Pillar-Structured Thermal Neutron Detector

One of the most important dimensions of protecting the borders of our country is new systems for detecting illicit special nuclear materials. Our team of LLNL researchers from the Center for Micro- and Nano-Technologies (CMNT) are applying microfabrication techniques to develop next-generation devices for detecting radiation.

Because special nuclear materials emit gamma rays and neutrons, it is possible to identify them from their radiation signatures. In the field, detectors must be inexpensive and robust, operate at ambient temperature, provide high efficiency, and potentially be suitable for covert operations. Current detector technology is limited in its ability to meet these requirements. For example, high-performance gamma-ray detectors operate only at the temperature of liquid nitrogen, which significantly limits their deployability.

Our team is demonstrating that microscale materials can be fabricated to produce a high-efficiency thermal neutron detector. Our device, called the Pillar Detector, promises to achieve height efficiency without the deployability issues associated with conventional 3He tube detectors. The Pillar Detector relies on a carefully constructed platform of etched silicon pillars that are interspersed with 10B. Incoming neutrons strike the boron nuclei, yielding reaction alpha and lithium particles that interact with the semiconductor to induce a measurable electrical current. The pillar etching depth can be adjusted to provide a thicker boron layer for high-neutron capture. The spacing between the pillars can also be optimized so that the reaction particles don't have to travel far, yielding a high efficiency. Currently, the device yields an efficiency of >40% and can be scaled to >50% by increasing the height of the pillars. The LLNL team is collaborating with Professor Barry Cheung from the University of Nebraska at Lincoln, who is assisting by depositing the boron layers between the silicon pillars.

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1. Applied Physics Letters, 93 (13), 133502, Sept. 2008.
2. R. J. Nikolić et al, Invited, Si Pillar Structured Thermal Neutron Detectors: Fabrication Challenges and Performance Expectations, SPIE Security and Defense Conference, Orlando, FL, Apr 25–29, 2011.
3. R. J. Nikolić, A. M. Conway, R. Radev, Q. Shao, L. F. Voss, T. F. Wang, et al., Invited, "Nine Element Si-based Pillar Structured Thermal Neutron Detector," Proceedings of the SPIE—The International Society for Optical Engineering, 7805, 78050O (9 pp.), San Diego, CA, US, Aug. 1–5, 2010.