Dear Bill,

you could check the purity of your He. I remember a 28 spike as well,
however, it had a different source. It derived from impurities of the oxygen.
After exchange of the oxygen the spike disappeared.

Kind regards

Bruno


------------------------------------------
Dr. Bruno Glaser
Institute of Soil Science and Soil Geography
University of Bayreuth
D-95440 Bayreuth
Germany
-------------------------------------------