<p> Radiation is a ubiquitous health risk. Contemporary populations are exposed to several hundred milliSieverts per person over their lifetimes from both natural and human made sources such as radon, cosmic rays, CT-scans, etc. Risk estimates based on studies of atomic bomb survivors suggest that these exposures induce excess cancer mortality at a rate of several percent per Sievert. </p><p> To develop accurate risk estimates, it is important to recognize that contemporary exposures are different than atomic bomb survivor exposures. Instead of a single acute high dose rate exposure from an atomic explosion, populations today experience many small, protracted exposures accumulating to moderate total doses over their lifetimes. Therefore, in order to estimate the risk of contemporary exposures using atomic bomb survivor data, it is important to determine the differences in radiation dose response following acute vs. protracted exposures. </p><p> The committee to estimate the biological effects of ionizing radiation exposure in humans (BEIR) is one of the central authorities in the United States tasked with estimating radiation risk. Their seventh and most recent report (BEIR VII) written in 2006 estimated that contemporary protracted exposures induce 1.5 fold less risk than atomic bomb survivor exposures. </p><p> The work presented in this dissertation leverages a large body of historical animal mortality data to argue that BEIR VII overestimates the risk of protracted exposures. Concretely, evidence is presented from animal exposures that support the concept that contemporary protracted exposures induce about 2 fold less risk than atomic bomb survivor exposures.</p>