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Alpha Particles from Radioactive Decay.
After a radioactive nucleus has emitted an a-particle,
the mass
number goes down by
4 and the atomic number goes
down by 2.
For example, Radium (Ra) becomes Radon
(Rn) by emitting an a-particle.
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, 224 = 220 +
4.
Similarly for the atomic
numbers, 88 =
86 + 2.
Radon is itself radioactive and decays by a emission.
You can work out what the
new element is by balancing the equation.
220 = 4 +
116, 86 = 2 + 84.
The element with atomic number 84 is Polonium
(see the Periodic
Table on the GCSE Chemistry
site).
If you are given the two elements
you can work out which particle
is emitted by balancing the equation.
Polonium is also
radioactive and decays to form other
radioactive nuclei.
One element turning into another
which turns into another
which turns into another etc. is called a decay series.
Eventually a stable nucleus is formed and the decay series stops.
The stable nucleus is often lead
(atomic number 82, mass number 206, 207
or 208).
Headings Radioactivity Search
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Copyright © 2008 Dr. Colin France. All Rights Reserved.