Radioactive Decay

1. Some isotopes are very stable, never spontaneously changing at all. However, some isotopes can spontaneous go through a transformation which causes them to emit radiation and usually change from one nuclear structure to another, transmuting the atom from one element to another.
2. Certain isotopes are radioactive because their nuclei are unstable. There has to be a balance between neutrons and protons in the nucleus. The larger the difference the more unstable the nucleus becomes. Also, as nuclei get larger they also become unstable, so that all elements with an atomic number greater than 89 are naturally radioactive.
3. When the nucleus breaks down in some way to become more stable, we call this a "decay". When atoms decay they give off radiation. Here we will explore several of the most common ways an atom can decay.
4. Alpha Decay
   1. If a nucleus ejects an a glob of two protons and two neutrons, then it has just emitted an alpha particle. See the illustration below:
      
      
      (Used with permission. Original source: http://www2.slac.stanford.edu/vvc/theory/nuclearstability.html)
      
      
   2. The symbolic representation of the above decay would be:
      
      
      
      
      
   3. Because alpha particles are so big compared with other emitted radioactive particles they can't penetrate very far into matter, but they do a great deal of damage where they are absorbed. Alpha particles can only travel a few centimeters through air and can be blocked by a piece of paper. However, if you ingested or inhaled even a microscopic dust grain of plutonium then there is a very high chance cancerous growth will occur wherever this grain of plutonium (an alpha emitter) gets lodged in your system.
   4. Practice. Try filling in the blanks below. Click on each one to see the answer:
5. Beta Decay
   1. If a nucleus ejects an electron, then it has just emitted a beta particle. You might ask how a nucleus can eject an electron because electrons are not in the nucleus. However, this happens through the transformation of a neutron into a proton. If a neutron becomes a proton, then an electron (beta particle) is ejected at high speed. Also, a neutrino is ejected as well, but neutrinos almost never interact with matter, so we don't worry about their biological effects. See the illustration below:
      
      (Used with permission. Original source: http://www2.slac.stanford.edu/vvc/theory/nuclearstability.html)
      
      
   2. The symbolic representation of the above decay would be:
      
      
      
      
      
   3. Beta particles are much smaller and can easily go through a piece of paper. They can travel several meters through air and can be stopped by a thin sheet of lead.
   4. Practice. Try filling in the blanks below. Click on each one to see the answer:
6. Gamma Decay
   1. Sometimes a nucleus is in an excited state, and to become stable it only needs to emit some energy. When pure energy is emitted with no material change in the nucleus, a photon of gamma radiation is emitted. See the illustration below:
      
      
      
      (Used with permission. Original source: http://www2.slac.stanford.edu/vvc/theory/nuclearstability.html)
      
      
   2. The symbolic representation of the above decay would be:
      
      
      
      
      
   3. Gamma rays have no mass at all and can penetrate matter extremely well. They can travel through many kilometers of air, but are blocked by thick sheets of lead.
7. An excellent summary of all these concepts can be found at: http://www.darvill.clara.net/nucrad/types.htm

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