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Radioactivity

Beta Particles from Radioactive Decay.

After a radioactive nucleus has emitted a b-particle,
the mass number stays the same and the atomic number goes up by 1.
A neutron in the nucleus has changed into a proton plus an electron.
The proton stays inside the nucleus but the electron is given out as a b-particle.
For example, Carbon-14 becomes Nitrogen-14 by emitting a b-particle.

Carbon Decay to Nitrogen

The nuclear equation is balanced because the mass number
 on the left of the arrow is equal to the sum of the mass numbers
 on the right of the arrow,  14 = 14 + 0.
Similarly for the atomic numbers,  6 = 7 - 1.

Some nuclei can decay by emitting either an a-particle or a b-particle.
An example is bismuth where 1/3 of the atoms emit an a-particle
 and 2/3 of the atoms emit a b-particle.
You can work out which particle is emitted by balancing the equation.
 Bismuth Decay to Thallium
The mass number is 212 - 208 = 4. The atomic number is 83 - 81 = 2.
The Unknown Particle is an Alpha Particle

What element would be formed if bismuth had emitted a b-particle?

Answer - it would have a mass number 212, atomic number 84.
The element is polonium.
Bismuth Decay to Polonium

This form of polonium and the form shown on page 6 are isotopes.

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Copyright © 2008 Dr. Colin France. All Rights Reserved.