X-DSMSND: A Neutron Camera with Integrated Pixel Read-Out

There is a need for compact, high-efficiency, and high spacial-resolution neutron scattering imagers. Improvements in neutron detectors for use at high-flux pulsed neutron sources are required for materials research involving neutron scattering experiments conducted at Department of Energy (DOE) laboratories, including single crystal diffractometers, neutron reflectometers, and time of flight (TOF) measurements. Generally, requirements for neutron detectors used in these facilities include spatial resolution on the order of 100 µm or less, neutron-detection efficiency exceeding 60% for 1-2 Å wavelength neutrons, ability to operate at rates exceeding 20 MHz with minimal dead-time, and gamma-ray rejection ratios of less than 1:106. Advances in sensor design, read-out technology, and data processing algorithms are required to meet these challenging requirements. These requirements will be met by integrating a piXelated Dual-Sided Microstructured Semiconductor Neutron Detector (DSMSND) with the Timepix3 read-out chip to create a detection assembly (the X-DSMSND) and software, capable of tiling into large imaging arrays. The objective of this project is to design, develop, fabricate, and test a neutron detector with very-high thermal-neutron detection efficiency and excellent spatial resolution, capable of operating in intense neutron fields. Previous researchers have shown that Timepix-based neutron detection is capable of sub-100 µm resolution via pixel interpolation. In the Phase I project, the DSMSND, which has demonstrated thermal-neutron detection efficiencies in excess of 69%, was redesigned to couple to the pixelated TimePix3 ASIC. The DSMSND presently consists of a conformal p-i-p junction read out with complicated bipolar electronics; for compatibility with a single pixel read-out chip, the revised pixelated DSMSND consists of a non-conformal p-i-n junction contact. Next, the frame-based Timepix read-out chip was replaced with the Timepix3, which offers a data- driven read-out for a maximum hit-rate of 80 MHz and provides both pixel-wise time-over-threshold (useful for direct imaging) and time-of-arrival (useful for TOF measurements) simultaneously, with the same spatial resolution as the Timepix, which is a 2-cm2 array of pixels with 55 µm pitch. Finally, simulations and models were revised and updated to accommodate the DSMSND geometry, sensor signal- formation characteristics, and demonstrate gamma-ray rejection-ratios on simulated data using energy and cluster-morphology discrimination. The product of Phase I is a prototype single-assembly detector with laboratory read-out electronics and software. In Phase II the team will focus on refinement of the X-DSMSND sensor design, perform pixel-wise energy calibration, demonstrate 2 x 2 tiling capability, develop more condensed readout, and mature associated software. Furthermore, the X-DSMSND hardware and software performance will be tested at the KSU TRIGA Mark II Nuclear Reactor Facility, and facilities such as the Los Alamos National Laboratory Neutron Science Center and the Spallation Neutron Source at Oak Ridge National Laboratory. The novel solid-state neutron detector array design will benefit a wide spectrum of applications beyond those of neutron scattering instruments. The scientific and commercial impact from the proposed research is expected to be significant, where the technology can meet the imaging demands of new generations of neutron scattering instruments. The neutron-imaging device has direct applications in many areas of science and engineering, such as high-resolution neutron radiography/tomography, neutron diffraction studies for stress/strain measurements in materials with internal defects, and surface diffraction studies of coatings.