Abstract
Indoor radon concentration was measured in selected elementary schools across Lafia, Nasarawa State, Nigeria, using passive diffusion cups fitted with CR-39 detectors. The rooms were selected based on varying natural ventilation conditions and height above ground level. Detectors were deployed in classrooms and offices for a period of 90 days. After exposure, the detectors were etched using sodium hydroxide (NaOH) at 90 °C for 3 hours. Alpha tracks were counted and photographed using a digital camera attached to a microscope and computer system. The arithmetic and geometric mean radon concentrations were 193.3 Bq m⁻³ and 182.4 Bq m⁻³, respectively. The mean annual effective lung dose was 0.24 mSv·y⁻¹, with an excess lifetime cancer risk of 1.0 MPY⁻¹. Factors such as ventilation rate, proximity to the ground, and construction materials of floors, walls, and ceilings were investigated. An inverse relationship (R² = 0.6) was observed between radon concentration and ventilation rate. Rooms situated closer to the ground exhibited higher radon levels. Concrete and asbestos materials were associated with higher radon concentrations, whereas painted and carpeted surfaces recorded lower values. The measured radon concentrations were below the International Commission on Radiological Protection recommended action level of 300 Bq m⁻³ for workplaces.