Lesson 3: How Radiation Interacts with Matter

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Description

 

In this lesson, we will learn about the different types of radiation, how they interact with different kinds of materials, and how that knowledge can be used to do amazing things!

Why it Matters

Most of the significant processes that we associate with the word "nuclear" - power, propulsion, medicine, weapons, etc. - would not be possible without understanding and controlling the behavior of particles that originated in nuclear reactions after they leave the nucleus. There is no nuclear power without neutron-loss prevention and moderation(maintaining adequate amounts of slowed neutrons in the core to undergo the fission chain reaction). There is no nuclear medicine without knowing the exact distance to which incident or injected particles will deposit most of their energy because if we didn't, we'd be killing more healthy cells than cancerous ones. We best prevent nuclear disasters by designing and constructing systems that can withstand intense bombardment and irradiation, all of which are reliant on sound, fundamental understandings of material-particle interactions.

Background Information

Radiation is a form of energy release common to unstable atomic particles, but it can characterize nearly all forms of transient particle movement(ex: x-rays, microwaves, alpha particle flight, cosmic radiation, etc.)

The label ionizing or non-ionizing depends on the strength of the energy deposition. If the particle has enough energy to break molecular bonds, it is ionizing(neutrons, x-rays, alphas, etc.); if it does not, it is non-ionizing(microwaves, 5G, visible light, heat).

The concept of wave-particle duality underpins all of these concepts. Fundamentally, a particle exists as both a wave and a particle: that is to say, it travels in a wave as it transits surrounding space, but it can be condensed into a finite particle. The only exceptions are photons, which have no mass, but can contain vast amounts of energy to be transferred, so they are often called waves.

When a fundamental particle is unstable, as we recall from the prior lessons(its charge distribution or geometry or both are out of balance), it will release energy in an attempt to become more stable. This energy is radiation, as the energy is stored in the kinetic or moving energy of the radiated particle.

The four basic types of radiated particles are alphas(helium nuclei, charged and relatively heavy on the atomic scale), betas(effectively an electron, but free from nuclear orbit, so very small but also charged), gammas(high-energy photons from the nucleus), and neutrons(come straight from the nucleus, relatively small and uncharged. Alphas love to interact with matter(because they are charged and thus lose energy by passing near any atom through electrostatic interactions), as demonstrated by a chip that is unable to get into the Plinko board, as alpha radiation can be stopped by something as thick as paper or your clothes. Beta radiation is similar in its ability to be stopped, as it's charged and thus interacts with everything it passes by to some extent, but because it is so much physically smaller and less charged, it takes a bit more material to stop. Gammas are very powerful and thus will only lose energy through many interactions, so they are best affected by high-density materials like lead. So, radiologists often wear lead shielding to protect from high-energy x-ray photons(they are different because of their energy and origin, gammas always come from the nucleus). Lastly, neutrons are uncharged and unreactive, so they fly through just about anything - your best chance to stop them is with atoms of similar size(like hydrogen or water since it has a lot of hydrogen), as each collision has the chance to reduce the incident energy of the neutron, like billiard balls.

a) elastic scattering

b) inelastic scattering

c) absorption

Learning Objectives

  1. Radiation is a form of energy release for unstable particles
  2. There are many types of radiation - we'll look at a few
  3. The difference between ionizing and non-ionizing radiation
  4. Understand alpha, beta, gamma, and neutron radiation
  5. Radiation interacts with materials according to mutual interactivity with factors like density, charged species, and particle mass being important
  6. We can stop, facilitate, and isolate radiation by using materials

Student Objectives

  1. Students will describe the behavior of certain radioactive particles
  2. Students can verbalize the difference between ionizing and non-ionizing radiation on the molecular scale
  3. Students can intuit how different radioactive species will move through or be stopped by different types of materials according to each of their characteristics
  4. Students can understand why studying the cross-over between radiation and matter is so crucial for all things nuclear 

Materials

  • A Plinko board of any variety, although non-distracting and manageable to have its angle changed are greatly preferred.
  • Chips to slide into the plinko board 
  • Small hooks(smaller than the chips, but big enough to catch the plinko board columns)
  • Tape
  • A laser pointer
  • A white/chalk/dark board for illustrating other collision types

Material Preparation

Sourcing:

Construction:

  • First and foremost is constructing the plinko board, which should be simple with their respective instructions. From there, most of the material prep will be making the standard particles we wish to demonstrate.
  • We'll start with the alpha particle. To the best of your ability in procuring adequately small hooks, tape one or two of them onto the top of one of the chips. If the chip is prevented entirely from entering the board, this is acceptable, but the intent is to show that most materials will stop it very readily.
  • Next is the beta particle. Using just one of the hooks, assuming they're noticeably smaller than the chips, this will qualify as your beta particle, and friction-willing(maybe through board angle manipulation), it should catch relatively early on.
  • Lastly, the neutron will be a regular chip, and the gamma will be the laser pointer. This demonstrates their ability to pass through the board without much change unless the pointer is directly blocked.

Lab Instructions

Printable PDF of Lab Instructions

  1. This lesson will help you learn about radiation, where it comes from and how it interacts with atoms. Before you start, talk with your classmates about what you want to know. Write down any questions you have.
  2. Set up the Plinko board. Place the alpha particle (the larger coin with 2 hooks) at the top.
    1. Draw the and label the alpha particle stopping point on the Plinko board diagram on page 5.
    2. Repeat five times. What is the farthest distance the alpha particle fell?
  3. Remove the alpha particle. Place the beta particle (the smaller coin with 1 hook) at the top.
    1. Draw the and label the beta particle stopping point on the Plinko board diagram on page 5.
    2. Repeat this five times. What is the farthest distance the beta particle fell?
  4. Remove the beta particle. Place the gamma ray (laser pointer) at the top of the field. Try to find 3 positions in which the laser reaches the botom of the board without touching any pegs. Draw the and label the laser path from top to botom on the Plinko board diagram on page 5.
  5. Answer the following questions:
    1. Place the three radiation forms you have already modeled in order from most likely to get to the bottom to least likely to get to the bottom.
    2. What do you think the hooks on the alpha and beta particles represent?
  6. If you haven't already, talk with your classmates about what you learned. Read the background section or listen to your teacher talk about alpha, beta, and gamma radiation. Write down your answers to the following questions:
    1. What is radiation? What makes radiation ionizing or non-ionizing?
    2. Where does radiation come from? How is it released?
    3. What is an alpha particle?
      1. What is its charge? 
      2. How thick would an alpha particle shield be? 
      3. What could it be made of? 
    4. What is a beta particle?
      1. What is its charge? 
      2. How thick would a beta particle shield be? 
      3. What could it be made of? 
    5. What is a gamma ray?
      1. What is its charge? 
      2. How thick would a gamma ray shield be? 
      3. What could it be made of? 
    6. Which kind of radiation source (alpha source, beta source, gamma source) do you think would be most dangerous if you were to eat it? Why?
  7. Neutron Absorption: Now pick up the ping pong ball. Set the ping pong ball on the table or floor and hold an empty cup in place on its side with the opening facing toward the ping pong ball. Try to launch the ping pong ball so that it rolls into the cup. If you miss, or if the ping pong ball bounces out, try again. Do this at least five times.
    1. What did you need to do to get the ping pong ball into the cup?
    2. If you couldn’t aim, what ideas do you have to ensure that a ping pong ball ends up in a cup?
  8. Neutron Elastic Scatering: Clear the table. Place something big and heavy (like a stack of textbooks) on the table. Launch the ping pong ball across the table at the big and heavy object so that it is going fast but not bouncing on the table.
    1. What happens after the ping pong ball hits the big and heavy object? How much speed does it lose?
  9. Neutron Inelastic Scatering: Clear the table. Place something tall and light (like a folded piece of paper) on the table. Launch the ping pong ball across the table at the light object so that it is going fast but not bouncing on the table.
    1. What happens after the ping pong ball hits the light object? How much speed does it lose?
  10. If you haven't already, talk with your classmates about what you learned. Read the background section or listen to your teacher talk about alpha, beta, and gamma radiation. Write down your answers to the following questions:
    1. What is a neutron?
      1. What is its charge?
      2. How thick would a neutron shield be? 
      3. What could it be made of?
    2. Define the following vocabulary words in terms of neutrons interacting with atoms: Elastic scattering, Inelastic scattering, Absorption
  11. Make any corrections you need to make to your previous answers.
  12. Now that you've learned how radiation interacts with mater, try making an obstacle course for your ping pong ball. No mater how fast and which direction the ping pong ball starts, try to make it land in a cup.
  13. If you have any unanswered questioons, ask your teacher to help you to find the answers.

Demonstration Video 

Suggested Evaluations

Some examples: 

Questions - 

  1. What are the similarities between alphas, betas, gammas, and neutrons? What are there differences?
  2. Why do some types of radiation hurt us while others don't?
  3. Why would a radioactive atom emit a radioactive particle? 

Brain teasers - 

  1. I have a cookie emitting alpha particles, a cookie emitting beta particles, a cookie emitting gamma particles, and a cookie emitting neutrons. If I can put one in my pocket, hold one in my outstretched hand, eat one, and throw one away - which cookie will I do what with? (answer if you want to preserve health: alpha in the hand and as far away from vital organs, beta in the pocket as it is blocked by clothing and generally less damaging, eat the gamma as it will get through you regardless, and throw the neutron one as far away as you can)
  2. How would you make a material that can consistently withstand hundreds of millions of degrees and tons of alpha and neutron bombardment like those in a nuclear fusion reactor?(answer: there aren't many proven ideas out there, if they have any, send our department's way!)

Further exploration -

A great way to evaluate their knowledge would be to ask them what they think they can do with their new knowledge! Can they protect themselves and others from radiation? Can they now begin to understand how to make new types of fission power reactors? Where else might they need to understand how materials react to nuclear bombardment(submarines, space stations, space vehicles, martian and lunar habitats, etc.)

Supplemental Materials