tNa 1204-7 17.6 «i, DEPOSIT RADIATION 17.6.1 Introduction "Deposit radiation” was defined Gec.17.32) as "the radiation due to radioactive materials, particularly radioactive fallout pert- icles that may deposit on a ship's exterior (or some interior) surfaces." Deposit radiations include both gamma rays and beta particles emitted by the radioactive deposited material, and may also include gamma rays emitted from neutron-induced activities. Assessment of the effects of the ganma radiation is based on the dose or time-integrated dose rate received at the exposure point. Thus, all available weaponstest data on residual gamma-dose and dose-rate can be of value either (1) in devising scaling techniques or (2) as guidance for calculational techniques that would permit estimation of either gamma dose or dose- rate histories due to deposit radiation at various ranges from surface vero for detonations of any yield. Beta particles have only a limited range in air (up to about 10 ft), and the range decreases so rapidly with increasing density of medium traversed that the average distance a beta particle of given energy can travel in water, wood, or body tissue 16 roughly 1/1000 of that in air. Thus, there will be no trana- mission through the steel of a ship (of still greater density than water or wood) of the beta particles emitted by the deposit radiation. However, beta radiation can affect personnel if beta activity is deposited on the ekin or ingested. Those effects of beta radiation will be considered in Chapter 18, where radiation effects on personnel are discussed. Deposit gamma-radiation dose and dose rate are functions of the photon energy emitted by deposited radioactivity. This emitted energy will depend on the time after burst and on the composition of the deposited material, which may differ not only with weapon composition, put alao with the location of the detonation point with respect to the water surface. Furthermore, the amount of deposited activity remaining on board a ship will depend on whether shipboard countermeasures, such @s washdown, are usec, and on the effectiveness of the countermeasures for the particular deposited material. It is expected that the deposited radioactivity from a true sur- face burst (at the surface of deep water and with no ship involvement) would result from (1) "slurry" fallout droplets composed of water, sea- salt, and weapon materials, and perhaps (2) some contaminated droplets from the base surge. Evaporation of such fallout probably would leave a residue invisible to the uneided eye. Ali available data on fallout from water-surface bursts are for barge shots over comparatively shallow water, which are not true water- surface bursts. Droplets of slurry fallout from all the barge shots have been analyzed,“ and as a result of the analysis have been defined 17-70 - ~_~—— me ee ee ee