Nuclear
Equations
Nuclear
equations can be used to show the decay
process.
These must balance
for nucleon
number and proton
number.
Alpha
Decay
Beta
Decay
Positron
Decay
Gamma
Emission
Alpha
decay
A nucleus that has
high mass and too many protons to be stable
tends to undergo alpha decay.
When alpha decay occurs
a group of two protons and two neutrons (helium nucleus) comes out of
the nucleus. Therefore the proton
number decreases by 2 but the nucleon
number decreases by 4. The resulting daughter
nucleus is of an element 2 positions to the left of the 'parent' in
the periodic
table.
To view a simulation 
The above equation
shows the radioactive decay of Uranium-238 by alpha
emission.
- Look at the
numbers on the top line (the nucleon numbers).
238 = 234 + 4
Therefore the
nucleon numbers balance
- Look at the
numbers on the bottom line (the proton numbers).
92 = 90 + 2
Therefore the proton
numbers balance
Beta
Decay
When a nucleus has
too many neutrons,
it tends to beta decay.
When beta decay occurs
a neutron
within the nucleus
emits the particle and changes into a proton.
Therefore the
proton number increases but the nucleon
number stays the same (only now you have one more proton and one less
neutron!). The resulting daughter
nucleus is of an element 1 position to the right
To view a simulation
Beta decay is basically
the decay of a neutron into the more stable proton
The above equation
shows the radioactive decay of Carbon-14 by beta
emission.
- Look at the
numbers on the top line (the nucleon numbers).
14 = 14 + 0
Therefore the
nucleon numbers balance
- Look at the
numbers on the bottom line (the proton numbers).
6 = 7 + (-1)
Therefore the proton
numbers balance
Positron Decay
When a nucleus
has too many protons,
it tends to positron decay. A positron is an antimatter
beta
particle. When a positron meets with an electron it annihilates
it! Both particles disappear and two gamma
rays are produced instead.
To view a simulation
Positron decay is
the changing of a proton into a neutron.
The above equation
shows the radioactive decay of Oxygen-15 by positron
emission
- Look at the
numbers on the top line (the nucleon numbers).
15 = 15 + 0
Therefore the
nucleon numbers balance
- Look at the
numbers on the bottom line (the proton numbers).
8 = 7 + 1
Therefore the proton
numbers balance
Sometimes, after its emission of an alpha,
beta
or positron
particle, the nucleus
is still in an excited state, called a metastable
state. In order to get to a lower energy state it emits a quantum
of energy in the form of a gamma
ray. This is not a highly unstable state otherwise the emission
of the gamma ray would accompany the alpha, beta or positron particle.
Nuclei in the metastable state produce gamma rays at a measurable half-life.
E.g. Cobalt 60m decays
to give cobalt 60 with a half-life of 5.3 years and technetium 99m decays
to give technetium 99 with a half-life of 6 hours.
No matter
is emitted from the nucleus therefore the nucleon
number and the proton
number remain the same. Before and after emission of the gamma ray
they are the same isotope
of the element
but they are different nuclide
because the term nuclide incorporates nuclear energy states as well basic
structure.
Click
here to find out why decay occurs.