1. Nuclear Physics
Chp 30

2. 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

3. 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

4. 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)

5. 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

6. Radioactive Decay Alpha Beta Gamma
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

7. 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)

8. 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

9. 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