The effect of impurities on the radiation damage of barium fluoride crystal

Barium fluoride crystal has been actively studied as a fast and a high density scintillation material for electromagnetic calorimeters for several years. However, the radiation damage of large BaF2 crystal prevents its use in a high radiation environment in high energy accelerators. Different impurities influence the radiation damage of barium fluoride (BaF2) crystal in different ways. Stable metal elements, such as alkali elements and alkali earth elements, have no effect on the radiation resistance. Most transition metal elements are harmful to the radiation resistance. There are three kinds of effects of rare earth elements. Stable trivalence elements, such as Y, La and Lu, have no effect on the radiation resistance, while the elements which changes its valence from +3 to +4 under irradiation, such as Ce and Pr, are harmful. The elements which changes its valence from +3 to +2 under irradiation, such as Sm, Eu, Dy and Yb, are useful in eliminating color centers in visible range. Oxygen and hydroxyl ions which were introduced into the crystal from the raw material of BaF2 or a low vacuum during crystal growing are very harmful to the radiation resistance. The formation of ''Complex Color Centers'' is considered as the cause of the radiation damage of BaF2 crystal in this paper