Year
2001
Abstract
In the early 1990's, the Member States of the Non-Proliferation of Nuclear Weapons Treaty (NPT) decided that it was necessary to strengthen the International Atomic Energy Agency’s (IAEA) safeguards measures. One of the approaches designed to detect undeclared nuclear activities was the environmental sampling program. Following successful field trials, environmental sampling has played a vital role as a routine part of safeguards inspections since early 1996. While environmental sampling and analysis has been shown to be a valuable addition to the traditional safeguards tools of materials accountancy, it has added a new series of challenges for the investigator. Environmental samples often contain only trace amounts of uranium or plutonium and there are often losses associated with extraction of the analyte from the sample prior to mass spectrometric analysis. Thus, efficient utilization of the available material during the isotope ratio analysis is crucial. However, the ionization efficiency of uranium using standard thermal ionization mass spectrometry (TIMS) is very low (0.2% under best conditions). Increasing the ionization efficiency by even a small amount will have a dramatic effect on the analysis of uranium, allowing very small samples (1 ng or less) to be analyzed precisely and accurately. In an effort to support the IAEA and its role in nuclear non-proliferation and nuclear safeguards, we have developed a high efficiency thermal ionization cavity ion source. Unlike traditional TIMS sources which employ a filament design, the cavity ion source uses a tungsten rod with a 0.5mm diameter cavity machined into one end. The high temperatures and high surface area in the confined volume of the cavity allow a greater ionization efficiency to be achieved. We have coupled a cavity ion source to one of our sector instruments at Oak Ridge National Laboratory. This device has demonstrated its ability to deliver highly precise measurements with a greater ionization efficiency than the instrument’s original single filament ion source. This prototype is also the basis for our ongoing development of a cavity source for the Safeguards Analytical Laboratory (SAL). Results of the design and testing of this new source will be reported. The installation of this device will broaden the capabilities of SAL allowing the analysis of samples that are designated as “difficult” - those that are either too low in concentration to be analyzed normally, or that experience difficulties in the extraction process.