Study On Age-dating Of Enriched Uranium By Gamma Spectroscopy

Preventing proliferation of nuclear material and its related technologies is a key issue of international nonproliferation regime. Highly enriched uranium (HEU) is the most important nuclear material to be often verified in nuclear safeguards inspection.The age of nuclear material is defined as the time passed since the date of nuclear material was produced. It is one of important information to investigate the history and characterization of nuclear material and to verify the declaration of nuclear material production. In addition, it may also be useful in other nuclear verification regime in future such as Fissile Material Cut-Off Treaty to identify the newly produced materials.The age of a Uranium sample is usually defined as the time passed since it has been chemically separated from its daughter nuclides and, possibly, enriched. The parent/daughter relations of ²³⁴U decay chain of ²³⁴U/²³⁰Th, ²³⁵U/²³¹pa and ²³⁴U/²¹⁴Bi are advantageously used to determine the age of HEU.This paper described three kinds of method for determining the age of uranium, and discussed advantages and limitations of these methods. The age of uranium samples are measured through the radioactivity ratio of ²³⁴U/²¹⁴Bi by gamma spectrometry. The principle of measurement for radioactivity ratio of ²³⁴U/²³⁵U, ²³⁴U/²³⁵U and ²¹⁴Bi/²³⁸U using intrinsic efficiency calibration is discussed. The measurement is a nondestructive assay method for uranium age-dating by gamma spectrometry which is applicable to materials with any physical form and geometrical shape.Two different physical form and geometrical shape samples are measured and investigated, one is U₃O₈ powder, the other is uranyl nitrate. The measurement results are 27.3±0.8 and 18.0±0.7 years respectively. For the uranyl nitrate sample, the relative standard deviation of highly enriched uranium (HEU) age determination is less than 5% between the measured and declared age.