The previous graph (500-5000 mR) has been compressed by a factor of 10 and is illustrated as the lower portion of the above bar.
It is only when the radiation exposure rises to three times the annually permitted dose for a radiation worker, given all at once, that more significant biological effects are seen. A decrease in sperm count is appreciated at 15 R of exposure. Radiation has its greatest effects on cells that are rapidly dividing. Since sperm cells are constantly being renewed, they are among the first to demonstrate their susceptibility to the effects of radiation. Other tissues that are highly susceptible would be the cells lining the gastrointestinal tract and the bone marrow.