Simultaneous two sample activation measurement immune to detector intercalibration

The requirement of accurate detector intercalibration in simultaneous two sample activation measurements is a major limitation of the method. A new method of measurement is described which avoids the intercalibration requirement. The method is based on switching the samples so that each detector sees each sample for a fraction of the total counting time. The results of the measurements are then linearly combined to give an estimate of the relative activity without requiring a knowledge of the ratio of the efficiencies of the detectors. The error propagation equations associated with the method are discussed for constant rate background conditions and graphs are presented to enable the optimum choice of the total and fractional counting times to achieve minimum variance.