To complement and support the work on ionizing radiation at the BIPM, there is a long-standing commitment to studies in counting statistics. This has led to the development not only of novel techniques, such as the selective sampling method, but also to a better understanding of the problem of the expression of the uncertainty of measurements. In particular, this work has contributed significantly to the internationally agreed Guide to the Expression of Uncertainty in Measurement.

For more information about selective sampling, see

Müller J.W., Selective sampling - an alternative to coincidence counting, Nucl. Instr. Meth., 1981, 189, 449-452.

Abstract. The classic coincidence method requires some important and insufficiently known corrections when it is applied to high count rates. We outline an experimental way of avoiding most of these difficulties, where the ratio of all the registered counts to those lacking a partner in the opposite channel is directly measured. From this the counting efficiency can be readily deduced. The new method is particularly useful for the absolute measurement of high activities.