The spectral post-processing algorithm Advanced Synthetically Enhanced Detector Resolution Algorithm (ASEDRA
(patent pending)) has shown to be a powerful tool for deconvolving full energy peaks from scintillation spectrometeracquired
gamma-ray spectra, effectively improving obtainable data-synthesized energy resolutions by a factor of four to
six times over what is rendered from the detector. An isotope attribution algorithm, SmartID, was developed to augment
ASEDRA in order to improve radionuclide identification accuracy. SmartID utilizes a novel, physics-based method of
importance weighting the ASEDRA-identified peaks and the emissions of a candidate isotope. This methodology
enhances the screening of potential false peaks and prevents isotope mismatches. As a final step, SmartID assigns a
physical matching attribution score to each possible isotope match to reflect goodness-of-fit. A test suite of 105 gammaray
spectra acquired with a 2"×2" NaI:Tl spectrometer under varying shielding conditions and various single and multisource
configurations were recorded for testing the accuracy of ASEDRA+SmartID. The sources utilized in the tests
included 133Ba, 109Cd, 57Co, 60Co, 137Cs, 152Eu, 54Mn, 22Na, 232Th, natural uranium rods and a PuBe source. Shielding
configurations varied widely, ranging from none to more than 2.5cm Pb. Overall, SmartID proved to be more than 95%
accurate in attributing the correct isotope(s) to the spectra.
We have developed a ground-breaking algorithm, ASEDRA, to
post-process scintillator detector spectra to render
photopeaks with high accuracy. The post-processed spectrum is comparable with resolved full energy peaks rendered by
high resolution HPGe semiconductor detectors. ASEDRA, or "Advanced Synthetically Enhanced Detector Resolution
Algorithm," is currently applied to NaI(Tl) detectors, which are robust, but suffer from poor energy resolution.
ASEDRA rapidly post-processes a NaI(Tl) detector spectrum over a few seconds on a standard laptop without prior
knowledge of sources or spectrum features. ASEDRA incorporates a novel denoising algorithm based on an adaptive
Chi-square methodology called ACHIP, or "Adaptive Chi-quare Processed denoising." Application of ACHIP is
necessary to remove stochastic noise, yet preserve fine detail, and can be used as an independent tool for general noise
reduction. Following noise removal, ASEDRA sequentially employs an adaptive detector response algorithm to remove
the spectrum attributed to specific gammas. Tests conducted using a 2"×2" NaI(Tl) detector, along with a HPGe
detector demonstrate the accuracy of ASEDRA; in this paper, we present results using a 152Eu source. Analysis of
ASEDRA results show correct identification of at least 15 photopeaks from 152Eu, with relative yield ratios of major
lines to better than a factor of two for most cases (referencing the 152Eu 344 keV photopeak), enabling better than a
factor of four improvement in resolving peaks compared with unprocessed NaI(Tl). Moreover, denoising and synthetic
resolution enhancement algorithms can be adapted to any detector. ACHIP and ASEDRA are covered under a
Provisional Patent, Registration Number #60/971,770, 9/12/2007, USPTO.
We have designed, built, and laboratory-tested a unique shield design that transforms the complex neutron spectrum
from PuBe source neutrons, generated at high energies, to nearly exactly the neutron signature leaking from a significant
spherical mass of weapons grade plutonium (WGPu). This equivalent "X-material shield assembly" (Patent Pending)
enables the harder PuBe source spectrum (average energy of 4.61 MeV) from a small encapsulated standard 1-Ci PuBe
source to be transformed, through interactions in the shield, so that leakage neutrons are shifted in energy and yield to
become a close reproduction of the neutron spectrum leaking from a large subcritical mass of WGPu metal (mean energy
2.11 MeV). The utility of this shielded PuBe surrogate for WGPu is clear, since it directly enables detector field testing
without the expense and risk of handling large amounts of Special Nuclear Materials (SNM) as WGPu. Also,
conventional sources using Cf-252, which is difficult to produce, and decays with a 2.7 year half life, could be replaced
by this shielded PuBe technology in order to simplify operational use, since a sealed PuBe source relies on Pu-239
(T½=24,110 y), and remains viable for more than hundreds of years.
The ASEDRA algorithm (Advanced Synthetically Enhanced Detector Resolution Algorithm) is a tool developed at the
University of Florida to synthetically enhance the resolved photopeaks derived from a characteristically poor resolution
spectra collected at room temperature from scintillator crystal-photomultiplier detector, such as a NaI(Tl) system. This
work reports on analysis of a side-by-side test comparing the identification capabilities of ASEDRA applied to a NaI(Tl)
detector with HPGe results for a Plutonium Beryllium (PuBe) source containing approximately 47 year old weapons-grade
plutonium (WGPu), a test case of real-world interest with a complex spectra including plutonium isotopes and
241Am decay products. The analysis included a comparison of photopeaks identified and photopeak energies between
the ASEDRA and HPGe detector systems, and the known energies of the plutonium isotopes. ASEDRA's performance
in peak area accuracy, also important in isotope identification as well as plutonium quality and age determination, was
evaluated for key energy lines by comparing the observed relative ratios of peak areas, adjusted for efficiency and
attenuation due to source shielding, to the predicted ratios from known energy line branching and source isotopics. The
results show that ASEDRA has identified over 20 lines also found by the HPGe and directly correlated to WGPu
energies.
The Florida Institute for Nuclear Detection and Security (FINDS) is currently working on the design and evaluation of a prototype neutron detector array that may be used for parcel screening systems and homeland security applications. In order to maximize neutron detector response over a wide spectrum of energies, moderator materials of different compositions and amounts are required, and can be optimized through 3-D discrete ordinates and Monte Carlo model simulations verified through measurement. Pu-Be sources can be used as didactic source materials to augment the design, optimization, and construction of detector arrays with proper characterization via transport analysis. To perform the assessments of the Pu-Be Source Capsule, 3-D radiation transport computations are used, including Monte Carlo (MCNP5) and deterministic (PENTRAN) methodologies. In establishing source geometry, we based our model on available source schematic data. Because both the MCNP5 and PENTRAN codes begin with source neutrons, exothermic (α,n) reactions are modeled using the SCALE5 code from ORNL to define the energy spectrum and the decay of the source. We combined our computational results with experimental data to fully validate our computational schemes, tools and models. Results from our computational models will then be used with experiment to generate a mosaic of the radiation spectrum. Finally, we discuss follow-up studies that highlight response optimization efforts in designing, building, and testing an array of detectors with varying moderators/thicknesses tagged to specific responses predicted using 3-D radiation transport models to augment special nuclear materials detection.
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