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Are there nuclear reactions going on in our bodies?
Category: Biology
Published: September 11, 2013
By: Christopher S. Baird, author of The Top 50 Science Questions with Surprising Answers and physics professor at West Texas A&M University
Yes, there are nuclear reactions constantly occurring in our bodies, but there are very few of them compared to the chemical reactions, and they do not affect our bodies much. All physical objects are made of molecules. A molecule is a series of atoms linked together by chemical (electromagnetic) bonds. Inside each atom is a nucleus which is a collection of protons and neutrons linked together by nuclear bonds. Chemical reactions are the making, breaking, and rearranging of bonds between atoms in molecules. Chemical reactions do not change the nuclear structure of any atoms. In contrast, nuclear reactions involve the transformation of atomic nuclei. Most of the processes surrounding us in our daily life are chemical reactions and not nuclear reactions. All of the physical processes that take place to keep a human body running (blood capturing oxygen, sugars being burned, DNA being constructed,etc.) are chemical processes and not nuclear processes. Nuclear reactions do indeed occur in the human body, but the body does not use them. Nuclear reactions can lead to chemical damage, which the body may notice and try to fix.
There are three main types of nuclear reactions:
- Nuclear fusion: this is the joining of two small atomic nuclei into one nucleus.
- Nuclear fission: this is the splitting of one large atomic nucleus into smaller fragments.
- Radioactive decay: this is the change of a less stable nucleus to a more stable nucleus.
Note that nuclear fission and radioactive decay overlap a little bit. Some types of radioactive decay involve the spitting out of nuclear fragments and could therefore be seen as a type of fission. For the purposes of this article, "fission" refers to large-scale nucleus fragmentation events that can clearly not be classified as radioactive decay.
Nuclear fusion requires high energy in order to be ignited. For this reason, nuclear fusion only occurs in stars, in supernovas, in nuclear fusion bombs, in nuclear fusion experimental reactors, in cosmic ray impacts, and in particle accelerators. Similarly, nuclear fission requires high energy or a large mass of heavy, radioactive elements. For this reason, significant nuclear fission only occurs in supernovas, in nuclear fission bombs, in nuclear fission reactors, in cosmic ray impacts, in particle accelerators, and in a few natural ore deposits. In contrast, radioactive decay happens automatically to unstable nuclei and is therefore much more common.
Every atom has either a stable nucleus or an unstable nucleus, depending on how big it is and on the ratio of protons to neutrons. Nuclei with too many neutrons, too few neutrons, or that are simply too big are unstable. They eventually transform to a stable form through radioactive decay. Wherever there are atoms with unstable nuclei (radioactive atoms), there are nuclear reactions occurring naturally. The interesting thing is that there are small amounts of radioactive atoms everywhere: in your chair, in the ground, in the food you eat, and yes, in your body.
Radioactive decay produces high-energy radiation that can damage your body. Fortunately, our bodies have mechanisms to clean up the damage caused by radioactivity and high-energy radiation before they become serious. For the average person living a normal life, the amount of radioactivity in his body is so small that the body has no difficulty repairing all the damage. The problem is when the radioactivity levels (the amount of nuclear reactions in and around the body) rise too high and the body cannot keep up with the repairs. In such cases, the victim experiences burns, sickness, cancer, and even death. Exposure to dangerously high levels of radioactivity is rare and is typically avoided through government regulation, training, and education. Common causes of human exposure to high radioactivity include:
- Naturally occurring radon in the ground. All forms (isotopes) of the element radon are radioactive. Radon testing in houses has become standard to prevent over-exposure.
- Employees working in nuclear reactors or nuclear weapons facilities. Strict policies and personal radiation gauges help prevent over-exposure.
- People being too close to a nuclear weapon when it is tested.
- People living near a nuclear power plant when it experiences a nuclear disaster.
- Medical treatment that uses radioactivity in a controlled way to combat disease.
Note that if you have a single medical scan performed that requires drinking or being injected with a radioactive tracer, you do indeed end up with more nuclear reactions in your body than normal, but the level is still low enough to not be dangerous, and therefore was not included on this list.
Low levels of radioactive atoms are constantly accumulating in every person. The ways we end up with radioactive atoms in our bodies include: eating food that naturally contains small amounts of radioactive isotopes, breathing air that naturally contains small amounts of radioactive isotopes, and being bombarded with cosmic rays that create radioactive atoms in our bodies. The most common natural radioactive isotopes in humans are carbon-14 and potassium-40. Chemically, these isotopes behave exactly like stable carbon and potassium. For this reason, the body uses carbon-14 and potassium-40 just like it does normal carbon and potassium; building them into the different parts of the cells, without knowing that they are radioactive. In time, carbon-14 atoms decay to stable nitrogen atoms and potassium-40 atoms decay to stable calcium atoms. Chemicals in the body that relied on having a carbon-14 atom or potassium-40 atom in a certain spot will suddenly have a nitrogen or calcium atom. Such a change damages the chemical. Normally, such change are so rare, that the body can repair the damage or filter away the damaged chemicals. The textbook Chemistry: The Practical Science by Paul B. Kelter, Michael D. Mosher and Andrew Scott states:
Whereas potassium-39 and potassium-41 possess stable nuclei, potassium-40 is radioactive. This means that when we consume a banana, we get a measurable amount of radioactive potassium-40. How much? The natural abundance of potassium-40 is only 0.012%, or approximately 1 atom in 10,000. A typical banana has approximately 300 mg of potassium. Therefore, with each banana that we eat, we ingest approximately 0.036 mg of radioactive potassium-40.
The natural occurrence of carbon-14 decay in the body is the core principle behind carbon dating. As long as a person is alive and still eating, every carbon-14 atom that decays into a nitrogen atom is replaced on average with a new carbon-14 atom. But once a person dies, he stops replacing the decaying carbon-14 atoms. Slowly the carbon-14 atoms decay to nitrogen without being replaced, so that there is less and less carbon-14 in a dead body. The rate at which carbon-14 decays is constant and well-known, so by measuring the relative amount of carbon-14 in a bone, archeologists can calculate when the person died. All living organisms consume carbon, so carbon dating can be used to date any living organism, and any object made from a living organism. Bones, wood, leather, and even paper can be accurately dated, as long as they first existed within the last 60,000 years. This is all because of the fact that nuclear reactions naturally occur in living organisms.