Nuclear Radiation

Ionizing radiation has many practical uses, but it is also dangerous to human health. Both aspects are discussed below.

Ionizing radiation is either particle radiation or electromagnetic radiation in which an individual particle/photon carries enough energy to ionize an atom or molecule by completely removing an electron from its orbit. If the individual particles do not carry this amount of energy, it is impossible for even a large flood of particles to cause ionization. These ionizations, if enough occur, can be very destructive to living tissue, and can cause DNA damage and mutations. Examples of particle radiation that are ionizing may be energetic electrons, neutrons, atomic ions or photons. Electromagnetic radiation can cause ionization if the energy per photon, or frequency, is high enough, and thus the wavelength is short enough. The amount of energy required varies between molecules being ionized. X-rays, and gamma rays will ionize almost any molecule or atom; Far ultraviolet, near ultraviolet and visible light are ionizing to some molecules; microwaves and radio waves are non-ionizing radiation.

However, visible light is so common that molecules that are ionized by it will often react nearly spontaneously unless protected by materials that block the visible spectrum. Examples include photographic film and some molecules involved in photosynthesis.

Ionizing radiation is produced by radioactive decay, nuclear fission and nuclear fusion, by extremely hot objects (the hot sun, e.g., produces ultraviolet), and by particle accelerators that may produce, e.g., fast electrons or protons or bremsstrahlung or synchrotron radiation.

In order for radiation to be ionizing, the particles must both have a high enough energy and interact with electrons. Photons interact strongly with charged particles, so photons of sufficiently high energy are ionizing. The energy at which this begins to happen is in the ultraviolet region; sunburn is one of the effects of this ionization. Charged particles such as electrons, positrons, and alpha particles also interact strongly with electrons. Neutrons, on the other hand, do not interact strongly with electrons, and so they cannot directly ionize atoms. They can interact with atomic nuclei, depending on the nucleus and their velocity, these reactions happen with fast neutrons and slow neutrons, depending on the situation. Neutron radiation often produces radioactive nuclei, which produce ionizing radiation when they decay.

In the picture at left, gamma quanta are represented by wavy lines, charged particles and neutrons by straight lines. The little circles show where ionization processes occur.

An ionization event normally produces a positive atomic ion and an electron. High energy beta particles may produce bremsstrahlung when passing through matter, or secondary electrons (Ð'-electrons); both can ionize in turn.

Gamma quanta do not ionize all along their path like alpha or beta particles (see particle radiation. They interact by one of three effects: photoelectric effect, Compton effect, or pair production. By way of example, the figure shows Compton effect: two Compton scatterings that happen sequentially. In every scattering event, the gamma quantum transfers energy to an electron, and it continues on its path in a different