In activation analysis with photons and charged particles, the activities of positron-emitting reaction products are determined by unfolding complex decay curves obtained from a pair of coincidence detectors. Certain interfering reaction products emit a high-energy gamma ray coincident with the positron, and the signal from these was distinguished from the signal from pure positron emitters by collecting a 0.51-MeV annihilation photon in one detector and the other 0.51-MeV annihilation photon plus the high-energy gamma ray in the other detector. Since the improvement in sensitivity is directly related to the interference removal, which increases with the probability of detecting the associated gamma ray, high efficiency was required. The method is illustrated by a photon activation analysis experiment in which oxygen was measured in sodium. The activation product, 15O, is the signal and 22Na and 38K are the interference reaction products. Experiments show that a large (8-in.-diam. × 12-in.-long) “well” detector will give five-fold sensitivity improvement over a 2.3- × 6-in. detector when each is in coincidence with a 2- × 2-in. detector. A time sequence of coincidence-gated spectra was taken, and the counts in specified energy increments were determined. Composite decay curves were constructed and unfolded into components. The large detector causes counts from the interference reaction products which would appear in the 0.57-MeV annihilation peak to appear in the higher energy portion of the spectrum because of the high probability of collecting additional energy from the associated gamma rays.