Although it seems like this post should include some commentary on zombies or video games, we’re going to focus on the term ‘half-life’ as it’s used in physics, this time. The reason for this is that important research has been published last month on geothermal heat produced by radioactive decay.
But before all that complicated stuff let’s start at the beginning. ‘Half-life’ is actually shortened from ‘half-life period’ which refers to the time in which exactly half of a radioactive substance decays. This measurement is especially useful because radioactive materials decay exponentially – meaning that they decay much more quickly at first than later on, where the decay process drags on more slowly. This decay rate is directly connected to the rate at which radioactive materials emit radiation.
Let’s take iodine as an example. I-131 has a radioactive half-life of just over 8 days and gives off both alpha and beta radiation (for a discussion of these radiation types see this post). As I-131 atoms give off radiation they transform into atoms of Xe-131, a stable (and non-radioactive) isotope
1. That means if you start with a pure sample of I-131, after 8 days about half of the sample will be I-131 and half will be Xe-131. If you wait another 8 days, 1/4 of the sample will be I-131 and 3/4 will be Xe-131, and so on. As you may expect, the sample of I-131 will emit much more radiation right at first versus many days later on, when the majority of the sample is Xe-131.
Not all materials have a half-life short enough to notice. In fact, the half-lives of radioactive materials can vary from fractions of a second to billions of years. These differences lend themselves to varied applications. Isotopes with short half-lives (such as I-131, Tl-201, In-111, and Tc-99) are commonly used in medical imaging and therapy because they show up clearly in the body and become non-effective quickly so that the patient is not exposed to too much radiation
2. Isotopes with long half-lives (such as U-238, C-14, and K-40) are often used in radiometric dating, where scientists can measure the abundance of these isotopes in various materials to determine their age
3.
Newly published research
4 from Japanese and Italian scientists also suggests that over half of the internal heat produced by the earth is caused by long-lasting radioactive materials such as thorium, uranium, and potassium – a quantity that adds up to nearly twice as much energy used annually by everyone on the planet
5. The fact that radioactive materials are responsible for the heat is important because it helps to explain why our earth is hot enough to produce volcanoes, mountain ranges, and general plate tectonics while other planets in our solar system have long since gone cold. The geothermal heat of our planet isn’t going to cool soon either, thanks to the fact that the isotopes producing the heat have half-lives of billions of years.
So although the adage “all good things must come to an end” (and all bad ones, too!) may be a great application to radioactive materials, there’ll be plenty of radiation and geothermal heat for years to come.
5)http://www.scientificamerican.com/blog/post.cfm?id=nuclear- fission-confirmed-as-source-2011-07-18
D-tect Systems is supplier of advanced radiation and chemical detection equipment sold around the world. www.dtectsystems.com.
