Lecture 12

The Nature of the Blast

1. Energy distribution
   1. Blast—40-60% of total energy
   2. Thermal radiation—30-50% of total energy
   3. Prompt ionizing radiation—5% of total energy
   4. Residual radiation (fallout)—5-10% of total energy.
2. Stages of a Nuclear Blast
   1. Initial radiation
   2. Electromagnetic pulse (EMP)
   3. Fireball (10-6 sec)
   4. Blast (Shock) wave (< 1 sec)
   5. Thermal radiation (Heat Wave) (~ 1 minute)
   6. Radioactive (mushroom) cloud (~ 4 minutes)
   7. Residual radiation (fallout) [hours-months].
3. Blast Classification
4. 1. Surface Blast: with a fireball in touch with the surface vaporization of surface structures through blast and firestorm; immediate radioactive fallout.  Prompt radiation released & absorbed in surrounding matter generates red-glow intense luminosity.  Expansion of fireball through internal pressure, making the fireball rise like a hot air balloon.
   2. High Altitude Air Blast: fireball > 100,000 ft  (>3000m), doesn't burn ground, but interrupts electronics and communications through electromagnetic pulse (EMP).
   3. Low Altitude Air Blast: fireball < 100,000 ft (without touching ground); generates shock waves, pressure difference; large areal damage.
   4. Subsurface Blast: underwater burst, generates surge.

Burst Physics

1. Expansion speed
2. Shock Front development
3. Size of Fireball
4. Evolution of Mushroom cloud
   1. Absorption of cool air triggers fast toroidal circulation of hot gases and causes upward motion forming the stem and mushroom.
   2. Condensation of water changes the color of the cloud from red brownish to white!
   3. Strong upward winds drag dirt and debris into the cloud, mixing with radioactive material.
   4. Cloud rises at a speed of ~ 440 ft/s.
5. Dirt
   1. Chimney effect again.
6. Cloud Altitude
7. 1. Maximum altitude for cloud rise is reached after ~ 4min.
   2. Cloud height & cloud radius depend on the magnitude of the explosion.  Both increase with explosion yield.