The process in which an electron is given enough energy to break away from an atom is called ionisation. This process results in the formation of two charged particles or ions: the molecule with a net positive charge, and the free electron with a negative charge.

Ionising radiation is the energy produced from natural or artificial sources. It has more energy than non-ionising radiation, enough to cause chemical changes by breaking chemical bonds. This effect can cause damage to living tissue.

X-ray and gamma ray radiation, which are at the upper end of electromagnetic spectrum, have very high frequencies (in the range of 100 billion billion hertz) and very short wavelengths (1 million millionth of a metre). Radiation in this range has high energy. It has enough energy to strip electrons from an atom or, in the case of very high-energy radiation, break up the nucleus of the atom.

Each ionisation releases energy that is absorbed by material surrounding the ionised atom. Ionising radiation deposits a large amount of energy into a small area. In fact, the energy from one ionisation is more than enough energy to disrupt the chemical bond between two carbon atoms. 

There are three main kinds of ionising radiation:

Alpha particles and beta particles are not part of the electromagnetic spectrum; they are energetic particles as opposed to pure energy bundles (photons).

What are the health effects of ionising radiation exposure and how does it affect human tissue?
Atoms are the extremely small particles that are the basic building blocks of ordinary matter.
What is the difference between radiation and radioactivity?
Alpha particles are relatively slow and heavy compared with other forms of nuclear radiation.
Beta particles have a mass which is half of one thousandth of the mass of a proton and carry a single negative charge.
Gamma rays are electromagnetic energy emitted by the nucleus of some radionuclides following radioactive decay.
X-rays are a form of electromagnetic radiation similar to radio waves, microwaves, visible light and gamma rays.
Alpha, beta and gamma radiation are the most common types of radioactive decay but there are other ways that unstable atoms can become stable.

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