Spontaneous emission of radiation when the nucleus of an atom breaks down to form a different element.

The constant level of radioactivity always present around us Caused by: Cosmic rays Naturally occurring uranium Radon in the air Radioactive isotopes in food and environment What is your radiation exposure? National Average: 500 mrem Background Average: 360 mrem

Nuclear reactions involve the nucleus (protons and neutrons) BUT chemical reactions involve the transfer and sharing of electrons

After element 83 (Bismuth) the elements are naturally unstable and may emit decay particles After element 83 (Bismuth) the elements are naturally unstable and may emit decay particles The bigger the atom gets and the further from a 1:1 ratio of protons and neutrons, the less stable the atom is

Electromagnetic Force Force of repulsion between positive charges of the protons in the nucleus Strong Force Force present that holds quarks together and therefore keeps the protons and neutrons tightly packed in the nucleus When the electromagnetic force wins out, the nuclei break apart!

Decay Type SymbolCharge Reaction Particle Strength Can be stopped by… Alpha Beta Gamma

The superscript indicates the mass number and the subscript indicates the atomic number. X A Z Mass Number Atomic Number Element Symbol

1.Write the nuclear symbol for the element that is given. 2.Draw an arrow. 3.Identify the type of particle that has decayed and write it after the arrow. 4.Balance the mass number (top) and the atomic number (bottom). 5.Identify the new element.

Loss of an alpha particle 4 2 He 4 2 α 239 Pu  U  92

Loss of a beta particle (electron) 0 e 0 β 42 K  19

Loss of a beta positive particle (positron) 42 K  e 0 β

Loss of a gamma particle Does it effect the outcome of the reaction? Alpha and gamma decay of: 0 0 γ 239 Pu  94

Time required for half a sample to decay The stability of the isotope is what determines the rate of decay. Less Stable = Faster Decay

After each half-life, half of the sample decays. Start = 100% 40 blue particles are present 1 half-life = 50% 20 blue remain 2 half-lives = 25% 10 blue remain 3 half-lives = 12.5% 5 blue remain 4 half-lives = 6.25% 2.5 blue remain Amount never becomes zero!!

After 10 half-lives sample considered nonradioactive because it approaches the level of background radiation. Because the amount never reaches zero, radioactive waste disposal and storage causes problems. Would you want radioactive waste stored in your community? How can we get rid of nuclear radioactive waste?

Example 1: The half-life of mercury-195 is 31 hours. If you start with a sample of 5.00 g, how much of it will still be left after 93 hours?

Example 2: How many half lives have passed if there is only g left of a 30 g sample? If the half life for this sample is 1 hour, how many total hours have gone by?

Sun is powered by nuclear reactions Electricity from nuclear power plants Medical: x-rays, cancer treatment, radioactive tracers Industrial: Sterilize equipment, sterilize (irradiate) food, x- rays of metal equipment (scan for cracks in airplanes) Military

Exposure to radiation can cause cell mutations and illness. Four factors that affect exposure: Dose (strength of radiation) Exposure time Area exposed Tissue exposed

Two light atoms combine to form a heavier atom of higher energy This reaction powers the sun!

One heavy atom breaks down into two or more smaller atoms and produces energy This becomes a chain reaction (as one atom splits and hits more, and those split and hit more) Supercritical: creates a great release of energy - atomic bomb Ping Pong Video

Particles reacting must have critical mass: The minimum amount of mass needed for the neutron to hit and react with No critical mass = no reaction Fission reactions can also be controlled to contain the energy.

Controlled Fission: used for nuclear power Controlled Diagram: Control Rods to limit nuclear fission! Fission heats the water that turns to steam and moves the turbines