Mahmood, Arif, M S Zafar, SA Mughal, and K Iamil. 1998. “?MEASUREMENT OF RADON CONCENTRATION LEVELS IN OLD BUILDINGS OF LAHORE, PAKISTAN”. Biological Sciences - PJSIR 41 (6):290-94. http://v2.pjsir.org/index.php/biological-sciences/article/view/2293.