My research will be in the area of the determination of the composition of high energy cosmic rays. A brief overview of cosmic rays showers will be presented. The current knowledge of the composition of cosmic rays will be reviewed. The various factors in cosmic ray showers which provide evidence of the composition of the primary cosmic rays will be discussed. These include the depth of shower maximum, the ratio of the muon component to the electromagnetic component in the shower, and the rise time of the signals in the ground array detector photomultiplier tubes at some distance from the shower axis.

Native and rare-earth-doped point-defects in  are studied in the framework of the pair-potential approximation coupled with the shell model description of the lattice ions. For the perfect lattice, a new set of potential parameters are obtained which reproduce structure, elastic and dielectric constants of  very well. The calculated formation energies for native defects suggest that the anion Frenkel disorder is preferred over the cation Frenkel and Schottky-like disorder in . The computed temperature behavior of the ionic conductivity agrees very well with the available experimental data. In the rare-earth doped , a site-preference of the charge-compensating fluorine interstitial appears to change from nearest to next-nearest neighbor with the increase in the rare-earth ionic radius. Further work then was suggested.