In this work, Neutron Depth Profiling (NDP) analysis capability has been added to the Oregon State University TRIGA® Reactor Prompt Gamma Neutron Activation Analysis Facility (PGNAA). This system has been implemented with an advanced digital spectroscopy system and is capable of rise time pulse shape analysis as well as coincidence measurements from multiple detectors. The digital spectroscopy system utilizes a high-speed multichannel digitizer with speeds up to 200 Megasamples/second (MS/s) with advanced hardware trigger and time stamping capabilities. These additions allow the facility to conduct simultaneous NDP and PGNAA combined measurements, which also enables cross calibration. The digital pulse processing is implemented with software programmed rise time pulse shape analysis capabilities for the analysis of the detector responses on a pulse-by-pulse basis to distinguish between different interactions in the detector. The advanced trigger capabilities of the digitizer were configured to accurately measure and correct for dead time effects from pulse pile up and preamplifier decay time.

Abstract: Neutron Depth Profiling (NDP) is a nondestructive analytical technique used to characterize the concentration of certain light isotopes in a material as a function of depth. The technique is based on the principle of measuring the residual energy of charged particles in neutron induced reactions. Historically, NDP has been performed using a single detector, resulting in low intrinsic detection efficiency, and limiting the technique largely to high flux research reactors. This work describes a new NDP instrument design with higher detection efficiency, achieved by summing the spectrum obtained from multiple detectors. A digital data acquisition system was chosen over the typical analog system for this instrument, as it allowed for an economical implementation of multiple detectors and a streamlined process for spectrum summing. This design is capable of acquiring a statistically significant charged particle spectrum at facilities limited in neutron flux and operation time. The spectrum obtained from a sample of Borophosphosilicate (BPSG) with this multidetector instrument was compared to the analysis performed on the same sample at the National Institute of Standards and Technology (NIST), using a benchmarked, single detector NDP instrument. Results of the analysis indicate the resolution of the multidetector instrument suffers slightly due to gamma contamination in the beam, but is capable of achieving nearly half the count rate of the NIST instrument. A model of the instrument investigating BPSG was constructed using the GEANT4 toolkit, and used to compare against the experimental results. A section of 6Li enriched scintillation screen was also analyzed using the multidetector instrument. This analysis gave insight into the concentration profile of this particular neutron converter, something that had previously been unknown.

Excerpt from Neutron Depth Profiling: Overview and Description of Nist Facilities The charged particle energy spectrum is collected using a transmission - type silicon surface barrier detector, electronic amplifiers, an analog to-digital converter and a multichannel analyzer (see Fig. For the ndp system at nist, a refer ence pulse is also fed into the electronics to moni tor the stability of the system thus allowing corrections to be made should electronic drift oc cur during the course of the measurement. Other ndp systems are described more specifically in the references By using a computer based data acquisition system, the depth profile can be displayed in real time. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.

Semiconductor neutron detector design, fabrication and testing are all performed at Kansas State University (KSU). The most prevalent neutron detectors built by the KSU Semiconductor Materials And Radiological Technologies Laboratory (SMART Lab) are comprised of silicon diodes with [superscript]6LiF as a neutron converter material. Neutron response testing and calibration of the detectors is performed in a neutron detector test facility. The facility utilizes diffraction with a pyrolytic graphite (PG) monochromator to produce a diffracted neutron beam at the northwest beamport of the KSU Training Research Isotope production General Atomics (TRIGA) Mark-II nuclear reactor. A 2-D neutron beam monitor can also be used in conjunction with the test facility for active calibrations. Described in the following work are the design, construction and operation of a neutron detector test facility and a 2-D neutron detection array. The diffracted neutron beam at the detector test facility has been characterized to yield a neutron beam with an average Gaussian energy of 0.0253 eV. The diffracted beam yields a flux of 1.2x10[superscript]4 neutrons/cm[superscript]2/s at 100 kW of reactor power. The PG monochromator is diffracting on the (002) plane that has been positioned at a Bragg angle of 15.5 degrees. The 2-D neutron detection array has been characterized for uniform pixel response and uniform neutron detection efficiency. The 2-D 5x5 array of neutron detectors with a neutron detection efficiency of approximately 0.5 percent has been used as a beam monitor when performing detector testing. The amplifier circuits for the 5x5 array were designed at the KSU Electronics Design Lab (EDL) and were coupled to a LabVIEW field-programmable gate array that is read out by a custom LabVIEW virtual instrument. The virtual instrument has been calibrated to produce a pixel response that varies by less than two percent from pixel to pixel. The array has been used for imaging and active monitoring of the diffracted neutron beam at the detector test facility. The following work is part of on-going research to develop various types of solid state semiconductor neutron detectors.