Nuclear Physics

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# Nuclear Physics - PowerPoint PPT Presentation

Nuclear Physics. Chp 30. The Atom. A nucleus of equal mass positive protons and neutral neutrons, surrounded by almost massless, negative electrons Atomic number = # protons Atomic mass = # protons + neutrons Most atoms are neutral, so electrons = protons

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## PowerPoint Slideshow about 'Nuclear Physics' - amela-frank

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Presentation Transcript

### Nuclear Physics

Chp 30

The Atom
• A nucleus of equal mass positive protons and neutral neutrons, surrounded by almost massless, negative electrons
• Atomic number = # protons
• Atomic mass = # protons + neutrons
• Most atoms are neutral, so electrons = protons
• The nucleus, although containing the most mass, takes up very little space in the atom
Isotopes
• Different versions of an element
• Only the atomic mass and # neutrons change (changing protons would change the element)
• Atomic mass as given on the periodic table is an average of all possible isotopes (this is why it’s a decimal)
• Use AZX to show isotopes
• A = atomic mass
• Z = atomic number
• X = element symbol
Strong Nuclear Force
• The force that holds an atomic nucleus together
• Must be very strong to hold like charges together (they normally repel each other)
• Even stronger than electricity
• Only works over a very short range though
• Energy must be added to take a nucleus apart (need to overcome that force)
E = mc2
• Mass is a form of energy
• That means if mass changes, energy is released or absorbed
• For atoms smaller than iron, they have less mass when they combine than when separate (fusion)
• For atoms larger than iron, they have less mass when they separate than when they are held together (fission)
• Iron is stable and undergoes neither fission or fusion
• Alpha
• A particle of 2 protons and 2 neutrons are emitted
• Most massive, but easiest to stop
• Beta
• A neutron turns into a proton and an electron, the electron is emitted and the proton stays
• Fairly easy to stop because its charged
• Gamma
• Massless energy is released
• Hardest to stop and most dangerous
• Substances often undergo the release of many of these particles in stages until a stable isotope is reached
Half Life
• The time required for half the atoms in a radioactive sample to decay
• The time it takes is unique and constant for each isotope
• If an isotope has a short half life, it decays more quickly, and therefore is more dangerous
• Used to “date” objects
• Carbon – 14 has a half life of 5730 yrs (good for living things)
• Uranium – 238 has a half life of 4.5 billion years (good for planets)
Nuclear Reactors
• Currently all based on fission of uranium - 235
• Needs a neutron to start the process, then 3 new neutrons are created
• Each of these can start a new reaction (chain reaction)
• Reactions are kept in check by mixing in U-238, which doesn’t react and having control rods, which can drop down and absorb neutrons to stop the reaction
Reactors, Cont’d
• The heat created by U-235 fusion, heats water which creates steam to turn turbines and generate electrical energy
• Creates tons more energy than coal burning, but does leave radioactive byproducts that must be properly disposed of