HELIUM SOLUBILITY, DIFFUSION AND INTERACTION IN IONIC-CRYSTALS

Results on He solubility and diffusion and the influence of He on defe ct properties of CaF2, SrF2 and BaF2 are reported. A method of extract ing the different-diffusion paths using thermodesorption data has been developed and high- and low-rate mechanisms of He transport in CaF2 h ave been observed. The interaction energy of He with crystals is - 0.4 eV for alkaline and - 0.5 eV for alkaline earth metal fluorides. The He interaction with fluoride ions is mainly repulsive. Low values of t he dissolution energy are attributed to the attractive interaction of He with cations with interaction energies of - 0.5 eV for alkaline and - 0.7 eV for alkaline earth metals. Some data indicate strong He-indu ced stabilization of defects in CaF2 and changes in thermostimulated l uminescence characteristics of He-doped crystals. He stimulates the st ructural conversion of the tetragonal lattice of zirconium hydrides in to the cubic modification. The experimental results provide evidence f or the chemical bonds formed by He in the crystals.