Radiation
Used with permission from NerZul1, Wikimedia; distributed under a CC BY-SA 4.0 license
Radiation can be highly dangerous in an uncontrolled situation such as a nuclear plant meltdown. There are various types of radiation, and the symptoms of exposure to it can take years to surface.
Used with permission from MikeRun, Wikimedia; distributed under a CC BY-SA 4.0 license
Alpha Particles
Alpha particles are high energy helium nuclei with 2 protons and 2 neutrons, and no electrons. They cannot penetrate most matter, being blocked by substances such as your skin. However, this type of radiation is extremely dangerous if it enters your body.
Used with permission from MikeRun, Wikimedia; distributed under a CC BY-SA 4.0 license
Beta Particles
Beta particles are high energy electrons. They can penetrate certain thin barriers, but can be blocked by substances such as thin cloth or aluminum. They can partially penetrate the skin, which can result in radiation burns.
Used with permission from Ethan3.14159, Wikimedia; distributed under a CC BY-SA 4.0 license
Gamma Rays
Gamma rays are very high energy electromagnetic waves. They can penetrate many types of matter, only being blocked by substances such as several feet of concrete or inches of lead. They can easily penetrate a human, damaging all cells in their path.
Potassium iodide pills, unknown author. Used with permission from Wikimedia; distributed under a CC CC0 1.0 license
Potassium Iodide
In the event of a nuclear reactor meltdown, you may be provided with or recommended to purchase potassium iodide supplements. Their purpose and effect may be unclear at first; however, these supplements are extremely important in supporting your health. During a meltdown, if you are exposed to it, radioactive iodine may enter your body and travel to your thyroid gland. However, if you have taken the potassium iodide supplement, then your thyroid will already be filled with regular iodine, effectively preventing the radioactive iodine from entering. This can prevent health complications such as thyroid cancer.