1. Department of Physics, Faculty of Science, Mazandaran University, P. O. Box 47415-416, Babolsar, Iran
2. Agricultural, Medical, Industrial Research School, Nuclear Science and Technology Research Institute, P. O. Box: 31485-498, Gohardasht, Karaj, Iran
3. Department of Physics, Islamic Azad University, Ayatollah Amoli Branch, P. O. Box 678, Amol, Mazandaran, Iran