DNA 1240H-2 fission products in the fireball, the plumes or colwm, and the cloud. For underwater bursts, only the early-time fission-product ganma rays are of significance, since prompt neutrons are completely absorbed by a relatively thin layer of water. F.P.C. radiation will be dis- cussed more completely in Section 17. 4. Residual radiation has been subdivided into (a) transit radiation, and (b) deposit radiation. Transit radiation is the radiation from airborne radioactive particles suspended in the base surge and mushroom cloud resulting from water detonations. These radioactive eerosols may pass over or envelop a ship, or enter a ship via any preek in the weather envelope. Deposit radiation is the radiation due to radioactive materials, particularly radioactive fallout particles, that may deposit on any of a ship's exterior (or some interior) surfaces. Residual radiation includes (1) gamma rays emitted by fission products in the aerosols or in deposited activity, (2) beta particles emitted from the decaying fission products in the aerosols or deposited activity, and (3) gamma rays emitted from neutron-induced activities. Residual radiation will probably cause the major portion of all shipboard rediation exposures for all underwater and most surface bursts, especially if the ship is dowmrind at ranges that are greater than those at which airblast causes loss of the ship. Although exposures to transit radiation are generally of short duration, extremely high dose rates (up to several hundred thousand r/hr) could be received at exposed topside locations of a ship enveloped by a base surge. Section17.5, Transit Radiation, includes a discussion of the attenuating effect of the ship's structure on dose rates and doses due to the base surge. If a ship's weather envelope were penetrated by any of the contaminated serosol, ventilation and combustion air could become a minor radiation source within the ship. In addition, the problem of deposit radiation could be somewhat increased if particles carried by the serosol were deposited in ducts or spaces within the ship. If a ship were caught in fallout or base surge, certain portions of the ship could become dangerous sources of deposit radiation unless countermeasures were employed to remove deposited particles. The extent to which dose rates from radioactive particles deposited topside would be attenuated at below-decks locations will be discussed in Section 17.6, Deposit Radiation. ‘The extent to which the water surrounding a ship may be a source of nuclear radiation from radioactive particles suspended in the water is considered in Section 17, 7. 17.3.4 Sources of Weapons-Test Data Weapons-test nuclear-radiation data from underwater and water- surface bursts have been obtained at the 4 underwater test shots* “Data from the more recent Sword Fish Shot were not available as this report was prepared. 17-16