Synchrotrons – making the light fantastic
Glossary
atom. The fundamental unit of all matter, consisting of a nucleus of protons and neutrons surrounded by orbiting electrons (or in the case of hydrogen, just one electron). For more information see Back to Basics: Atoms and molecules (Australian Academy of Science).
electromagnetic force. One of the four forces – gravity, strong force, electromagnetic force, weak force – that act on particles. Electromagnetic force acts on charged particles and is made up of electric and magnetic forces (eg, moving magnets produce electric forces and moving electric charges produce magnetic forces).
The electric charge that is the source of electromagnetic force can either be positive or negative. Because there are two types of charge, the electromagnetic force can be either attractive or repulsive. Opposite charges attract, like charges repel. Physics theory explains that electromagnetic force is carried by photons (packets of electromagnetic radiation). For more information see Force and motion (Southern Nevada RPDP, USA).
electromagnetic radiation. Electromagnetic radiation is simply energy which travels through space at about 300,000 kilometres per second – the speed of light. We imagine radiation moving like a wave. The distance between two adjacent wave crests is called a wavelength. The shorter the wavelength, the more energetic the radiation is said to be. Also, the shorter the wavelength, the greater the frequency of the radiation. Other than wavelength, frequency and energy there is no difference between a radio wave, an X-ray and the colour green. They all possess the same physical nature. For more information see Back to Basics: Electromagnetic radiation (Australian Academy of Science) and Electromagnetic Spectrum (NASA Goddard Space Flight Center, USA).
electron. A negatively charged particle that is a constituent of an atom. Electrons can move from atom to atom. When they do, they produce an electric current.
elementary particle. A particle that cannot be subdivided into component parts. These particles are also referred to as fundamental particles. For more information see Theory – fundamental particles (Stanford Linear Accelerator Center, USA).
infrared light. A form of electromagnetic radiation with wavelengths between 0. 7 micrometres (0.0007 millimetres) and 1 millimetre. These wavelengths are longer than those of visible light, but shorter than those of microwaves. (The prefix 'infra' means 'below; infrared refers to radiation below the frequency of red light.) Infrared light is primarily thermal radiation, and we can think of this as being heat.
microwaves. The highest frequency radio waves, with wavelengths between about 1 millimetre and 30 centimetres and frequencies between about 300 gigahertz and 300 megahertz. Microwaves are a type of electromagnetic radiation.
neutron. A particle having no charge that is a constituent of an atom. It has a mass similar to a proton.
protein. A large molecule composed of a linear sequence of amino acids. This linear sequence is a protein's primary structure. Short sequences within the protein molecule can interact to form regular folds (eg, alpha helix and beta pleated sheet) called the secondary structure. Further folding from interaction between sites in the secondary structure forms the tertiary structure of the protein.
Proteins are essential to the structure and function of cells. They account for more than 50 per cent of the dry weight of most cells, and are involved in most cell processes. Examples of proteins include enzymes, collagen in tendons and ligaments and some hormones. More information can be found at Protein structure and diversity (Molecular Biology Notebook, Rothamsted Research, UK).
protons and neutrons. Small particles that form the nucleus of an atom. Protons have a small positive charge; neutrons have no charge.
X-ray. A high energy form of electromagnetic radiation with very short wavelengths (less than 1 x
Page updated January 2007.