one kindElementary particleThe mass and other properties are the same as neutrons, but the magnetism is opposite to neutrons.When it meets a neutron, it releases much more energy than the nuclear polymerization reaction.An antineutron is formed when an antiproton loses its charge when it approaches an ordinary proton but has not yet joined it.[1]
Neutron (n): consists ofUpper quark(u, charge+2/3), composed of two lower quarks (d, charge - 1/3)
Antineutron (n bar): It is composed of one anti upper quark (u bar, charge - 2/3) and two anti lower quarks (d bar, charge+1/3).
The antineutron is uncharged but has a magnetic moment. The value is - 1.91280 nucleon. The negative sign indicates that it is opposite to the spin directionThe difference between antineutron and neutron is that the magnetic moment of antineutron (n) is positive, that is, the magnetic moment of antineutron is in the same direction as the spin.[1]
principle
The rest energy of ordinary neutrons is almost equal to the rest energy of neutrons. Neutrons are not charged, but they have magnetic moments and moments (spins). We have long known that all neutrons have spins in the opposite direction to their magnetic moments.according todirac theory In addition to neutrons with positive energy, there are also neutrons with negative energy, which are filled evenly. For them, all possible energy bands, so we cannot observe antineutrons.
If a neutron gets enough energy, it can jump into the positive energy band, acting like an ordinary neutron.In this way, a "hole" is formed in the negative energy band, which behaves like a particle with the same mass and positive energy as the neutron.The absence of a neutron whose spin direction is opposite to the direction of the magnetic moment shows that a neutron whose spin is consistent with the direction of the magnetic moment is produced.Such "holes" are antineutrons.After the antineutron meets the ordinary neutron, they annihilate themselves and become mesons with large energy.[1]As shown in Figure 1
Figure 1
Antimatter theory
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As early as 1928, Dirac predictedAntiprotonBut it took more than 20 years to prove its existence.According to Dirac's theory, the antiproton has the same mass as the proton and opposite charge. The proton and antiproton appear or annihilate in pairs. The antiproton can be obtained by collision of two ordinary protons, but the threshold energy of antiproton production is 6.8 GeV.In 1954University Of California OfLawrence Radiation LaboratoryA 6.4 billion electron volt proton synchronous phase stabilized accelerator has been builtAntiparticleConditions are provided.In 1955, Chamberlain and Segory confirmed the existence of antiprotons observed the previous year with the above accelerators.Since antiprotons have very few opportunities, only a small number of antiprotons can be generated every 100 billion high-energy proton collisions, so it is extremely difficult to confirm the existence of antiprotons.In 1955, their experimental group measured 60Antiproton。Because the background of accidental coincidence is not large, the numeration system is not good, but it is more reliable.
Soon they found thatneutron。althoughHigh-energy particleAntineutrons can also be generated when shooting, but because the antineutron is not charged, it is more difficult to identify it from other particles.They use antiprotons andNucleusCollision, the antiproton gives its negative charge to the proton, or obtains positive charge from the proton, so that the proton becomes a neutron, and the antiproton becomes an antineutron.
Discovery process
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The antineutron was discovered by four American physicists -- Caulke, Longertsen, Maijon and Wanzel -- using the same set of equipment that discovered the antiproton and the overcharge phenomenon of the antiproton.The antiproton beam (800-600 antiprotons per hour) passes through the liquid scintillation complement A (as shown in Figure 2 below), and this counter is filled with the solution of triphenyl in toluene.In solution, some antiprotons "annihilate" by interaction with protons, but some antiprotons (about 03%) give their charge to protons and turn themselves into antineutrons.
The generated antineutron enters a Cherkov counter B made of lead glass. In the counter, the antineutron and ordinary neutron annihilate to get the star of meson.
