Background measurements with different shielding and anticoincidence systems

Extremely low background count rates are a necessary condition for both the measurement of 39Ar concentrations in ground and ocean water and of 14C activities in small samples using gas proportional counting techniques. A systematic comparison of the performance of three different designs of shielding systems in four different installations has been made. Background values of selected gas proportional counters were measured, compared and separated into their various components. Acceptably low backgrounds were obtained in all the systems tried. The performance of a NaI shield in a surface laboratory was found to be at least equal to the best obtained with a gas anticoincidence detector in a deep underground laboratory