Radioactive Decay Cards

Introduction

Determine the natural decay of uranium–238 by arranging element cards and radioactive particles to create the uranium-238 decay series.

Concepts

• Radioactive decay
• Beta particle
• Alpha particle
• Half-life

Background

Nuclear stability and radioactive decay are important concepts to understanding nuclear chemistry, the size of the nucleus, and the energy that holds it together. Radioactive decay also plays an important role in society in the form of energy, medical tracers and weapons. The radioactive decay of uranium isotopes has been extensively studied due to its abundance in nature and the important role uranium plays in nuclear power and weapons. The uranium–238 isotope is the predominant species (99.3%) found in nature and undergoes a slow radioactive decay to lead–206. Natural uranium also contains 0.7% of uranium–235. When bombarded with neutrons, uranium-235 will undergo nuclear fission and break into two lighter elements, releasing substantial amounts of energy. This is the principle behind the nuclear power industry and nuclear weapons.

Most textbooks have at least one chapter devoted to Nuclear Chemistry. Several important terms will be clarified here and should be understood prior to beginning the activity.

A Nuclide is a unique atom, represented by the symbol

where X is the symbol for the element, A is the mass number or total number of neutrons and protons and Z is the atomic number or the total number of protons in the nucleus.

A Beta Particle (β) is an electron produced in a radioactive decay. The β-particle is represented as It has no mass and a charge of –1. β-particle production is the most common type of decay and the net effect is to change a neutron into a proton. During β-particle decay, the mass of the nuclide stays the same but the atomic number increases by one and a new element is produced. This is the process that occurs during the radioactive decay of carbon–14. An Alpha Particle (α) is a helium atom produced during radioactive decay. α-particle production is a very common mode of decay for heavy radioactive isotopes and is represented by The net result is the loss of two neutrons and two protons from the nucleus and subsequently a smaller atomic number (–2) and mass number (–4). A Half-Life (t½) is described as the time required for one-half of the nuclides to undergo radioactive decay. It is a constant for each radioactive nuclide.

The splitting of a heavy nucleus by a neutron into two lighter nuclei, accompanied by a large release of energy in known as nuclear fission.

Experiment Overview

In this activity, the order of natural decay of a radioactive element (U–238) to a stable species (Pb–206) must be determined. There will be thirteen (13) nuclide species between U–238 and Pb–206. Each radioactive decay will emit an alpha or beta particle.

Materials

Procedure

1. Arrange the element cards in order of the natural radioactive decay with either an alpha or beta particle between each element.
2. After putting the cards in order, make a graph of mass number (y-axis) vs. atomic number (x-axis) for each element in the series. Write the element’s symbol at its point on the graph and connect the appropriate points in order of decay with an arrow.
3. Finally, give one example each for an alpha decay equation and a beta decay equation from the graph.

References

Special thanks to Steven Purkis, Charles Sumprer, Kirstin Distante and Brian Adler at Tappan Zee High School, Orangeburg, NY, for providing us with the idea and instructions for this activity.

ChemCom, Chemistry in the Community, 3rd ed; Kendall/Hunt: Dubuque, IA, 1996; Unit 5.

Purkis, S.; Sumprer, C; Distante, K., Adler, B. Chem 13 News, April 1997, p 19.

Zumdahl, S. S. Chemistry, 4th ed: Houghton Mifflin: New York, 1997; Chapter 20.