Investigating enhanced thorium ionization in TIMS using Re/Pt porous ion emitters

Improved sample utilization in thermal ionization mass spectrometry isotope ratio measurements: refined development of porous ion emitters for nuclear forensic applications

“…Despite PIEs exhibiting enhanced ionization efficiencies relative to traditional filaments during the analyses of trace levels of thorium [10], findings herein suggest that, under the analytic conditions employed during this study, PIEs were unable to provide the anticipated improvements in thorium isotope measurements. Based on the results we can conclude that the thorium sample preparation method outlined in this paper is not suitable for analysis with PIEs and requires modification.…”

“…Traditional filaments, on the other hand, exhibited the highest precision ratio results at 10 000 cps; this was the highest count rate attempted using traditional filaments during this investigation. The inability of PIE filaments to maintain stable ion beams at higher aiming intensities relative to traditional filaments was unexpected as previous ionization efficiency studies conducted using PIE sources at picogram mass loading levels of uranium [9], americium and plutonium [3], and, most notably, thorium [10] have demonstrated a substantial increase in sample utilization when compared to standard single rhenium filaments. Ionization efficiency studies presented in Chapter 3 of this Dissertation show that PIEs were not only capable of significantly boosting ion yield, but generating stable ion beams with several times the intensity of those emitted from standard filaments at mass loading levels of less than 10 pg as well.…”

“…The addition of H 3 PO 4 appears to have a profound effect on a PIEs ability to generate and maintain a stable ion beam at higher count rates, >3000 cps for the thorium mass loading levels investigated during this study. To date, thorium analyses have never been conducted at such small quantities using PIEs; 30 pg mass loadings atop PIE filaments are the smallest quantity of thorium tested [10]. This is approximately one hundred times the size of thorium samples samples tested in this study.…”

“…The extent to which an element can be ionized is highly contingent on the work function of the ionizing surface. This process can be described by the Saha- exhausted within the first fifteen minutes of analyses [10]. Due to the highly refractory nature of thorium, TIMS analyses of thorium are conducted at much higher temperatures than those for plutonium.…”

“…Such low efficiencies significantly limit the ability make accurate and precise measurements of high priority elements (e.g., americium, plutonium, uranium and thorium) that could potentially provide critical signatures in nuclear forensic, non-proliferation, and safeguards efforts. additional ions may be generated via collisions between escaped neutral atoms with platinum ion emitted as the PIE material is consumed during heating [10]. The extent to which each mechanism contributes to the overall boost in ionization efficiency is unknown at this time.…”