Thesis (Ph. D.)--University of Chicago, Department of Astronomy and Astrophysics, 2001. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Chicago, Department of Astronomy & Astrophysics, August 2001. / Includes bibliographical references. Also available on the Internet.

For verifying the Comprehensive Nuclear-Test-Ban Treaty (CTBT), different monitoring technologies (seismic, infrasound, hydroacoustic, and radionuclide detection) are combined. The monitoring of radioactive xenon isotopes is one of the principal methods for the determination of the nuclear nature of an explosion. After an underground nuclear detonation the radioxenon isotopes [superscript 131m]Xe, [superscript 133m]Xe, ¹³³Xe, and ¹³⁵Xe, and the radioargon isotope ³⁷Ar have an increased probability of detection. In order to effectively utilize these isotopes as indicators of nuclear testing, an accurate background must be calculated. This work examines the fission products produced by spontaneous fission of ²³⁸U, which is naturally present in the earth's crust, and of ²⁴⁰Pu which is present as a product of nuclear weapons and nuclear reactor accidents. These calculations provide a range of production values for radioxenon in a variety of geologies as well as at various historic locations. The activation of geologic calcium and potassium by cosmic ray neutrons is considered for a variety of properties effecting the neutron flux. These calculations provide a range of radioargon production values across a selection of geologies. The impact of latitude and the solar activity cycle are also examined. In order to examine the transport of the isotopes through soil a model of the transport of xenon and argon through various geologies was developed. This model incorporates both the introduction of xenon from the atmosphere and that produced by spontaneous fission. This is then considered in light of what might be observed in an on-site inspection (OSI). What this work finds is that the radioxenon natural background does exceed detection limits in particular locations and geologies, however, a careful examination of the location and the ideal sampling depths can minimize the impact during an OSI. Radioargon, however, has a much larger natural background at shallow depths which are the realm of OSI sampling. Should radioargon sampling be used in an OSI the sampling time is crucial in distinguishing a nuclear explosion from the natural background. In some scenarios the natural background production of radioargon may be sufficient to interfere with the detection of an underground nuclear weapon test. This information may be beneficial in the development of future OSI noble gas monitoring techniques. / text

No description available.

No description available.

No description available.

Trafficking of radioactive material, particularly special nuclear material (SNM), has long been a worldwide concern. To interdict this material the US government has installed radiation portal monitors (RPMs) around the globe. Building materials surrounding an RPM can greatly effect the detector’s background radiation levels due to Naturally Occurring Radioactive Material (NORM). In some cases this effect is so great that the initial RPM setup had to be rebuilt. This thesis develops a methodology for quick and efficient determination of the specific activity and composition of building materials surrounding a RPM to predict background levels, therefore determining the minimum detectable quantity (MDQ) of material. This methodology builds on previous work by Ryan et al by generating material and source cards for a detailed Monte Carlo N-Particle (MCNP) deck, based on an experimental RPM setup to predict the overall gamma background at a site. Gamma spectra were acquired from samples of building materials and analyzed to determine the specific activity of the samples. A code was developed to estimate the elemental composition of building materials using the gamma transmission of the samples. These results were compared to previous Neutron Activation Analysis (NAA) on the same samples. It was determined that densitometry provided an elemental approximation within 5% of that found through NAA. Using the specific activity and material composition, an MCNP deck was used to predict the gamma background levels in the detectors of a typical RPM. These results were compared against actual measurements at the RPM site, and shown to be within 10% of each other.

Thesis (M.Sc.). / Written for the Dept. of Physics. Title from title page of PDF (viewed 2009/08/07). Includes bibliographical references.

Thesis (Ph. D.)--University of Chicago, Dept. of Astronomy and Astrophysics, March 2000. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Chicago, Dept. of Astronomy and Astrophysics. / Includes bibliographical references. Also available on the Internet.