Radioactive Fallout: How it Spreads
Why a Geiger Counter is necessary to record Radioactive Fallout
Nuclear fallout is the residual, radioactive material propelled by a nuclear blast into the upper atmosphere; the name is due to the material falling out of the sky following an explosion and the shockwave. These radioactive materials are chiefly the fireball vaporized fission products and some amount of nuclear material that didn’t undergo fission. These form a fine suspension, with particle sizes ranging between 10 nm and 20 µm. The particles are drawn-up into the stratosphere and through dispersal contaminate the ecosystem.
Dangerous radioactive fallout can spread across the globe in a matter of days, contaminating land, water and air. The effects can be devastating. Breathing radioactive particles are particularly hazardous since the soft tissues within the lung are prime candidates for radiation induced tumors. Worse still, hazards are long-term due to radioisotopes like strontium-90 and caesium-137; which have a long half-life. With all that risk it makes sense to understand how fallout travels so people and governments can take protect themselves.
Tracking a significant release of radiation through fallout is a meteorological matter, since the movements of a radiation cloud depends on regional weather patterns. It also depends on the distance of the cloud from earth surface due to the wide variation between wind speed and direction near the earth's surface and the upper atmosphere. Horizontal and vertical turbulence will disperse particulate matter and dilute the radioactivity depending upon wind direction.
Some patterns are very predictable. For example, both America and Japan are in the Northern mid-latitudes and share similar (westerly) wind patterns, which dominate their weather. As fallout (radioactive particles) reach the earth the influence of low-level winds are more significant and can affect the range and concentration of the dispersal - of course these winds vary and are much less predictable.
Nuclear fallout dispersion on a global scale is entirely a function of time, distance and atmospheric wind. The flight distance from China to United States is 7,215 miles, from Japan, 6,247 miles. The radiation from the Fukushima Daiichi meltdown took 7 days to reach the U.S, plenty of time for individuals to purchase Geiger counters and Radiation Detectors, seal their dwellings, stock up on iodine tablets, and take other precautions to protect themselves from potentially life-threatening ionizing nuclear radiation.