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Misner, Alex C.

Publications and source records attributed to Misner, Alex C..

5 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Underground Sources of Radioactive Noble Gas

It is well known that radon is present in relatively high concentrations below the surface of the Earth due to natural decay of uranium and thorium. However, less information is available on the background levels of other isotopes such as 133Xe and 131mXe produced via spontaneous fission of either manmade or naturally occurring elements. The background concentrations of radioxenon in the subsurface are important to understand because these isotopes potentially can be used to confirm violations of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) during an On-Site Inspection (OSI). Recently, Pacific Northwest National Laboratory (PNNL) measured radioxenon concentrations from the subsurface at the Nevada Nuclear Security Site (NNSS—formerly known as the Nevada Test Site) to determine whether xenon isotope background levels could be detected from spontaneous fission of naturally occurring uranium or legacy 240Pu as a result of historic nuclear testing. In this paper, we discuss the results of those measurements and review the sources of xenon background that must be taken into account during OSI noble gas measurements.

radioxenon, noble gas, soil gas sampling, CTBT, On↗
DOE OSTI2012

Technical Cross-Cutting Issues for the Next Generation Safeguards Initiative's Spent Fuel Nondestructive Assay Project

Ever since there has been spent fuel (SF), researchers have made nondestructive assay (NDA) measurements of that fuel to learn about its content. In general these measurements have focused on the simplest signatures (passive photon and total neutron emission) and the analysis has often focused on diversion detection and on determining properties such as burnup (BU) and cooling time (CT). Because of shortcomings in current analysis methods, inspectorates and policy makers are interested in improving the state-of-the-art in SF NDA. For this reason the U.S. Department of Energy, through the Next Generation Safeguards Initiative (NGSI), targeted the determination of elemental Pu mass in SF as a technical goal. As part of this research effort, 14 nondestructive assay techniques were studied . This wide range of techniques was selected to allow flexibility for the various needs of the safeguards inspectorates and to prepare for the likely integration of one or more techniques having complementary features. In the course of researching this broad range of NDA techniques, several cross-cutting issues were. This paper will describe some common issues and insights. In particular we will describe the following: (1) the role of neutron absorbers with emphasis on how these absorbers vary in SF as a function of initial enrichment, BU and CT; (2) the need to partition the measured signal among different isotopic sources; and (3) the importance of the “first generation” concept which indicates the spatial location from which the signal originates as well as the isotopic origins.

Next Generation Safeguards Initiative↗
DOE OSTI2011

HIGH ENERGY DELAYED GAMMA SPECTROSCOPY FOR PLUTONIUM ASSAY OF SPENT REACTOR FUEL

Nuclear safeguards requires accountancy of plutonium present in spent reactor fuels. Current non-destructive methods do not directly measure plutonium content but instead rely on indirect measurements that require operator declarations of the fuel history. Delayed gamma spectroscopy is one method being investigated which can overcome these limitations. Delayed gamma rays from fission depend on the isotopic fission yield of the fissile isotope, and thus can be used to fingerprint the isotopes undergoing fission. However, difficulties arise because of the intense background due to long lived fission radionuclides already present in the fuel. We report on progress on simulated measurements of the delayed gamma spectrum in the presence of this background, using neutrons from a D-T source thermalized in an interrogation chamber slipped over a fuel assembly. By focusing on delayed gammas in the 3 to 4 MeV range, the passive spectrum becomes negligible, while allowing the preferential attenuation of the passive background to acceptable levels.

Campbell, Luke W.↗
DOE OSTI2011

Image-Based Verification Algorithms for Arms Control

PNNL is developing and evaluating radiographic image analysis techniques (active and passive) for verifying sensitive objects in a material control or warhead counting regime in which sensitive information may be acquired and processed behind an information barrier. Since sensitive image information cannot be present outside the information barrier, these techniques are necessary to extract features from the full images and reduce them to relevant parameters (attributes) of the inspected items. This evaluation can be done behind the information barrier, allowing for reporting and storage of non-sensitive attributes only. Several advances have been made to radiographic object verification algorithms, in the areas of spectral imaging for passive detectors and estimation of material density in active radiographic images. Both of these advances are pertinent in an arms control context. While passive radiographic images produced by previous work may be evaluated for the presence of emissive objects, approaches which leverage the spectroscopic potential of the detectors allow a much greater discrimination of SNM from background and other sources. Spectral passive imaging approaches to warhead discrimination and counting include specific materials and geometric arrangement localization, as well as “spectral difference” metrics which group regions with similar spectra together. These approaches may improve resolution for discrimination between materials in addition to locating SNM within surrounding shielding and/or structural elements. Previous work by our group has developed the capability to discern material density and composition in radiographic images by examining the edge transition characteristics of objects. The material construction of an object can be investigated in this way. In a weapons counting or discrimination context, unknown occultation of objects of interest, as well as additional elements of warhead construction, construction materials of varying geometry and makeup and various angles of radiograph are expected to impact algorithm performance. Advances in material discrimination algorithms are presented as a mechanism to help make these approaches robust to these sorts of variations.

Robinson, Sean M.↗