Glossary:�

• Atom�The smallest building blocks of physical matter.�
• Alpha particle�A small particle, made of 2 protons and 2 neutrons. It has a positive charge.

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• Nucleus�The centre of an atom, containing protons and neutrons.�
• Isotopes�These are versions of atoms that contain different amounts of neutrons.�
• Radioactive decay�This is the random process in which an unstable nuclei breaks down and emits radiation.�
• Radiation�This is emitted from the nuclei during decay. It can be either Alpha, Beta, or Gamma radiation. �
• Half life�The time taken for half of (the nuclei in) a radioactive sample to decay.�
• Irradiation�This occurs when you are exposed to radiation from a radioactive source. �
• Contamination�This is when a radioactive sample is found in, or on, another material/person. �
• Nuclear Fission�This is the release of energy from the nuclei of decaying atoms in a chain reaction. �
• Nuclear Fusion�This is the fusion of two light nuclei, creating a heavier nuclei, and releasing energy in the process.

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Alpha scattering experiment�This experiment was used to disprove the plum pudding model of atomic structure, and suggest the structure of the atomic model .

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Alpha scattering experiment – Outcomes and suggestions�

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Isotopes

These are 2 isotopes of Carbon. The one on�the right is heavier, with two extra neutrons.

• Same number of Protons
• Different number of Neutrons

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P4: Radioactivity

Half Life

Decay is a random process, however all radioactive substances will see half of their nuclei decay in a specific amount of time. This time if known as a “half-life”. This can be monitored by watching the count rate of the material. The time taken for the count rate to reduce by 50% is the half life time. ��In the graph on the right�hand side, you can see�that the count drops from�40 to 20 in 2 days. ��This repeats again, with �the count dropping from �40 to 20 over another 2�days.

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Properties of Radiation

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Exposure to Radiation

Radiation is ionising, and can be highly dangerous. Exposure comes in 2 forms:-

• Irradiation -This occurs when you are exposed to radiation from a radioactive source. This is often a short experience.
• Contamination -This is when a radioactive sample is found in, or on, another material/person. These effects are long lasting.

Nuclear Fission�In Fission, a neutron collides with a �nuclei. This causes the nuclei to break,�producing two smaller nuclei, and�releasing energy in the process.

P4: Radioactivity