Welcome!  Most people are not aware that radiation is part of our natural environment.  Our world (and the universe) is naturally radioactive with sources of radiation and radioactive materials coming from the earth's rocks and soils, cosmic radiation from the Sun and outer space, and from the air, water and food we consume every day.  In addition, there are human generated sources of radiation that are part of our background exposure.  The discovery of x-rays revolutionized medicine but we receive an exposure from this radiation every time we have a dental x-ray, CAT scan, or other diagnostic procedure.  Most radiologic procedures involve small exposures and the benefits greatly outweigh the risks.  Radioactive materials also play an important role in the quality of our health by allowing us to image and measure the function of our organs like the heart, brain, liver, etc. as well as treating and curing cancer. Without nuclear reactors or accelerators we would not have essential medical radioactive materials like Technecium-99m, Iodine-131, Fluorine-18, and many others.  Radiation sources have also helped us probe the depths of the sub-atomic world to the expanses of the universe, kept us healthy and safe, and shown us the inner workings of life itself.