A low-background γγ-coincidence spectrometer for radioisotope studies

The performance of a new, low-background NaI(Tl) spectrometer, based on γγ-coincidence counting, is discussed. We present experimental coincidence efficiencies, timing resolutions, background count rates, and minimum detectable activities. The spectrometer has been simulated using Geant4, and the results are used for estimating coincidence efficiencies for volume sources. To test the device, we measured the cosmogenic 26Al activity in a small (17.7 g) meteorite fragment. We find a value of 52.9±7.8dpm∕kg, in agreement with the activity measured previously in a much larger fragment of the same meteorite using a HPGe detector.