DNA 1240H-2 17.7. RADIATIONS FROM CONTAMINATED WATER 17.7.1 General Introduction , Water in the region of a nuclear water-surface or underwater burst will become contaminated by the radioactive particles produced by the detonation. These particles, suspended in the water, emit gamma rad- dations that may add to the nuclear-radiation exposures aboard a ship traversing the area or immobilized in it. Determination of the interaction of a ship with the radiation field from the contaminated water, involves measuring or computing the expo- ure-point dose rate due to the water. This dose rate is dependent not only on the source strength (determined by the distribution of radio- active particles in the water), but aleo on the source gamma-ray spectral distribution, the source geometrical distribution, and the energy degradations that occur in the water and in penetrating the ship. The distribution of particles in the water will differ with burst conditions, as well as with water currents and weather conditions. The mechanisms by which radioactivity is distributed in the water by surface and underwater bursts are briefly described in 17.7.2, followed by available water-contamination data gathered at test shote in 17.7.3, and by shipboard dose-rate data, due to the “hot” water, in 17.7.4. summary of the section is given in 17.7.5. <A 17.7.2 Mechanisms of Water Contamination Radioactive particles reach the water by several mechanisms. Some activity mixes with the water of the column or plume thrown up into the air, and a region of contaminated water results when the plume or colum falls back to the surface. The water may also become contaminated from radioactive fallout, as well as from activity suspended in the base surge, which eventually deposits on water surface. Some of the radioactivity never is thrown into the air, but remains in the water near the burst point. For an underwater burst, some of this radioactivity is brought to the surface by the event, and some is trapped below the surface. The nature of the radioactive particles formed will depend on the mass of water and any ship material engulfed by the fireball. The distribution of these particles in the water is governed by their size and density as well as by wind speed and direction and by ocean layering and currents. If the burst occurs on free water and the fireball engulfs no solid material, the radioactive particles will be so small that they will be colloidal in nature. Thus, they will slowly become distributed in the mixed layer, where they will remain for a long period of time. Lateral dispersion of the particles will occur, and the whole contaminated area will move with the ocean currents. If the burst is a hit or near-miss, 17-90 wee ree ee ee rn ee ne ee ee ee ee eee re ee eee