Another possible way to measure dead layer thickness would be to use two different energies from a single source. The dead layer thickness in Monte Carlo simulations could then be optimized so that the efficiency ratio between these two energies matches the experimentally found ratio. For
instance, Bochud et al. [19] use the 121.8 and 1408.0 keV full energy peaks from 152Eu. However, at 1408.0 keV a significant portion of the photons penetrate the crystal completely, and thus the detection efficiency at this energy represents more a measurement of the active crystal
volume, rather than of the dead layer thickness. This adds a set of new uncertainties to the measurements such as the dimensions of the central hole. Ideally, one would use lower energies and a collimated photon beam. However, there must be sufficient separation in energy in order to
have a significant change in attenuation, and this might result in the higher energy photons reaching the crystal hole to a greater extent.