Types of Radioactive Decay
There are three main types of radioactive decay: alpha, beta, and gamma.
Let's pause here a minute to define "decay." When an element decays the
parent element's nucleus changes - it will actually decay to turn into a
different daughter element altogether! How is this possible? Because during
radioactive decay the number of protons in the nucleus can change (I know,
right?).
Alpha Radiation/Decay
During Alpha decay an atom spits out two protons and two neutrons from its
nucleus. This little bundle is called an "alpha particle."
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Alpha decay usually happens in larger, heavier atoms.
The symbol looks like Helium because Helium-4 has the same number of
protons and neutrons as an alpha particle (no electrons, though).
Since Alpha particles have two protons and no electrons, they have a net
charge of 2+.
During Alpha radiation an atom's proton count drops by two, and we know
what that means - a NEW element is formed!
Alpha radiation can be stopped by PAPER.
Beta Radiation/Decay
Remember we said a neutron is a proton with an electron attached? In beta
decay a neutron sends its electron packing, literally ejecting it from the
nucleus at high speed. The result? That neutron turns into a proton!
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Beta decay increases an atom's electron count by 1 (notice the 1- in the
symbol).
During Beta radiation an atom's proton count grows by one. Once again,
NEW element!
Beta radiation can be stopped by WOOD.
Gamma Radiation/Decay
Gamma rays (remember that term from when we studied the EMS?) is
electromagnetic radiation similar to light. Gamma decay does not change the
mass or charge of the atom from which it originates. Gamma is often emitted
along with alpha or beta particle ejecton.
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Gamma radiation can be stopped by LEAD.
Comparison of Alpha, Beta and Gamma Radiation/Decay
The diagram below shows the difference between alpha, beta and gamma
particles.
The diagram below should make you think back to the cathode ray tube
experiment - notice how the negatively charged beta particles are attracted to
the (+) plate while the positively charged alpha particle is attracted to the (-)
plate. Since gamma radiation has no charge its path does not bend.
The diagram below shows what materials can block each type of radiation.
Notice it's easy to block alpha radiation (paper will do!) but tough to block
gamma radiation (you'll need a lead vest).
These resources will help you understand the different types of radioactive
decay:
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Alpha vs. Beta vs. Gamma Radiation
How do you write equations for alpha decay?
Fair warning - these reactions look more complicated than they are! If you can
subtract 4, 2, 1 or 0 from whole numbers you can write basic nuclear
equations.
Remember when an element spits out an alpha particle it loses two protons
(changing the atomic number) and two neutrons (changing the isotope's mass
number). Your job is to make sure all the mass numbers (top) and atomic
numbers (bottom) add up.
Let's start with a non-chemistry example to prove this is a piece of cake
(mmmm, cake!):
210 = 4 + ?
Not so bad, right? The ? = 206 In a nuclear equation for alpha decay you'd be
half done! This is how you balance the top part of the equation. So let's finish...
84 = 2 + ?
Again, easy. The ? = 82. In solving a nuclear equation you're approaching the
finish line! The 82 is the atomic number of the daughter element, so find
element 82 in your trusty periodic table and you are done. This is how it looks
as the full equation for the alpha decay of Polonium-210.
How do you write equations for beta decay?
Same idea and even easier since the mass number doesn't even change during
alpha decay.
Remember when an element spits out a beta particle all it loses is one electron.
It still changes the atomic number because what used to be a neutron is now
an extra proton. Your job here is to make sure all the atomic numbers
(bottom) add up.
Once again we'll start with a non-chemistry example to prove this is easy
cheesy (mmmm, cheese!):
144 = 0 + ?
There's gotta be a catch, right? Too easy? Nope. The ? = 144. Remember the
mass number doesn't change during beta decay.
50 = -1 + ?
The only trick here is remembering you're working with negative numbers, so
the daughter will have a HIGHER atomic number than the parent (extra
proton, remember?). This is how it looks as the full equation for the beta decay
of Cerium-144.
Practice your equation writing skills here! (Answers provided so you can check
your answers) .
How much do you need to know about nuclear decay?
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Know the names and descriptions of the three main types of nuclear decay
(alpha, beta, gamma).
Know the symbols and charges for alpha and beta particles.
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Know how to write basic nuclear reactions for alpha and beta decay.
©2012 Linda Bennett