Summary

In this activity, students will use a radioactive decay simulation to investigate why radioactive decay occurs, the changes that occur in the nucleus during three common types of decay (alpha, beta, and gamma decay), and what types of materials can be used to protect against each type of radiation. Students will also have a chance to test their understanding of these concepts with a 10-question quiz.

Grade Level

Middle School, High School

NGSS Alignment

This activity will help prepare your students to meet the performance expectations in the following standards:

• HS-PS1-8: Develop models to illustrate the changes in the composition of the nucleus of the atom and the energy released during the processes of fission, fusion, and radioactive decay.
• Scientific and Engineering Practices:
  • Developing and Using Models
  • Analyzing and Interpreting Data

Objectives

By the end of this activity, students should be able to:

• Identify changes in the nucleus that occur as a result of alpha, beta, and gamma decay.
• Write radioactive decay equations for alpha, beta, and gamma decay.
• Identify materials that effectively shield against different types of external sources of radiation.

Chemistry Topics

This activity supports students’ understanding of:

• Radioactive decay equations
• Alpha, beta, and gamma decay

Time

Teacher Preparation: minimal
Lesson: 30-40 minutes

Materials

• Computer, tablet, or phone with internet access
• Student handout
• https://teachchemistry.org/classroom-resources/radioactive-decay-simulation

Safety

• No specific safety precautions need to be observed for this activity.

Teacher Notes

• The simulation can be found at the following link (note that students can access the simulation without an AACT login):
  • https://teachchemistry.org/classroom-resources/radioactive-decay-simulation
• Students should be familiar with the structure of the atom, particularly the locations and charges of the subatomic particles, and the concept of isotopes prior to using this simulation.
• There is some variation in terminology used to describe radioactive decay, so you may want to make students aware of the following synonyms:
  • Radioactive decay: Nuclear decay
  • Alpha/beta/gamma decay: Alpha/beta/gamma radiation or emission
  • Parent/daughter nucleus: Parent/daughter nuclide or isotope
    • Daughter nucleus: Decay product
• This simulation introduces the three main types of radioactive decay that students are most likely to encounter in a high school chemistry course: alpha decay, beta decay, and gamma decay. There are, however, other types of nuclear decay that are not addressed here, including:
  • β⁺ (“beta-plus”) decay: technically, what is described as beta decay in the simulation, when a neutron becomes a proton and emits an electron, is only one type of beta decay, β^- (“beta-minus”) decay; there is also β⁺ decay, which is when a proton becomes a neutron and emits a positron. Since this is not as common, and most students aren’t familiar with positrons (an antimatter particle with the same mass as an electron but a +1 charge), this type of radioactive decay is not usually covered in high school chemistry. The resulting daughter nuclide has no significant change in mass, -1 in atomic number.
  • Electron capture: this occurs when an inner orbital electron is “captured” by the nucleus and turns a proton into a neutron. The net change in the nucleus is the same as that which occurs with β⁺ decay (no significant change in mass, -1 in atomic number).
  • Spontaneous fission: very large, unstable nuclei can sometimes spontaneously break apart into two (or more) smaller nuclei, usually of approximately equal size, along with one or more free neutrons. The daughter isotopes vary based on the parent isotope.
• The shielding section shows that some radioactive decay products can be shielded against more easily than others. Students should find that a substance such as paper can effectively shield against alpha radiation, aluminum is effective against alpha and beta radiation, and a lead shield is required to protect against gamma radiation (in addition to alpha and beta). Since X-rays are slightly below gamma rays in the electromagnetic spectrum in terms of energy and also have the potential to damage living tissues, lead shielding is sometimes used when taking X-rays. If students have had X-rays for dental work, broken bones, etc., they may recall a heavy vest or apron placed over parts of their bodies for this purpose. (However, recently there has been a push to stop the practice of using lead aprons, as we develop a better understanding of how radiation affects the body and as modern imaging technology uses smaller doses of radiation.)
• Students may ask which type of radiation is the “most dangerous.” This is a tricky question because it depends on the source of the radiation as well as the type. The relatively large alpha particles have the greatest potential to cause damage (“ionizing power”) but the least ability to cut through materials (“penetrating power”) so external sources of alpha radiation are easily shielded against by paper, skin, clothing, etc. However, if alpha particles were ingested or inhaled somehow, they would cause the most damage inside the body. Beta particles are smaller than alpha particles and therefore have less ionizing power, but more penetrating power than alpha particles. They are also much more harmful if the source of radiation is ingested rather than external. Gamma radiation is massless (energy only) so it has the most penetrating power but the least ionizing power. This online textbook provides a good overview of these concepts.
• Students will need to have access to a periodic table for some of the quiz questions to identify elements based on atomic number.
• In the quiz section, remind students of the following:
  • On the questions where they are typing in isotope symbols, they should only be typing in numbers, letters, and/or “-” in the fields. If any extra characters are entered (such as spaces or punctuation) it will be marked as incorrect by the simulation.
  • Improper capitalization in the element symbols will be marked as incorrect.
  • When writing products for questions on the quiz, the daughter nucleus should be entered first, followed by the symbol for the radiation. (In reality, the order doesn’t matter, but the way the quiz is designed requires the daughter nucleus to be entered in the first set of blanks to be marked as correct.)
• The quiz randomly presents 10 of the 22 possible questions, so that students could repeat the quiz and not get the same 10 questions if they need additional practice – if students finish early or could use more practice, you could print additional copies of the second and third pages of the student document and see if they can get all 22 unique questions!
• Related classroom resources from the AACT Library that may be used to further teach this topic:
  • Activity: Nuclear Decay Investigation
  • Activity: Case Study: The Lung Cancer Mystery
  • Activity: Radiological Applications of Isotopes