Call number: LD2668 .T4 1957 C45 / Master of Science

samples were irradiated for approximately 45 minutes to allow for the saturation of fission products. The first method used the beam port shutter and allowed for longer counting and irradiation times, but was unsuitable for examining fission products with half-lives below 10 seconds. The on/off method used a cycle of equal irradiation and counting times of one minute. The second method is able to measure track the production of fission products with half-lives of less than 10 seconds. This method used a borated aluminum wheel beam chopper to stop the irradiation of the sample during counting. The beam chopper was set to cycle for approximately one second of counting following half a second of irradiation. The spectra from both methods were analyzed and the peaks were assigned to the appropriate fission products. The majority of the peaks were composed of gamma-rays from multiple nuclides. The peaks created by gamma-rays from decays of a single nuclide were used to calculate the detection limits of the system. Using the beam chopper system, 21 peaks would be above the detection limits of our system 95% of the time for uranium samples of less than one kilogram. / text

This study was an evaluation of the applicability of the neutron generator in identifying the manufacturing sources of drugs by studying; trace elements present in drug samples. The motivation w1as the possible assistance to law enforcement agencies in tracing illicit drugs to their origins.Eight samples of dextroamphetamine sulfate were used in the evaluation process. The samples were activated with a neutron generator producing a 14MMeV neutron flux of the order of 1010 neutrons/sec/cm2. A pair of NaI detectors and a multichannel analyzer were used to study, the decay spectra of the samples.The analytical system was found in most cases to be quite capable of detesting elements which were present in a few parts per million. Little success was encountered in detecting elements present at levels commonly considered to be trace amounts. Phosphorus, silicon, sodium, iron, and strontium where found in amounts ranging from 65 to 250,000 parts per million.Ball State UniversityMuncie, IN 47306

AbstractThe purpose of this study was the evaluation of various neutron activation cross sections using 2.8 MeV neutrons. This area of study was chosen because only a small amount of research has been done using generator produced 2.8 MeV neutrons.Most of the cross section values listed in the literature were small, requiring the use of various methods to increase the number of reactions occurring.A relative measure of the neutron flux was made using indium standards. The efficiency of the detection system was experimentally measured by the use of standardized radioisotopes.The product isotopes, produced by (n,ﻻ) or (u,n’ﻻ) reactions, and their measured activation cross sections were: 116mIn - 104 + 5 mb; 137mBa - 459 + 45 mb; 139Ba - 5.48 + 0.47 mb; 128I, - 38.5 + 3.0 mb; 56Mn - 4.28 + 0.34 mb; and 87mSr - 219 ± 26 mb. Errors from 4.8% for 116mIn to 12% for 87mSr were determined.Ball State UniversityMuncie, IN 47306

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 112-118). Also available on the Internet.

The 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. / text

The ability to quickly and accurately quantify fissile constituents in bulk materials remains essential to many aspects of nuclear forensics and for safeguarding nuclear materials and operations. This often entails the analysis of trace quantities of nuclear debris or effluents, and typically requires bulk sample digestion followed by actinide separation and mass spectrometry. Because destructive methods are time and labor intensive, efforts have been made to develop alternative nondestructive methods for this type of analysis. This work, performed at Oak Ridge National Laboratory at the High Flux Isotope Reactor (HFIR), seeks to utilize delayed neutron activation analysis on samples of interest containing multiple fissile constituents. Based on the variances in the fission product yields of individual fissile nuclides, this work utilizes methods of linear regression to derive a technique that allows for such analysis, forgoing chemical separation and using only a single irradiation and counting step. / text

Accurate estimates for the molecular transport coefficients are critical to predicting the movement of gases in geological media. Here I present a novel methodology for using prompt gamma activation analysis to measure the effective diffusivity of noble gases in a porous medium. I also present a model to estimate the connectivity parameter of a soil from measurements of its saturated conductivity, macro porosity, and pore volume and pore surface fractal dimensions. Experiments with argon or xenon diffusing through a nitrogen saturated geological media were conducted. The noble gas concentration variations at its source were measured using prompt gamma activation analysis and later compared to a numerical diffusion model to estimate the effective diffusion coefficient. Numerical simulations using the estimated diffusivity and the experimental argon data produced results with a correlation parameter R² = 0.98. However, neglecting transport mechanisms other than diffusion largely under-predicted the xenon depletion rates observed during the first hours of experiment. To explain these results, a second model was developed which included the effect of pressure gradients and bulk convection that might arise from the faster molecular migration of the light species in a non-equimolar system and gravitational currents. Finally, the fractal model developed for this dissertation was used to estimate the connectivity parameters and walking fractal dimension of a group of geological samples that were previously characterized. This model successfully predicted positive connectivity factors and walking fractal dimensions between two and three for every sample analyzed. / text

The need for trace, minor and main element analysis becomes more prevalent each year with an every expanding variety of applications. Neutron Activation Analysis (NAA) is an attractive non-destructive analysis tool that can be utilized on small samples regardless of what physical state the material is in. The analysis process however, typically requires researchers to physically handle a radioactive sample in order to transport the sample to detection systems for data gathering. The purpose of this project was to design a Fully Automated Rapid Irradiated Sample Transit (FARIST) system that could deliver samples into a reactor core and then transfer them to a detector for analysis with zero human interaction. The system would be designed to hold up to 30 samples prior to analysis with the irradiation, decay, and counting times programmed in initially so that once analysis was initiated, no user interaction was required for the next 29 samples. The last requirement of the system was that it supports cyclic NAA. This work discusses the science and history behind NAA as well as the design, construction, installation, and testing of the new FARIST system. / text

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