RADON is a colorless, odorless, tasteless, radioactive gas that comes from uranium and radium in the ground. All leading health organizations consider radon a health hazard due to its radioactivity. It is the leading cause of lung cancer among non-smokers. According to the Environmental Protection Agency, radon kills approximately 21,000 people every year in the United States.


Video courtesy of the Environmental Protection Agency (www.epa.gov/radon).

Radon is formed as one intermediate step in the normal radioactive decay series, through which uranium and thorium slowly decay into stable lead. Thorium and uranium are the two most common radioactive elements on earth, and they have been on Earth since it formed 4.6 billion years ago. As radon itself decays, it becomes new radioactive elements called radon daughters or radon decay products (RDPs). Although radon is a gas, the elements it becomes when it decays are solids and, therefore, stick to surfaces, such as dust and smoke particles in the air. If such contaminated dust and smoke is inhaled, these particles can stick to the airways of the lungs and increase the risk of developing lung cancer.


Radon is dangerous, because parts of its nucleus spontaneously break off. That is what it means to be "radioactive". A radioactive element has an unstable nucleus, and small pieces of the nucleus spontaneously break off, resulting in a more stable element. The spontaneous emission of a chunk of nucleus is called "radioactive decay". A radioactive atom will decay until its nucleus becomes stable, at which time the atom stops decaying.


There are two different chunks that break off of a radioactive atom's nucleus. The largest chunk is an alpha particle, which is composed of two protons and two neutrons. The smaller chunk is a beta particle, which is a super-high energy electron. At the same time alpha and beta particles are emitted, extremely high energy gamma rays are also released from the nucleus. Alpha particles, beta particles, and gamma rays all cause cancer, and are known as "radiation"


The video below allows us to "see" the alpha particles and beta particles released by radon and other radioactive elements. I use quotation marks because we actually see the vapor trail created by alpha and beta particles; We can't see the particles themselves. 

Indoor radon gas is the second leading cause of lung cancer in the United States and breathing it over prolonged periods can present a significant health risk to families all over the country. It’s important to know that this threat is completely preventable. Radon can be detected with a simple test and fixed through well-established venting techniques.
— U.S. Surgeon General Health Advisory