The objective of this work was to asses the radiation hazards associated with gamma rays form building materials and radon indoors. For this purpose the largest city in the province of Punjab, Lahore and the capital of Pakistan, Islamabad, and its twin city Rawalpindi were selected. The radon measurements were also made in made in the coal mines of Makarwal. The possibility of radon measurements for geological/ geophysical studies have also been explored.
Natural γ-ray activities due to 226Ra, 232Th and 40K in the samples of building materials consisting of soil , bricks, sand, cement, gravel aggregate, marble chips, glass and points collected from different areas of Pakistan have been measured using HPGe based spectrometer. The values of the activities of these isotopes do not clearly reflect the radiation hazard associated with these materials. The radium equivalent (Raeq) concentration is, therefore, defined which takes into account the effectiveness of these isotopes in creating the radiation hazard. Radium equivalent activities, and external and internal hazard indices have been calculated from the activities of 226Ra, 232Th and 40K for the assessment of suitability of the materials. The largest average value of Raeq for soil bricks and sand samples of Islamabad/ Rawalpindi area are 167,168, and 108 Bq. Kg-1 , respectively , and those for the samples of Lahore area are 211,209,and 157 Bq.kg-1 , respectively. For Kasur this value for brick is 219.50 Bq.kg-1 . Therefore the activity concentrations increase as one proceeds from north towards south in the area of investigation in Pakistan. Radium equivalent activities are less than the limiting value of 370 Bq.kg-1. The calculated hazard indices are less than unity except for some ceramic samples where the value of internal hazard index excess unity. Therefore, the nature γ-ray activity of the materials is of minor nature.
The gamma doses from the walls of a standard size room have been calculated by using the mesh adaptive model. The indoor occupancy factor of .08 has been used for calculations of these doses. The annual doses are .073 and 0.27 mSv in the rooms made of bricks and concrete, respectively. The excess whole body caner risk at the age of 70 for a female living in the houses constructed from clay bricks is 113 per MPY(million persons per year) whereas for a male this risk is 65 per MPY. However, if the houses are made are made from concrete the whole body risk for female is 42 per MPY and for male 24 per MPY respectively.
Solid state nuclear track detector(SSNTDs) have been used for the passive measurements of indoor radon concentrations. The etching parameters have been studied by irradiating them with charged particles and neutrons to establish the criteria for track registration. The track etch diameter depends upon the energy of the particle,. The effect of sunlight exposure on the sensitivity of CR-39 for fission fragments, alpha particles and neutrons; and LR-115 and CN-85 detectors for neutrons have been studied. It is found that sensitivity decreases with sunlight exposure. The properties of CR-39 detector for heavy charged particle can be preserved if the detectors are wrapped in black carbon paper.
A theoretical treatment of the radon registration by SSNTDs has been reviewed and the discrepancies in the calibration coefficients have been discussed. A simplified theoretical model is presented and a simpler and more efficient method for deriving working level rations is suggested
Concentrations of radon(222Rn) have been measured in some houses of Islamabad, Rawalpindi and Lahore, and in the coal mines of Markarwal, Pakistan. The measurements have been made in bedrooms, sitting rooms, kitchens and TV lounges using CN-85 solid sate nuclear track detectors in box type dosemeter. The concentration in the dwellings of Islamabad / Rawalpindi varies from 20 to 93 Bq. m-3 and with an average value of 40 Bq.m-3 . In Lahore the concentration varies is related with the radium (226Ra) concentration in the soil of those areas. The average value of radium concentration is 43.2 and 49.7 Bq. kg-1 for Islamabad/ Rawalpindi and Lahore areas, respectively. In the coal mines, concentration of radon daughters has been measured using air sampling techniques. The exposure due to radon daughter in the coal mines has been determined. The exposure value is about 0.9 WLM(working level month ) in these mines.
Using the standard models, the dose and dose equivalent received by tracheobronchial (T-B) and pulmonary (P) regions of human lungs from exposure to radon daughter products have been estimated. Effective dose equivalent rates determined by OECD, ICRP and UNSCEAR have been compared and conversion factor of 7-17 nSv h-1 per Bq.m-3 as recommended by ICRP has been adapted to determine the dose equivalent rate for the resident in the cities under consideration. In the bedrooms of these cities the estimated dose equivalent rate comes out to be about 2 mSv. Y-1 .For mine workers the conversion factor of 10 mSv Y-1 per WLM has been adapted.. The coal mines of Makarwal, Pakistan, deliver about 4-6 times more dose to the miners than the dwellings of Islamabad / Rawalpindi and Lahore deliver to their occupants.
The life time excess lung cancer risk from radon in the dwelling of Islamabad / Rawalpindi and Lahore has been estimated using the UNSCEAR conversion factor of 200-400 cancer deaths per million persons per WLM. The excess risk in the dwellings varies from 10-102 MPY at the age of 70 years. The estimated values are compared with similar data available for other countries in the world.
Radon has been measured using SSNTDs for geological and geological and geophysical applications such as earthquake predications, uranium with depth in a deep hole. A reasonable correlation has been observed between radon signal variations and the desired application.