236U/238U measurements in uranium ore concentrates at CAMS
Corinne Dorais1, Scott Tumey1, Naomi Marks1, Gregory Brennecka1
1LLNL, Livermore, United States
Uranium ore concentrate (UOC), the refined uranium product that is subsequently enriched for use in reactors and weapons, is one of the nuclear materials most frequently targeted for theft and trafficking. In the event that questioned UOC is recovered, nuclear forensic analyses are conducted to assist in provenance assessment. Such investigations rely on multiple forensic signatures that provide complementary information about the origin and processing history of a sample. One such signature that is still being developed is the 236U/238U ratio of a sample. Generally considered to be an anthropogenic isotope, 236U is also produced naturally at ultra-trace levels via neutron capture on 235U. Variation in the natural 236U/238U ratio, which has been shown to range from 10- 14 to 10-10, is thought to be controlled by factors that affect the production or moderation of neutrons in the ore body such as ore grade, deposit age, the amount of certain trace elements present, and water content. However, because 236U is present at such low concentrations in natural materials, AMS is the only technique with the sensitivity to measure this ratio. Recently, the Center for Accelerator Mass Spectrometry (CAMS) at Lawrence Livermore National Laboratory (USA) made upgrades to the heavy element beamline, including the installation of a new 15º bending magnet, in an effort to further suppress 235U, which is up to 1011 times more abundant than 236U and can interfere with the 236U measurement. Details of the new 236U/238U measurement setup at CAMS along with preliminary results from a suite of UOC samples will be presented.
Corinne is a postdoc at LLNL’s CAMS with a background in mass spectrometry and radioanalytical chemistry. Her current research focuses on developing ultra-trace measurements for nuclear forensics applications.