Isotopic analysis of uranium in NIST SRM glass by femtosecond laser ablation MC-ICPMS

We employed femtosecond Laser Ablation Multicollector Inductively Coupled Mass Spectrometry for the determination of uranium isotope ratios in a series of standard reference material glasses (NIST 610, 612, 614, and 616). The uranium in this series of SRM glasses is a combination of isotopically natural uranium in the materials used to make the glass matrix and isotopically depleted uranium added to increase the uranium elemental concentration across the series. Results for NIST 610 are in excellent agreement with literature values. However, other than atom percent U-235, little information is available for the remaining glasses. We present atom percent and isotope ratios for U-234, U-235, U-236, and U-238 for all four glasses. Our results show deviations from the certificate values for the atom percent U-235, indicating the need for further examination of the uranium isotopes in NIST 610-616.