Microstructured Semiconductor Neutron Detector Arrays for Neutron Scattering Measurements

The objective of this project is to design and build a high-efficiency neutron detector array consisting of 3000 pixels, with each pixel being 100 microns wide and 4 cm tall, all based on the microstructured semiconductor neutron detector (MSND) technology. The MSND technology resulted in over 40 publications, three allowed patents, one patent pending, and recently received an R & amp;D 100 award in 2009. The Spallation Neutron Source (SNS) requires a variety of neutron detectors for their beam port instruments. Three specific instruments need high spatial resolution thermal-neutron detector arrays that are presently not commercially available. The VULCAN Engineering Diffractometer, the TOPAZ crystal diffractometer, and the liquid reflectometer all need thermal-neutron detecting arrays capable of 100 micron spatial resolutions. Furthermore, the devices must be insensitive to gamma rays while retaining high thermal-neutron intrinsic detection efficiency, preferably above 30%. A last requirement is that the neutron-imaging detectors must have a relatively fast response-time, namely, less than 10 microseconds. The microstructured neutron detector technology developed in a previous NSF CED phase of the IMR-MIP program can fulfill the stringent requirements laid forth by instrument scientists at the SNS. Compact neutron detectors with high counting efficiency and low voltage operation were fabricated by etching micro-cavity patterns into a semiconductor diode. These microscopic patterns were backfilled with 6LiF, a neutron conversion material. Neutron interactions in the 6LiF converter cause the spontaneous emission of energetic charged particles which are subsequently detected in the adjacent semiconductor diode walls. The deep trenches backfilled with neutron reactive material increases the neutron absorption efficiency, and for devices with narrow trenches, the probability of registering the energetic reaction products is dramatically increased. These detectors were fashioned into prototype linear arrays. Further, special readout ASICs were designed and built, along with the supporting electronics, to couple this small array to the existing infrastructure at the SNS. In the present SBIR/STTR phase I proposal, a 64-channel unit of a full high-resolution, high-efficiency 3000-pixel linear neutron detector array will be constructed. The long term phase II goal will be a 3000 pixel array. Each pixel will have 100 micron spatial resolution and approximately 30% intrinsic thermal-neutron detection efficiency. Further, the new design has no dead space or neutron streaming paths, hence preventing loss of data at locations between pixels. The proposed project is aggressive and will push the state-of-the-art for neutron scatter imaging to new levels. Successful completion of this project will produce the highest spatial resolution linear array to date. Further, the new technology will deliver compact, high-efficiency, thermal- neutron detectors capable of real-time neutron measurements; such devices currently do not exist. Dr. Steven Bellinger, has 7 years of experience with the design and fabrication of microstructured semiconductor neutron detectors, and presently holds the record for intrinsic thermal neutron detection efficiency at 42%. Timothy Sobering, who will be consulted to design the improved readout electronics, has over 25 years of experience producing electronics for detector data acquisition and designed the prototype electronics for the first MSND neutron scattering detector.