way of being exposed to radiation is through internal exposure, or internal contamination, This can happen through two ways: direct contamination or indirect contamination, It should be recalled that a nuclear explosion results in the creation of approximately 200 radioactive elements, or isotopes, short-lived, such as polonium (Po 222 minutes, or astatine Many of these are oy po84) which has a half-life of 3,0 (at218 or at85) with a half-life of 2.0 seconds (FRP, p. 55) and actually become ineffective or return to their stable forms hefore they can reach the ground. and cesium (csi37) However, longer-lived isotopes like strontium (sr29) have half-lives of about 30 years, (7331) has a half-life of about eight days, Radioactive iodine It is these three elements which are among the most dangerous to man in terms of fallout, or the material which returns to earth after being lifted into high altitudes hy the explosion, This fallout material may result in exposure of human beings (and animals and fish) should they fall into their source of drinking water, onto food, or if they are inhaled. Or, as happened in a few cases where the fallout material landed on or near the people, curiosity compelled them to pick up a flake of material and taste it to determine what it was, All of these result in the radioactive material, which emits both gamma and beta radiation, being deposited internally into the human body. A second way ian may be exposed to radioactivity internally is what might be called “indirect" exposure. It is through a more complicated mechanism: the processes of his own environment, The emphasis on ecology and environmental protection during the past few years helps clarify how a person can become radioactively contaminated internally from a nuclear explosion which occurred thousands of miles away and years aqo, The present emphasis on protection of our environment from pollution has made the general public aware of the interrelationships between 16