David M. Pfund

Examination of Count-starved Gamma Spectra Using the Method of Spectral Comparison Ratios

We discuss the determination of energy region (bin) boundaries and decision metrics for gamma-ray spectra, acquired using a mid-resolution detector, that are useful for detecting illicit sources at low total counts. The bins are designed to produce the lowest minimum detectable counts using a spectral comparison ratio technique at a given false-positive rate for a specified population of benign-source spectra. Spectra from the benign source population consist of observations taken by a detector on a moving vehicle, as would be obtained during a search for a missing or hidden source. Raw counts in bins are transformed into a vector of background-corrected count differences. Bin boundaries are determined to yield large values of a standardized length of this vector for benign-plus-benchmark sources by applying an optimization technique. The objective function includes penalties for overlap with the spectral features of naturally occurring radioactive materials. We compare estimated minimum detectable count values for such bins applied to depleted uranium and barium-133 sources with those based on gross counting, and we examine the effect of nuisance potassium-, radium- and thorium-dominated sources. Using this methodology, we demonstrate that energy bins may be chosen to be sensitive to special nuclear materials, improving the likelihood of detection in low-count or masked-source searches.

Low Count Anomaly Detection at Large Standoff Distances

Searching for hidden illicit sources of gamma radiation in an urban environment is difficult. Background radiation profiles are variable and cluttered with transient acquisitions from naturally occurring radioactive materials and medical isotopes. Potentially threatening sources likely will be nearly hidden in this noise and encountered at high standoff distances and low threat count rates. We discuss an anomaly detection algorithm that characterizes low count sources as threatening or non-threatening and operates well in the presence of high benign source variability. We discuss the algorithm parameters needed to reliably find sources both close to the detector and far away from it. These parameters include the cutoff frequencies of background tracking filters and the integration time of the spectrometer. This work is part of the development of the Standoff Radiation Imaging System (SORIS) as part of DNDOs Standoff Radiation Detection System Advanced Technology Demonstration (SORDS-ATD) program.

High‐pressure, capillary x‐ray absorption fine structure cell for studies of liquid and supercritical fluid solutions

A method is described to acquire x‐ray absorption fine structure (XAFS) spectra of high‐pressure liquid and supercritical fluid solutions. The technique employs a short length of fused‐silica capillary tubing that has an inner diameter of 250 μm and an outer diameter of 360 μm. A hairpin bend is formed near the center of the capillary and the bend is then placed end‐on directly in the focused x‐ray beam. Fluorescence spectra were acquired in a 90° geometry using a 13 element Ge detector. Demonstration XAFS spectra are reported for a Mn organometallic complex dissolved in subcritical and supercritical CO2. Although the maximum pressure of these studies was 160 bar, with slight modification, the method will be applicable to studies requiring pressures as high as 4 kbar.

Thermal Measurements in Rectangular Microchannels

This paper reports on an experimental study of heat transfer in high aspect ratio (width/depth), rectangular micro-channels. A single channel with width of 10 μm was cut into polycarbonate spacers of various thicknesses, resulting in channel depths of 128 μm, 263 μm and 521 μm. Heat transfer experiments were performed with a constant heat flux boundary condition applied at the surface of the channel. Experiments conducted for refrigerant R-124 working fluid in the range Re = 300 − 900 and Pr = 3.6 − 3.8 showed small or no departure from macro-scale predictions for channels with hydraulic diameters larger than 500 μm. Results for the 80:1 aspect ratio channel showed a significant departure from theoretical predictions. Experimental values of local Nusselt numbers were approximately 25 percent lower than predicted using macro-scale theory.Copyright

A diamond‐window XAFS cell for studies of high‐temperature, high‐pressure aqueous solutions

We describe a method to collect x‐ray absorption fine structure (XAFS) spectra of ions in a supercritical water solvent. Supercritical water (SCW), at temperatures above water’s critical point of 374 °C, is an interesting solvent for chemical reactions and hazardous waste destruction due to the high solubility of organics and the aggressive oxidizing environment. XAFS may provide a better understanding of the solvent environment in SCW. The XAFS cell used in these studies was composed of a block of high‐nickel alloy, Hastelloy C‐22, containing two windows for transmission of the x‐ray beam and a single optical view window. All internal wetted surfaces were platinum plated. The maximum operating conditions for this design were 500 °C and 700 bar. The x‐ray transmission windows consisted of CVD (chemical vapor deposition) diamond windows (3 mm diameter ×0.5 mm thick) that were brazed to the tip of a standard 1/4‐in. high‐pressure, coned‐shape fitting. Spectra are reported for strontium and rubidium ions in ...

Improvements in the method of radiation anomaly detection by spectral comparison ratios.

We present a new procedure for configuring the Nuisance-rejection Spectral Comparison Ratio Anomaly Detection (N-SCRAD) method. The procedure minimizes detectable count rates of source spectra at a specified false positive rate using simulated annealing. We also present a new method for correcting the estimates of background variability used in N-SCRAD to current conditions of the total count rate. The correction lowers detection thresholds for a specified false positive rate, enabling greater sensitivity to targets.

Unattended Sensor System With CLYC Detectors

We have developed an unattended sensor for detecting anomalous radiation sources. The system combines several technologies to reduce size and weight, increase battery lifetime, and improve decision-making capabilities. Sixteen Cs2LiYCl6:Ce (CLYC) scintillators allow for gamma-ray spectroscopy and neutron detection in the same volume. Low-power electronics for readout, high voltage bias, and digital processing reduce the total operating power to 1.7 W. Computationally efficient analysis algorithms perform spectral anomaly detection and isotope identification. When an alarm occurs, the system transmits alarm information over a cellular modem. In this paper, we describe the overall design of the unattended sensor, present characterization results, and compare the performance to stock NaI:Tl and 3He detectors.

Development of Millimeter-Wave Velocimetry and Acoustic Time-of-Flight Tomography for Measurements in Densely Loaded Gas-Solid Riser Flow

The MFDRC was formed in 1998 to advance the state-of-the-art in simulating multiphase turbulent flows by developing advanced computational models for gas-solid flows that are experimentally validated over a wide range of industrially relevant conditions. The goal was to transfer the resulting validated models to interested US commercial CFD software vendors, who would then propagate the models as part of new code versions to their customers in the US chemical industry. Since the lack of detailed data sets at industrially relevant conditions is the major roadblock to developing and validating multiphase turbulence models, a significant component of the work involved flow measurements on an industrial-scale riser contributed by Westinghouse, which was subsequently installed at SNL. Model comparisons were performed against these datasets by LANL. A parallel Office of Industrial Technology (OIT) project within the consortium made similar comparisons between riser measurements and models at NETL. Measured flow quantities of interest included volume fraction, velocity, and velocity-fluctuation profiles for both gas and solid phases at various locations in the riser. Some additional techniques were required for these measurements beyond what was currently available. PNNL’s role on the project was to work with the SNL experimental team to develop and test two new measurement techniques, acoustic tomography and millimeter-wave velocimetry. Acoustic tomography is a promising technique for gas-solid flow measurements in risers and PNNL has substantial related experience in this area. PNNL is also active in developing millimeter wave imaging techniques, and this technology presents an additional approach to make desired measurements. PNNL supported the advanced diagnostics development part of this project by evaluating these techniques and then by adapting and developing the selected technology to bulk gas-solids flows and by implementing them for testing in the SNL riser testbed.

Ultrasonic methods for characterization of liquids and slurries

In the field of process monitoring and control technology, Pacific Northwest National Laboratory is utilizing unique technical capabilities and drawing upon knowledge gained through many years of government- and industry-sponsored research activities to develop and deploy advanced sensor and measurement systems for the monitoring and control of process operations. This includes non-invasive, on-line and realtime technologies that use ultrasound characterization to measure the physical and chemical properties of flowing materials, such as liquids and slurries. Ultrasonic velocity, attenuation, reflection coefficients, and scattering amplitudes are measurable parameters related to fundamental physical properties of fluids and slurries of interest to food processors and manufacturers of consumer products. Accordingly, ultrasonic methodologies have been developed that offer on-line, real-time analysis of many physical properties, including particle size distribution, concentration, settling and plug formation, fluid viscosity, density and shear rate, fouling and pipeline wall buildup detection, liquid-liquid interface detection, and chemical identity confirmation.

Improved Heat Transfer Using Micro-Structures in Trifold Solar Energy Conversion Systems

The worldwide renewable energy sources harvesting grew recently at rates of 10–60% annually for many technologies, due to improvements made in all areas. In solar energy conversion, an improvement recently presented in literature is the hybrid system that provides both electricity and thermal energy for domestic applications. For the trifold PV-TE-DHW system, the electrical conversion efficiency is increased by using a thermoelectric (TE) module. This paper proposes the use of micro-channeled heat exchangers at both hot and cold sides of the TE module to improve the heat exchange from the working fluids. The authors developed prior works and published papers in the area of fluid flow and heat transfer in microstructures, heat transfer augmentation, and in solar thermal systems. Results obtained show an improved efficiency energy transfer.