.
Horn Professor and Edward E. Whitacre Jr. Chair in Electrical and Computer Engineering
Jingyu Lin, Ph.D.
Horn Professor and Linda F. Whitacre Chair in Electrical and Computer Engineering
Edward E. Whitacre Jr. College of Engineering
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