The Fermi Chronicles - Part 7: Radioactive Decay and Half-Life

I've already discussed in this blog what radioactivity is - the means by which unstable atoms get stable. Unstable atoms are not always isotopes. That is, they exist only in radioactive form. Such atoms are typically large. Small atoms, such as hydrogen, helium, etc., tend to be stable and not radioactive (albeit they have radioactive isotopes). When you look at the periodic table of elements, there are some big dudes out there that have so many nuclides in the nucleus that they are never fully stable. Unstable atoms are always radioactive - they emit radiation (in various forms and various quantities) to become stable. Uranium, most commonly U-238, is one of these large dudes that have a huge number of protons and neutrons packed in its center (238 to be exact). Therefore, uranium and its isotopes are all radioactive. When uranium, most commonly U-238, gives off radiation, it becomes something else. Uranium, by the way, is the heaviest off all atoms that occur naturally. Everything on the periodic table bigger than uranium is synthetic, including plutonium that I will discuss in another post. Historically, these elements are pretty new on the discovered list. From DOE handbook 1019/1-93:

In 1896, the French physicist Becquerel discovered that crystals of a
uranium salt emitted rays that were similar to x-rays in that they were highly penetrating, could affect a photographic plate, and induced electrical conductivity in gases. Becquerel's discovery was followed in 1898 by the identification of two other radioactive elements, polonium and radium, by Pierre and Marie Curie.

Heavy elements, such as uranium or thorium, and their unstable decay chain elements emit radiation in their naturally occurring state. Uranium and thorium, present since their creation at the beginning of geological time, have an extremely slow rate of decay. All naturally occurring nuclides with atomic numbers greater than 82 are radioactive.

Element 82 (that's the atomic number meaning it has 82 protons) is lead. From there in numerical order are the naturally radioactive elements: polonium, astatine, radon (everyone has heard of this one, no?), francium (the wimpy atom), radium, actinium, thorium (symbol should be a big hammer and a lightning bolt), protactinium, and uranium.

Since all these elements are naturally radioactive, they will undergo radioactive decay - that is, they will give off radiation (either electromagnetic or particle or both) and become something else that is more stable. For instance, U-234 gives off alpha and gamma radiation and becomes thorium. Because of the alpha radiation, it is called alpha decay. Other processes include beta decay. Yet another process occurs when a proton captures an electron from orbit and becomes a neutron (weird). When a radioactive decay occurs, the nucleus takes time to stabilize, and is called an isomer in its excited stage.

How quickly radioactive materials decay to more stable elements and isotopes can best be quantified by it's half-life. After one half-life, half that material is now gone and became something else. Of the remaining 50%, half of that will be gone in another half-life, etc. Some atoms have a half-life of a fraction of a second, others, like uranium, are much longer, which is thankfully the reason that any uranium remains on this planet. Interestingly, plutonium-239 which is synthetic has a very long half life into the thousands of years.

Previously:
The Fermi Chronicles - Part 6: Atomic Structures
The Fermi Chronicles - Part 5: Nuclear Waste Storage
The Fermi Chronicles - Part 4: Radiation Types and Radiation "Dose"

The Fermi Chronicles - Part 3: Radiation Types

The Fermi Chronicles - Part 2: A week of training

The Fermi Chronicles - Part 1: The alpha post