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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.
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Radioactive Decay
TEKS Par 112.35 #12b
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.
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.
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-.
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
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.
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)
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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.
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Beta decay changes the charge and the element identification and
chemical properties, not the mass
Summary
Common Nuclear Decay
Type Symbol Particle given off
Change in charge
Change in mass
Alpha α Heliumnucleus
Down by2
Down by4
Beta β electron Up by 1 None
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