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
