Khan, K., S. D. Orfi, and H. M. . Khan. “Distribution of Primordial Radionuclides in Phosphate Fertilizers and Rock Deposits of Pakistan”. Journal of Himalayan Earth Sciences, vol. 37, no. 1, Nov. 2004, pp. 59-64, http://ojs.uop.edu.pk/jhes/article/view/1574.