H. Ismail, L., H. Al-Shamma, S. and I. Azawi, M. 1970. An analytical expression for the K shell ionization cross section of some heavy atomic elements by electron impact. Journal of Education and Science. 24, 4 (Jan. 1970), 123–130. DOI:https://doi.org/10.33899/edusj.1970.58959.