Radiation Protection Glossary

A radiation protection glossary for Radiation Protection Supervisors (RPS), Radiation Protection Advisers (RPA) and anyone else interesting in radiation safety terms and definitions. The glossary is a mixture of health physics , phrases related to radiation protection legislation, transport, practical safety, technical terms and similar.

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For formal advice, see our Radiation Protection Adviser pages. 


    X-ray Fluorescence (XRF)

    If an Element is exposed to X-Rays of a certain energy (or wavelength) it is possible to transfer the x-ray energy to the orbital Electron making up the atoms of the element. The electrons move up an 'energy level' in the process. As these energised electrons fall back to their normal state, energy is released in the form of characteristic discrete x-ray Photons which are unique to the element in question. The process is used in analytical techniques where element identification is required.

    The process is especially useful with materials which are made up of multiple elements (steel for example). XRF can be used to grade the steel by looking for % composition of certain elements such as chromium, molybdenum, and nickel. This can often be achieved with handheld XRF devices which are brought close to the specimen requiring analysis, and provides a near instantaneous results.


    X-rays are part of the Electromagnetic spectrum. They are a penetrating form of electromagnetic radiation and consist of quantum's of energy (Photon). X-rays are commonly produced by the excitation of atomic Electrons, by firing electrons between a high potential difference towards a target (which is the principle of an x-ray machine).

    The target electrons are excited, and as they de-excite x-ray photons are produced. X-rays can also be produced as a result of Bremsstrahlung or by nuclear reactions. X-rays have many uses including medical imaging and industrial quality assurance.

    Whilst commonly stated (or assumed) that gamma rays are emitted by certain radioactive materials, x-rays can also be emitted if the process involves photons being produced within the electron orbit (cloud) around the nucleus (such as in the case of electron capture). An example is the radioactive substance I-125 which emits gamma rays during decay and x-rays from the post decay product(Te-125).

Atoms are very special: they like certain particular partners, certain particular directions, and so on. It is the job of physics to analyze why each one wants what it wants.

– Richard P. Feynman -