Short introduction to what radioactive decay is and how to balance nuclear decay equations. Suggested you use after the introduction to alpha, beta and gamma radiation.

1. Radioactive Decay
TEKS Par 112.35 #12b

2. What's Causing the Radiation?
 Scientists discovered that certain elements give off
rays
- Alpha (helium ion)
- Beta (electron)
- Gamma (high-energy, low-wavelength light)
 They wanted to know why that happens, and how.
- They know that there are different kinds of atoms,
with the same chemical behavior but differing
masses, called isotopes.

3. Stable or Unstable?
 Some isotopes are stable.
- They don't give off radiation
- An example is the isotope of carbon, C-12
 Some isotopes are not stable.
- They give off radiation
- Example, “radiocarbon,” C-14
- This isotope is used to find the age of objects that
contain carbon
- As time goes on, there is less and less C-14 in it.

4. What's Happening to C-14?
Frankswebspace.org.uk
The graph shows
how much C-14
remains after a
certain number of
years.
Other tests show
that N-14, the
next element in
the periodic table,
has taken its
place.
C-14 has turned into N-14, by
giving off a beta particle, e-.

5. Balancing the Equation
 We can write the decay process, using a shorthand
everyone has agreed on.
 It's called a nuclear equation, because it shows the
decay of the nucleus.
 Here is the equation for the decay of carbon-14 into
nitrogen-14 and an electron:
Cyberphysics.co.uk

6. How to Write a Nuclear Decay Equation
 Start off with what you know decays, and what it
decays into.
 Write the starting “reactants”, then write a right-facing
arrow, and then write the decay products.
 Make certain that the numbers on top (the mass) are
equal on both sides.
 Make certain that the numbers on the bottom (the
charge) are equal on both sides.
 Manipulate those numbers so they match.

7. Radium example
 A radium isotope, mass 222, gives off an alpha
particle. What new isotope is produced?
 Start with the only “reactant”, Ra-222
+
 Add the known product, an alpha particle.
 Determine what the top and bottom numbers on the
other product must be by subtraction.
 Look up the product on the periodic table (bottom
number)

8. You Do One!
 Iodine-131 decays by giving off an electron and
gamma radiation. What isotope is also given off?
 Hint—the gamma radiation has no charge and no
mass.
+
Beta decay changes the charge
and the element identification and
chemical properties, not the mass

9. Summary
Common Nuclear Decay
Type Symbol Particle
given off
Change
in
charge
Change
in mass
Alpha α Helium
nucleus
Down by
2
Down by
4
Beta β electron Up by 1 None

10. Summary
Common Nuclear Decay
Type Symbol Particle
given off
Change
in
charge
Change
in mass
Alpha α Helium
nucleus
Down by
2
Down by
4
Beta β electron Up by 1 None