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Ionizing radiation is radiation with sufficient energy to remove tightly bound electrons from atoms, creating ions. It is widely used in diagnostic radiology, nuclear medicine, radiotherapy, and occurs in nature (cosmic rays, radioactive decay).

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![Graphic showing relationship between radioactivity and detected ionising radiation, including the transport element. Incorporates inverse square law by author borb and alpha decay svg by author Inductiveload.

Doug Sim - CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=33608316](attachment:d524770c-eb85-41af-8cb5-5d1b869548f0:image.png)

Graphic showing relationship between radioactivity and detected ionising radiation, including the transport element. Incorporates inverse square law by author borb and alpha decay svg by author Inductiveload.

Doug Sim - CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=33608316

Types of Ionizing Radiation

Electromagnetic Radiation

• X-rays (man-made, from X-ray tubes).
• Gamma rays (from radioactive nuclei).

![Nomogram of the electromagnetic spectrum (not to scale) from long wavelengths (radio waves) to very short wavelengths (x rays). The wavelengths and photon energies are indicated. Distance units used are m (meter), mm (millimeter), µm (micrometer), nm (nanometer), pm (picometer), and energy units used are eV (electron-volt), keV (kilo-electron-volt), and MeV (mega-electron-volt)

Mainprize, J.G., Yaffe, M.J., Chawla, T. et al. Effects of ionizing radiation exposure during pregnancy. Abdom Radiol 48, 1564–1578 (2023). https://doi.org/10.1007/s00261-023-03861-w](attachment:b3d7325b-f374-4646-a3c0-1d5969a692e9:261_2023_3861_Fig1_HTML.webp)

Nomogram of the electromagnetic spectrum (not to scale) from long wavelengths (radio waves) to very short wavelengths (x rays). The wavelengths and photon energies are indicated. Distance units used are m (meter), mm (millimeter), µm (micrometer), nm (nanometer), pm (picometer), and energy units used are eV (electron-volt), keV (kilo-electron-volt), and MeV (mega-electron-volt)

Mainprize, J.G., Yaffe, M.J., Chawla, T. et al. Effects of ionizing radiation exposure during pregnancy. Abdom Radiol 48, 1564–1578 (2023). https://doi.org/10.1007/s00261-023-03861-w

Particulate Radiation

• Alpha particles (α) – heavy, highly ionizing, low penetration (stopped by paper/skin).
• Beta particles (β) – electrons/positrons, moderate penetration (stopped by few mm of plastic/aluminum).
• Neutrons – indirect ionization, high penetration, biologically very damaging.
• Protons, heavy ions – used in particle therapy.

![Alpha (α), beta (β), and gamma (γ) radiation and their unique characteristics.

Najjar R (July 10, 2023) Radiology's Ionising Radiation Paradox: Weighing the Indispensable Against the Detrimental in Medical Imaging. Cureus 15(7): e41623. doi:10.7759/cureus.41623](attachment:591dcbdf-a043-43fe-a1e1-d6be15f85ccf:image.png)

Alpha (α), beta (β), and gamma (γ) radiation and their unique characteristics.

Najjar R (July 10, 2023) Radiology's Ionising Radiation Paradox: Weighing the Indispensable Against the Detrimental in Medical Imaging. Cureus 15(7): e41623. doi:10.7759/cureus.41623

Sources of Ionizing Radiation

Natural background (80% of annual dose):

• Cosmic rays, terrestrial (radon gas), internal radionuclides.

Man-made (20%):

• Diagnostic X-rays, CT, nuclear medicine, radiotherapy.