Without a doubt, the single biggest fear the average person has of nuclear energy is radiation. Much of this fear comes from a lack of understanding. It is with this in mind that I will offer a brief explanation of the four types of radiation associated with commercial nuclear power plants. The first is known as alpha radiation.
Alpha radiation, also known as alpha decay, is the process in which an unstable atom emits an alpha particle. An alpha particle consists of two protons and two neutrons. In short, an alpha is a Helium atom sans electrons.
Let’s look at a particle of Uranium 238 undergoing alpha decay. Uranium 238 has 92 protons (atomic number 92) and 146 neutrons (mass number 238). The unstable Uranium atom will emit an alpha particle consisting of 2 protons and 2 neutrons. The result is two completely separate atoms. The first is the Helium ion (alpha particle) and the second is the new Thorium 234 atom produced by the remaining 90 protons (atomic number 90) and 144 neutrons (mass number 234). The Thorium atom is also unstable and will continue to decay for a long time until it eventually sheds so many particles that it becomes Lead.
When an alpha is first shed from an atom, it is traveling at about 5% of the speed of light. This might seem like ludicrous speed, but remember that the particle consists of two protons and zero electrons. This gives the atom a +2 charge and causes it to quickly interact with the surrounding matter. An alpha particle tends to lose most or all of its kinetic energy after traveling only a few inches. Believe it or not, alpha decay is the source of nearly all of the Helium on Earth. So the next time you take a deep breath from that balloon, remember that you are inhaling the byproducts of radioactive decay.
Alpha radiation is found exclusively in heavier atoms. Those larger atoms like Uranium or Thorium are strong alpha emitters. The process is caused when the repulsive force between two protons in the nucleus of an atom overcomes the nuclear force holding them together. This only happens in the larger elements because the nuclei of these atoms are so large that the atom is unstable. In a nutshell, the atom is so big that it tears itself apart.
Externally, alpha radiation is relatively harmless. It can be shielded in some cases with just a piece of paper. Alpha emitters are theoretically safe to touch even. However, I certainly don’t recommend this because the possibility of picking up a hot particle and eventually ingesting it remains. Also, the atoms tend to be accompanied by Beta and Gamma emitters which certainly are not materials you want to handle.
The only real danger with alpha emitters comes from the unlikely possibility that one becomes ingested or inhaled. Remember, these particles lose their energy in just an inch of air or a piece of paper. Nothing bad on the outside, but if that first inch happens to be internal tissue the result could be cellular damage or possibly cancer over prolonged periods of heavy exposure. Alpha particles also have an extremely long half-life associated with them. The large, unstable atoms can remain radioactive for tens of thousands of years.
In short, materials that give off alpha radiation are long lived, easily shielded, dangerous if ingested, and produce Helium. If the proper precautions are taken, radioactive materials emitting alpha radiation can be properly stored and allowed to live out their half-lives just as naturally occurring materials have done underground since the planet was born.
~Man Overboard
Image used in this post
Alpha Decay photo courtesy of Wikimedia Commons published under the CC license.
3 Comments
Jack – this was really nicely done. I have a couple of questions:
Do Uranium (both 235 and 238) masses passively emit alpha particles? I am assuming you can encounter alpha particles at any and all points of the process (mining, enriching, fission, and in waste), but do these various stages have different levels of alpha radiation? One more ! – Do atoms other than Uranium produce alpha particles?
Yes, both are Alpha emmiters. Basically the larger atoms are natural alpha emiters, anything bigger than Lead. There are other ways to get smaller atoms to emit an alpha but they are very complicated. You are correct in that you can find alpha at any stage of the process. This is why some claim that the military using Depleted Uranium for armor-peircing rounds is not safe for soldiers. But these are exrtremely low levels. You will find the most alpha emission immediately following the fission process.
Why are tailings from Uranium mines guarded, and what kills the fish in the lakes around them? (Elliot Lake Ontario Canada)
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