How Do We Make Use of Antimatter? – PET

PET stands for positron emission tomography, and works due to the theory of what happens when antimatter meets matter. When matter and antimatter meet (that is, the particles that make up everything in our universe), they destroy each other and radiation is released. The “P” in PET, standing for positron, refers to the antiparticle of the electron. Antimatter was predicted in 1928 by the English physicist Paul Dirac, before the positron was discovered. Dirac’s theory stated that for every type of particle, there is an antiparticle, that has the same rest mass as the particle, has exactly the opposite charge of the particle (if the particle carries a charge), and that it would annihilate itself and the particle if the meet, converting their total mass into photons. The process of annihilation results in the emission of two gamma photos, which can be detected outside the human body by a gamma camera.

However, first we must look at the process in which positrons are emitted, known as positron emission or beta plus decay (β˖ decay). Unstable nuclei due to too many protons relative to the number of neutrons in the nucleus undergo β˖ decay, converting a proton into a neutron, which then ejects a positron to conserve the electric charge. For example;

Hence, due to the theory of the annihilation between a particle and its antiparticle emitting 2 gamma photons, PET can be used in medicine for scans. A positron-emitting isotope is emitted to the patient, which will travel to the desired location within the body through the blood stream. Once there, the isotope will decay, releasing the positron, which will travel no further than a few millimetres before coming into contact with an electron, and they will then annihilate each other releasing the two gamma rays travelling in opposite directions (in order to conserve momentum). By mapping gamma rays that arrive at the same time the PET system is able to produce an image with high spatial resolution. Therefore, PET scans are ideal for detecting tumours and for the detection of conditions such as Alzheimer’s.