In one of my practice questions, It stated that gamma rays represent ionizing radiation.
I know that gamma rays are high energy and high frequency. How does this relate to ionizing radiation?
We are surrounded 24/7 by radiation. To understand the biological effects of radiation we must first understand the difference between
ionizing radiation and
non-ionizing radiation. In general, two things can happen when radiation is absorbed by matter: excitation or ionization.
Excitation occurs when the radiation excites the motion of the atoms or molecules, or excites an electron from an occupied orbital into an empty, higher-energy orbital.
Ionization occurs when the radiation carries enough energy to remove an electron from an atom or molecule.
Human tissue is 70-90% water , the dividing line between radiation that excites electrons and radiation that forms ions is often assumed to be equal to the ionization of water: 1216 kJ/mol. Radiation that carries less energy can only excite the water molecule. It is therefore called
non-ionizing radiation. Radiation that carries more energy than 1216 kJ/mol can remove an electron from a water molecule, and is therefore called
ionizing radiation.
Not all forms of radiation have the same efficiency for damaging biological organisms. The faster energy is lost as the radiation passes through the tissue, the more damage it does. I can't see the MCAT asking you to memorize a bunch of different radiation types and know which is ionizing or not, but you are expected to know the EM spectrum and you can reason that radiation with more energy than UV light (i.e. X-rays, gamma rays are likely to show up on test day, cosmic rays not so much) are ionizing and will be harmful (or beneficial in some cases of cancer treatments) to human cells.
Hope this helps, good luck!
