Cosmic Rays From Space
Question: What are cosmic rays?
Answer: Fast moving particles from space:
90% high energy protons
10% high energy alpha particles (helium nuclei),
Question: How are cosmic rays involved in the formation of carbon-14? Answer:
Cosmic rays bombard the nuclei of gases in earth’s atmosphere resulting in neutrons and protons being “kicked” out of the nuclei.
When one of the high energy emitted neutrons collides with the nucleus of a nitrogen-14 atom, the neutron is absorbed by the nitrogen nucleus and a proton from the nitrogen nucleus is ejected. See diagram for the Formation of Carbon-14.
Question: Is carbon-14 still being produced?
Answer: Yes. It is estimated that about 21 pounds of C-14 is produced in the upper atmosphere each year.
Why is carbon-14 different from other carbon isotopes (atoms of an element with different amounts of neutrons), such as carbon-12 and carbon-13?
Answer: Carbon-14, Carbon-13, and Carbon-12 are all natural forms of the carbon element. They differ in the number of neutrons in their nuclei, but are alike in the number of protons in their nuclei, which is six. Carbon-14 is also unstable, which means that its nucleus undergoes radioactive decay. Radioactive decay is a process by which the nuclei of atoms spontaneously emits particles. The radioactive decay for a C-14 nucleus occurs by the emission of a beta particle. This is called beta decay.
Question: What does beta decay mean? What is a beta particle?
Answer: Beta decay means that the nucleus of an atom emits a beta particle, which is an electron. Since nucleons (particles in the nucleus) include protons and neutrons, the big question is where does the beta particle come from? The answer is that each neutron can be split into one proton and one electron.
1 neutron = 1 proton + 1 electron
The following diagram show the changes in the nucleus of a carbon-14 atom during beta decay. Notice the second circle shows the production of the beta particle (the electron) by the decay of a neutron. Question: If carbon-14 continues to be produced, is it accumulating? In other words, is the amount of carbon-14 greater now than in the past?
Answer: Actually, the amount of carbon- 14 remains relatively the same. This is because the nuclei are unstable and undergo beta decay. It decays about as fast as it is being made. Thus, the production of C-14 and decay of C-14 are at equilibrium or close to equilibrium.
Question: How does C-14 get into animals and rocks and other stuff?
Answer: As soon as C-14 is produced in the atmosphere it combines with oxygen forming carbon dioxide gas. Plants use carbon dioxide they take in from air and through a process called photosynthesis, the carbon-14 becomes part of the chemicals stored in the plant, such as sugar and starch. When animals and people eat plants, the C-14 comes part of the chemicals in their bodies, such as proteins, muscle, etc..
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