title: Rhenium filament oxidation: Effect on TIMS performance and the roles of carburization and humidity.
abstract: This communication presents findings on the effect of rhenium filament oxidation on thermal ionization mass spectrometry (TIMS) analyses of plutonium. Additionally, the roles of atmospheric humidity and carburization on the oxidation characteristics (i.e. aging) of rhenium filaments were studied. Degassed and carburized filaments were aged for up to 79 days under dry and humid conditions, and the growth of oxo-rhenium crystallites was investigated intermittently by scanning electron microscopy (SEM) to construct growth profiles. SEM images were analyzed to determine average crystallite size, number density, and percent surface coverage. Crystallite growth was found to be suppressed by both filament carburization and dry storage conditions (~13% relative humidity). Under humid conditions (75% relative humidity), crystallite growth progressed steadily over the investigatory period, reaching >2.3% surface coverage within 79 days of aging. Atomic ion production of Pu (Pu+) was suppressed by approximately 20% and the standard deviation of isotope ratio measurements was increased by 170% when filaments with 1% oxide surface coverage were used in sample loading. Measurement sensitivity and reproducibility are imperative for applications involving ultra-trace analysis of plutonium by TIMS. These findings offer validation for observations regarding the detrimental effect of excessive filament aging post-degassing, improve the understanding of conditions that impel the oxidation of rhenium filaments, and provide practical means to suppress the growth of oxides.
authors.affiliation: Department of Chemical and Biomolecular Engineering, Clemson University, 127 Earle Hall, Clemson, SC 29634, USA.
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Mannion
authors.affiliation: Savannah River National Laboratory, National Security Directorate, Aiken, SC 29808, USA.
authors.forename: Charles R
authors.initials: CR
authors.lastname: Shick
authors.affiliation: Savannah River National Laboratory, National Security Directorate, Aiken, SC 29808, USA.
authors.forename: Glenn A
authors.initials: GA
authors.lastname: Fugate
authors.affiliation: Savannah River National Laboratory, National Security Directorate, Aiken, SC 29808, USA.
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Wellons
authors.affiliation: Department of Environmental Engineering and Earth Sciences, Clemson University, 342 Computer Court, Anderson, SC 29625, USA.
authors.forename: Brian A
authors.initials: BA
authors.lastname: Powell
authors.affiliation: Department of Chemical and Biomolecular Engineering, Clemson University, 127 Earle Hall, Clemson, SC 29634, USA. Electronic address: shusson@clemson.edu.
authors.forename: Scott M
authors.initials: SM
authors.lastname: Husson
keywords: Isotopic analysis; Nuclear forensics; Rhenium oxide; Surface passivation; Thermal ionization mass spectrometry