IMR-MIP: High-Detection-Efficiency and High-Spatial-Resolution Thermal Neutron Imaging System for the Spallation Neutron Source using Pixelated Semiconductor Neutron Detectors

Kansas State University, Manhattan KS

Investigators

Abstract

This is award from the Instrumentation for Materials Research - Major Instrumentation Project supports the development of pixilated semiconductor neutron detector for the Spallation Neutron Source. The detector will a high-detection-efficiency and high-spatial-resolution thermal neutron imaging system. Neutron beams are a powerful probe used to elicit the structure of matter, and, for this reason, the international Spallation Neutron Source (SNS) is currently being constructed at Oak Ridge National Laboratories. To use such a source, specialized diffractometers, which sort out different neutron energies, are used. Key to the use of such instruments are neutron detectors that can measure neutrons scattered by a specimen whose structure is sought. Traditionally, large gas-filled neutron detectors located many meters from the specimen are used, the large distances necessary to provide the necessary angular resolution of the scattered neutrons. This project will lead to an array of novel semiconductor neutron detectors that can measure scattered neutrons very close to the specimen, thereby eliminating neutron interactions in the air between specimen and detector and other complications inherent in traditional measurement techniques. The proposed device is unique in that it utilizes a semiconductor wafer with a matrix of evenly spaced etched cavities (narrow holes or thin trenches) filled with the neutron reactive material The holes are etched into the front of the device such that the penetrations reach deeply (50 to 300 microns) into the semiconductor. With such cavities, together with traditional surface coatings, the semiconductor wafer is thus completely permeated with neutron reactive material. An array of semiconductor diodes will be produced with the necessary properties for use at the SNS, namely (1) a high thermal-neutron intrinsic detection efficiency that approaches 50%, (2) a spatial resolution of less than 100 microns, (3) a relatively fast response time of less than 10 microseconds, (4) is resistant to radiation damage, and (5) is insensitive to the gamma-ray background. In additiona, these devices require only small power sources to operate, are rugged and extremely reliable, and are much less costly than traditional gas-filled detectors. No such imaging array presently exists, either as a commercial or a prototype device, nor is one presently under development anywhere in the world. The goal of the present research is to manufacture prototype neutron imaging detectors using a new and novel technology that can meet the instrumentation requirements for three SNS experiments, namely the VULCAN Engineering Diffractometer, the SNAP High Pressure Diffractometer, and the Single Crystal Diffractometer (SCD). The target of the project is to build a high-resolution linear array for the VULCAN Diffractometer. The detector will have 1000 pixel strips, each 4 cm long and 100 microns wide. An Application Specific Integrated Chip (ASIC), not presently available, will also be designed and manufactured to operate the miniaturized detector array. Hence, along with the neutron detector array, an ASIC will be developed to read the neutron-induced signals from the neutron detector array. This technology can then be transferred to the SNAP and SCD diffractometers. This project will involve at least eight students in various phases of the project, including the development, measurement, fabrication, and analysis tasks. By introducing young experimentalists to this project, detector expertise will be developed within the United States. This is vital since there are very few remaining experimentalists in this area. This project will result in advanced degrees for at least five graduate students with practical experience and involvement with researchers at a national laboratory (ORNL/SNS). This is award from the Instrumentation for Materials Research - Major Instrumentation Project supports the development of pixilated semiconductor neutron detector for the Spallation Neutron Source. The detector will a high-detection-efficiency and high-spatial-resolution thermal neutron imaging system The Spallation Neutron Source (SNS), due to begin operation in the year 2007, requires a variety of neutron detectors for the beam port instruments. Several of the instruments need small, high-efficiency, high-spatial-resolution neutron imaging detectors. Those instruments include the VULCAN Engineering Diffractometer, the SNAP High Pressure Diffractometer, and the Single Crystal Diffractometer (SCD). The neutron imaging devices must be insensitive to gamma rays while retaining high thermal-neutron intrinsic detection efficiency that approaches 50%. The spatial resolutions must be at least 500 microns for the SNAP and SCD Diffractometers, and 100 microns for the VULCAN Diffractometer. A last requirement is that the neutron-imaging detector must have a relatively fast response time less than 10 microseconds. No such instrument presently exists, either as a commercial or a prototype device, and is not presently under development anywhere in the world. It is the goal of the present research effort to manufacture prototype neutron imaging detectors using an new and novel technology that can meet the instrumentation requirements at the SNS for the VULCAN, SNAP, and SCD Diffractometers. The new devices operate at room temperature, are compact, rugged, and reliable in design. Monte Carlo modeling coupled with the MCNP codes will be used to guide the development and fabrication of optimized device designs. Preliminary results indicate that the 50% detection efficiency target is achievable. The target of the proposed effort is to build a high-resolution linear array for the VULCAN Diffractometer. The detector will have 1000 pixel strips, each 4 cm long and 100 microns wide. An Application Specific Integrated Chip (ASIC), not presently available, will be designed and manufactured to operate the miniaturized detector array. Hence, along with the neutron detector array, an ASIC will be developed to read the neutron-induced signals from the neutron detector array. The technology developed can be transferred to the SNAP and SCD Diffractometers for the spatial arrays. This project will involve at least eight students in various phases of the project, including the development, measurement, fabrication, and analysis tasks. By introducing young experimentalists to the project through key involvement in tasks, expertise is developed within the United States. This is vital since there are very few remaining experimentalists in this area. This project will result in advanced degrees for at least five graduate students with practical experience and involvement with researchers at a national laboratory (ORNL/SNS).