Annihilation Physics Gcse Coursework

Positron annihilation

During β+ decay, a proton [proton: A sub-atomic particle with a positive charge and a relative mass of 1 found in the nucleus of the atom.]  is converted into a neutron [neutron: Uncharged sub-atomic particles, with a mass of 1 relative to a proton.]  and a positive beta particle or β+. This is called a positron and has the same mass as an  [electron: A very small negatively-charged particle found in an atom in the space surrounding the nucleus.]  but the opposite charge (positive).

When an electron and a positron collide an annihilation event occurs and gamma rays [gamma ray: A type of ionising radiation that consists of a high-energy electromagnetic wave.]  are produced. This is a frequent occurrence in PET scanning [PET scanning: Positron emission tomography scanning. A medical scanning technique, based on the emission of gamma rays, that produces 3D images of processes occurring inside the body.]  in hospitals.

The positron and electrons have opposite charges and so the overall charge before annihilation is zero. The resulting gamma rays have no charge. So charge is conserved in this collision.

In annihilation, the positron and electron collide head on moving at the same speed. The overall momentum is therefore zero. The resulting gamma rays move in opposite directions with equal and opposite momentum. So momentum is also conserved.

Einstein’s famous equation E = mc2 means that the mass of an object is a measure of its energy content, and that mass and energy can be converted into each other (mass energy).

In annihilation, the masses of both the positron and electron are converted into energy (gamma rays). The energy of the gamma rays is the same as the mass energy of the original positron and electron and so mass energy is also conserved.

E = mc2 can be used to calculate the energy of gamma rays following annihilation:

The difference between these two forms of matter is more elementary than it seems. What we call matter is everything that is composed of protons (sub-atomic particle with a positive charge), electrons (sub-atomic particle with a negative charge), and neutrons (sub-atomic particle with no charge). All these particles form what we call atoms. In the atom, the protons and neutrons make up the nucleus, which is the core, and the electrons orbit the nucleus much like a planet around a star.

In antimatter, the charges of each particle are reversed. Instead of a proton, its antimatter equivalent is called an anti-proton with a negative charge. Instead of an electron, its antimatter equivalent is called a positron with a positive charge. The exception to this reversal rule is the neutron, whose antimatter counterpart, the anti-neutron, shares the same traits (since a neutron has no charge, its anti-form would retain no charge).

If one were to combine antimatter and matter together, you would create a large explosion of energy. This is caused by joining the opposite charges of each counterpart, which thus causes them to be reversed into the form of energy based on the equation e=mc^2, e meaning energy, m equaling mass, and c equaling the speed of light, roughly 186,000 miles per second. But not to worry, since the only method of generating antimatter on Earth, involving particle accelerators, only produces a few particles at a time, thus preventing any disastrous reactions.

In fact, scientists were able to create an antiatom in 1995.This hinted at the ability to take several of these and make an antimolecule. In 2007, David Cassidy at the University of California at Riverside was able to take two positronium atoms, each one consisting of an electron and a positron in a strange bond, and combined them into an antimolecule (Dickinson 16). Of course, the molecule was short-lived as the electron and positron annihilated each other.

Something that scientists are unsure of is if antimatter falls differently than normal matter. It seems like such a silly thing to question but we do not have evidence to show how antimatter responds to gravity. Using new super-cooling techniques and interferometry, scientists may be able to finally know by slowing down the antiatom and measuring its behavior (Choi). Who knows what new advances will be made that make use of these differences, but as we can see many similarities also exist.

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