Optimized Chemical Separation and Measurement by TE TIMS Using Carburized Filaments for Uranium Isotope Ratio Measurements Applied to Plutonium Chronometry

Abstract

An optimized method is described for U/Pu separation and subsequent measurement of the amount contents of uranium isotopes by total evaporation (TE) TIMS with a double filament setup combined with filament carburization for age determination of plutonium samples. The use of carburized filaments improved the signal behavior for total evaporation TIMS measurements of uranium. Elevated uranium ion formation by passive heating during rhenium signal optimization at the start of the total evaporation measurement procedure was found to be a result from byproducts of the separation procedure deposited on the filament. This was avoided using carburized filaments. Hence, loss of sample before the actual TE data acquisition was prevented, and automated measurement sequences could be accomplished. Furthermore, separation of residual plutonium in the separated uranium fraction was achieved directly on the filament by use of the carburized filaments. Although the analytical approach was originally tailored to achieve reliable results only for the (238)Pu/(234)U, (239)Pu/(235)U, and (240)Pu/(236)U chronometers, the optimization of the procedure additionally allowed the use of the (242)Pu/(238)U isotope amount ratio as a highly sensitive indicator for residual uranium present in the sample, which is not of radiogenic origin. The sample preparation method described in this article has been successfully applied for the age determination of CRM NBS 947 and other sulfate and oxide plutonium samples.

Precise determination of 244Cm by 244Cm/239Pu alpha ratio measurements

“…A TIMS (TRITON, Thermo Fisher Scientific, USA) with continuous heating was used to measure the isotopic ratios of curium on the filaments. The measurements were carried out in total evaporation (TE) mode, 4–8 which is a frequently applied technique to minimize mass fractionation effects. The TE method development was based on 239 Pu from certified reference materials, CRM 6 and CETAMA Pu MP2.…”

“…The measurements were carried out in total evaporation (TE) mode, 4–8 which is a frequently applied technique to minimize mass fractionation effects. The TE method development was based on 239 Pu from certified reference materials, CRM 6 and CETAMA Pu MP2. 11 The target Cm amount for filament loading was 100 ng added by direct pipetting (2 times 1 μL) of a 50 ng μL −1 Cm solution.…”

“…The determination of an isotopic vector is commonly carried out by thermal ionization mass spectrometry (TIMS). 4–9 In safeguard analysis, this is a dedicated method and instrument for the analyses of uranium and plutonium. Performance and traceability of isotopic vector analyses are ensured by availability of certified uranium and plutonium standards accurately prepared from pure reference metals.…”

High-Resolution Inductively Coupled Plasma Optical Emission Spectrometry for 234U/238Pu Age Dating of Plutonium Materials and Comparison to Sector Field Inductively Coupled Plasma Mass Spectrometry

“…For nuclear forensic studies the period elapsed since the last purification/separation of a radioactive sample, i.e., its “age”, provides valuable hints largely helping in identifying the origin of such a material . Because the radioactive material is chemically purified, i.e., separated from impurities including its decay products during its production, the in-growth of a daughter nuclide can be determined relative to its parent isotope eventually yielding the age of the sample. − …”

“…The Pu isotopes 238 Pu, 239 Pu, 240 Pu, and 242 Pu all decay by emission of α particles, while 241 Pu undergoes β decay to produce 241 Am. As such, Pu age dating has been carried out using various chronometers, for instance exploiting 234 U/ 238 Pu, 235 U/ 239 Pu, 236 U/ 240 Pu, 241 Am/ 241 Pu, and 238 U/ 242 Pu isotope ratios. − While radiometric age dating of an unknown sample is based on various boundary conditions (complete removal of daughter nuclide from parent nuclide, sample considered as a closed system, etc. ), − the following equation describes the corresponding mathematical approach for the daughter-to-parent ratio of 234 U/ 238 Pu: where t denotes the elapsed time since the last separation, λ is the decay constant, and is the amount ratio of the respective isotopes.…”