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Close Encounters (of the Cosmic Kind)
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Right now, in our atmosphere, there are countless numbers of nitrogen atoms floating high above the Earth's surface. These atoms are, in a sense, vulnerable.

Animation of neutron displacing a proton from a nitrogen atom Cosmic radiation, in the form of neutrons, zips through the atmosphere at a high rate of speed. Occasionally, and purely by chance, some of these neutrons collide with the nuclei of some of the nitrogen atoms.

The nucleus of each nitrogen atom contains seven protons and seven neutrons. That is, it does until a collision happens. The incoming neutron hitting the nucleus causes a proton to shoot out of the nucleus, just as a cue ball on a pool table, hitting one of two balls that are touching, might cause the ball that it hits to stay in place and the other ball to shoot off.

The nitrogen atom now has six protons and eight neutrons. This means two things. One, with this arrangement of protons and neutrons, it's unstable. In other words, it's radioactive. And two, it's no longer nitrogen. The reason is that the number of protons an atom contains determines what that atom is. Since it now contains six protons, it's carbon. Carbon usually has six neutrons as well—in this form it's called carbon-12 (6+6=12). The unstable, eight-neutron version, however, is carbon-14 (6+8=14).

Animation of  an electron escaping from a neutron All radioactive atoms will eventually decay, or change, in some way. When a carbon-14 atom decays, one of its eight neutrons turns into a proton, emitting an electron (with a charge of -1) in the process. The atom is now stable. And with seven protons and seven neutrons, it is again nitrogen-14.

Next: Eating It and Eating It...

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