Characterization of uranium samples of unknown origin

Due to its geographical location, Hungary is a transit country on the route of illicit trafficking of nuclear materials. During the 1990-ies there were several events in Hungary involving the seizure of such materials. According to Hungarian legislation, the Institute of Isotopes is responsible for on-the-spot and laboratory analysis of nuclear material of unknown origin. In order to decrease the threat of "nuclear terrorism" it is of paramount importance to find out as much as possible about the nuclear materials coming in this way into Hungary, as well as about their possible origin. Several methods of nuclear forensic science are used in the Institute for this purpose. In particular, the Nuclear Section of the Department of Radiation Safety has developed methods based on high-resolution gamma-spectrometry for the non-destructive assay of nuclear materials of unknown origin.

Development of a gamma-spectrometric method for Uranium age dating. An example of a method for nuclear forensics

The age of uranium samples is an important piece of information relevant both in combating illicit trafficking and in nuclear safeguards. It can help in determining the origin of seized or found nuclear materials, and, on the other hand, knowing the date of production of the material can help the safeguards expert to decide whether a highly-enriched Uranium-sample originates from excess weapons-usable materials or it is freshly produced. This method for age dating relies on measuring the daughter/parent activity ratio 214Bi/234U by low-background, high-resolution gamma-spectrometry. The initial methodology was derived during a "Round Robin" exercise, in which the properties of a HEU material relevant to nuclear forensics were assessed by several laboratories. The Uranium-age obtained by this gamma-spectrometric method was in agreement with the results reported by other participating laboratories, which used mass-spectrometry. The original method relied on using an efficiency calibrated geometry, which was easily achieved for thin samples in powder form. Since then, using a uranium sample of medium enrichment, the method was extended to determining the age of Uranium material of any physical form and geometrical shape. This is made possible by using the peaks of 238U for relative efficiency calibration, provided that they can be evaluated from the spectrum.

See also: Research in nuclear forensics