8.1.7

# Nuclear Instability

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## Nuclear Instability

Some isotopes of atoms are more stable than others. The unstable isotopes can decay radioactively.

### Stability

• Above is a graph of the number of neutrons against the number of protons in an atom
• There is a pattern where some atoms are more stable.
• An unstable atom will decay to a more stable atom.

### Types of decay

• Atoms usually decay through alpha or beta radiation untill they reach a stable point.
• Any chain of alpha and beta radiation is possible to reach a stable point.
• Alpha radiation reduces the atom by two neutrons and two protons.
• Beta radiation reduced the atom by one neutron and increases by one proton.

## Decay Equations

When an atom decays it may release radiation and a new atom is created. We can write equations for this decay.

• Alpha radiation is made up of two protons and two neutrons.
• The mass number will reduce by four and the atomic number by two.
• Beta radiation changes a neutron into a proton and releases an electron.
• The mass number will not change but the atomic number will increase by one.
• Gamma radiation is a wave and will only change the energy of the atom, not the form

### Equations of decay

• A decay equation shows the mass and atomic numbers for all of the atoms or radiation present.
• Charge and mass must be conserved so we know that the sum of the mass number before and the sum after have to be the same.
• We can work out what type of radiation is produced if we know the mass and atomic number before and after.
• Remember radiation is a product, not a reactant. It should be after the arrow.

## Excited States in Nuclei

Just as atoms have excited states, nuclei also have excited states.

### Atomic excited states

• In an atom, an electron can gain energy and be promoted to a higher energy level.
• When the electron returns to the original level, the energy is released as electromagnetic waves.

### Nuclear excited states

• Nuclei also have excited states. This is because of the different arrangements of protons and neutrons within a nucleus.
• When the protons and neutrons rearrange to a lower energy state, the excess energy is released as gamma radiation.

### Technetium-99m

• It is possible to work out the energy of the gamma radiation released.
• Technetium-99m is a valuable resource as it is used in gamma cameras in hospitals. It is produced from the beta decay of molybdenum-99.

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