Explanation of Antimatter - Succeed in Physical Science. Also refer to physics, matter, antiparticle, electron, anti-electron, positron, proton, antiproton, neutron, antineutron, chemical reactions, mass, energy, joule, newton-meter, atomic bomb, Universe, antigravity, rocket propulsion, Ron Kurtus, School for Champions. Copyright © Restrictions
Antimatter
by Ron Kurtus (revised 31 December 2008)
The building blocks of matter are protons, neutrons and electrons. Antimatter is matter that is made up of the antiparticles, which are either the opposite electrical charge or consist of antiquarks. The antiproton, antineutron and positron are the building blocks of antimatter.
Apparently, the behavior of antimatter is exactly the same as matter, since everything is the same except for the electrical charges of the particles. The only antimatter atom made by scientists is the anti-hydrogen atom.
When matter and antimatter collide, an enormous amount of energy is released. Although our part of the Universe is made up of matter, it is possible that other parts consist of stars and galaxies made up of antimatter.
Questions you may have include:
- What is an antimatter atom like?
- What happens when matter and antimatter combine?
- Is there any antimatter in the Universe?
This lesson will answer those questions. There is a mini-quiz near the end of the lesson.
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Antimatter atoms
Antimatter atoms consist of antiparticles. The atoms appear similar, except with opposite electrical charges. Their chemical characteristics are the same, as long as they react with other antimatter atoms.
Antiparticles
Antiparticles that make up an antimatter atom are the positron (anti-electron), antiproton and antineutron.
Positron
The positron has an positive (+) electrical charge, as opposed to the negative (−) charge that an electron has.
Antiproton
The antiproton has a negative (−) electrical charge instead of the positive (+) charge that a proton has. The proton consist of quarks, while the antiproton consists of antiquarks, which have the opposite charge of quarks.
Antineutron
An antineutron and neutron both have zero (0) electrical charge, but they are made of quarks, which have electrical charges. The neutron is made up of one up quark and two down quarks. The resulting electrical charge of the neutron is: (+2/3) + (-1/3) + (-1/3) = (0). The antineutron is made up of one anti-up quark and two anti-down quarks. The resulting electrical charge of the neutron is: (-2/3) + (+1/3) + (+1/3) = (0).
(See Subatomic Particles and Antiparticles for more information.)
Atoms
The illustrations below compares a Lithium atom with its antimatter counterpart.
Lithium atom and antimatter version of Lithium
Anti-hydrogen
The only man-made antimatter particle is the anti-hydrogen atom, consisting of a positron and an antiproton nucleus. Anti-hydrogen can be kept at extremely low temperatures and held in place by magnetic fields. Once an anti-hydrogen atom strikes the wall of a container or hits some other atom, it is annihilated and results in high-energy gamma rays being emitted.
Combining matter and antimatter
When matter comes in contact with antimatter, an enormous amount of energy is given off in the form of electromagnetic radiation. The total of the mass of the two particles is converted into electromagnetic energy through Einstein's famous E = mc² equation.
That means that if a gram of matter would come into contact with a gram of antimatter (0.001 kg), the amount of energy that could be released would be E = 0.001*(9*1016) = 9*1013 joules or newton-meters. This is 20 times greater than the energy of the first atomic bomb.
Rocket propulsion
The tremendous energy released from a small amount would seem to make combining matter and antimatter a great candidate for powering rockets into space. Two things hold such a power source back. One is that we have no source of even a gram of antimatter. The second problem is that there would be no way to contain the antimatter and keep it from coming in contact with matter before it was used.
Gamma rays
The result when matter and antimatter combine is electromagnetic radiation in the form of gamma rays, which are high-energy rays with a wavelength shorter than x-rays. When a single atom and its antimatter counterpart combine, the gamma radiation is in the form to two photon particles, moving in the opposite direction.
NOTE: On an individual basis, electromagnetic radiation can be considered to consist of photon particles. When there are a large number of photons, the radiation is considered a waveform.
The reason the photons or gamma radiation move in opposite directions is due to the Law of the Conservation of Momentum. If the photons went in only one direction, that would mean there was a momentum in that direction that was not there before the atoms combined.
Antimatter in the Universe
As far as we can tell, the Universe is made up of matter and not antimatter. But it seems strange that there should be a preference of one type of matter over the other. Or is it possible that one half of the Universe is made up of matter and the other half of antimatter? Suppose when the Big Bang occurred, the matter went in one direction and the antimatter went in the other direction. This would follow from the Laws of Conservation of Momentum and of Energy.
Everything in our part of the Universe could consist of matter and in the other part, antimatter. Since the Universe is expanding, matter and antimatter would not have a chance to mingle and cause problems. Since photons (light particles) or electromagnetic radiation has no antiparticle, it could go from one part of the Universe to the other with no effect.
Antigravity
There is a theory that perhaps there is an antigravity. In this theory, objects consisting of antimatter attract other antimatter object through antigravity, just as matter attracts other matter through gravity.
If antigravity exists, then antimatter would repel matter. The only way that matter and antimatter would then come together would be when particles and antiparticles collide in an atomic accelerator.
Antigravity could explain why the Universe is expanding and not even require the Big Bang Theory.
Summary
Antimatter is matter that is made up of positrons, antiprotons and antineutrons. The behavior of antimatter is the same as matter, except for the electrical charges of the particles. The only antimatter atom made by man is the anti-hydrogen atom. An enormous amount of energy is released when matter and antimatter collide. Although our part of the Universe is made up of matter, it is possible that other parts consist of stars and galaxies made up of antimatter.
Consider the impossible
Resources
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Mini-quiz to check your understanding
1. Why isn't the neutron and antineutron exactly the same?
2. What would happen if antimatter was placed in a closed container?
3. How could we tell if another part of the Universe consisted of antimatter?
If you got all three correct, you are on your way to becoming a Champion in Physical Science. If you had problems, you had better look over the material again.
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Antimatter