Gamma Rays
Image Source (Slate)
What are gamma rays?
Gamma radiation is the most energetic form of light in the electromagnetic spectrum. Gamma rays used to be defined by wavelength but due to the similarity between them and X-rays. They are more accurately defined by how they are made, X-rays are produced from electrons in an atom but gamma rays are produced from electrons outside of an atom. [G1]
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Gamma rays, although high energy and ionising (for more information on ionising radiation click here) can be used to have a positive impact on health rather than just a negative one. Most of the medical applications of gamma rays are diagnostic (and for most ionising radiation in general). The radiation doses must be carefully controlled to maintain safe levels for the patient and have adequate shielding for the health workers who administer the treatments.
How are gamma rays produced?
There are 3 main ways to make gamma rays[G2]:
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1. Particle Collisions
When two particles collide (with a high energy) such as a proton and another proton, some of their energy upon impact is converted into light in the form of gamma rays. This also happens when a matter and antimatter particle collide, although this interaction is slightly different it produces a similar effect.
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2. Radioactive decay
When an element changes to another element in an unstable form spontaneously, this is radioactive decay. The unstable isotope then wants to become stable, so the atom emits gamma rays and decays to a lower more stable energy state.
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3. Particle acceleration
This involves a magnetic field exerting a force on a charged (positive or negative) particle, which causes it to emit light. For gamma rays, this particle is normally an electron.
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For these medical procedures, only the first 2 ways are used. PET scans use particle collisions to generate gamma radiation, whereas the gamma knife and medical tracers rely on radioactive decay.
Image 1: Collision of two protons at CERN (lines are charged particles). Source (CERN, Image by Lucas Taylor)