Development and Characterization of Large La-Halide Gamma-Ray Scintillators for Future Planetary Missions

Future planetary missions such as BepiColombo are resource limited in both mass and power. Due to the vicinity of the spacecraft to the Sun, the instrumentation will face harsh environments as far as radiation levels and thermal loads are concerned. Only radiation hard detectors that need no or little cooling will be able to successfully operate after long cruise times and during the expected mission life times. The next generation of Lanthanum Halide (LaX) scintillators promises to provide sufficient resolution in the spectral range between 1 and 10 MeV where most of the elemental gamma-ray emission lines can be detected. In order to be suitable for planetary gamma-ray spectrometers with sufficient sensitivity it had to be proven that larger crystals of size 3" can be produced and that they maintain their resolution of ~3% at 662 keV. For that purpose we have produced and characterized several larger LaBr crystals and assessed their radiation hardness by exposure of the crystals to radiation doses that are representative to the expected conditions in space environment. Systematic measurements on several crystals allowed the determination of the activation potential and the performance verifications from which consequences for instrument flight performance can be derived. From these investigations we conclude that these scintillators are well suited for planetary missions with stable and excellent performance.