Indoor radon concentration levels, gamma dose rates and impact of geology – A case study in Kotli, State of Azad Jammu and Kashmir, sub-Himalayas, in Pakistan

Abstract

Inhalation of indoor radon has been recognized as the largest contributor to the total effective dose received by human beings. Indoor radon data were collected from the dwellings lying on the sedimentary rocks (sandstones, siltstones and clays) of the Murree Formation, Nagri Formation, Dhok Pathan Formation, Mirpur conglomerate and surficial deposits of the Kotli area in Azad Jammu and Kashmir, Pakistan. Radon measurements were made using the passive time-integrated method using Kodak CN-85 Solid-State Nuclear Track Detectors. The radon concentration in dwellings varied from 13 ± 6 Bq.m-3 to 185 ± 23 B. qm-3 , with an average of 73 ± 15 Bq.m-3 .The radon concentration in the Murree Formation, Nagri Formation, river terrace and Dhok Pathan Formation were 89.7 ± 16.5, 72 ± 15, 68.5 and 69 Bq.m-3 , respectively. The average value of all the measured concentrations (73 ± 15 Bq.m-3 ) within the framework of this study is more than the world average value of 40 Bq.m-3 given by UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation, report to the General Assembly, United Nations, New York, 2000) and is within the action level of 200-600 Bq.m-3 fixed by the ICRP(International Commission on Radiological Protection, ICRP publication65, Protection against radon at home and at work, 1993). The ambient gamma dose rates both indoors and outdoors in different parts of Kotli were also measured. The average value of gamma absorbed dose rates prevailing in the indoor environment was 131.2 ± 16.6 nGy/h. The gamma exposure rates recorded outdoors were 35% lower than in the indoor environment. The measured gamma dose rates have a weak positive correlation with indoor radon concentration. The annual effective dose for inhabitants in Kotli due to radon ranged from 0.32 to 4.7 mSv.y-1 , with an average value of 1.8 mSv.y-1 . This dose is relatively higher than the world mean dose of 1.15 mSv/y. That is explained by the particular geology of the state of Azad Jammu and Kashmir, and the method of construction of the dwellings.