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  • Author or Editor: S. Biegalski x
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Abstract  

Beta-gamma coincidence counting is one of two acceptable noble gas monitoring measurement modes for Comprehensive Nuclear-Test-Ban-Treaty (CTBT) verification purposes defined in CTBT/PC/II/WG.B/1. Rigorous derivations of detection limits and minimum detectable activity concentrations for - coincidence data are derived in this paper. Different sampling methodologies are modeled to show how the MDC is affected by different sample collection times, spectral collection times, background radon levels, and other factors.

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Abstract  

Aerosol samples were collected on Whatman 41 filters at two sites near Lake Huron and one site near Lake Ontario. These samples were then analyzed by instrumental neutron activation analysis (NAA) at the University of Illinois. The detection limits for certain trace elements were enhanced by irradiation with both thermal and epithermal neutrons and also by counting with Compton suppression techniques. The sample was divided in half to allow for four irradiations. Short-lived thermal NAA resulted in the determination of Al, Br, Ca, Cl, Cu, K, Mn, Na, Ti, and V. A short epithermal irradiation was used to determine Cu, I, In, Si, Sn and U. A one and one-half hour epithermal irradiation was utilized for the determination of As, Au, Br, Sm, Sb, and W. The elements Cr, Cs, Fe, Hf, Ni, Sc, Se, Th. Zn, and several rare earths were determined with a long thermal irradiation. Utilizing a Compton suppression gamma-ray counting system reduced the background and enhanced the detection of several isotopes which primarily emit only a single gamma-ray upon decay. Counting was simultaneously performed with a normal counting mode so that the detection of isotopes with multiple decay gamma-rays was not impaired.

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Abstract  

Bromine can be determined by neutron activation analysis (NNA) through either the activation of79Br (50.69% naturally abundant) or81Br (49.31% naturally abundant). When79Br is activated, both80mBr and80Br are produced.80mBr (4.42 h) decays to80Br (17.66 m) which then beta decays to either80Se or80Kr. If one would like to determine bromine concentrations with short lived NAA, special equations must be used to account for the parent daughter relationship between80mBr after their simultaneous production. The development of the equations needed to calculate bromine concentrations with short-lived NAA is described including variations on irradiation times, decay times, and count times.

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Abstract  

The Spectral Deconvolution Analysis Tool (SDAT) software was developed to improve counting statistics and detection limits for nuclear explosion radionuclide measurements. SDAT utilizes spectral deconvolution spectroscopy techniques and can analyze both β–γ coincidence spectra for radioxenon isotopes and high-resolution HPGe spectra from aerosol monitors. The deconvolution algorithm of the SDAT requires a library of β–γ coincidence spectra of individual radioxenon isotopes to determine isotopic ratios in a sample. In order to get experimentally produced spectra of the individual isotopes, we have irradiated enriched samples of 130Xe, 132Xe, and 134Xe gas with a neutron beam from the TRIGA reactor at The University of Texas. The samples were counted in an Automated Radioxenon Sampler/Analyzer (ARSA) style β–γ coincidence detector. The spectra produced show that this method of radioxenon production yields samples with very high purity of the individual isotopes for 131mXe and 135Xe and a sample with a substantial 133mXe to 133Xe ratio.

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Abstract  

The Spectral Deconvolution Analysis Tool (SDAT) software was developed at The University of Texas at Austin. SDAT utilizes a standard spectrum technique for the analysis of β–γ coincidence spectra. Testing was performed on the software to compare the standard spectrum analysis technique with a region of interest (ROI) analysis technique. Experimentally produced standard spectra and sample data were produced at the Nuclear Engineering Teaching Laboratory (NETL) TRIGA reactor. The results of the testing showed that the standard spectrum technique had lower errors than the ROI analysis technique for samples with low counting statistics. In contrast, the ROI analysis technique outperformed the standard spectrum technique in high counting statistics samples. It was also shown that the standard spectrum technique benefitted from a compression of the number of channels within the spectra.

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Summary  

In view of the terrorist threats to the United States, the country needs to consider new vectors and weapons related to nuclear and radiological threats against our homeland. The traditional threat vectors, missiles and bombers, have expanded to include threats arriving through the flow of commerce. The new commerce-related vectors include: sea cargo, truck cargo, rail cargo, air cargo, and passenger transport. The types of weapons have also expanded beyond nuclear warheads to include radiation dispersal devices (RDD) or “dirty' bombs. The consequences of these nuclear and radiological threats are both economic and life threatening. The defense against undesirable materials entering our borders involves extensive radiation monitoring at ports of entry. The radiation and other signatures of potential nuclear and radiological threats are examined along with potential sensors to discover undesirable items in the flow of commerce. Techniques to improve radiation detection are considered. A strategy of primary and secondary screening is proposed to rapidly clear most cargo and carefully examine suspect cargo.

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Abstract  

In support of the Comprehensive Nuclear-Test-Ban Treaty (CTBT), improvements have been made to the model of the Automated Radioxenon Sampler/Analyzer (ARSA) β-γ coincidence detector for radioxenon monitoring. MCNPX is used to simulate the detector response for all the electrons and photons emitted from 131mXe, 133Xe, 133mXe, 135Xe, and 137Cs signals. A MatLab code was written to incorporate the MCNPX results in the calculation of β-γ coincidence spectra. These will aid in the development of the Spectral Deconvolution Analysis Tool (SDAT)1 and to calibrate β-γ coincidence systems. The models developed for this work include improvements over previous models in their ability to address Compton scattering in the β-cell, and the β-distribution offset in the 31 keV γ-ray region for 133Xe.

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Abstract  

The Spectral Deconvolution Analysis Tool (SDAT) software was developed to improve counting statistics and detection limits for nuclear explosion radionuclide measurements. SDAT utilizes spectral deconvolution spectroscopy techniques and can analyze both β-γ coincidence spectra for radioxenon isotopes and high-resolution HPGe spectra from aerosol monitors. Spectral deconvolution spectroscopy is an analysis method that utilizes the entire signal deposited in a gamma-ray detector rather than the small portion of the signal that is present in one gamma-ray peak. This method shows promise to improve detection limits over classical gamma-ray spectroscopy analytical techniques; however, this hypothesis has not been tested. To address this issue, we performed three tests to compare the detection ability and variance of SDAT results to those of commercial-off-the-shelf (COTS) software which utilizes a standard peak search algorithm.

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Abstract  

Activation experiments were conducted to assess the bremsstrahlung continuum produced from the activation of the 7Li isotope and the subsequent short-lived 13 MeV beta decay of 8Li (T 1/2 = 843 ms). The combination of the high energy beta-decay and the high atomic numbered metals used in piping for 7Li liquid metal coolants is a scenario in which bremsstrahlung production is a principal shielding concern. A series of fast pneumatic activation experiments have been performed to obtain the spectral distributions of bremsstrahlung gamma-rays transmitted through stainless steel shield samples. Detectors were used in both pulse-height and multichannel scaling analysis modes for energy spectra determination and half-life verification, respectively. Experimental results were utilized to validate the electron transport and bremsstrahlung production models used in the Monte Carlo MCNP code.

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Abstract  

High-purity germanium (HPGe) and lithium drifted germanium (Ge(Li)) detectors have been the detector of choice for high resolution gamma-ray spectroscopy for many years. This is primarily due to the superior energy resolution that germanium detectors present over other gamma-ray detectors. In order to perform quantitative analyses with germanium detectors, such as activity determination or nuclide identification, one must know the absolute full-energy peak efficiency at the desired gamma-ray energy. Many different methods and computer codes have been developed throughout history in an effort to predict these efficiencies using minimal or no experimental observations. A review of these methods and the computer codes that utilize them is presented.

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