Evaluation of natural radiation in houses built with black schist.

Natural radiation in houses built with black schist slabs located at an altitude of 1,000 m in the mountainous southern part of Taiwan were investigated by studying the naturally occurring radionuclides present in the black schist. Both indoor and outdoor radon concentrations were monitored. The cosmic-ray contribution to the dose received by the inhabitants was also estimated. Gamma-ray spectroscopy was performed for radionuclide analyses. In situ measurements were carried out using a survey meter coupled to a sodium iodide detector. Cellulose nitrate films, ZnS (Ag) scintillation cells, and alpha spectroscopy were used to study radon and radon daughters. Radiation doses due to all natural sources were calculated and compared with that incurred in common concrete dwellings at lower altitudes.