  The 10Be/7Be ratio is a sensitive tracer for the study of atmospheric
transport, particularly with regard to stratosphere-troposphere exchange.
Measurements with high accuracy and efficiency are crucial to 7Be and 10Be
tracer studies. This article describes sample preparation procedures and
analytical benchmarks for 7Be and 10Be measurements at the Xian Accelerator
Mass Spectrometry (Xian-AMS) laboratory for the study of rainwater samples. We
describe a sample preparation procedure to fabricate beryllium oxide (BeO) AMS
targets that includes co-precipitation, anion exchange column separation and
purification. We then provide details for the AMS measurement of 7Be and 10Be
following the sequence BeO- -> Be2+ -> Be4+ in the Xian- AMS. The 10Be/7Be
ratio of rainwater collected in Xian is shown to be about 1.3 at the time of
rainfall. The virtue of the method described here is that both 7Be and 10Be are
measured in the same sample, and is suitable for routine analysis of large
numbers of rainwater samples by AMS.
