Be-7 detections in ambient air samples

[Bill Lohner <Bill.Lohner@epa.state.oh.us>]

During routine gamma analyis of high volume particulate air samples (originally looking for Co-60 and Cs-134), our laboratory has detected somewhat elevated readings for Be-7.

The only natural source we've been able to fing would be from upper atmosphere interactions with N and O.  Does anyone have any information regarding the presence of Be-7 in ambient air samples, such as possible sources, "normal concentrations", etc.?
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
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