Characterization and Application of a Novel Neutron Detection Method to Replace Helium-3 in Advanced Neutron Detectors.

Large area neutron detectors with high efficiency, high resolution, high count-rate capability, and fast timing capabilities are required to meet the specific neutron diffraction and imaging needs of the Spallation Neutron Source (SNS) at the Oak Ridge National Laboratory. Due to the current shortage of helium-3, recently developed and existing commercial gas detectors using helium-3 as a neutron converter are not a viable option for neutron detector systems at the SNS. As a common alternative for neutron detection, boron-10 lined tubes are gaining credibility. However, for applications in neutron scattering instruments such as at the SNS (where fast timing and high resolution are important considerations), advancements in boron-10 detectors are needed. Studies have shown that gamma sensitivity of boron-10 lined detectors can be reduced significantly by reducing the diameter (or gas volume) of the detector. A small 0.5 cm3 pixel cell detector will have much less gamma sensitivity than a conventional tube detector. By lining the inside of each pixel-cell cube with boron-10, a high efficiency to neutrons can be maintained. Since each pixel-cell is an independent detection volume, the resolution is fixed (by the size of the pixel-cell) and there are no position encoding or parallax issues. Pixel-cell arrays can be combined to form large area detectors to achieve the same active areas and resolution as an array of boron-10 tube detectors without the gamma sensitivity issues or signal timing issues. Small independent cube chambers, or pixel-cells, have been successfully developed and demonstrated as excellent neutron detectors using helium-3. Within the Phase I effort, we will investigate methods of applying a boron-10 layer to the individual chamber walls of an existing pixel-cell area detector (8 cm x 8 cm). The pixel-cell detector will be lined with boron-10 and tested with thermal neutrons at the High Flux Isotope Reactor in Oak Ridge to verify the capabilities of the detector. As a result of the investigation and subsequent testing, techniques will be developed for construction and testing (in Phase II) of a large area (32 cm x 32 cm) position sensitive detector array using boron-10 lined pixel-cells.Commercial Application and Other Benefits: Substantial technical and economical benefits are anticipated from the proposed work here and in future Phase II and III projects. The cost of neutron production and beam time at neutron-scattering facilities is large compared to the cost of improving neutron detection systems. The available neutron flux and spatial resolution capabilities at these facilities could be more fully utilized by removing the limitations imposed on neutron-scattering experiments by the neutron detection systems. Advancing detector capabilities is equivalent to increasing operational efficiency and reduction of experiment beam time at these facilities, which in turn results in important savings in operation cost and increased experimental output.