Assessment of gamma radiation exposure inside a newly constructed building and a proposed regulatory guideline for exposure control from natural radioactivity in future buildings

Naturally occurring radionuclides in building materials are one of the sources of radiation exposure of the population. The various materials used for constructing a new building were assessed for 40 K, 232 Th and 238 U radioactivity and the external gamma dose rate inside the building was predicted by using the computer code QAD-CGGP. The external dose rate was also measured by a scintillation gamma monitor after the construction of the building. In the building studied, the floor and the ceilings are seen to contribute about 35% each of the total radiation dose inside the building from the natural radioactivity present in the construction materials and the underlying soil; the walls contributed about 15%. A sensitivity analysis assuming extreme conditions of radioactivity concentrations as are normally observed in the Indian context, indicates the possibility of indoor gamma radiation fields varying by two orders of magnitude. The possible control methodologies and recommendations are also discussed for keeping the population exposure as low as reasonably achievable. It is evaluated that radioactivity limits of 370 Bq.kg −1 of radium equivalent and 85 Bq.kg −1 of 226 Ra when applied concurrently, might limit the indoor exposures to reasoably accepted low levels of health risks