Ultra-trace analysis of plutonium by thermal ionization mass spectrometry with a continuous heating technique without chemical separation

摘要

Thermal ionization mass spectrometry (TIMS) with a continuous heating technique is known as an effective method for measuring the isotope ratio in trace amounts of uranium. In this study, the analytical performance of thermal ionization mass spectrometry with a continuous heating technique was investigated using a standard plutonium solution (SRM 947). The influence of the heating rate of the evaporation filament on the precision and accuracy of the isotope ratios was examined using a plutonium solution sample at the fg level. Changing the heating rate of the evaporation filament on samples ranging from 0.1 fg to 1000 fg revealed that the influence of the heating rate on the precision and accuracy of the isotope ratios was slight around the heating rate range of 100-250 mA/min. All of the isotope ratios of plutonium (SRM 947), Pu-238/Pu-239, Pu-240/Pu-239, Pu-241/Pu-239 and Pu-242/Pu-239, were measured down to sample amounts of 70 fg. The ratio of Pu-240/Pu-239 was measured down to a sample amount of 0.1 fg, which corresponds to a PuO2 particle with a diameter of 0.2 mu m. Moreover, the signals of Pu-239 could be detected with a sample amount of 0.03 fg, which corresponds to the detection limit of Pu-239 of 0.006 fg as estimated by the 3-sigma criterion. Pu-238 and U-238 were clearly distinguished owing to the difference in the evaporation temperature between Pu-238 and U-238. In addition, Pu-241 and Am-241 formed by the decay of Pu-241 can be discriminated owing to the difference in the evaporation temperature. As a result, the ratios of Pu-238/Pu-239 and Pu-241/Pu-239 as well as Pu-240/Pu-239 and Pu-242/Pu-239 in plutonium samples could be measured by TIMS with a continuous heating technique and without any chemical separation processes. (C) 2015 Elsevier B.V. All rights reserved.