Yonggang Zhao

Primary studies on particle recovery of swipe samples for nuclear safeguards

Environmental sampling plays a significant role in nuclear safeguards. Isotopic ratio in uranium-bearing particles from swipe samples provides important information for detecting undeclared activities. Particle recovery which is the primary step of particle analysis, would affect the following analysis. The particle recovery efficiency of ultrasoneration recovery and vacuum suction-impact recovery were measured by alpha spectrometer with standard particles produced via aerosol spray pyrolysis method. The conditions of ultrasoneration were optimized and both recovery methods were evaluated. Finally, a procedure of particle recovery for unknown swipe samples was set up.

US-DOE and CIAE international cooperation in age-dating uranium standards

In 2014 the United States Department of Energy and the China Institute of Atomic Energy collaborated in a study measuring the model ages of uranium certified reference materials. Lawrence Livermore National Laboratory (LLNL) and Los Alamos National Laboratory (LANL), and the Chinese Institute of Atomic Energy (CIAE) determined 230Th–234U model ages for uranium certified reference materials U010 and U850. The aim of this work was to collaborate with CIAE and compare methods for measuring the age of bulk uranium materials using the 230Th–234U radiochronometer. Accurate results for age-dating depend on the accurate calibration of the tracer materials (e.g., 229Th and 233U) used for the isotope dilution mass spectrometry (IDMS) analyses. To facilitate inter-comparison of results, samples of a 230Th standard reference material were distributed to each laboratory for 229Th tracer inter-calibration. The resulting 230Th–234U model ages from this collaboration for U010 ranged from March 1956 to January 1959, which agree with the known material production date of June 5th, 1958. The determined model ages for U850 were from December 1955 to October 1957, which agree with the material production date of December 31, 1957. All three laboratories used independent methods to determine model ages for uranium standards that agree with known production ages and with previously reported results.

A comparison of two calibration methods of the 229 Th spike for uranium age dating by 230 Th/ 234 U radiochronometer

Abstract230Th/234U radiochronometer was commonly used for uranium age determination which could help to reveal the origin of the nuclear material. 229Th was a relatively appropriate spike for measuring 230Th by isotope dilution mass spectrometry and its concentration needs to be calibrated before using as spike. A prepared 229Th solution which was used as Th isotope spike for age dating of CRM U850 sample were calibrated separately by 232Th and 230Th standard materials. The calibrated results were compared and evaluated.