Best Practices for Determination of Initial 10Be/9Be in Early Solar System Materials by Secondary Ion Mass Spectrometry.

Beryllium-10 (t 1/2 = 1.4 Ma) is a short-lived radionuclide present in the early Solar System. It is produced solely by irradiation reactions and can provide constraints on the astrophysical environment of the Sun's formation. Calcium- and aluminium-rich inclusions (CAIs), the first solids formed in the Solar System, show clear evidence for live 10Be at their time of formation, but it is unclear whether they record the same initial 10Be/9Be ratio. In this study, we examine the secondary ion mass spectrometry methods used to determine the initial 10Be/9Be ratio in meteoritic inclusions. Based on analyses of synthesised matrix-matched glass reference materials, we show that the effects of differing major element bulk compositions on the secondary ion yields of Be and B are minor for relevant phases. We demonstrate the importance of using the mean square weighted deviation (MSWD) to interpret the significance of the initial 10Be/9Be value. For thirty-two CAIs, we re-calculated the regressions using literature data, finding that several have unacceptably high MSWD. We calculate the effects of possible sources of isotopic disturbance. Finally, we outline best practices for reporting 10Be-10B data, to enable a more refined determination of the initial 10Be/9Be ratio in the early Solar System.