Title: A NanoSIMS 50 L Investigation into Improving the Precision and Accuracy of the 235U/238U Ratio Determination by Using the Molecular 235U16O and 238U16O Secondary Ions

Abstract

A NanoSIMS 50 L was used to study the relationship between the ²³⁵U/²³⁸U atomic and ²³⁵U¹⁶O/²³⁸U¹⁶O molecular uranium isotope ratios determined from a variety of uranium compounds (UO₂, UO₂F₂, UO₃, UO₂(NO₃)₂·6(H₂O), and UF₄) and silicates (NIST-610 glass and the Plesovice zircon reference materials, both containing µg/g uranium). Because there is typically a greater abundance of ²³⁵U¹⁶O⁺ and ²³⁸U¹⁶O⁺ molecular secondary ions than ²³⁵U⁺ and ²³⁸U⁺ atomic ions when uranium-bearing materials are sputtered with an oxygen primary ion beam, the goal was to understand whether use of ²³⁵U¹⁶O/²³⁸U¹⁶O has the potential for improved accuracy and precision when compared to the ²³⁵U/²³⁸U ratio. The UO₂ and silicate reference materials showed the greatest potential for improved accuracy and precision through use of the ²³⁵U¹⁶O/²³⁸U¹⁶O ratio as compared to the ²³⁵U/²³⁸U ratio. For the UO₂, which was investigated at a variety of primary beam currents, and the silicate reference materials, which were only investigated using a single primary beam current, this improvement was especially pronounced at low 235U+ count rates. In contrast, comparison of the ²³⁵U¹⁶O/²³⁸U¹⁶O ratio versus the ²³⁵U/²³⁸U ratio from the other uranium compounds clearly indicates that the ²³⁵U¹⁶O/²³⁸U¹⁶O ratio results in worse precision and accuracy. This behavior is based on themore » observation that the atomic (²³⁵U⁺ and ²³⁸U⁺) to molecular (²³⁵U¹⁶O⁺ and ²³⁸U¹⁶O⁺) secondary ion production rates remain internally consistent within the UO₂ and silicate reference materials, whereas it is highly variable in the other uranium compounds. Efforts to understand the origin of this behavior suggest that irregular sample surface topography, and/or molecular interferences arising from the manner in which the UO₂F₂, UO₃, UO₂(NO₃)₂·₆(H₂O), and UF₄ were prepared, may be a major contributing factor to the inconsistent relationship between the observed atomic and molecular secondary ion yields. Overall, the results suggest that for certain bulk compositions, use of the ²³⁵U¹⁶O/²³⁸U¹⁶O may be a viable approach to improving the precision and accuracy in situations where a relatively low ²³⁵U⁺ count rate is expected.« less

Authors:

Zirakparvar, N.; Hexel, Cole ;

• Search DOE PAGES for author "Hexel, Cole"
• Search DOE PAGES for ORCID "0000-0001-8101-2422"

Miskowiec, Andrew; Smith, Julie; Ambrogio, Michael; Duckworth, Douglas ;

• Search DOE PAGES for author "Duckworth, Douglas"
• Search DOE PAGES for ORCID "0000-0002-8161-5685"

Kapsimalis, Roger; Ticknor, Brian

Publication Date:

Sat May 18 00:00:00 EDT 2019

Research Org.:

Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1529710

Alternate Identifier(s):

OSTI ID: 1515674

Grant/Contract Number:  

AC05-00OR22725

Resource Type:

Published Article

Journal Name:

Minerals

Additional Journal Information:

Journal Name: Minerals Journal Volume: 9 Journal Issue: 5; Journal ID: ISSN 2075-163X

Publisher:

MDPI AG

Country of Publication:

Switzerland

Language:

English

Subject:

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY; NanoSIMS; uranium; isotope ratio mass spectrometry; secondary ion; matrix effect