The radiation hard BGO crystals for astrophysics applications

The scintillation crystal bismuth germanate Bi₄Ge₃O₁₂ (BGO) is widely used in many applications. The developed in the Nikolaev Institute of Inorganic Chemistry, Novosibirsk, Russia, unique technique allows routine production of top quality large sized BGO crystals. One of the important properties of the scintillation crystal is its radiation hardness. The intensive study of the radiation hardness of BGO crystals has been carried out by the collaboration of the institutes of Siberian Branch of the Russian Academy of Science, Novosibirsk. The influence on radiation hardness of the raw material purity and growth procedure has been studied. The final tests of the crystal radiation hardness were done by irradiation with gamma rays from ¹³⁷Cs radioactive source. The degradation of a light output of the best crystals is less than 10% after irradiation with expected at astrophysics experiment at satellite doses of 10-100 krad. Based on results of this research, the radiation hard BGO crystals for “INTEGRAL” and “ASTRO-H” satellite missions have been made. The self-recovering of the crystal light output is clearly seen. The time scale of the self-recovery strongly depends on a dose of the irradiation. It is days for 1 krad irradiation, weeks - for 10 krad irradiation and much more time is required for 100 krad irradiation. The all irradiated with 100 krad dose completely recover after annealing. It reveals that will be no essential degradation if this dose will be integrated over years of operation.