Prof. Short introduces a new invention which uses radiation-induced color changes in binary salts to function as a real-time dosimeter for proton cancer therapy, using physics introduced in this course. Sources of background and human-made radiation, levels of public exposure, and routes of exposure are introduced, and exposures in the form of cosmic rays, terrestrial sources, medical procedures, building materials, food, radon gas, and other sources are quantified to give intuition for how much radiation is naturally present around us.