What are the ionisation effects of x rays?
Ionisation is a process in which neutral atoms or molecules lose or gain electrons, resulting in the formation of electrically charged ions. When X-rays interact with matter, they can cause the ionisation of atoms or molecules through several mechanisms:
Photoelectric effect: This occurs when an X-ray photon transfers all its energy to a tightly bound inner-shell electron, causing the electron to be ejected from the atom. This leaves behind a positively charged ion. The probability of the photoelectric effect decreases as the photon energy increases.
Compton scattering: In this process, an X-ray photon collides with a loosely bound outer-shell electron and transfers some of its energy to the electron. The electron is ejected from the atom, and the scattered photon has a lower energy than the incident X-ray photon. Compton scattering is most likely to occur when the photon energy is in the intermediate range.
Pair production: When an X-ray photon with enough energy (greater than 1.022 MeV) passes near the nucleus of an atom, it can undergo pair production. In this process, the X-ray photon is converted into an electron-positron pair. The positron is the positively charged antiparticle of the electron. Pair production is only possible when the photon energy is high enough to create the mass of the electron and positron.
The ionisation effects of X-rays are significant in various applications, including:
Medical imaging: X-rays are widely used in medical imaging techniques such as radiography and computed tomography (CT scans) to create images of internal body structures. The differential absorption of X-rays by different tissues and structures allows for the visualisation of bones, organs, and soft tissues.
Radiation therapy: X-rays are also employed in radiation therapy to treat cancer. By delivering a controlled dose of X-rays to the affected area, ionisation and damage to cancer cells can be achieved, leading to their destruction or inhibition of growth.
Industrial and research applications: X-rays are used in various industrial and research settings for imaging and analysis. For instance, they are employed in non-destructive testing to detect defects in materials and components. X-ray crystallography is a technique that utilises X-rays to determine the atomic structures of crystals.
The interaction of X-rays with matter can be complex, and the ionisation effects depend on factors such as the photon energy, the atomic number of the material, and the density of the material. Understanding these interactions is essential for optimising the benefits of X-rays in various applications while also minimising potential harmful effects.