- 12 “- these tissues. ‘ This energy produces chemical changes in the molecule of the cells; for example, such a chemical change could be a mutation in a gene. The radiation dose is actually a measure of the energy transferred to or absorbed by the tissue. The basic unit of dose is the rad (one rad represents the absorption of 100 ergs of energy per gram of material). In addition to X-rays, radionuclides emit gamma rays r (high energy X-rays), beta particles (electrons), and alpha - particles (helium nuclei). In radiobiological experiments, it was determined that, while these various types of radiation produced the same biological effects, such as cancer, the Magnitude of the effect was not the same per rad. For example, it was found that 100 rad of alpha radiation would produce roughly 10 times as many cancers as 100 rad of X-rays. Moreaver, it was foundthat because of the special way in which Fu-239 deposits in the bone, its alpha particles were 5 times more effective in producing bone cancer than the alpha particles from radium’, To account for these diiferences ‘in the magnitude of the observed effects at the same absorbed cose in rad, the maximum permissible dose limits are given in rem rather than rad. The MPLD is given in rem in Tables I and II. The 17/ ICRP Publication 11, "A Review of the Radicsensitivity of the Tissues in Bone," Pergamon Press, New York, N. Y., 18°07, x.