Unit DNUCLEAR ENERGY: POWERING THE UNIVERSE (11:17 HANK)

D.1 Splitting the Atom

During WWII, OttoHahn and Fritz Strassman bombarded uranium with neutrons to create a more massive nucleus.

Instead, they produced barium with only half the atomic weight.

Scientist Lise Meitner proposed that U atom was split into two parts equal in size.

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Nuclear fission

The splitting of the Uranium atom is a nuclear fission reaction.

Uranium-235 can fission (split) into numerous combinations such as barium or krypton.

U-235 is the only naturally occurring isotope that undergoes fission with slow (thermal) neutrons.

Many synthetic nuclei also fission under bombardment.

D.2 The Strong Force

Fissionable isotopes such as uranium release a million times more energy then other chemical reactions.

The strong force is the force that holds the nucleus together. It is a thousand times stronger than other types of chemical (electrical) forces that hold compounds together.

Chemical vs. nuclear

In a chemical reaction, the total amount of energy involved is conserved—it does not change—it is just transferred.

Mass is also conserved in a chemical reaction.

A nuclear reaction conserves both the mass and the energy together.

Nuclear reactions: E = mc2

Energy released (E) is equal to the mass lost (m) multiplied by the speed of light squared.

One gram of nuclear matter can produce energy equal to 700,000 gallons of octane fuel.

D.3 Chain Reactions

In nuclear fission, two or three neutrons from each fragment are released. These in turn can keep the reaction going by bombarding more nuclei in a chain reaction.

Critical Mass

Since atoms are mostly empty space, the probability of a neutron splitting another nucleus is small unless a minimum quantity of material is available. This is called the critical mass.

When a critical mass of fissionable material is present a chain reaction occurs.

Such technology led to the production of the atomic bomb.

How Nuclear Bombs Work

There are two basic ways that nuclear energy can be released from an atom.

Nuclear fission splits the nucleus of an atom into two smaller fragments. (U-235, U-233 or Pu-239)

Nuclear fusion brings together two smaller atoms (H, H-2, H-3) and forms a larger one (He, He isotopes).

Fission Bombs

Fission bombs use an element like U-235 which can undergo induced fission. If a free neutron runs into its nucleus, it is absorbed, the nucleus becomes unstable and then splits immediately.

The two new atoms emit gamma radiation and heat as they settle into their new states.

The energy released is due to the fact that the fission products and the neutrons together weigh less than the original U-235 atom.

The energy released by a pound of highly enriched uranium is equal to the amount released from the combustion of a million gallons of gasoline.

A pound of uranium is the size of a baseball, while a million gallons of gasoline would fill a 50 ft cube. (50 ft = a five story building).

Fat Man was an implosion-triggered fission bomb with a 23-kiloton yield and a 17% efficiency. The fission usually occurred in 560 billionths of a second.

Hiroshima

Fusion Bombs-H bomb

Fusion bombs, also called thermonuclear bombs have greater efficiencies and higher kiloton yields than fission bombs but aren’t as efficient because of the chemical properties of deuterium and tritium.

However, fusion bombs release more energy than fission bombs.

Consequences of Nuclear Explosions

The degree of damage depends on the distance from the center of the bomb, also called the hypocenter or ground zero. The closer, the more damage. Damage is caused by: Intense heat from explosion. Pressure from the shock of explosion. Radiation Radioactive fallout (fine radioactive particles

that fall back to the ground). At the hypocenter, everything is vaporized in

500 million degree F /300 million degree C temperatures.