Lecture 12

In this Lecture:
The Nature of the Blast
Burst Physics
Altitude Test Delivery Systems

The Nature of the Blast

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.
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].
Blast Classification
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

Expansion speed
Shock Front development
Size of Fireball
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.
Dirt
1. Chimney effect again.
Cloud Altitude
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.

High-Altitude Test Delivery Systems

Early planning and developments - Germany invested successfully in long range missile systems during WW II in the belief that they were crucial weapons for final victory. However, the limitations in transport capabilities were too severe to allow a sufficient load of explosive material. The production was limited,1000 V2 missiles were employed, and the final impact on the war development was negligible.
High Altitude tests - In the early 1960s, the United States government (both the Defense Atomic Support Agency DASA and the Atomic Energy Commission AEC) conducted a series of high-altitude nuclear tests.
1. The electromagnetic pulse (EMP) from these tests sent power line surges through Oahu (800 miles away), knocking out street lighting, blowing fuses and circuit breakers, and triggering burglar alarms.
2. The blast from Starfish Prime (1962) was seen at 800 miles distance from Honolulu, Hawaii. This blast triggered the Auroral light phenomena through radiation-induced excitation effects in the atmosphere.

Aurora borealis or "northern lights" seen from Space Shuttle Endeavor.
Image courtesy of NASA. Click to enlarge.

Citation: Mathews, G. (2008, May 30). Lecture 12. Retrieved May 24, 2013, from Notre Dame OpenCourseWare Web site: http://ocw.nd.edu/physics/nuclear-warfare/notes/lecture-12.