Radioactivity

3 Types of Radioactive Decay

• Three rays can be emitted during radioactive decay:
• Alpha (α)
• Beta (β)
• Gamma (γ)
• Alpha Particle
• Always positive
• 2 protons and 2 neutrons
• A helium nucleus

Beta particle

• Beta particle
• Always negative
• An electron
• Gamma rays
• Always neutral (i.e. no charge)
• No mass
• Very high energy EM waves

Radiation Penetrating Power

• There is a great difference between the penetrating power of the 3 types of radioactive rays
• Alpha rays are the easiest to stop
• They can be stopped by a heavy sheet of paper
• Alpha particles move the slowest
• Beta rays go thru paper but are stopped by sheets of Aluminum foil
• Electrons move faster than alpha particles
• Gamma rays require lead to block them
• Move at the speed of light

Check Your Understanding

• Pretend you are given radioactive cookies-one alpha, one beta, and the other gamma. If you MUST eat one, hold one, and pocket one, which would you do what to in order to minimize your exposure to radiation?

• Hold the alpha; your skin will protect you
• Pocket the beta; your clothing will protect you.
• Eat the gamma; it will penetrate your body anyway.

Radioactive Isotopes

• An atom has more than one form, based on the # of neutrons it has
• These are called isotopes
• Some isotopes are more stable than others
• Unstable isotopes are also called radioactive isotopes
• Ex: Carbon 14 is a radioactive isotope because it can decay over time
• BrainPop Isotopes

Radioactive Half-Life

• Half-life: The time required for half of the atoms of a radioactive isotope of an element to decay.
• Radioactive isotopes decay at different rates
• The amount of a substance halves every half-life
• Ex: Uranium 238 has a half-life of 4.5 billion years, Carbon 14 has a half-life of 5730 years