Mahmood, A., M. S. Zafar, S. Mughal, and K. Iamil. “?MEASUREMENT OF RADON CONCENTRATION LEVELS IN OLD BUILDINGS OF LAHORE, PAKISTAN”. Biological Sciences - PJSIR, vol. 41, no. 6, Dec. 1998, pp. 290-4, http://v2.pjsir.org/index.php/biological-sciences/article/view/2293.