Unit D NUCLEAR ENERGY: POWERING THE UNIVERSENUCLEAR 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.  Play Audio Play Audio

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 = mc 2  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.