Radioactive elements have a nucleus which is unstable, emit alpha, beta, or gamma rays, and will eventually decay to become elements which are stable. 35 elements are radioactive. Radioactivity has nothing to do with radio waves, and is well beyond radio on the electromagnetic spectrum.
Radiation damages tissue, and the most vulnerable parts of the body are those with many dividing cells, such as the digestive tract and bone marrow. A very high dose can be fatal, while smaller amounts cause illness, burns, and a higher risk of cancer.
The Different Forms of Radiation
Alpha particles are helium nuclei, emission of which reduces an element’s atomic number by two and its atomic weight by four. Beta particles are electrons or positrons. Electron emissions increases the atomic number by one while positron emission decreases it by one. Gamma rays are high frequency electromagnetic radiation, which changes the energy level of a nucleus.
Alpha particles are quite large and do not penetrate skin. They can be stopped by a few sheets of paper, or even several inches of air. Outside of the body they are harmless. If they are swallowed or inhaled, however, they are very dangerous. Beta particles are smaller than alpha particles and can penetrate some way into skin and cause burns. A thin sheet of metal can stop beta particles, and again, if they get inside the body they can cause damage. Gamma rays are similar to X-rays and will harm the body whether inside or out. It requires lead or several feet of concrete to stop them.
Nuclei are said to be isotopes when they have the same atomic number but a different atomic weight. Isotopes are chemically the same but different physically. An example is carbon, which has isotopes of carbon-14 and carbon-12. Both have the same atomic number of six, but a different number of neutrons. The one which has two extra neutrons is radioactive. Carbon’s radioactive isotope was used to develop carbon dating.
Another term which must be understood to understand radioactivity is half-life. This is the period of time required for half of a radioactive element to decay. The half-life of carbon-14 is 5,730 years: if you take one ounce of the stuff, half of it will have decayed 5.73 millennia later.
The Discovery of Radioactivity
Radioactivity was discovered in 1896. February 26 of that year was overcast, which presented a problem to French physicisist, Henri Bequerel, as he had been hoping to demonstrate a connection between minerals which glow in strong light and the X-rays which had recently been discovered by Wilhelm Röntgen. Bequerel was seeking to prove that flourescing materials emitted X-rays. The next day was also cloudy, forcing Bequerel to again postpone his experiment. The fluorescing material he used was potassium uranyl sulfate, a uranium compound. He wrapped it in black cloth with a photographic plate and a copper Maltese cross.
Days later, Bequerel took the package from the drawer, and found to his surprise that a clear image of the cross was on the plate, despite its never having been exposed to sunlight. The crystal must have emitted radiation. He repeated the experiment, and wrote in his diary of what he had found. The term, radioactivity, was coined by Bequerel’s doctoral student, Marie Curie. She shared a Nobel Prize for Physics with Bequerel and her husband, Pierre, in 1903. The Curies discovered two new radioactive elements, radium and polonium, and Marie realized that X-rays killed tumors.
Radioactive isotopes now have many applications which range from atomic energy to medicine. Disposal of radioactive elements is difficult because they are harmful.