SUMMARY
The current work deals with indoor radon (222Rn) concentrations measurements in the Calabar Study Centre of the National Open University of Nigeria using a Corentium Arthings digital radon detector meter for seven days representing a short–term average measurement of indoor radon gas concentration level. The geographical coordinates were recorded using a hand-held geographical positioning system for the sample point. Measurement were taken for seven days and the following data where obtained 83±2.19 Bq/m3,80±3.69 Bq/m3,86±5.57 Bq/m3,84±1.59 Bq/m3,82±3.59 Bq/m3,81±4.89 Bq/m3 and 85 ±5.59 Bq/m3.The average radon(222Rn) concentration level was found to be 83 ± 3.87 Bq/m3 with a geometric mean of 82 ± 3.54 Bq/m3. It was observed that the radon concentration was below the reference level of 100 Bq/m3 recommended by the World Health Organization (WHO). Although the current exposure of members of the public to natural radiation is not critical, the situation could change abruptly when other activities commenced. The excess life time cancer risk calculated for 70 years, 60 years, 50 years, 40 years and 30 years were 1.72 × 10-3,1.65× 10-3,1.39× 10-3,1.44× 10-3 and 0.69× 10-3 respectively. The calculated values of the excess life time cancer risk are all higher than the set limit of 0.029 × 10-3 by International Commission on Radiological Protection. However, there are no observed cases of lung cancer epidemic in this Centre. Therefore, it is advised to use fans and effective ventilation techniques to reduce radon levels. Identifying the regions of the country where people are most at risk from radon exposure should be the main goal of any national radon policy.