A LaBr3:Ce-NaI(Tl) Phoswich for X- and low energy astronomy

We report about the testing and performance of a Phoswich detector made of 3 in. diameter and 0.5 in. thick LaBr3:Ce with 3 in. diameter and 1 in. thick NaI(Tl). A pulse shape analysis using the zero-crossover technique was used to separate the signals from the individual layers. A significant reduction in general background and about 20% reduction in the X-ray peak due to internal activity around 30 keV was achieved by using the detector in anti-coincidence mode. This reduction of internal activity around 30 keV was also found to be in good agreement with the result from GEANT4 simulation. The energy resolution of the LaBr3:Ce is found to be inferior in the Phoswich configuration due to the absorption of the photons in the thicker NaI(Tl).