DEVELOPMENT OF THE NBS 10Be/9Be ISOTOPIC STANDARD REFERENCE MATERIAL.

The National Bureau of Standards (NBS), in conjunction with the Oak Ridge National Laboratory (ORNL) and the Accelerator Mass Spectrometry (AMS) community, is in the process of developing a **1**0Be/**9Be isotopic solution Standard Reference Material (SRM). The starting **1**0Be/**9Be solution was provided by the ORNL after Secondary Ionization Mass Spectrometric characterization for isotopic concentration. The radioactivity purity of the ORNL Master solution was confirmed by gamma-ray spectrometry, then diluted at NBS with solutions made from zone-refined single-crystal beryllium metal and sub-boiling double-distilled hydrochloric acid. Four serial dilutions were necessary to achieve a final **1**0Be/**9Be isotopic composition of approximately 3 multiplied by 10** minus **1**1. The accuracy of the dilutions was confirmed by liquid scintillation and AMS measurements. The isotopic composition of the ORNL Master solution was also confirmed at NBS by Resonant Ionization Mass Spectrometry. The isotopic composition of the final solution is being confirmed at the present time through international laboratory AMS measurments.