Radon concern the international scientific community from early 20th century. Initially as radium emanation, almost the second half of the century as severe harmful to human health. Initial brilliant period of use as medicine, followed by a period of intense concern for its health effects. Primary target groups surveyed were miners early in Europe later in U.S. There is now compelling evidence that radon and its progeny can cause lung cancer. Human activities may create or modify pathways increasing indoor radon concentration compared to outdoor background. These pathways can be controlled by preventive and corrective actions. Indoor Radon and its short-lived progeny attached on aerosol particles or free compose an air mixture that carry a significant energy amount (PAEC). Exposure on PAEC and dose delivered reviewed in detail. Special attention was paid to the case of water workers because lack of adequate data. Radon risk assessment and current legislation regulates dose from radon and its progeny, also were reviewed.

Gd/sub 2/SiO/sub 5/:Ce (GSO:Ce) is a high-Z, nonhygroscopic fast emitting scintillator used in detectors of positron emission tomography (PET) systems. The purpose of this study was to evaluate the luminescence efficiency of GSO:Ce scintillator under irradiation conditions employed in X-ray medical imaging, since findings may be of value in novel applications such as computed tomography breast imaging or modern fast image producing X-ray computed tomography. To this aim the absolute luminescence efficiency (emitted light flux over X-ray exposure), the spectral matching factor (compatibility to optical detectors), and the effective efficiency (the product of absolute efficiency and spectral compatibility) were determined for X-ray tube voltages ranging from 20 to 140 kV. The efficiency of GSO:Ce was found to increase with increasing X-ray tube voltage, while the GSO:Ce spectrum, peaking at 440 and 490 nm, was found compatible to most optical detectors (photodiodes, photocathodes, and charge-coupled devices).