P4 - Atomic Structure

P4 - Atomic Structure

1. The idea of the atom as the building block of matter has developed over time. What was thought of as a single particle about 1 × 10‾¹º m across is now known to be a collection of smaller particles.

2. Atoms are made up of protons, neutrons and electrons. Change the number of neutrons in an atom and it becomes an isotope, change the number of electrons, it becomes an ion.

3. With the wrong number of neutrons, nuclei can fall apart. A nucleus will regain stability by emitting alpha or beta particles and then ‘cool down’ by emitting gamma radiation.

4. People are exposed to sources of radiation in all aspects of everyday life. Radioactive sources can be very useful but need handling carefully to ensure safety.

5. Alpha - these are fast moving helium atoms. They have high energy, typically in the MeV range, but due to their large mass, they are stopped by just a few inches of air, or a piece of paper.

6. Beta - these are fast moving electrons. They typically have energies in the range of a few hundred keV to several MeV. Since electrons are might lighter than helium atoms, they are able to penetrate further, through several feet of air, or several millimeters of plastic or less of very light metals.

7. Gamma - these are photons, just like light, except of much higher energy, typically from several keV to several MeV. X-Rays and gamma rays are really the same thing, the difference is how they were produced. Depending on their energy, they can be stopped by a thin piece of aluminum foil, or they can penetrate several inches of lead.

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