The chart below lists all of the decay products of radon gas (radon-222) in their order of appearance. They are called the "radon progeny" (formerly "radon daughters"). Each radioactive element on the list gives off either alpha radiation or beta radiation -- and sometimes gamma radiation too -- thereby transforming itself into the next element on the list. Lead-206, the last element on the list, is not radioactive. It does not decay, and therefore has no half-life.
When radon gas is allowed to build up in an enclosed space, such as a mine shaft or basement, the radioactive hazard increases enormously because of the build-up of radon progeny. Conversely, when radon gas migrates through the atmosphere, the solid radon progeny are deposited on the soil and water below, entering into the food chain and hence the bodies of birds, animals, fish and insects.
NOTES ON THE CHART
The vertical axis measures the MASS NUMBER,
while the horizontal axis measures the ATOMIC NUMBER.
DIAGONAL ARROWS indicate alpha decay
while HORIZONTAL ARROWS indicate beta decay.
MeV = MILLION ELECTRON-VOLTS.
It is a measure of the ENERGY of the alpha radiation.
The more energetic it is, the more damaging it is.
What are the Mass Number
and the Atomic Number?
All the atoms of a given element are identical. Each atom has a tiny core called a "nucleus", containing even smaller particles called "protons" and "neutrons". The number of protons in the nucleus is the "atomic number", while the number of protons and neutrons together is the "mass number". These numbers are characteristics of the particular element.
Elements having the same atomic number are chemically indistinguishable, even if the mass numbers are different. They are called "isotopes". For example, polonium-218, polonium-214, and polonium-210 are three isotopes of polonium. They have different mass numbers -- as indicated by their names -- but they share the same chemical properties because they all have the same atomic number, 84.
During "alpha decay", the nucleus gives off an alpha particle, which is made up of two protons and two neutrons. Thus the atomic number goes down by two and the mass number goes down by four.
During "beta decay", one of the neutrons in the nucleus spontaneously turns into a proton giving off a high-velocity electron in the process. Thus the atomic number increases by one (as there is now an extra proton) and the mass number is unchanged. The escaping electron is called a beta particle.
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