How Far Does Nuclear Radiation Reach?
Nuclear radiation comes in two forms: initial radiation (instant) and residual radiation (fallout). They travel very different distances.
Initial Radiation
The intense burst of gamma rays and neutrons at the moment of detonation. For a 2 megaton weapon:
Lethal dose (500+ rem): ~3.8 km (surface burst)Significant exposure: ~5-6 kmTravels at the speed of light — no warningInitial radiation is actually less dangerous than blast and thermal effects at the same distance, because the blast radius exceeds the radiation radius.
Radioactive Fallout
This is the real long-distance threat. Fallout from a 2MT surface burst:
Lethal doses within 24 hours: Up to 30-50 km downwindDangerous levels: Up to 150-300 km downwindDetectable radiation: 500+ km downwindGlobal trace amounts: Weeks later, worldwideFactors Affecting Fallout Travel
Wind Speed and Direction
30 km/h winds carry fallout ~700 km in 24 hoursWind direction determines the fallout plume shapeUpper atmosphere winds (jet stream) can carry fine particles globallyDetonation Type
Surface burst: Maximum fallout — fireball contacts groundAir burst: 80-90% less falloutWeather
Rain causes washout — concentrating fallout locallySnow accumulates radioactive particlesClear weather spreads fallout more evenlyThe 7-10 Rule
Radiation intensity decreases predictably:
7 hours after detonation: 1/10th the initial level49 hours (2 days): 1/100th2 weeks: 1/1,000th14 weeks: 1/10,000thCheck your nuclear fallout risk
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