ATMOSPHERIC IONIZATION

Atmospheric ionization is an increase in the density of electrons in the atmosphere around a nuclear burst. These electrons affect radio and radar signals by removing energy from the waves. This decreases the strength of the signals and refracts the wave front, thereby changing the direction of transmission. For detonations below 100,000 feet, this effect disappears in a matter of seconds. At higher altitudes the effect can last up to several hours. The effect can be of considerable importance where communications are over a long range and where radar targets are in or above the ionized layer.

ELECTROMAGNETIC PULSE

An electromagnetic pulse (EMP) will be produced by high-altitude bursts, airbursts, and surface bursts. The initial nuclear ionizing radiation will ionize the atmosphere around the point of detonation. This will produce the EMP, which will contain frequency components in the range from a few to several hundred kilocycles per second. The EMP has magnetic and electric field components which exist for only a fraction of a second. The magnetic field component is significant inside the radius of the ionized atmosphere. It can induce large currents in cables and long-lead wires. These large transient currents can burn out electronic and electrical equipment. The electric field component can also produce transient signal overloads and spurious signals on communication nets and in computer-driven systems. At ranges where ships suffer minor damage from other weapon effects, the major effect of the EMP is expected to be the tripping of circuit breakers and blowing of fuses in protective circuitry. At closer ranges, there is a high probability of permanent damage to the electronic and electrical equipment.

INITIAL NUCLEAR RADIATION

Initial nuclear radiation is defined as the radiation (essentially neutrons and gamma rays) that is emitted by the fireball and the cloud during the first minute after detonation. All significant neutron radiation is emitted in less than 0.1 second, and gamma radiation up to 20 or 30 seconds, depending on weapon yield. The l-minute limit is set, somewhat arbitrarily, as the maximum time for the nuclear cloud to rise beyond the range in air at which gamma radiation is a significant hazard. Generally, initial nuclear radiation might not produce significant material damages, but it will incapacitate personnel.

FALLOUT

Fallout is a major effect of a surface, shallow underground, or underwater burst. It is the radioactive material that falls from the nuclear cloud and is deposited on exposed surfaces. The fallout consists primarily of fission products (gamma and beta emitters) mixed with material that was vaporized by the fireball and drawn up into the nuclear cloud. Fallout, whether airborne or deposited, is a major hazard because it emits gamma radiation. This radiation can penetrate ship structures, buildings, and aircraft, to name a few. It can also reach personnel, causing radiation injury, incapacitation, and even death. Deposited fallout also presents a contamination hazard to personnel. The militarily significant fallout, often called early fallout, is usually deposited in less than 24 hours in an area downwind of SZ.

The area contaminated by fallout is determined by the wind directions up to the top of the cloud. In a complete calm, the fallout pattern is roughly circular. A constant wind direction causes an elongation of the pattern. Complicated wind patterns (wind shear) as well as variations in wind speed and direction cause complicated ground patterns. The fallout pattern is difficult to predict accurately except under calm and very stable wind conditions.

An airburst or a smaller weapon will reduce fallout. Also, the complete containment of an underground burst will eliminate fallout.

Fallout landing on water will sink and will not be a hazard to ships that pass through the area after the fallout has stopped coming down. Fallout over a land area will remain on the surface and will be a hazard to personnel living in or passing through the area. Eventually all fallout will decay to a militarily insignificant level.

BASE SURGE

Base surge from an underwater burst is a rapidly expanding cloud or mist of water droplets. This cloud is produced by the collapse of the water column which was thrown up by the underwater detonation. After the early, rapid expansion of the visible base surge (2 to 4 minutes), the base surge moves downwind at the speed of the surface wind. The base surge will become invisible in less than one-half hour. The radioactivity initially will occupy about the same volume as the visible base surge. However, as the water droplets evaporate, the radioactive particles and gases will remain in the air and continue to disperse as an invisible radioactive base surge. For approximately 30 minutes after the burst, the base surge is highly contaminated with fission products and is a source of intense transit radiation.

Airborne fallout and base surge contamination can enter a ship or shore installation through the ventilation and combustion-air systems. This could present a radiological hazard. In some instances, hazardous amounts of contamination could concentrate in ventilation ducts, boiler air passages, and interior spaces. High concentrations of radioactive material in these trunks may produce a gamma-radiation hazard to personnel working nearby. Radioactive material deposited in interior spaces may also present radiation hazard to personnel coming into contact with beta particles, even though there may be only a minor penetrating gamma-radiation hazard. For aircraft in flight, the entry of airborne radioactive materials will not be a hazard during the flight but may represent a hazard to maintenance personnel later.