Rate equation model of laser induced bias in uranium isotope ratios measured by resonance ionization mass spectrometry

Isselhardt, Brett H.; Prussin, S. G.; Savina, M. R.; Willingham, David; Knight, Kim B.; Hutcheon, I. D.

doi:10.1039/c5ja00249d

Cited by 5 publications

(3 citation statements)

References 37 publications

(59 reference statements)

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“…We are currently developing a description of laser ionization based on a rate equation model that can be deployed spatially. 31 The spatial convolution of eqs 1 and 2 gives ion fractions (ions produced per atom sputtered) ranging from 75% for the shortest primary ion pulse (95 ns) to 37% for the longest pulse (1000 ns). For uranium, this fraction must be scaled by the ground state occupancy of 79% as discussed above.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…This function does not describe a real multilevel system far from saturation; we use it only to estimate the ionization volume for resonance ionization schemes in which the first two steps are strongly saturated and the autoionizing transition is at close to saturation, which is an accurate description of our scheme. We are currently developing a description of laser ionization based on a rate equation model that can be deployed spatially …”

Section: Resultsmentioning

confidence: 99%

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High Useful Yield and Isotopic Analysis of Uranium by Resonance Ionization Mass Spectrometry

et al. 2017

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Useful yields from resonance ionization mass spectrometry can be extremely high compared to other mass spectrometry techniques, but uranium analysis shows strong matrix effects arising from the tendency of uranium to form strongly bound oxide molecules that do not dissociate appreciably on energetic ion bombardment. We demonstrate a useful yield of 24% for metallic uranium. Modeling the laser ionization and ion transmission processes shows that the high useful yield is attributable to a high ion fraction achieved by resonance ionization. We quantify the reduction of uranium oxide surface layers by Ar and Ga sputtering. The useful yield for uranium atoms from a uranium dioxide matrix is 0.4% and rises to 2% when the surface is in sputter equilibrium with the ion beam. The lower useful yield from the oxide is almost entirely due to uranium oxide molecules reducing the neutral atom content of the sputtered flux. We demonstrate rapid isotopic analysis of solid uranium oxide at a precision of <0.5% relative standard deviation using relatively broadband lasers to mitigate spectroscopic fractionation.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

High Useful Yield and Isotopic Analysis of Uranium by Resonance Ionization Mass Spectrometry

et al. 2017

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“…Our previous work used a three-color scheme based on the work of Schumann et al 14 that has been reported on previously. 9,15,16 This scheme ionizes atoms that originate in the ground state; however, Wright et al showed that ∼17% of atoms sputtered from metallic U exist in a low-lying 5 K 5 state at 620.323 cm −1 and that >99% of sputtered atoms exist in either this 5 K 5 or the 5 L 6 ground state. 12 (All state energies reported in this study refer to the 238 U isotope unless otherwise noted.)…”

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confidence: 99%

New Resonance Ionization Mass Spectrometry Scheme for Improved Uranium Analysis

et al. 2018

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Resonance ionization mass spectrometry (RIMS) combines tunable laser spectroscopy with mass spectrometry to provide a high-efficiency means of analyzing solid materials. We previously showed a very high useful yield of 24% for analysis of uranium using three lasers to excite and ionize atoms sputtered from metallic uranium and uranium dioxide. A new resonance ionization scheme using only two lasers achieves a higher useful yield of 38% by accessing both the ground electronic state and a low-lying electronic state of atomic uranium that is significantly populated by sputtering. The major loss channel in analyzing uranium dioxide is the formation of UOx molecules during sputtering. Prebombardment of the surface with 3 keV noble gas ions prior to analysis reduces the surface and results in a sputtered flux with a greatly enhanced proportion of atomic U. This method of surface reduction results in uranium useful yields as high as 6.6% for uranium dioxide analysis, compared to 2% from previous work.

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Analysis of sub-picogram quantities of 238Pu by thermal ionization mass spectrometry

Maassen

Inglis

Wende

et al. 2019

J Radioanal Nucl Chem

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Rate equation model of laser induced bias in uranium isotope ratios measured by resonance ionization mass spectrometry

Abstract: RIMS rate equation model of uranium ionization to facilitate the study of laser induced bias on measured isotope ratios.

Cited by 5 publications

References 37 publications

High Useful Yield and Isotopic Analysis of Uranium by Resonance Ionization Mass Spectrometry

High Useful Yield and Isotopic Analysis of Uranium by Resonance Ionization Mass Spectrometry

New Resonance Ionization Mass Spectrometry Scheme for Improved Uranium Analysis

Analysis of sub-picogram quantities of 238Pu by thermal ionization mass spectrometry

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