H. Al-Shamma, Salim, Muzahim I. Azawi, and Lubna H. Ismail. 1970. “An Analytical Expression for the K Shell Ionization Cross Section of Some Heavy Atomic Elements by Electron Impact”. Journal of Education and Science (JES) 24 (4):123-30. https://doi.org/10.33899/edusj.1970.58959.