91 research outputs found
PASSIVATED IMPLANTED PLANAR SILICON (PIPS) DETECTORS FOR MEASUREMENT OF RADIOXENON
No full textSilicon detectors are analyzed as an alternative to plastic scintillators for beta detection based on their higher energy resolution. A radioxenon detection setup was created with the intent of comparing the absolute efficiency of the beta-gamma coincidence measurements between a silicon detector (PIPS) with each a NaI(Tl) scintillator and a high purity germanium (HPGE) semiconductor detector. The absolute efficiencies of both setups are calculated and compared.M.S
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Production of [beta-gamma] coincidence spectra of individual radioxenon isotopes for improved analysis of nuclear explosion monitoring data
No full texttextRadioactive xenon gas is a fission product released in the detonation of nuclear devices that can be detected in atmospheric samples far from the detonation site. In order to improve the capabilities of radioxenon detection systems, this work produces [beta-gamma] coincidence spectra of individual isotopes of radioxenon. Previous methods of radioxenon production consisted of the removal of mixed isotope samples of radioxenon gas released from fission of contained fissile materials such as ²³⁵U. In order to produce individual samples of the gas, isotopically enriched stable xenon gas is irradiated with neutrons. The detection of the individual isotopes is also modeled using Monte Carlo simulations to produce spectra. The experiment shows that samples of [superscript 131m]Xe, ¹³³Xe, and ¹³⁵Xe with a purity greater than 99% can be produced, and that a sample of [superscript 133m]Xe can be produced with a relatively low amount of ¹³³Xe background. These spectra are compared to models and used as essential library data for the Spectral Deconvolution Analysis Tool (SDAT) to analyze atmospheric samples of radioxenon for evidence of nuclear events.Mechanical Engineerin
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Compton suppression and gamma-gamma coincidence
No full texttextThis project aims to improve research in gamma-ray spectroscopy by using advanced detector systems. These systems are designed to reduce interference inherent in gamma-ray spectroscopy by rejecting Compton scattering events from high-energy gamma-rays, as well as look at cascading decays of gamma-rays through gamma-gamma coincidence counting. By combining these methods, one is able to lower detection limits for many elements than would otherwise be possible. This work also takes advantage of neutron activation analysis, which allows stable elements to be analyzed by activating them with neutrons, causing them to become unstable and decay with radioactive signatures. By analyzing these signatures, one is able to detect trace levels of elements with relatively small samples sizes (< 1g) and in a nondestructive manner.Mechanical Engineerin
Novel manufacture of radioactive sources by stereolithography
No full textIn this work, a method for creating radioactive sources using additive manufacturing is considered. The work includes an overview of the theories a practice of stereolithographic printing as well as an in-depth study of the materials and manufacture of radioactive sources using standard and elastic resins. Various mixing techniques are used and compared. A number of tests were conducted to determine the homogeneity and radiological properties of the mixed resins. Consideration was given to the environmental effects of the sources.M.S
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Open source software package using a semi-empirical mesh-grid method for the modeling of germanium detector efficiencies
No full texttextTraditional approaches in gamma-ray spectroscopy for determining the absolute full-energy peak efficiencies of germanium detectors are primarily either too time consuming or not economically viable. In addition, these approaches are difficult to use for arbitrary source shapes and counting geometries. An open source software package, KMESS (Kevin's Mesh Efficiency Simulator Software), was developed to address these problems. KMESS uses a new semi-empirical mesh-grid method to predict the absolute full-energy peak efficiencies of n- and p-type germanium detectors in both coaxial and closed-ended configurations. The model assumes that any gamma-ray source shape can be treated as a collection of point sources. The code was written in a modular form, making it easy to adapt for other detector configurations and materials. A suite of webbased graphical front-end tools was also developed to make the execution of KMESS user-friendly. KMESS can predict most full-energy peak efficiencies to within 10% accuracy for the energy range 100-1800 keV in less than 10 minutes.Mechanical Engineerin
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Short lived radionuclide modeling from nuclear weapons test sites and nuclear power plant accidents
No full texttextNuclear accidents and weapons tests are monitored by a worldwide network of air sensors, seismic detectors and several other techniques. At the site of the incident, contaminants are distributed and can provide insight into the time of the incident and type of incident. That information can then be used to affect policy decisions or better understand health risks. In order to evaluate a post nuclear test scenario, we must better understand the background readings at potential test sites where false positive or false negative allegations are more likely (e.g. the Nevada Test Site, the Chernobyl Nuclear Power Plate, etc.) Data from these sites have been compiled and compared to high purity germanium detector background readings and activities from a hypothetical nuclear weapon test. The results indicate that the following nuclides would be the best indicator of a recent nuclear test: ⁸⁹Sr, ⁹¹Y, ⁹⁵Zr, ¹⁰³Ru, ¹²⁶Sb, ¹²⁹[superscript m]Te, ¹⁴⁷Nd, ¹⁵⁶Eu. Nuclides such as ⁹¹Sr or ⁹⁷Zr have a steady state concentration due to plutonium spontaneous fission thus would not be a good indication of a recent nuclear test.Mechanical Engineerin
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Measuring the radioactivity of ²³⁵U, ²³⁸U, ²³²Th, and ⁴⁰K in geological matrices using instrumental neutron activation analysis
No full texttextThe radioactivity contributions of several daughter products of the 235,238 U and 232Th isotope decay chains within geological matrices can be assumed to be in equilibrium due to their age if they have remained undisturbed for an extended period of time. Similarly, one can assume that the isotopic mass proportions are equal to natural isotopic abundance. Current methods used to ascertain activity in these decay chains involve alpha particle spectrometry or ICP-MS, both of which can be laborious and time consuming. In this research, thermal and epithermal neutron activation analysis of small samples of various geological materials is used in order to ascertain activities. Through the use of NAA, cumbersome sample preparation and the need for large sample size and extended counting time are obviated. In addition to the decay chains of uranium and thorium, 40K, another large contributor to naturally occurring radioactivity, is determined using epithermal neutron activation analysis to determine total potassium content, and then calculating its isotopic contribution based on its natural isotopic abundance.Mechanical Engineerin
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Evaluation of nylon 6,6 in use in Fire Foe® fire suppression systems within plutonium gloveboxes
No full texttextGloveboxes, where special nuclear material is handled and such as those present at Los Alamos National Labs, LANL, provide an experimental area confined within a protective shell and with strict environmental controls. These gloveboxes allow workers to indirectly interact with hazardous material. Unfortunately, these gloveboxes are not fail proof and are subject to occasional accidental failures resulting in possible breaches of containment and release of nuclear material. In particular, fires within the gloveboxes are of major concern with regard to the potential for breaches and damage to not only the glovebox but also to surrounding areas as well. Another, potentially even catastrophic, result of
glovebox fires is the potential for the spread of radioactive contamination. There is some historical precedent of contaminant release resulting from glovebox fires, such as those at the Rocky Flats Plant (Buffer, 2012).
Gloveboxes at LANL are currently equipped with manually activated fire suppression systems. In the event of an incident, a worker would hit a nearby emergency button and the system would be activated. However, this method relies on the worker to have the presence of mind in the face of danger to activate the system, and as such there is no true guarantee that the systems will be triggered. Since the level of consequence is dire, then the ideal situation requires that other fire suppression systems be present which do not rely on human interaction to function. The Fire Foe™ system has been chosen as a secondary failsafe measure in order to meet this need.
Analysis of how the casing of the Fire Foe™ system, composed of nylon 6,6 polymer, weathers under irradiation in gloveboxes is paramount in determining the effectiveness and potential lifetimes of the systems within the gloveboxes. Samples of nylon 6,6 were exposed to a 5 Ci PuBe neutron source located at the University of Texas as well as a high dose rate beam of 4.5 MeV alpha particles located at Los Alamos to determine the effect of neutron and alpha particle damage on the polymer material. Subsequent mechanical testing was conducted to determine alteration to the tensile properties of the nylon 6,6 material for both irradiated and non-irradiated samples.Mechanical Engineerin
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Monte Carlo simulations of Germanium detector efficiency curves
No full textThe use of Germanium detectors to study gamma-rays has become common practice in most modern science laboratories. These detectors often need to be calibrated and characterized for different gamma-ray source geometries, energies, and source-to-detector distances. The use of Monte Carlo based simulations allows one to perform these characterizations in the absence of radioactive material and for arbitrary experimental setups. The usefulness of these simulations and Monte Carlo based codes for modeling Germanium detector efficiencies is studied here. Two C language programs have also been written to perform analysis of efficiency curves and multiple decay components.Mechanical Engineerin
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Development of fast pneumatic system for the study of 14 MeV fission product yields
No full texttextThe use of fission product yield data is pervasive among nuclear calculations, particularly in the realm of nuclear forensics and active interrogation for special nuclear material. The capital source of fission product yield data is the work of T.R. England and B.F. Rider, of Los Alamos National Laboratory, in the early 1990s. Though their work was certainly substantial, a great deal of data was generated computationally, in lieu of done empirically—particularly with low-yield, short-lived progeny. Due to this, relative uncertainties in the measurements can be as high as 64%, and vary wildly from database to database (oft times not even within one standard deviation of one another). The purpose of this work is to build a pneumatic system capable of cyclic irradiation coupled to a D-T neutron source, in order to cumulate proper counting statistics, by which one can backcalculate independent and cumulative fission yields. Beyond the design and control parameters of the pneumatic system, a precise flux characterization of the facility is presented, and finally, proof-of-concept is demonstrated by causing 14 MeV neutron-induced fission and identifying every observed fission product photopeak.Mechanical Engineerin
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