The RBE of some test radiation (r) compared with x-rays is defined by the ratio D250/Dr where D250 and Dr are, respectively, the doses of x-rays and the test radiation required for equal biologic effect. (National Bureau of Standards, 1954)
U.S. Department of Health and Human Services, Office of the Assisstant Secretary for Preparedness and Response, National Library of Medison, Radiation Emergency Medical Management (REMM), Dictionary of Radiation Terms, Washington, DC, USA 2014. http://www.remm.nlm.gov/dictionary.htm, (Dzstr/ Rad Emr - Amer) {822}