Ten years low-level counting in the underground laboratory in Bern, Switzerland

Although new techniques of direct atom counting have been developed, which are also discussed at this conference, the good old low-level counting technique is still important. Looking back to the first decade of measurements in our underground laboratory, we realize that many interesting results have been obtained. The following examples are discussed:

39Ar is up to now only measured in Bern. This isotope has been used for ice and groundwater dating and for studying ocean water circulation, mixing and equilibrating with the atmosphere.

37Ar results have already been presented at the two preceding High Tatras LLC conferences. Now the full 15 years' series of measurements is given and shortly discussed.

3H measurements are possible without enrichment by direct liquid scintillation counting down to the present low environmental levels of 20–80 pCi/l in precipitation. Series of results of two selected areas are presented.

14C is measured routinely in several gas proportional counters. With each counter about 60 samples and 40 standard, background or blank samples are measured per year. As an example, the 14C results measured in tree leaves at reference stations in Switzerland, unaffected by man-made contributions, are presented.