Finally, we'll examine the processes of nuclear decay, nuclear fusion, and nuclear fission. Unlike all other types of chemical reactions, which involve electrons, nuclear reactions involve the nucleus of the atom. In this unit we discuss different types of nuclear decay, learn how to write equations that describe nuclear reactions, review the concept of half-life in the context of radioactive decay, and learn how we use nuclear fission to generate electric energy.
Completing this unit should take you approximately 2 hours.
First, let's discuss what it means for something to be radioactive and undergo nuclear decay. Nuclear decay can produce immense amounts of energy, and when nuclear decay occurs, the identity of the element changes. This is because nuclear decay involves changing the number of protons in the nucleus of the atom, which in turn changes the identity of the atom.
Read this text for a brief introduction to nuclear decay. Look at the reaction in the text. Recall from Unit 1 that we can write elements with the mass number (A) as a superscript and the atomic number (Z) as a subscript before the element symbol. The atomic number is the number of protons, while the mass number is the sum of the number of protons and neutrons. In the reaction, the element changes because the atomic number changes. The other product is called an alpha particle, which we will discuss in our next reading.
Read this text, which introduces alpha decay and provides an example of an alpha-decay equation. Notice that an alpha particle is helium. Take note of the conditions listed that must be met when writing an alpha decay reaction.
Read this text, which introduces beta decay and provides an example of a beta-decay equation. A beta particle is a high energy electron. In a beta decay reaction, there is no change in the mass number in beta decay, but the atomic number increases by one.
There are four different types of nuclear decay. In addition to alpha and beta decay, gamma and positron emission can occur. Gamma emission does not have mass and often accompanies other types of nuclear emission. In positron decay, there is no change in mass number, but the atomic number decreases by one.
This video shows examples of how to write nuclear equations for alpha, beta, and gamma decay.
Now, we'll discuss the half-life of radioactive isotopes. The half-life is the time it takes half of the atoms in a sample to decay. The sample size does not matter: whether you have one gram or one ton of isotope, half of the sample will decay during the first half-life. The sample will continue to shrink by half during each successive half-life.
Read this text. Pay attention to the figure with the red and blue circles, which illustrates how samples shrink by half during each successive half-life.
Note that Equation 1 shows the equation for the radioactive decay rate constant.
If you know the rate constant for the decay of a given material, you can determine the half-life of the material using this equation. Also pay attention to Equation 2, which shows how to determine the initial concentration of the material if you know the half-life and the rate constant for the material. Carefully read the step-by-step example of this type of calculation in the text.
Read this text, which explains how we can use carbon dating to determine the age of an object. Scientists use these calculations extensively in archaeology, anthropology, and paleontology. Since the half-life for C-14 is approximately 5,700 years, carbon dating is only useful for fossils that are younger than approximately 50,000 years old. For older fossils, scientists use isotopes with longer half-lives.
Finally, we'll discuss the reactions of nuclear fusion and fission and how we can use nuclear chemistry to produce energy. These types of nuclear reactions involve the process of transmutation, which is the conversion of one element into another. In this process, we bombard the nucleus of stable isotopes with neutrons to achieve transmutation. Historically, we have used transmutation to synthesize new elements.
Read this text to see examples of transmutation using the types of nuclear decay you have already studied in this course.
Read this text, which introduces the concept of mass defect. Mass defect refers to the difference observed in the atomic mass of an atom, and the sum of the masses of the protons, neutrons, and electrons that make up the atom. The unaccounted-for mass is converted to energy in nuclear reactions, which is why nuclear reactions produce an enormous amount of energy.
As we just learned, the mass defect can potentially lead to an enormous release of energy. Read this text to learn about this type of nuclear reaction. Fission means to break up. This text shows the chain reaction that can occur when a nuclear fission reaction is started. In the example in the text, each reaction between a neutron and a uranium isotope produces three more neutrons, which can each react in turn with another uranium. A certain amount of fission material must be available to sustain this reaction. We call this the critical mass.
Read this text, which explains how a nuclear reactor works. It also covers the different parts of the nuclear reactor (the core, coolant, turbine, containment, and cooling towers) and their functions. While nuclear reactors are generally clean and efficient at producing power and accidents are rare, there is an issue of storing radioactive waste. There are extreme dangers if a nuclear reactor malfunctions, as radiation poisoning can be deadly, lead to cancer, and cause birth defects.
Read this text. Fusion means merging together, which is what occurs during fusion reactions when two atoms fuse to form an atom of a larger element. The fusion of two hydrogen isotopes into helium is the process that powers the stars in the universe, such as our sun. There have been attempts to harness nuclear fusion to produce power, but so far these attempts have been unsuccessful.
Read this text which summarizes the real and imagined danger of nuclear energy.
Read this text to learn more about how countries around the world are using nuclear energy to solve their energy needs. Its use remains controversial. Nuclear accidents have been catastrophic, but proponents argue that the benefits of nuclear energy outweigh these troubling events. The number of fatalities has been low. Nuclear reactors do not produce carbon dioxide and other pollutants that contribute to global warming. Uranium also generates far more power per unit weight of volume than fossile fuels. However, the disposal of radioactive waste continues to be a serious issue.
Take this assessment to see how well you understood this unit.