Gamma ray irradiation induced point defects in BaF_2

Ｇａｍｍａｒａｙｉｒｒａｄｉａｔｉｏｎｉｎｄｕｃｅｄｐｏｉｎｔｄｅｆｅｃｔｓｉｎ ＢａＦ_２ＨｏｕＢｉ－Ｈｕｉ（候碧辉）ａｎｄＹａｎｇＨｏｎｇ－Ｂｏ１）（杨洪波）（ＤｅｐａｒｔｍｅｎｔｏｆＰｈｙｓｉｃｓ，ＤｅｐａｒｔｍｅｎｔｏｆＭｏｄｅｒｎＰｈｙｓｉ?..

There are some original nonmagnetic point defects in the BaF2 crystallite powder, such as interstitial and vacant F- which can become paramagnetic centers by γ-ray-irradiation at room temperature. After γ-ray irradiation the paramagnetic point defects Vk, H, F and M centers, have been observed in the sample with experiment of electron spin resonance (ESR). Frenkel exciton, a nonmagnetic point defect, can also be induced by the γ-ray irradiation in the sample at room temperature, the existence of the Frenkel exciton isaffirmed by an anomalous change of the ESR signal of Vk center with temperature. The signals of the ESR of the H, F and M centers weaken and vanish with the temperature increasing monotonously. But the ESR signal of the Vk enhances when the temperature goes up about 127℃, then weakens and vanishes. An increase in the Vk center follows an annihilation of the Frenkel excitoll with heating.