What is it to be Radioactive?

• Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves.

• There are numerous types of radioactive decay. The general idea:

• An unstable nucleus releases energy to become more stable

Nuclear Reactions• Fission: Bombarding

substances with neutrons and splitting an atom into 2 smaller (what we can do in nuclear power plants)

• Fusion: Joining two atoms into one, creating a different element (what occurs in stars)

Nuclear energy: energy produced from changes to the nucleus of an atom

1) fusion: joining atoms (sun)

2)fission: splitting atoms (nuclear power plants)

Three Common Types of Radioactive Emissions

Alpha

Beta

Gamma

Science Park HS -- Honors Chemistry

Kinds of Radioactivity

The three main decays are Alpha, Beta and Gamma

Alpha Decay• When two protons and two neutrons (a

Helium nucleus) are ejected from the nucleus. Can be stopped with a piece of paper

Uranium Thorium

Beta Decay• Beta particles : electrons ejected from the

nucleus when neutrons decay n -> p+ +-

• Can be stopped by aluminum foil or a block of wood.

Thorium Protactinium

• Gamma radiation • electromagnetic energy

• that is released. 

• Gamma rays are electromagnetic waves.

• They have no mass.• Gamma radiation has no charge.

– Most Penetrating, can be stopped by 1m thick concrete or a several cm thick sheet of lead.

Gamma Decay

Radioactive Half-Life (t1/2 ):

• The time for half of the radioactive nuclei in a given sample to undergo decay.

Common Radioactive Isotopes

Isotope Half-Life Radiation Emitted

Carbon-14 5,730 years

Radon-222 3.8 days

Uranium-235 7.0 x 108 years

Uranium-238 4.46 x 109 years

Radioactive Half-Life

• After one half life there is 1/2 of original sample left.

• After two half-lives, there will be

1/2 of the 1/2 = 1/4 the original sample.

Example

You have 100 g of radioactive C-14. The half-life of C-14 is 5730 years.

• How many grams are left after one half-life?

• How many grams are left after two half-lives?