Antimatter

Constructing a dissertation on a topic my peers were alien to was definitely an experience. Throughout studying chemistry, we learn how atoms relate to each other and act in different situations. But what about how matter, as we know it, has come to form our very surroundings?

At the time of the Big Bang, energy existed in equal amounts of matter and antimatter. Now, as Einstein has proven that energy has neither be created, nor destroyed, where is all the antimatter?

After many attempts of simplifying the concept of antimatter, it came to my attention that it had to be explained through something we already understand; matter. So starting from the Bohr-Rutherford model, the image of an electron orbiting the nucleus at regular intervals of energy, the stability of matter as an atom is established. We then came to learn from Schrödinger how pairs of electrons can be found in orbitals. The formations of s, p, d and f orbitals are ones most are familiar with, where there are positive and negative lobes with a node in the middle where the electron is least likely to be found. The Schrodinger equation quantifies the probability of finding an electron in a given space relative to the atom nucleus; the origin (0,0,0). The values can be graphically presented (Fig.1) to show an oscillating wave with positive and negative values. However, these numbers are squared to give a positive percentage since the electron must exist in space.

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Fig. 1. One-dimensional particle in a box graphs. On the left the wavefunction, 𝝍, of an electron is mapped against a boundary, a. On the right, the probability, 𝝆, of finding an electron at a point within the boundary, a, when wavefunction is squared, 𝝍𝟐.

Dirac wanted to simplify the equation to eliminate the negative values completely. This is where antimatter come to play. The Schrodinger equation is one of second order, whereas the Dirac equation is linear. The results however, still consist of negative wavefunction values which cannot be ignored in order to obey the conservation of energy.

This has come to show that each particle has an antiparticle. Each has exactly the same mass and charge. The only difference is the charge of each particle. One will be positively charged and the other negatively charged. For example, an electron has an antiparticle known as the positron.

As we know, energy can be converted to mass and mass to energy. Electromagnetic radiation is a form of energy with no mass or charge, such as gamma rays, which can be used to excite an electron. As a result, the gamma ray is converted to mass as an electron-positron pair to account for the neutral charge of a gamma ray.

Experimental picture proof (Fig. 2) soon published by C. D. Anderson shows this is action. As gamma radiation is induced into a vacuum with electrons, the electrons are excited and form two particles at the same time, of the same size, that travel the same way only in opposite directions. This shows that the total energy is conserved as the energy is converted to matter.

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Fig. 2. An image showing the trails of two electron-positron pairs created in a cloud chamber.

When an electron meets a positron they annihilate as a flash of light, (Fig. 3). As light has no mass or charge, the particles disappear. This is how matter is converted to energy as electromagnetic radiation.

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Figure 3. Feynman diagram of electron-positron annihilation, ChemDraw.

The big question is how does matter still exist when there were equal parts formed at the big bang?

Something crucial happened in this event to lead to a universe of matter. An incredibly small asymmetry in a particle of matter, the kaon, occurred to allow matter to survive the annihilation process. This is known as the Charge-Parity-Time, CPT, Violation. Now, our universe consists of energy mostly in the form of matter.

Experiments are now carried out at CERN where antimatter is formed by converting matter to energy by colliding high-energy particles together. They have built special equipment for the antimatter to be stored and analysed appropriately. In the near future, there are proposed experiments, AEGIS and GBAR (Fig. 4, 5), to test the gravity of antimatter to see if there is an antigravity or if the two types of matter are more alike than we think. Investigating this now foreign matter is paving the pathway to a more advanced knowledge of matter.

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Fig. 4. Experimental device setup for AEgIS.

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Fig. 5. Diagram showing the GBAR experimental procedure.

One of the ways we can relate to the outcomes of the research are through the Anti-Cancer Experiment, ACE, which is in progress developing an alternative to chemotherapy. Using antimatter prevents the falling out of hair and is less prone to damaging healthy cellls, whilst being more effective at eliminating the cancerous cells at a lower dose level, (Fig. 5).

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Fig. 5. Dose of energy from positrons, protons and 12C ions.

Overall the knowledge of antimatter from nearly a century of research has come a long way. Although the rumours of it being used as a revolutionary energy source still has a long way to go as it should be acknowledged that antimatter is an entity from the conservation of energy. Therefore, an input of the same amount of energy is required, alongside very expensive storage methods to outweigh the huge risk factor of annihilation.

Learning about an entirely foreign area of our existence may not seem important at first but the impact of the results can be the solution to an entirely new horizon of possibilities.

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