Matter-Antimatter Annihilation

Matter is defined as everything that has mass and takes up space. Everything we see around us is made of matter. Not only the air we breathe but also everything in our environment is made up of matter. Massive structures, bridges, electrons revolving around a nucleus, DNA in our cells, the ground beneath our feet, and so on are all composed of matter.

Classification of Matter

Based on the physical state, the matter can be classified into three states:

Solids

Solids are substances in which the particles are held close to one another by strong intermolecular forces. The particles are firmly fixed in place and only move in a vibratory manner. Solids have a defined shape as well as a defined volume. Some examples of solids are metals, plastic, and wood.

Liquids

The liquid state of matter possesses different properties than solid and gas. They have more intermolecular space in their molecules than solids and less than that of gases. They also have spaces between their molecules. Liquid molecules move randomly but still attract each other. Different liquids have specific boiling and melting points. When a liquid is heated to its boiling point, it evaporates. This process is known as vaporisation. It is one of the crucial properties of liquids. Liquids can be obtained after melting solids to their melting points. 

Gases

The molecules in this form of substance have very weak forces between them, so they are free to move. Compared to solids and liquids, the space between gas molecules is large. Gases do not have a set shape or a defined volume. They tend to fill the container they are placed in, for example, air, oxygen, hydrogen, methane, etc.

By varying the temperature and pressure, matter can be changed from one state to another. The composition of matter also influences its nature. A mixture is defined as a substance that contains more than one type of particle, whereas a pure substance is defined as a substance that contains just one type of particle. Mixtures are of two types: homogeneous and heterogeneous mixtures. Elements and compounds are subdivisions of pure substances.

Annihilation

Annihilation is the radiation produced by the amalgamation of a particle and its antiparticle. Generally, they have the same mass, but the charges are opposite in nature. Collisions of different subatomic particles and antiparticles produce several distinct particles in the endmost stage. During the course of time, several scientists worked on annihilation. Thibaud and Joliot were attributed for the discovery of annihilation. The concept obeys the conservation of energy and conservation of momentum.

Examples for Annihilation

Electron-Positron Annihilation

Annihilation happens between electron and positron, where the electron is the particle and the positron is the antiparticle. In this process, the positron combines with the electron to form positronium, which is a quasi-atom. Here, an electron is a subatomic particle that is negatively charged, which either occurs freely or is bound to the nucleus of the atom.

Proton-Antiproton Annihilation

When a proton annihilates with the antiproton, it initially produces gluons. After this, the gluons along with the remains of quark-antiquark lead to the production of mesons. The mesons produced are unstable unless they integrate with other particles. Finally, they decay to produce photons (electromagnetic energy), electrons, positrons and neutrinos. The energy value of the released particles accounts for nearly 2 GeV (Giga electron Volt).

A similar process occurs on the annihilation of an antinuleon with an atomic nucleus.

Theories of Annihilation

The process of annihilation can be depicted by the Feynman Diagram. It is the pictorial representation of mathematical expressions of the interaction of subatomic particles. It was put in place by Richard Feynman, an American physicist, in the year 1948. His diagram helps us understand the complex process of the interaction of subatomic particles in a very simple way.

In the Feynman Diagram, the electron-positron annihilation is represented as follows.
An electron (e-) and a positron (e+) annihilate to produce photons () which later becomes a quark-antiquark pair [quark (q) antiquark (q-) ]. Thereafter, the antiquark radiates gluon (g).

The later theories explain annihilation with respect to empirical observations by fitting mathematical models to it.

Use of Annihilation

• One of the novel applications of positron annihilation is the positron annihilation spectrography.
• It is used in various imaging processes such as SPECT (Single Photon Emission Computed Tomography), PET (Positron Emission Tomography), gamma camera, etc
• Positron Annihilation Spectrography is used in the study of defects such as the crystallographic defects in metals.

Conclusion

Physics is divided into different branches and one such branch is particle physics. In simple terms, it is the branch of physics that deals with the study of nature, properties, and constituents of the particles that make up matter. In particle physics, annihilation is the radiation produced by the amalgamation of a particle and its antiparticle. Matter and its nature support various properties, such as physical and chemical properties, properties based on the state of matter i.e. solids, liquids, or gases and their characteristics. However, the nature of matter remains a large field of study, and recent advances have revealed several new states of matter. The Boson-Einstein condensate and plasma are two more states of matter that scientists have recently discovered.