Estimation of Weapon Yield from Inversion of Dose Rate Contours

This research studies the uncertainty in yield estimation from inversion of dose rate contours. The Hazard Prediction and Assessment Capability (HPAC) and a simple FORTRAN95 based Fallout Deposition Code (FDC) are used to recreate dose rate contours from historic nuclear tests. Fallout footprints from six atomic tests are recreated using balloon wind soundings and high resolution mesoscale weather reanalysis data. Dose rate contour plots are created for different yields for a single set of weather conditions. Dose rate contours are compared to determine uncertainty in yield estimation from inversion of dose rate contour plots. Results of these dose rate recreations are compared to historical patterns found in the Defense Nuclear Agency\u27s (DNA) DNA 1251-1-EX Compilation of Local Fallout Data From Test Detonations 1945-1962 Extracted from DASA 1251. Recreated dose rate contours are compared against historic patterns using a Figure of Merit (FOM) developed from the Measure of Effectiveness (MOE) and the Normalized Absolute Difference (NAD) techniques. This research provides a method to estimate the minimum yield required to create a dose rate contour to within a factor of two. This research determined that use of ground zero balloon soundings and reanalysis winds thereafter allowed the most accurate recreation of historic dose rate contours

Evaluation of Eu:LiCAF for Neutron Detection Utilizing SiPMs and Portable Electronics

With the increasing cost and decreasing availability of 3He, there have been many efforts to find alternative neutron detection materials. Lithium calcium aluminum fluoride (LiCAF) enriched to 95% 6Li doped with europium was evaluated here as a replacement material for 3He. Wafers 0.5 cm thick, consisting of LiCAF crystals in a rubberized matrix, were embedded with wavelength shifting fibers (WSF) and mated to silicon photo-multipliers (SiPMs) to measure the photon response in a flux of neutrons from a DD neutron generator. Excellent discrimination was realized between neutrons and gammas, and both pulse-height discrimination and pulse-shape analysis were explored. A Figure of Merit (FoM) of 1.03 was achieved. By applying pulse-shape analysis, a simple neutron count output was generated by utilizing a low-pass filter to suppress fast pulses from the SiPM output and subsequently applying a threshold to the remaining signal. Custom electronics were built to bias the SiPMs, then amplify, filter, discriminate, and digitize the LiCAF/WSF scintillation photons, resulting in a digital pulse that can easily be counted with any microcontroller or field programmable gate array. A significant advantage of LiCAF is that it can be fabricated into any shape/size (when embedded in a rubberized matrix), and the light output and transparency is sufficient to allow for thicker scintillators which enable detection of both thermal and epithermal neutrons. This work demonstrated that Eu:LiCAF is capable of discriminating gammas from neutrons and is a potential replacement material for 3He, especially for nuclear security applications and neutron spectroscopy

Efficient, Dual-particle Directional Detection System Using A Rotating Scatter Mask

A directional radiation detection system and an omnidirectional radiation detector. The omnidirectional radiation detector detects radiation comprising at least one of: (i) gamma rays; and (ii) neutron particles. A radiation scatter mask (RSM) of the radiation detection system includes a rotating sleeve received over the omnidirectional radiation detector and rotating about a longitudinal axis. The RSM further includes: (i) a fin extending longitudinally from one side of the rotating sleeve; and (ii) a wall extending from the rotating sleeve and spaced apart from the fin having an upper end distally positioned on the rotating sleeve spaced apart or next to from a first lateral side of the fin and a lower end proximally positioned on the rotating sleeve and spaced apart from or next to a second lateral side of the fin

Rotating Scatter Mask Optimization for Gamma Source Direction Identification

Rotating scattering masks have shown promise as an inexpensive, lightweight method with a large field-of-view for identifying the direction of a gamma emitting source or sources. However, further examination of the current rotating scattering mask design shows that changing the geometry may improve the identification by reducing or eliminating degenerate solutions and lower required count times. These changes should produce more linearly independent characteristics for the mask, resulting in a decrease in the mis-identification probability. Three approaches are introduced to generate alternative mask geometries. The eigenvector method uses a spring–mass system to create a geometry basis. The binary approach uses ones and zeros to represent the geometry with many possible combinations allowing for additional design flexibility. Finally, a Hadamard matrix is modified to examine a decoupled geometric solution. Four criteria are proposed for evaluating these methodologies. An analysis of the resulting detector response matrices demonstrates that these methodologies produced masks with superior identification characteristics than the original design. The eigenvector approach produces the least linearly dependent results, but exhibits a decrease in average efficiency. The binary results are more linearly dependent than the eigenvector approach, but this design achieves a higher average efficiency than original. The Hadamard-based method produced a lower maximum, but a higher average linear dependence than the original design. Further possible design enhancements are discussed

Monte Carlo and Experimental Analysis of a Novel Directional Rotating Scatter Mask Gamma Detection System

Excerpt: This work demonstrates successful experimental operation of a prototype system to identify source direction which was modeled using a library of signals simulated using GEANT and a novel algorithm...

Development of a Neutron Spectrometer Utilizing Rubberized Eu:LiCAF Wafers

portable ten-layer neutron spectrometer has been developed using a novel material, LiCAF. The spectrometer consists of rubber matrix wafers with embedded europium doped lithium calcium aluminum fluoride (Eu:LiCAF) crystals and crosshatched wave shifting fibers (WSF). Layers of high density polyethylene (HDPE) separating each Eu:LiCAF wafer serve as neutron moderating material. Neutrons entering the spectrometer react in the Eu:LiCAF crystal, creating scintillation photons. The photons travel down the WSFs to silicon photomultipliers (SiPMs) that convert the photons to an electrical signal. Custom electronics are used to gather, amplify, process, and readout the signal. A library of several neutron response curves was created in Geant4 and MCNP. The experimental output of the spectrometer was unfolded using a maximum entropy algorithm, MAXED. The spectrometer was tested using two separate DD generators. These two tests resulted in unfolded neutron spectra with average neutron energies of 2.71 and 2.78 MeV and chi-squared values of 0.88 and 1.51 x2 /D.O.F. respectively, when fit to a 2.45 MeV monoenergetic energy spectrum

Characterization of Novel Rotating Scatter Mask Designs for Gamma Direction Identification

The Rotating Scatter Mask system is a low cost, directional radiation detection system with a nearly 4π field-of-view over a broad range of photon energies. However, the original mask design is limited by numerous similarities in the detector response directional modes. These similarities introduce potential misidentification errors when determining a source’s direction. Previous studies identified a better mask design, the Mace, which significantly reduced the similarities between the modes. In this work, a new design class was simulated and compared to the Mace mask design using the modal assurance criterion to assess the differentiability between directional modes. At the expense of a reduced field-of-view, 93% of a full 4π steradians, these novel mask designs were shown to successfully decouple the angular components of the source’s direction, improving the average criterion value by up to 66%. The new designs also significantly improved the system’s detection efficiency, reducing the time to identify the source’s direction by up to 60%, while enabling a simplified, alternative algorithm for identifying the source direction. This alternative approach, called the geometric correlation method, further improved detection efficiency leading to a near-real time analysis for locating a source direction with the Rotating Scatter Mask