POGIL Activity:
Types of Radioactive Decay

Radioactive Decay Processes

Non-ionizing radiation is produced in a variety of ways. Infrared light is radiated by everything around us: anything with a temperature glows, just not visibly. Visible light can be produced by heating a solid, such as the heating element in a toaster which glows red. It can also be produced by atomic emission, which is how LED lights work.

If something is hot enough it will even produce ultraviolet light, as the Sun does. X-rays are produced by very violent or energetic astronomical events and by special x-ray vacuum tubes in medical labs. Gamma rays, being strictly nuclear radiation, are only produced by excited atomic nuclei.

Ionizing radiation can also be particles with mass, charge, and a very high speed. Such particles are emitted by unstable atomic nuclei. These nuclei change from an unstable parent nucleus to a more stable daughter nucleus, usually by emitting a particle. For one type of decay it involves absorbing a particle.

Alpha Decay	Positron Decay
An americium-241 nucleus emits an alpha particle and becomes a neptunium-237 nucleus.	A carbon-11 nucleus emits a positron and becomes a boron-11 nucleus.
Beta Decay	Electron Capture
A hydrogen-3 (or tritium) nucleus emits an electron and becomes a helium-3 nucleus.	A beryllium-7 nucleus absorbs an orbiting electron and becomes a lithium-7 nucleus. Nothing is emitted.
Gamma Decay
An excited helium-3 nucleus releases excess potential energy as a gamma-ray photon.

Answer the following questions using Model 1.

1. How many protons and neutrons does the americium-241 nucleus have? How many does the neptunium-237 nucleus have?
2. What is the meaning of the colors used for the circles that make up each atomic nucleus? What does a dark-gray circle represent? Light-gray?
3. What is an alpha-particle? What is it made of and what is its atomic symbol (^A_ZX)?
4. Formulate a rule for what happens to a nucleus during alpha decay. What changes are made to the mass number (A) and the atomic number (Z)? What changes are made to the number of each type of particle (p⁺ and n⁰)?
5. Make a prediction about the daughter nucleus for each of the following unstable nuclei, all of which decay by alpha decay. For example, neptunium-237 is the daughter nucleus for the alpha-decay of americium-241.
   ²³⁵₉₂U -->                     ²⁴⁴₉₄Pu -->                     ²²²₈₆Rn -->                     ²²⁶₈₈Ra -->
6. How many protons and neutrons do hydrogen-3 and helium-3 each have? How did the number of each particle change when hydrogen-3 became helium-3?
7. What is a beta-particle? What is its charge and mass?
8. The atomic symbol for a beta-particle can be written in two ways: ⁰_–1β or ⁰_–1e^–. Explain why the mass number of zero is correct for these symbols. Also, why is the atomic number a negative one?
9. Formulate a rule for what happens to a nucleus during beta decay. What changes are made to the mass number (A) and the atomic number (Z)? What changes are made to the number of each type of particle (p⁺ and n⁰)?
10. Make a prediction about the daughter nucleus for each of the following unstable nuclei, all of which decay by beta decay.
    ¹⁴₆C -->                     ⁶⁰₂₇Co -->                     ²⁴₁₁Na -->                     ³²₁₅P -->
11. Does the nucleus of a helium-3 atom change its number of protons or neutrons when it emits a gamma-ray photon? What happens to it in the picture?

Atomic nuclei are much, much smaller than atoms. Atoms include the orbiting electrons. As you know from other studies you have done the electrons can enter excited states in which they have a larger amount of potential energy. They release this energy by releasing a photon. Atomic nuclei can also become excited but their energy levels are spaced much farther apart than the energy levels occupied by electrons. As a result, when a nucleus goes back to the ground state it releases a gamma-ray photon, which is much higher in energy than visible or ultra-violet photons. A nucleus will often be in an excited state just after emitting an alpha-particle or a beta-particle. Gamma rays (also written γ-rays using the Greek letter) are often detected alongside these other types of decay. For example, cobalt-60 decays by beta-decay and emits two gamma-ray photons right afterward.

12. Formulate a rule for how a nucleus changes when it undergoes gamma decay.
13. How many protons and neutrons do carbon-11 and boron-11 each have? How did the number of each particle change when carbon-11 became boron-11?

A positron is a particle of anti-matter. Each particle of matter has an anti-matter partner that has the same mass but the opposite charge. Anti-protons have a mass of 1 amu and a charge of –1. Anti-electrons, also known as positrons, have the same mass as an electron but a +1 charge. Anti-matter is extremely rare because whenever a single particle of it touches a matching matter partner both particles are annihilated and become pure energy. They cease to exist and instead two gamma-ray photons come into existence whose combined energy equals the mass of the annihilated particles. Matter and energy are sometimes interchangeable as the equation E = mc² demonstrates.

14. The atomic symbol for a positron (or beta-plus-particle) can be written in two ways: ⁰₊₁β⁺ or ⁰₊₁e⁺. Explain why the mass number of zero is correct for these symbols. Also, why is the atomic number a positive one?
15. Formulate a rule for what happens to a nucleus during positron decay. What changes are made to the mass number (A) and the atomic number (Z)? What changes are made to the number of each type of particle (p⁺ and n⁰)?
16. Make a prediction about the daughter nucleus for each of the following unstable nuclei, all of which decay by positron decay.
    ³⁴₁₉K -->                     ⁴⁷₂₇Co -->                     ⁶⁸₃₅Br -->                     ²⁵₁₅P -->
17. Fluorine-18 is used in a medical imaging technology called positron emission tomography. What is the daughter nucleus produced in its decay?
18. Are the positrons emitted by fluorine-18 nuclei directly observable? Why or why not? What observable effects do the positrons have?
19. How many protons and neutrons do beryllium-7 and lithium-7 each have? How did the number of each particle change when beryllium-7 became lithium-7?
20. Formulate a rule for what happens to a nucleus during electron capture decay. What changes are made to the mass number (A) and the atomic number (Z)? What changes are made to the number of each type of particle (p⁺ and n⁰)?
21. What makes electron capture decay different from all four of the other decay modes?
22. Do you think that an observer outside the nucleus could tell that electron capture had occurred? Why or why not?
23. Make a prediction about the daughter nucleus for each of the following unstable nuclei, all of which decay by electron capture decay.
    ³⁷₁₈Ar -->                     ⁵⁶₂₈Ni -->                     ⁷³₃₃As -->                     ⁹³₄₂Mo -->
24. Based on what you have learned in this activity do you think it is possible for protons to change into neutrons when an unstable nucleus decays? Justify your answer using two examples.
25. Can a neutron change into a proton? Justify your answer using an example.
26. Define the words emit and absorb in the context of this lesson.
27. Define the terms parent nucleus and daughter nucleus.

28. In the space below create an outline that contains all of the main points that you believe you were meant to learn by doing this activity. Do it with bullets or with headings and sub-headings (A., B., 1., 2., etc.) Work with your group on this part and consult with your teacher before moving on to the next part of the activity.
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
29. In the space below use your outline to write a short paragraph that summarizes all of the main points you wrote above. Do this part completely independently but share your work with your group members after you are finished. Make any changes or additions you find necessary to make a final draft of this information. Type up this draft to turn in as the recorder’s report.