Rainout
Encyclopedia
A rainout is the process of precipitation causing the removal of radioactive particles from the atmosphere onto the ground, creating nuclear fallout
by rain. The rainclouds of the rainout are often formed by the particles of a nuclear explosion
itself and because of this, the decontamination of rainout is more difficult than a "dry" fallout.
or the contamination could be carried aloft before deposition depending on the current atmospheric conditions and how the explosion occurred. The explosion, or burst, can be air, surface, subsurface, or seawater
. An air burst will produce less fallout than a comparable explosion near the ground due to less particulate being contaminated. Detonations at the surface will tend to produce more fallout material. In case of water surface bursts, the particles tend to be rather lighter and smaller, producing less local fallout but extending over a greater area. The particles contain mostly sea salts with some water; these can have a cloud seeding effect causing local rainout and areas of high local fallout. Fallout from a seawater burst is difficult to remove once it has soaked into porous surfaces because the fission products are present as metallic ions which become chemically bonded to many surfaces. For subsurface bursts, there is an additional phenomenon present called "base surge". The base surge is a cloud that rolls outward from the bottom of the subsiding column, which is cause by an excessive density of dust or water droplets in the air. This surge is made up of small solid particles, but it still behaves like a fluid. A soil earth medium favors base surge formation in an underground burst. Although the base surge typically contains only about 10% of the total bomb debris in a subsurface burst, it can create larger radiation
doses than fallout near the detonation, because it arrives sooner than fallout, before much radioactive decay
has occurred. For underwater bursts, the visible surge is, in effect, a cloud of liquid (usually water) droplets with the property of flowing almost as if it were a homogeneous fluid. After the water evaporates, an invisible base surge of small radioactive particles may persist.
Meteorogically, snow and rain will accelerate local fallout. Under special meteorological conditions, such as a local rain shower that originates above the radio-active cloud, limited areas of heavy contamination just downwind of a nuclear blast may be formed.
Rain on an area contaminated by a surface burst changes the pattern of radioactive intensities by washing off higher elevations, buildings, equipment, and vegetation. This reduces intensities in some areas and possibly increases intensities in drainage systems; on low ground; and in flat, poorly drained areas.
Nuclear fallout
Fallout is the residual radioactive material propelled into the upper atmosphere following a nuclear blast, so called because it "falls out" of the sky after the explosion and shock wave have passed. It commonly refers to the radioactive dust and ash created when a nuclear weapon explodes...
by rain. The rainclouds of the rainout are often formed by the particles of a nuclear explosion
Nuclear explosion
A nuclear explosion occurs as a result of the rapid release of energy from an intentionally high-speed nuclear reaction. The driving reaction may be nuclear fission, nuclear fusion or a multistage cascading combination of the two, though to date all fusion based weapons have used a fission device...
itself and because of this, the decontamination of rainout is more difficult than a "dry" fallout.
Factors affecting rainout
A rainout could occur in the vicinity of ground zeroGround zero
The term ground zero describes the point on the Earth's surface closest to a detonation...
or the contamination could be carried aloft before deposition depending on the current atmospheric conditions and how the explosion occurred. The explosion, or burst, can be air, surface, subsurface, or seawater
Seawater
Seawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% . This means that every kilogram of seawater has approximately of dissolved salts . The average density of seawater at the ocean surface is 1.025 g/ml...
. An air burst will produce less fallout than a comparable explosion near the ground due to less particulate being contaminated. Detonations at the surface will tend to produce more fallout material. In case of water surface bursts, the particles tend to be rather lighter and smaller, producing less local fallout but extending over a greater area. The particles contain mostly sea salts with some water; these can have a cloud seeding effect causing local rainout and areas of high local fallout. Fallout from a seawater burst is difficult to remove once it has soaked into porous surfaces because the fission products are present as metallic ions which become chemically bonded to many surfaces. For subsurface bursts, there is an additional phenomenon present called "base surge". The base surge is a cloud that rolls outward from the bottom of the subsiding column, which is cause by an excessive density of dust or water droplets in the air. This surge is made up of small solid particles, but it still behaves like a fluid. A soil earth medium favors base surge formation in an underground burst. Although the base surge typically contains only about 10% of the total bomb debris in a subsurface burst, it can create larger radiation
Radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
doses than fallout near the detonation, because it arrives sooner than fallout, before much radioactive decay
Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...
has occurred. For underwater bursts, the visible surge is, in effect, a cloud of liquid (usually water) droplets with the property of flowing almost as if it were a homogeneous fluid. After the water evaporates, an invisible base surge of small radioactive particles may persist.
Meteorogically, snow and rain will accelerate local fallout. Under special meteorological conditions, such as a local rain shower that originates above the radio-active cloud, limited areas of heavy contamination just downwind of a nuclear blast may be formed.
Rain on an area contaminated by a surface burst changes the pattern of radioactive intensities by washing off higher elevations, buildings, equipment, and vegetation. This reduces intensities in some areas and possibly increases intensities in drainage systems; on low ground; and in flat, poorly drained areas.