Gary Perrin, age 14, of Des Moines, Iowa, for his question:
What kind of charge is carried by an anti neutron?
Many students still assume that the atom is composed of only three types of particles. This notion is way behind the times. In the last few years more than 20 atomic particles have been identified, and more are expected. One newcomer is called the anti neutron.
The orbiting electron carries a negative electrical charge, and the proton in the atomic nucleus carries an equal and opposite positive charge. The neutron of the nucleus is somewhat more massive than the proton and equal in mass to 1838.65 electrons ¬and it is electrically neutral. The concept of anti particles arose in the 1930s, and physicists began to suspect that certain atomic particles had sister particles of the same mass, but with opposite charges.
The anti-electron was discovered and proved to have the same infinitesimal mass as its sister electron but it carried a positive charge equal to that of a proton. This anti particle of matter is called the positron. It may be created when speeding cosmic rays collide with certain atoms, and it exists only long enough to meet a sister electron. The two opposites then annihilate each other into fragments of gamma rays.
The anti proton was found among atomic fragments in the mighty bevatron. It carried a negative charge, but its mass equaled that of the proton. The anti proton also lives only a fraction of a second. It collides with a sister proton, and the pair shatter each other to energy fragments. Once in a while an anti neutron occurs in this debris. Since the neutron is neutral, the anti neutron cannot have an opposite electric charge. The two are of equal mass, and both are neutral nevertheless they are opposite particles of matter and anti matter.
An atomic particle, like a giant planet, spins on its axis and creates a surrounding magnetic field. Electrons and positrons bear opposite charges and spin in opposite directions. So do protons and anti protons. The neutron and its sister anti neutron both are electrically neutral. But the two particles spin in opposite directions, surrounding themselves with different magnetic fields.
Scientists have found opposites for all the atomic particles, and the concept of anti matter leads to some astounding ideas. Perhaps there is a world of anti matter somewhat like a mirror image of our normal world. Perhaps anti matter is scarce in our world and plentiful in others. Some astronomers suspect that certain cosmic upheavals are actually collisions between galaxies of matter and anti matter.