Timothy J. Sobering

Improved High Efficiency Stacked Microstructured Neutron Detectors Backfilled With Nanoparticle

Silicon diodes with large aspect ratio trenched microstructures, backfilled with 6LiF, show a dramatic increase in thermal neutron detection efficiency beyond that of conventional thin-film coated planar devices. Described in this work are advancements in the technology using detector stacking methods to increase thermal neutron detection efficiency, along with the current process to backfill 6LiF into the silicon microstructures. The highest detection efficiency realized thus far is over 42% intrinsic thermal neutron detection efficiency by device-stacking methods. The detectors operate as conformally diffused pn junction diodes each having 1 cm2 area. Two individual devices were mounted back-to-back with counting electronics coupling the detectors together into a single dual-detector device. The solid-state silicon device was operated at 3 V and utilized simple signal amplification and counting electronic components that have been adjusted from previous work for slow charge integration time. The intrinsic detection efficiency for normal-incident 0.0253 eV neutrons was found by calibrating against a 3He proportional counter.

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Silicon diodes with large aspect ratio 3D microstructures backfilled with 6LiF show a significant increase in neutron detection efficiency beyond that of conventional thin-film coated planar devices. Described in this work are advancements in the technology using detector stacking methods and summed-detector 6×6-element arraying methods to dramatically increase the sensitivity to thermal neutrons. The intrinsic detection efficiency of the 6×6 array for normal-incident 0.0253 eV neutrons was found 6.8% compared against a calibrated 3He proportional counter.

LiF

Silicon diodes with large aspect ratio perforated microstructures backfilled with 6LiF show a dramatic increase in neutron detection efficiency beyond that of conventional thin-film coated planar devices. Described in this work are advancements in the technology with increased microstructure depths and detector stacking methods that work to increase thermal-neutron detection efficiency. Models for ion energy deposition and intrinsic thermal-neutron detection efficiency for the straight trench design are described and results presented. A dual stacked device was fabricated by coupling two detectors back-to-back, along with counting electronics, into a single detector. Experimentally verified results and modeled predictions are compared. The stacked device delivered 37% intrinsic thermal-neutron detection efficiency, lower than the predicted value of 47%. It was determined that this lower observed efficiency is due to detector misalignment in the stacked structure and ballistic deficit from slow charge collection from the deep trench structures. The intrinsic thermal-neutron detection efficiency depends strongly upon the geometry, size, and depth of the perforated microstructures. This work is part of on-going research to develop solid-state semiconductor neutron detectors with high detection efficiencies.

High-efficiency microstructured semiconductor neutron detectors that are arrayed, dual-integrated, and stacked.

Decreased agricultural profit margins and recent bioterrorism concerns have led to an increased interest in monitoring livestock health. Heart rate and core body temperature are traditional vital parameters for cattle health assessment, as they provide warnings for illness and disease. However, obtaining these data in the field is time and labor intensive, which speaks to the need for solutions that provide continuous and automatic acquisition of these parameters. This paper presents the design of a pill that can remain in an animals reticulum and use electrocardiographic techniques to ascertain heart rate. The wired prototype has been tested with a fistulated steer. These tests demonstrate that consistent heart vector data can be acquired even in the presence of animal movement and rumination. After minor processing, these signals are suitable for use with peak detection circuitry that can automate heart rate determination.

Characteristics of the stacked microstructured solid state neutron detector

Recent food poisoning incidents have highlighted the need for inexpensive instrumentation that can detect food pathogens. Instrumentation that detects the relatively strong ultraviolet (UV) fluorescence signal from the aromatic protein amino acids in bacteria could provide a solution to the problem of real-time pathogen measurements. The capabilities of UV fluorescence measurements have, however, been largely ignored because of the difficulty in identifying pathogens in the presence of interfering backgrounds. Implementation of fluorescence measurements thus requires methodologies that can distinguish fluorescence features associated with pathogens from those associated with proteins, harmless bacteria, skin, blood, hair follicles, pesticide residue, etc. We describe multispectral UV fluorescence measurements that demonstrate the feasibility of detecting and identifying protein, DNA, and bacteria using a relatively simple UV imaging fluorometer and a unique multivariate analysis algorithm.

Electrocardiographic pill for cattle heart rate determination

Silicon diodes with large aspect ratio perforated microstructures backfilled with 6LiF show a dramatic increase in neutron detection efficiency beyond that of conventional thin-film coated planar devices. Described in this work are advancements in the technology using detector stacking methods to increase thermal neutron detection efficiency. The highest efficiency devices thus far have delivered over 42% intrinsic thermal neutron detection efficiency by device-coupling stacking methods. The detectors operate as conformally diffused pn junction diodes each having 1cm2 square-area. Two individual devices were mounted back-to-back with counting electronics coupling the detectors together into a single dual-detector device. The solid-state silicon device operated at 3V and utilized simple signal amplification and counting electronic components. The intrinsic detection efficiency for normal-incident 0.0253 eV neutrons was found by calibrating against a calibrated 3He proportional counter.

Ultraviolet fluorescence identification of protein, DNA, and bacteria

A. first generation 120 micron pitch pixel array system for neutron detection using the PATARA amplifier chip was assembled and tested. The pixel array was tested for neutron response and spatial resolution. Pulses from the PATARA were observed at 0.5 V in height and 500 ns wide from neutron interactions. The spatial resolution of the array was determined to be 119 micrometers. Leakage current tests and alpha particle irradiation tests were conducted for a second generation prototype silicon sensor with 175 micrometer deep perforated trench structures in each pixel. The second generation sensor incorporates several design improvements to ease fabrication.

High efficiency dual-integrated stacked microstructured solid-state neutron detectors

In data acquisition applications where the signals being digitized are produced in a time-division multiplexed system, the required dynamic performance of the analog-to-digital converter (ADC) is no longer bound by the conditions set forth in the sampling theorem. This results from the introduction of very high-frequency information by the multiplexing process which, while not necessarily containing information of interest, must be processed by the input circuitry of the ADC. In this situation, signal bandwidths and slew rates can greatly exceed those produced in a Nyquist limited system and can surpass the capability of the ADC, thus degrading overall system performance. This paper examines two common multiplexing schemes and their impact on ADC dynamic requirements. First, the authors examine a simple voltage multiplexing scheme typically found in state-of-health or data-logging applications and develop the necessary equations to show how the ADC dynamic requirements are affected. Then, the analysis is extended to a multiplexed photodiode array readout to see how this application further challenges the dynamic performance of the ADC. Finally, the issues associated with developing dynamic test methodologies for assessing ADC performance in multiplexed systems are discussed.

Preliminary tests of a high efficiency 1-D silicon pixel array for small angle neutron scattering

Microstructured semiconductor neutron detector (MSND) devices have achieved 42% intrinsic efficiency when operated as a dual-detector device. The neutron energy spectrometer has alternating layers of MSND arrays, cadmium, and high-density polyethylene (HDPE) in a linear arrangement. The detector arrays consist of 4 dual-detector devices with 1-cm2 detector elements in a stacked configuration. A 2 mm thick layer of cadmium separates each detector from the following layer of HDPE. The cadmium layer prevents thermalized neutrons from backscattering into the previous detector. The 3-cm thick HDPE layers act as a moderator for the epithermal and fast neutrons, allowing them to disperse energy within the spectrometers volume and reach thermal energies to be detected by the MSND arrays. The resultant device is a neutron energy spectrometer with a large surface area for the incident neutron beam.

The impact of multiplexing on the dynamic requirements of analog-to-digital converters

Low-power microstructured semiconductor neutron detector (MSND) devices have long been investigated as a high-efficiency replacement for thin-film diodes for thermal neutron detection. The detector devices were improved by stacking two 1cm2 devices and integrating their responses together to act as a single diode, increasing detection efficiency to over 42%. The need for larger active area devices has driven further improvement of the technology. A large active area device has been developed by arraying seventy-two 1cm2 devices together into two 6×6 configurations, dual-stacking them, and integrating their responses together in order to act as a single detector device. The intrinsic thermal neutron detection efficiency was found to be 7.03±0.04%. The leakage current of the 36cm2 device was −42nA at −5V bias and the capacitance was found to be 54pF at −5V bias.