Natural Sources A. External to the body 1. From cosmic radiation 50.0 2. From the earth 47.0 3. From building materials 3.0 B. Inside the body 1. Inhalation of air 5.0 2. Elements found naturally in human tissues 21.0 Total, Natural sources 126.0 Man-made Sources A. Medical Procedures 1. Diagnostic X rays 50.0 2. Radiotherapy X ray, radioisotopes 10.0 3. Internal diagnosis, therapy 1.0 Subtotal 61.0 B. Atomic energy industry, laboratories 0.2 C. Luminous watch dials, television tubes, 2.0 radioactive industrial wastes, etc. D. Radioactive fallout 4.0 Subtotal 6.2 Total, man-made sources 67.2 Overall total 193.2 Dosage Rates Another difference between the genetic and somatic effects of radiation rests in the response to changes in the rate at which radiation is absorbed. It makes a considerable difference to the body whether a large dose of radiation is absorbed over the space of a few minutes or a few years. When a large dose is absorbed over a short interval of time, so many of the growing tissues lose the capacity for cell division that death may follow. If the same dose is delivered over years, only a small bit of radiation is absorbed on any given day and only small proportions of growing cells lose the capacity for division at any one time. The unaffected cells will continually make up for this and will replace the affected ones. The body is, so to speak, continually repairing the radiation damage and no serious symptoms will develop. Then, too, if a moderate dose is delivered, the body may show visible symptoms of radiation sickness but can recover. It will then be capable of withstanding another moderate dose, and so on.