Nuclear Weapons
Units of Radiation Dose
• Roentgen – Ability to create a specified
electric charge per volume of air
• Rem (Roentgen equivalent man) –Biological
effect of one roentgen of X-rays
• Rad (Radiation absorbed dose) – Energy
absorption: 400,000 rads heat H2O 1 deg
• For general human exposure, these units
are roughly equivalent
Background Radiation
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•
•
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Cosmic Rays
Solar Wind
Decay of Natural Radioactivity
Typical Doses
– Global Average 0.1 rem/year (80% natural)
– Some areas up to 1 rem/year
– Ramsar, Iran: up to 26 rem/year
Human Radiation Sources
• Nuclear Fallout from Atmospheric Testing
(US and Russia, 1963; France, 1974; China,
1980)
• Chernobyl 1986
• Uranium Mining
• Radon release from construction and earthmoving
• Conventional power plants
Human Survival Limits
• 200 rem (whole body): few immediate
fatalities
• 500 rem (whole body): 50% fatalities
• 1000 rem (whole body): No survivors
Chain Reaction
Nuclear Fission
• Chain reaction requires a critical mass to
proceed
• 10 kg U-235 = 2.5 x 1025 atoms
• 1,2,4,8 … 2.5 x 1025 = 85 steps
• @ 1/1,000,000 sec per step = 1/10,000 sec
• After 64 steps, T = 10,000 K (twice as hot as
sun)
• Have only completed 1/1,000,000 of fission
Nuclear Weapons
To get a nuclear explosion, you have to
• Assemble a critical mass in millionths of a
second
• Retain a high percentage of the neutrons
• Hold the material together against
temperatures hotter than the Sun
• Imposes limits on yield of weapon
• Unless something is specifically designed to
be a nuclear weapon, it will not explode
Yields of Nuclear Weapons
• Kiloton = 1000 tons of explosives = 4.2 x
1012 joules = 1012 calories
– Texas City, Texas, April 16-17, 1947
– Collapse of World Trade Center
– Impact of 10-m asteroid
• Megaton = 1,000,000 tons of explosives =
4.2 x 1015 joules = 1015 calories
– Magnitude 7 earthquake
– Impact of 100-m asteroid
“Das war keine gute Idee”
Effects of Nuclear Weapons
• Direct ionizing radiation
• Heat (Fireball)
– Rising fireball sucks dust upward, creates
“mushroom cloud”
– Any large explosion will create a “mushroom
cloud”
• Blast (Expansion of Fireball)
• Fallout
• Volume α Yield: Radius α 3√Yield
All Large Explosions Make Mushroom
Clouds
Nuclear Explosion
Weapons Terminology
• Warhead: The Actual Explosive Component of
a Nuclear Weapon
• Warhead Section: The Delivery Casing for a
Nuclear Weapon. Includes casing, radars,
timers, detonators, etc
• When most people say “Warhead,” they
actually mean “Warhead Section.”
• Tactical = Range < 500 km
• Strategic = Range > 500 km
Some Nuclear Factoids
• Nuclear weapons are always under armed
guard
• Nobody Ever Goes Near a Nuke Alone. U.S.
Protocols Call for a “Two Man” Rule
• There are persistent rumors we allowed
designs of our locking mechanisms to be
leaked to the Russians
• Information on locations of nuclear weapons
is classified “Secret” or above
• Do not confirm/deny
Nuclear Weapons Systems
• All military explosive weapons have had
nuclear versions
– Artillery Shells
– Bombs
– Depth Charges
– Rockets
– Missiles
– Anti-Aircraft
– Stationary charges
DASA and SASCOM
“Little Boy” Gun Type, Uranium
“Fat Man” Implosion, Plutonium
Early Strategic Nuke
Early Strategic Nuke
Trinitite
Atomic Bomb
Delivery Systems
Titan Warhead
Minuteman Warheads
Minuteman
Warheads
Minuteman Missile Silo, SD
MIRV
Tactical Nukes
Nuclear
Artillery Shell
Atomic Cannon
“Birdcage”
for Artillery
Shell
Fissionable
Material
Davy Crockett
SADM
MADM
Cradle For Nuclear Artillery Shell
Palomares, Spain: My Bad
Russian Nukes
Nuclear Winter
• Publicized by Carl Sagan and others in
1980’s
• Global nuclear exchange would raise large
amounts of dust and soot into upper
atmosphere
• Would absorb or reflect sunlight, cooling
the surface
• Would be above most precipitation
processes
• Did not happen in Gulf War 1991
Fusion
• Natural: how stars (and the sun) generate
energy
• Artificial and uncontrolled: Thermonuclear
Weapon (hydrogen bomb)
• Fusion Reactor: controlled
• “Energy source of the future. Always has
been, always will be.”
Core of the Sun
• Energy output: 90 billion megatons/second
• Energy output = 6 microwatts/kg – less than a
candle
• Human body outputs 1.2 W/kg – 200,000
times greater
• Trying to duplicate sun’s energy output not
practical on Earth
• Energy takes 10,000 – 100,000 years to reach
surface
Uncontrolled Fusion
• We cannot achieve T and P necessary to
use ordinary hydrogen
• Have to use H-2 (deuterium) or H-3
(tritium)
• Still need T = 1,000,000 K+
• Initiated by a nuclear (fission) weapon
• Fission weapons yield up to 20 kilotons
• Fusion (hydrogen or thermonuclear)
weapons yield up to 20 megatons
Controlled Fusion
• Temperatures too high for any material
• Need to contain by magnetic fields, achieve
small-scale reactions for short periods
• Have not achieved break-even
• Apparatus will be incredibly complex and
expensive
• Reactions give off neutrons: there will still
be radioactive waste
• No spent fuel or fissionable residue
Detecting Nuclear Explosions
• Vela System (US)
• Space: X-ray and Gamma Ray pulses
• Atmospheric:
– Double-humped light pulse
– Initial Fireball
– Obscured by ionized gas in shock wave
– Revealed again as shock wave cools
– Vela Incident, September 22, 1979
• Subsurface: Seismic First Motion Analysis
Nuclear Powers and Wannabes