nuclear weapons. units of radiation dose roentgen – ability to create a specified electric charge...

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

• 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 earth-

moving• 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 WeaponsTo 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

MinutemanWarheads

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