## Lessons

Modeling Atoms : Mini Rutherford

Description: With the Mini Rutherford Activity, students deduce shapes and sizes of unseen objects by tracking the movements of objects they can see, in relation to the unseen object. By extension, this device is a useful analogy to Rutherford’s alpha scattering experiments and to atomic particle detection utilizing accelerators. (Since the particles are too small to be seen, it was necessary to deduce their sizes by other means in both of these instances.) This experiment is best used by students working in pairs.

5-12

Disciplinary Core Ideas (DCI, NGSS)
5-PS1-1, MS-PS1-1, MS-PS1-4, HS-PS1-8

Time for Teacher Preparation
40-60 minutes – To make the Rutherford boards
40-60 minutes – To prepare for the classroom

Activity Time:
40-60 minutes (1 Class Period)

Materials

• 5-10 blocks of various shapes 20 cm (8” x 10″ x 3/4″)
• 5-10 30.5 x 30.5 cm (12” x 12” x 1/8”) masonite boards
• Pkg./30-1.9 cm (3/4”) or (5/8”) marbles
• Paper
• Pen, marker, or pencil
• Ruler
• Student Data Collection Sheets

Safety

• Students should use care when handling marbles
• Students should not throw marbles
• Students should avoid stepping on marbles

Science and Engineering Practices (NGSS)

• Define Problems
• Use Models
• Plan and Carry out investigation
• Analyze and interpret Data
• Construct Explanations
• Communicate Information

Cross Cutting Concepts (NGSS)

• Patterns
• Cause and Effect
• Scale, Proportion, and Quantity
• Systems and System Models

Objective
Students will try to determine the shape of an unknown object by using the scientific thought process of creating a hypothesis, then testing it through inference. It is based upon the Rutherford Gold Foil Experiment where scientists discovered that the structure of the atom includes the nucleus in the center surrounded by electrons in empty space. It is a great introduction to the scientific process of deducing, forming scientific theories, and communicating with peers. It is also useful in the mathematics classroom by plotting the angles of incidence and reflection

Background
From 1911 to 1913, British physicists Geiger and Marsden, working in the laboratory of Ernest Rutherford, conducted experiments with beams of positively charged, alpha particles to penetrate gold, silver, and copper atoms. They observed that most of the alpha particles went directly through the foil. However, some particles were deflected and others recoiled back toward the source. Rutherford systematically investigated the results Geiger and Marsden obtained with alpha particles; Rutherford concluded
that most of the mass of an atom is concentrated in a small region in its center, now called the nucleus.

Fundamental Particles Detection
Light has a wavelength of 10-7 m. Light microscopes enable us to view parts of a cell as small as 10-6 m. Electron microscopes enable us to see an image with a wavelength as small as 10-9 m. With the help of scanning electron microscopes, we can see fuzzy images of atoms. To detect a smaller image, such as a fundamental particle, we need to produce particles with greater energy, and thus, a shorter wavelength. The smallest fundamental particle is less than 10-18 m in diameter! Although scientists have not yet been able to actually see fundamental particles, they can infer the presence of these particles by observing events and applying conservation laws of energy, momentum, electric charges, etc. One way to do this is with a particle accelerator. Essentially, a
particle accelerator works by shooting particles at high speed toward a target. When these bullet particles hit a target, a detector records the information about the resulting event.

Necessary Components for Particle Detection
1. Bullet Particles. These can be either electrons, positrons (the anti-particle of an electron), or protons. The particles
are collected as follows:

• Electrons are collected the same way a TV picture tube collects them; a metal plate is heated and electrons are emitted.
• To obtain positrons, a beam of electrons collides with a target, resulting in a photon. From the photon, electrons and positrons may be formed and are separated by their charges in a magnetic field.
• Protons are obtained by ionizing hydrogen gas. Ionization requires collisions at energy great enough to strip electrons from hydrogen, leaving protons.

2. An accelerator increases the speed of bullet particles to greater energy levels. The particles are accelerated with an electric field by riding on traveling electromagnetic (EM) waves. The EM waves are created in devices called klystrons, which are large microwave generators.

3. The steering device directs the bullet particles to their target. Magnets are used to steer the particles around a circular accelerator and to focus the particles so they will hit the target. The same magnets make positive and negative particles traveling in the same direction bend in opposite directions.

4. A target can be any solid, liquid, or gas, or another beam of particles.

5. A detector interprets the paths of the resulting particles once the bullet particles have collided with their target. Modern detectors have several layers, to detect the many particles produced in a collision event. A detector can be up to three stories tall. An advanced computer system is used to reconstruct the many paths of the particles detected in the layers associated with a collision. By viewing particle paths through each layer of the detector, scientists can determine the results of an event. Charged particles leave a track in the inner (tracking) layer of the detector. The positive or negative charge of the resulting particle can be determined by the direction it curves in a magnetic field. A particle with great momentum (speed x mass) will have a less curved path compared to one with less momentum. After a collision, electrons and protons will leave showers of particles in certain detector layers. Photons and neutrons travel a little further through the layers before their collisions create a shower of particles. Muons (one type of a fundamental particle), however, can be detected in the outer layer of a detector. They travel right through the inner layers with little or no interaction.

Teacher Lesson Plan:

To make Rutherford boards:
Velcro, glue, or nail block shapes underneath the masonite boards. Note: Some hardware stores will cut shapes for you free of charge.

Potential Block Shapes:

Triangle, Square,Rhombus, Isosceles Trapezoid, Hexagon

Place the Rutherford boards on a large table or on the floor, obstructing the shapes from your students’ view. Place a piece
of paper on top of each Rutherford board. Beware: your students may be tempted to peek. The student activity, described in the accompanying worksheet, should take about five minutes to complete. The activity can be repeated several times during a class period, using different shapes and/or marbles each time. Some shapes are more difficult to detect than others.

NGSS Inquiry
Explain Rutherford’s experiment. Tell students that they will design their own experiment, using rolling marbles as alpha particles to discover the shape of a hidden geometric shape, which simulates the nucleus. You might suggest that the students experiment with rolling a marble at different angles at a straight surface and seeing the different ways the marble deflects.

Student Procedure

Using the Rutherford boards:
Middle School
Part 1

Working in small groups, roll one of the marbles at the hidden object underneath the Rutherford board while one student draws the marble’s path in, and the deflected path out, on the piece of paper placed on the Rutherford board. Map the paths of the marbles that do not deflect or deflect slightly, as well. Make sure you roll the marble fast enough so that it makes a clean shot in and out.

Repeat Step 1 as many times as needed to define the outline of the hidden shape, using the same size marble each time. Make sure you roll the marble from many points on each side of the board.

Once you are satisfied that you know the shape of the object under the Rutherford board, draw the shape onto the piece of paper. (You might want to trace the shape from the paper with the outline formed by the collision paths).

Before looking at the actual block shape, show your instructor the shape you have drawn. Then look at the block underneath the Rutherford board, and discuss any parts of the shape you have drawn that are ill-determined.

Part 2: Have the instructor place a different block back under the Rutherford board (or switch boards if they are permanently attached). Place a clean sheet of paper on the top of the Rutherford board and repeat the procedure (Steps 1-4).

High School
Repeat steps 1-5 as per the Middle School procedure. Place the Rutherford board on a large piece of butcher paper, and then have the students record the shapes on the large paper. Do not put the paper on the board so that students must infer the shape from the surrounding angles of incidence/reflection.

5-12

Disciplinary Core Ideas (DCI, NGSS):
5-PS1-1, MS-PS1-1, MS-PS1-4, HS-PS1-8, HS-PS4-2, HS-PS4-5

Time for Teacher Preparation:
30-60 minutes – To gather materials and set-up

Activity Time:
30-60 Minutes (1 Class Period)

Materials:

• Pen, Marker, or Pencil
• Plastic cloud chamber kit, 3 1/4″ diameter: (Petrie dish with band of black construction paper around the sides and bottom painted black or lined with black construction paper)
• 3 each- Cloud Chambers
• 3Radioactive Sources: radioisotope disks, Coleman Lantern Mantle pieces (thoriated), Uranium ore, or orange Fiestaware piece.
• Dry ice
• Rubbing alcohol – 95% ethyl
• Flashlights
• Styrofoam plates
• Gloves
• Magnet (Optional)
• Student Data Collection Sheets
• Safety:

• Students should use care when handling rubbing alcohol
• Students should not touch dry ice with their bare hands
• Students should not touch radioactive materials
• Science and Engineering Practices (NGSS):

• Ask questions and define problems
• Use models
• Plan and carry out investigation
• Analyze and interpret data
• Using mathematics, information and computers
• Argue from Evidence
• Obtain, evaluate and communicate information
• Cross Cutting Concepts (NGSS):

• Patterns
• Cause and Effect
• Scale, Proportion, and Quantity
• Systems and System Models
• Energy and Matter: Flows, Cycles, and Conservation
• Structure and Function
• Stability and Change of Systems
• Objectives:

• To visually demonstrate the concepts of ionizing radiation
• Background:
Radioactive elements continually undergo a process of radioactive decay during which their nuclei emit high-speed particles and rays. These are much too small to be seen under a microscope. The Cloud Chamber was invented by an English physicist, C. T. R. Wilson, in 1911. It is an instrument designed for the study of the trails of radioactive emissions. The investigation is accomplished in the following way. First, the air must be saturated with water or alcohol vapor. When the high-energy particles flow through the air, electrons are knocked loose from some of the atoms and form ions. Ions act as excellent centers for condensation. This condensation, however, must be stimulated by cooling the air. The water vapor or alcohol condenses on the ions, leaving a vapor tail which clearly reveals the path of the ray.

Cloud chambers detect the paths taken by ionizing radiation. Much like the vapor trail of a jet airplane, the tracks in a cloud chamber mark where ionizing radiation has been traveling. The radiation itself is not visible. Radioactive materials are one source of ionizing radiation. Three types of rays are given off by a radioactive element. They are alpha particles (positive nuclei of helium atoms traveling at high speed), beta particles (high-speed, negative electrons), and gamma rays (electromagnetic waves similar to X-rays). Most of the tracks will be about one-half inch long and quite sharp. These are made by alpha radiation. Occasionally you will see some twisting, circling tracks that are so faint that they are difficult to see. These are caused by beta radiation.

• Making Atoms Visible : Cloud Chamber
Description:Allow students to visualize and understand ionizing radiation.
5-12
Disciplinary Core Ideas (DCI, NGSS):
5-PS1-1, MS-PS1-1, MS-PS1-4, HS-PS1-8, HS-PS4-2, HS-PS4-5
Time for Teacher Preparation:
30-60 minutes – To gather materials and set-up
Activity Time:
30-60 Minutes (1 Class Period)
Materials:

• Pen, Marker, or Pencil
• Plastic cloud chamber kit, 3 1/4″ diameter: (Petrie dish with band of black construction paper around the sides and bottom painted black or lined with black construction paper)
• 3 each- Cloud Chambers
• 3Radioactive Sources: radioisotope disks, Coleman Lantern Mantle pieces (thoriated), Uranium ore, or orange Fiestaware piece.
• Dry ice
• Rubbing alcohol – 95% ethyl
• Flashlights
• Styrofoam plates
• Gloves
• Magnet (Optional)
• Student Data Collection Sheets
• Safety:

• Students should use care when handling rubbing alcohol
• Students should not touch dry ice with their bare hands
• Students should not touch radioactive materials
• Science and Engineering Practices (NGSS):

• Ask questions and define problems
• Use models
• Plan and carry out investigation
• Analyze and interpret data
• Using mathematics, information and computers
• Argue from Evidence
• Obtain, evaluate and communicate information
• Cross Cutting Concepts (NGSS):

• Patterns
• Cause and Effect
• Scale, Proportion, and Quantity
• Systems and System Models
• Energy and Matter: Flows, Cycles, and Conservation
• Structure and Function
• Stability and Change of Systems
• Objectives:

• To visually demonstrate the concepts of ionizing radiation
• Background:
Radioactive elements continually undergo a process of radioactive decay during which their nuclei emit high-speed particles and rays. These are much too small to be seen under a microscope. The Cloud Chamber was invented by an English physicist, C. T. R. Wilson, in 1911. It is an instrument designed for the study of the trails of radioactive emissions. The investigation is accomplished in the following way. First, the air must be saturated with water or alcohol vapor. When the high-energy particles flow through the air, electrons are knocked loose from some of the atoms and form ions. Ions act as excellent centers for condensation. This condensation, however, must be stimulated by cooling the air. The water vapor or alcohol condenses on the ions, leaving a vapor tail which clearly reveals the path of the ray.

Cloud chambers detect the paths taken by ionizing radiation. Much like the vapor trail of a jet airplane, the tracks in a cloud chamber mark where ionizing radiation has been traveling. The radiation itself is not visible. Radioactive materials are one source of ionizing radiation. Three types of rays are given off by a radioactive element. They are alpha particles (positive nuclei of helium atoms traveling at high speed), beta particles (high-speed, negative electrons), and gamma rays (electromagnetic waves similar to X-rays). Most of the tracks will be about one-half inch long and quite sharp. These are made by alpha radiation. Occasionally you will see some twisting, circling tracks that are so faint that they are difficult to see. These are caused by beta radiation.

Teacher Lesson Plan

Cloud Chambers:

1. Prepare three cloud chambers in accordance with the Cloud Chambers instructions:
1. Open the lid of the cloud chamber and saturate the felt strip inside with alcohol.
2. Put the radiation source inside the cloud chamber and replace the lid tightly.
3. Place the palm of your hand firmly on top of the cloud chamber for about 5 minutes to evaporate the alcohol.
4. Place the cloud chamber on a piece of FLAT dry ice that is at least a little larger than the chamber.
5. Turn off the lights in the room and shine the flashlight through the cloud chamber to make the ion trails easier to see. Trails should begin a few minutes after placement on the dry ice.
• Note: You can use radioisotope disks in each chamber in lieu of Coleman lantern mantle pieces. By providing Alpha, Beta, and Gamma sources , students will find that only the Alpha and Beta sources will produce tracks. This is because Gamma radiation is electromagnetic radiation not particles, and it’s the particles moving through the alcohol cloud that makes the tracks.

NGSS Guided Inquiry
Give the students radioactive samples and ask them to reduce/block the radiation to normal background levels with things they find in the classroom.

Explain about the different types of radiation and radioactivity. Tell students to design their own experiment, to detect different types of radiation, and then share their results with the class.

Student Procedure
Observe the vapor trails produced within the cloud chamber and answer the questions provided by your teacher.

High School

1. Prepare three cloud chambers in accordance with the Cloud Chambers instructions:
1. Open the lid of the cloud chamber and saturate the felt strip inside with alcohol.
2. Put the radiation source inside the cloud chamber and replace the lid tightly.
3. Place the palm of your hand firmly on top of the cloud chamber for about 5 minutes to evaporate the alcohol.
4. Place the cloud chamber on a piece of FLAT dry ice that is at least a little larger than the chamber.
5. Turn off the lights in the room and shine the flashlight through the cloud chamber to make the ion trails easier to see. Trails should begin a few minutes after placement on the dry ice.
• Note: You can use radioisotope disks in each chamber in lieu of Coleman lantern mantle pieces. By providing Alpha, Beta, and Gamma sources , students will find that only the Alpha and Beta sources will produce tracks. This is because Gamma radiation is electromagnetic radiation not particles, and it’s the particles moving through the alcohol cloud that make the tracks.

Post Discussion/Effective Teaching Strategies

Questions:

1. What is creating the vapor trails?
2. How is it creating them?
3. How far did each type of radiation travel away from the source? List your answers from furthest traveling to shortest traveling distance.
4. Are any tracks visible when no source of radiation is near the chamber? What kinds of radiation can be found in our environment?
• Assessment Ideas

• Have students draw a diagram of what is happening at the atomic level when a vapor trail is created.
• Hold the north end of a strong magnet next to the chamber. How does magnetism affect the radiation tracks?
• If you have access to a Geiger counter, count the number of tracks that you can see in ten seconds and then compare that number to the number of clicks produced by the Geiger counter in the same amount of time. Which is more accurate?
• If you shield the source, which types of radiation are still visible?
• Materials to experiment with shielding include: aluminum foil, plastic, cloth. Which types of radiation are shielding by each type of material?
• Differentiated Learning/ Enrichment

Enrichment Question

1. How do you think shielding is useful to the nuclear industry? Give three examples.
5-12

Disciplinary Core Ideas (DCI, NGSS)
5-PS1-1, MS-PS1-1, MS-PS1-4, HS-PS1-8, HS-PS4-2, HS-PS4-5

Time for Teacher Preparation
30-60 minutes – To gather materials and set-up

Activity Time:
30-60 minutes (1 Class Period)

Materials

• Pen, Marker, or Pencil
• Balloon
• Foam plate
• Foam cup
• Drinking straw
• Glue
• Aluminum pie pan
• Aluminum foil
• Wool fabric
• Comb
• Plastic ruler
• Student Data Collection Sheet
• Safety

• Students should use care when handling aluminum foil
• Students should use care when handling glue
• Science and Engineering Practices (NGSS)

• Ask questions and define problems
• Use models
• Plan and carry out investigation
• Analyze and interpret data
• Using mathematics, information and computers
• Argue from evidence
• Obtain, evaluate and communicate information
• Cross Cutting Concepts (NGSS)

• Patterns
• Cause and Effect
• Scale, Proportion, and Quantity
• Systems and System Models
• Energy and Matter: Flows, Cycles, and Conservation
• Structure and Function
• Stability and Change of Systems
• Objective
Make a simple instrument to detect static electricity and radiation.

Background
An electroscope is a very simple instrument that is used to detect the presence and magnitude of electric charge on a body such as static electricity. The type of electroscope detailed in this experiment is called a pith-ball electroscope. It was invented in 1754 by John Canton. The ball was originally made out of a spongy plant material called pith. Any lightweight nonconductive material, such as aluminum foil, can work as a pith ball. The pith ball is charged by touching it to a charged object. Since the ball is nonconductive and the electrons are not free to leave the atoms and move around the ball, when the charged ball is near a positively charged body, or source, the negatively charged electrons are attracted to it and the ball moves towards the source. Conversely, a negatively charged source will repel the electrons, and therefore the ball. Electroscopes can also be used to detect ionizing radiation. In this case, the radiation ionizes the air to be more positively or negatively charged depending on the type of radiation, and the ball will either be attracted or repelled by the source. This is how electroscopes can be used for detecting x-rays, cosmic rays, and radiation from radioactive material.

Teacher Lesson Plan:

1. Lecture students on background
2. Provide them with materials and procedure
3. Provide balloons and radiation sources to test the electroscopes with
• NGSS Guided Inquiry

1. After students construct electroscopes, have them experiment with charged and neutral sources to experiment.
2. Have students analyze radioactive sources with electroscopes.
• Student Procedure

1. Make two holes near the bottom of a foam cup on opposite sides.
2. Push a plastic straw through the holes in the cup.
3. Turn the cup upside down and glue it onto the bottom of an aluminum pie pan. Make sure that the cup is right at the edge so that the straw sticks out over it. If you don’t want to wait for the glue to dry, tape the cup to the pan.
4. Cut a piece of thread about 8 inches long and tie a few knots in one end of the thread.
5. Cut a one-inch square of aluminum foil. Use it to make a ball around the knots in the thread. The ball should be about the size of a marble. It should be just tight enough so it doesn’t fall off the thread.
6. Tape the end of the thread to the straw so that the ball of foil hangs straight down from the straw, right next to the edge of the pan.
7. Tape the straw to the cup so it doesn’t move around when you use the electroscope.
8. To test the electroscope, create some static electricity. An easy way to create static is by rubbing a balloon on a foam plate. When you do this, you “charge” the plate, which means you cause a buildup of electrons on one side. Even though the plate is charged, the electrons don’t move because foam doesn’t conduct electrons.
9. Once you’ve created some static electricity, place the electroscope on top of the foam plate. Be sure to hold the electroscope by the foam cup and not the aluminum pan, otherwise it won’t work. Electrons move easily through metal, so when you put the pie pan onto the foam plate, the electrons travel into the pan and the foil ball. When the electroscope detects static electricity, the foil ball pushes out from the pan.
10. Try charging different objects, like a comb or ruler, with static electricity. Test them on the electroscope and record your results on the data sheet.
• Data Collection
Students should record which objects hold a charge and which do not

Post Discussion/Effective Teaching Strategies

Questions

1. Which objects hold an electric charge? Which don’t?
2. Why is the ball attracted or repelled by different objects?
3. How is using an electroscope similar to testing the charge of a balloon with your hair?
4. How is the electroscope able to detect radioactivity?
• Assessment Ideas
Have students use electroscopes to discern between radioactive sources and nonradioactive sources.

Differentiated Learning/Enrichment
Have students compare radioactivity of different sources.

Enrichment Question

1. Why did John Canton invent the first electroscope and what did he use it for?

Disciplinary Core Ideas (DCI)
3-5ETS1-2, MS-ESS1-4, HS-ESS1-6

Time for Teacher Preparation
40-60 minutes – To gather materials

Activity Time:
40-60 minutes (1 Class Period)

Materials:

• Bag of: M&M’s ®, pennies or, puzzle pieces
• Paper – 8.5˝ x 11˝
• Graph Paper
• Zip-Lock Bags
• Pen, Marker, or Pencil
• Student Data Collection Sheets
• Safety

• Students should not eat M&M’s®, Pennies, or Puzzle Pieces
• Science and Engineering Practices

• Ask questions and define problems
• Use models
• Analyze and interpret data
• Use mathematics and computational thinking
• Construct explanations
• Argue from evidence
• Obtain, evaluate and communicate information
• Cross Cutting Concepts

• Patterns
• Cause and Effect
• Scale, Proportion, and Quantity
• Systems and System Models
• Energy and Matter: Flows, Cycles, and Conservation
• Objectives
Students try to model radioactive decay by using the scientific thought process of creating a hypothesis, then testing it through inference. It is a great introduction to the scientific process of deducing, forming scientific theories, and communicating with
peers. It is also useful in the mathematics classroom by the process of graphing the data.

Students should begin to see the pattern that each time they “take a half-life,” about half of the surrogate radioactive material becomes stable. Students then should be able to see the connection between the M&M’s and Puzzle Pieces and radioactive elements in archaeological samples. Seeing this connection will help students to understand how scientists can determine the age of a sample by looking at the amount of radioactive material in the sample.

• To define the terms half-life and radioactive decay
• To model the rate of radioactive decay
• To create line graphs from collected data
• To compare data
• To understand how radioactive decay is used to date archaeological artifacts
• Background
Half-Life
If two nuclei have different masses, but the same atomic number, those nuclei are considered to be isotopes. Isotopes have the same chemical properties, but different physical properties. An example of isotopes is carbon, which has three main isotopes, carbon-12, carbon-13 and carbon-14. All three isotopes have the same atomic number of 6, but have different numbers of neutrons. Carbon-14 has 2 more neutrons than carbon-12 and 1 more than carbon-13, both of which are stable. Carbon-14 is radioactive and undergoes radioactive decay.

Radioactive materials contain some nuclei that are stable and other nuclei that are unstable. Not all of the atoms of a radioactive isotope (radioisotope) decay at the same time. Rather, the atoms decay at a rate that is characteristic to the isotope. The rate of decay is a fixed rate called a half-life.

The half-life of a radioactive isotope refers to the amount of time required for half of a quantity of a radioactive isotope to decay. Carbon-14 has a half-life of 5730 years, which means that if you take one gram of carbon-14, half of it will decay in 5730 years. Different isotopes have different half-lives.

The ratio of the amounts of carbon-12 to carbon-14 in a human is the same as in every other living thing. After death, the carbon-14 decays and is not replaced. The carbon-14 decays, with its half-life of 5,730 years, while the amount of carbon-12 remains constant in the sample. By looking at the ratio of carbon-12 to carbon-14 in the sample and comparing it to the ratio in a living organism, it is possible to determine the age of a formerly living thing. Radiocarbon dates do not tell archaeologists exactly how old an artifact is, but they can date the sample within a few hundred years of the age.

Teacher Lesson Plan:

M&M’s® (or Pennies or Puzzle Pieces)

1. Give each student 10 M&M’s® candies of any color and a zip lock bag. All of M&M’s® candies are considered radioactive.
2. Have the student put the M&M’s® into the zip lock bag and shake the bag. Have the students spill out the candies onto a flat surface.
3. Instruct the students to pick up ONLY the candies with the “m” showing – these are still radioactive. The students should count the “m” candies as they return them to the bag.
4. Have the students record the number of candies they returned to the bag under the next Trial.
5. The students should move the candies that are blank on the top to the side – these have now decayed to a stable state.
6. The students should repeat steps 2 through 5 until all the candies have decayed or until they have completed Trial 7.
7. Set up a place on the board where all students or groups can record their data.
8. The students will record the results for 9 other groups in their data tables and total all the Trials for the 100 candies
• NGSS Guided Inquiry
Explain about radiation and half-lives of isotopes. Tell students to design their own experiment, using paper, M&M’s®, Pennies, other 2 sided material or Licorice as a radioactive material undergoing decay to discover the nature of the half-life of that material.

You might suggest that the students experiment with their graphing results to see if trends begin to form.

Student Procedure

M&M’s® (or pennies or puzzle pieces)

1. Put 10 M&M’s® candies of any color into a zip lock bag. Each group is starting with 10 M&M’s® candies, which is recorded as Trial 0 in the data table. All of the M&M’s® candies are considered to be radioactive at the beginning.
2. Shake the bag and spill out the candies onto a flat surface.
3. Pick up ONLY the candies with the “m” showing – these are still radioactive. Count the “m” candies as you return them to the bag.
4. Record the number of candies you returned to the bag under the next Trial.
5. Move the candies that are blank on the top to the side – these have now decayed to a stable state.
6. Repeat steps 2 through 5 until all the candies have decayed or until you have completed Trial 7.
7. Record the results for 9 other groups and total all the Trials for the 100 candies.
• Data Collection
Student Data Collection Sheets

Post Discussion/Effective Teaching Strategies
Questions provided on theStudent Data Collection Sheets

Questions

M&M’s® (or Pennies or Puzzle Pieces)

1. Define the term half-life.
2. What does it mean when we say an atom has “decayed”?
3. Do the number of atoms you start with affect the outcome? Explain.
4. Did each group get the same results?
5. Did any group still have candies remaining after Trial 7?
6. Why do the totals for the 10 groups better show what happens during half-life rather than any other group’s results?
7. What happens to the total number of candies with each trial (half-life)?
8. Plot the total results on a graph with number of candies on the vertical axis and trial number on the horizontal axis. Is the result a straight or a curved line? What does the line indicate about the nature of decay of radionuclides?
9. How do scientists use radioactive decay to date fossils and artifacts?
• Assessment Ideas

• Question the student about how this experiment is similar to Carbon Dating.
• Differentiated Learning/Enrichment
• Have the students calculate the age of objects when given the half-life, original amount, and current amount of that material.
• Enrichment Question
• The population of the earth is doubling every 40 years. If the population of the earth is now 7 billion people, how many people will be here when you are 95 years old?
5-12

Disciplinary Core Ideas (DCI)
3-5ETS1-2, MS-ESS1-4, HS-ESS1-6

Time for Teacher Preparation
40-60 minutes – To gather materials

Activity Time:
40-60 minutes (1 Class Period)

Materials

• Bag of licorice
• Paper – 8.5˝ x 11˝
• Graph Paper
• Pen, Marker, or Pencil
• Rulers
• Student Data Collection Sheets
• Safety

• Students should not eat licorice
• Science and Engineering Practices

• Ask questions and define problems
• Use models
• Analyze and interpret data
• Use mathematics and computational thinking
• Construct explanations
• Argue from evidence
• Obtain, evaluate and communicate information
• Cross Cutting Concepts

• Patterns
• Cause and Effect
• Scale, Proportion, and Quantity
• Systems and System Models
• Energy and Matter: Flows, Cycles, and Conservation
• Objectives
Students model the exponential nature of radioactive decay by using the scientific thought process of creating a hypothesis, then testing it through inference, and applying computational thinking. It is a great introduction to the scientific process of deducing, forming scientific theories, and communicating with peers. It is also useful in the mathematics classroom by the process of visualizing data.

Students should begin to see the the exponential nature of radioactive decay regardless of the length of an element's half-life.

• To define the terms half-life and radioactive decay
• To model the rate of radioactive decay
• To create line graphs from collected data
• To compare data
• To understand how radioactive decay is used to date archaeological artifacts
• Background
Half-Life
If two nuclei have different masses, but the same atomic number, those nuclei are considered to be isotopes. Isotopes have the same chemical properties, but different physical properties. An example of isotopes is carbon, which has three main isotopes, carbon-12, carbon-13 and carbon-14. All three isotopes have the same atomic number of 6, but have different numbers of neutrons. Carbon-14 has 2 more neutrons than carbon-12 and 1 more than carbon-13, both of which are stable. Carbon-14 is radioactive and undergoes radioactive decay.

Radioactive materials contain some nuclei that are stable and other nuclei that are unstable. Not all of the atoms of a radioactive isotope (radioisotope) decay at the same time. Rather, the atoms decay at a rate that is characteristic to the isotope. The rate of decay is a fixed rate called a half-life.

The half-life of a radioactive isotope refers to the amount of time required for half of a quantity of a radioactive isotope to decay. Carbon-14 has a half-life of 5730 years, which means that if you take one gram of carbon-14, half of it will decay in 5730 years. Different isotopes have different half-lives.

The ratio of the amounts of carbon-12 to carbon-14 in a human is the same as in every other living thing. After death, the carbon-14 decays and is not replaced. The carbon-14 decays, with its half-life of 5,730 years, while the amount of carbon-12 remains constant in the sample. By looking at the ratio of carbon-12 to carbon-14 in the sample and comparing it to the ratio in a living organism, it is possible to determine the age of a formerly living thing. Radiocarbon dates do not tell archaeologists exactly how old an artifact is, but they can date the sample within a few hundred years of the age.

Teacher Lesson Plan:

Licorice

1. Instruct the students to label the horizontal axis of the graph paper “Time (seconds)” and the vertical axis “Radioactive Licorice (%)”. Show them how to calibrate the horizontal axes so that one block equals 5 seconds and two blocks equal 10 seconds. Instruct them to mark the horizontal axis at 10-second intervals.
2. Give each student one piece of licorice to place onto the graph paper. Tell them to stretch the full length of the licorice vertically over the time “zero” mark and to make a mark on the paper at the top of the licorice. This mark represents 100% of the radioactive material at time zero.
3. Call out “GO” or “HALF-LIFE” at 10-second intervals for up to 90 seconds. When you say “GO” or “HALF-LIFE,” the students will have ten seconds to remove one-half of their licorice and set it aside. They place the remaining piece of licorice on the 10 seconds line and mark its current height. At 20 seconds, they should again remove half of the licorice and set it aside, then mark the height of the remaining portion on their graphs at the 20 second line. Repeat this process until 90 seconds have gone by.
4. Now, the students should connect all the height marks with a “best fit” line, completing a graph of the “Half-Life of Licorice.”
NOTE: The original strip of licorice represents radioactive material; the portion which is “set aside” during the activity represents the material that has “decayed” and is no longer radioactive.
NGSS Guided Inquiry
Explain about radiation and half-lives of isotopes. Tell students to design their own experiment, using paper, M&M’s®, Pennies, other 2 sided material or licorice as a radioactive material undergoing decay to discover the nature of the half-life of that material.
You might suggest that the students experiment with their graphing results to see if trends begin to form.
• Student Procedure

Licorice

1. Label the horizontal axis of the graph paper “Time (seconds)” and the vertical axis “Radioactive Licorice (%)”. Calibrate the horizontal axes so that one block equals 5 seconds and two blocks equal 10 seconds. Mark the axis at 10-second intervals.
2. Start with one piece of licorice to place onto the graph paper. Stretch the full length of the licorice vertically over the time “zero” mark, which is the same as the vertical axis. Make a mark on the graph paper at the top of the licorice. This mark represents 100% of the radioactive material at time zero.
3. Your teacher will call out “GO” or “HALF-LIFE” at 10-second intervals for up to 90 seconds. When your teacher says “GO” or “HALF-LIFE” you will have ten seconds to remove one-half of your licorice and set it aside. Place the remaining piece of licorice on the 10 seconds line and mark its current height. At 20 seconds, you should again remove half of the licorice and set it aside, then mark the height of the remaining portion on your graph at the 20-second line. Repeat this process until 90 seconds have gone by.
4. Now, connect all the height marks with a “best fit” line, completing a graph of the “Half-Life of Licorice.”
NOTE: The original strip of licorice represents radioactive material. The portion which is “set aside” during the activity represents the material that has “decayed” and is no longer radioactive.
Data Collection
Student Data Collection Sheets
Post Discussion/Effective Teaching Strategies
Questions provided on the Student Data Collection Sheets

## Activities

Even the youngest students find nuclear science fascinating! Foster their interest with these coloring pages.

coloring pages.pdf

Materials:

• Table salt (NaCl) that has been irradiated with at least 180,000 RADs of gamma radiation. (Keep in DARK container or protected from light until ready to perform demonstration.)
• A frying pan or other flat-surfaced item on a hot plate
• A dark room (the darker the better).

Background:

When the salt is irradiated, gamma rays pass through the crystals and the energy deposited there excites electrons and causes them to move to a higher energy state. Due to the nature of salt crystals, the electrons become trapped in that higher energy state. After being irradiated, the salt appears as a cinnamon color rather than white; that is because the repositioned electrons affect the way that light is reflected by the crystal.

Procedure:

Preheat a dry frying on a hot plate set at its highest temperature. OR, put the pan above a lab burner. Continue heating the pan. In acompletely darkened room,sprinkle or pour some of the irradiated salt into the hot frying pan. Carefully observe what happens! Then, observe the salt which remains in the bottom of the frying pan after your experiment.

Explanation/Analysis:

You should see tiny flashes of light as the irradiated salt comes into contact with the frying pan surface. (You must be fairly close; the flashes are not bright.)

Heating the salt causes increased motion (vibration) in the salt crystal. This allows the electrons to return to their normal (somewhat lower) energy state. As the electrons move to lower energy states, the previously stored energy is released in the form photons of visible light. After the electrons return to normal energy states, the salt crystals reflect light as normally and appear white.

Optional:

Concepts you can teach:

• Irradiation may change a material physically, but it does not make it radioactive.
• Applying energy (gamma radiation) to a substance may move electrons to different energy states.
• People who work in environments with radiation often wear a Thermoluminescent Dosimeter. Such dosimeters contain substances (often LiF crystals) that are sensitive to ionizing radiation. Filters are used in the badge to discriminate between alpha, beta, and gamma radiation. Periodically, the dosimeter is tested to determine how much radiation exposure the worker has received. (The flashes of light observed in our activity are a very crude representation of such a test.)

If the irradiated salt is exposed to sunlight or artificial light, it will gradually lose its coloration and turn back to white. The light exposure causes some changes in the lattice, the electrons gradually return to their original energy states and the salt returns to its original white color. Be sure to keep it protected in a dark or opaque container.

Penn State University, Breazeale Reactor, phone 814-865-6351

Other scientific supply companies may offer irradiated salt; check with your normal supply sources.

Frequently Asked Question: Is the irradiated salt safe to eat? The dose of radiation given to the salt was higher than FDA allows for this type of food; the laboratory where it was irradiated does not meet USDA/FDA standards for food handling. However, the salt is not radioactive – either before or after heating in the demo. The salt never releases ionizing radiation, only visible light.

Description:

With the Critical Mass Demonstration, students gain a better understanding of critical mass and how a chain reaction can become uncontrolled. Students are able to visualize what is meant by subcritical, critical, and supercritical mass. By extension, this experiment is a useful analogy to nuclear fission. This experiment is best used by students working in groups.

5-12

DCI:

5-ESS3-1, 3-5 ETS1-1, 3-5ETS1-2, MS-PS1-4, MS-PS3-4, MS-ESS3-1, MS-ESS3-3, MS-ESS3-4, MS-ESS3-5, MS-ETS1-1, MS-ETS1-2, MS-ETS1-3, MS-ETS1-4, HS-PS1-1, HS-PS1-8, HS-PS3-3, HS-PS3-4, HS-ESS2-4, HS-ESS2-6, HS-ESS3-2, HS-ESS3-3, HS-ESS3-4, HS-ESS3-6

Time for Teacher Preparation: 30-60 minutes – To gather materials and set-up

Activity Time: 30-60 Minutes (1 Class Period)

Materials:

• Pen, Marker, or Pencil
• Student Data Collection Sheets
• 1 Stopwatch per group of students
• Light weight balls, ping pong balls, marshmallows, etc. (# of students * 2)
• Alternatively, the activity can be demonstrated with mousetraps

Safety:

It is important that students throw their balls straight up into the air and not aim directly for their fellow students.

Science and Engineering Practices:

• Ask questions and define problems
• Use models
• Plan and carry out investigation
• Analyze and interpret data
• Construct explanations
• Argue from Evidence
• Obtain, evaluate and communicate information

Cross Cutting Concepts:

• Patterns
• Cause and Effect
• Scale, Proportion, and Quantity
• Systems and System Models
• Energy and Matter: Flows, Cycles, and Conservation
• Stability and Change of Systems

Objectives:

Learn the concept of critical mass and how a chain reaction can become uncontrolled

Define Critical Mass

Background:

The splitting of a massive nucleus into two fragments, each with a smaller mass than the original, is known as nuclear fission. A typical example of nuclear fission is the splitting of a uranium-235 nucleus. This is a reaction that is used in nuclear reactors to generate heat by which steam is produced and used to turn turbines that generate electricity. The fission of uranium-235 begins when the uranium-235 nucleus captures a slow moving neutron and forms an unstable “compound nucleus”. The compound nucleus quickly disintegrates into two smaller nuclei, such as barium-141 and krypton-92, two or three neutrons (2.5 average), and a tremendous amount of energy (~200MeV per fission).

Because the uranium-235 fission reaction produces 2 or 3 neutrons, it is possible for those neutrons to initiate a series of subsequent fission reactions. Each neutron released can initiate another fission event, resulting in the emission of more neutrons, followed by more fission events, and so on. This is a chain reaction – one event triggers several others, which in turn trigger more events, and so on. In a nuclear power plant the chain reaction is controlled by restricting the number of neutrons available to collide with the uranium. This is accomplished by absorbing some of the released neutrons with various materials. In an uncontrolled chain reaction (such as an atom bomb explosion) there is nothing to control the number of neutrons being released, so the rate of the chain reaction increases dramatically.

There are two parameters needed to create a critical mass, the number of atoms and the spacing of the atoms. In this demonstration each student represents a uranium atom inside of a nuclear reactor. Each uranium atom releases two neutrons when it fissions. For this demonstration, the larger the number of student participants, the better the results.

Teacher Lesson Plan:

Arrange the students in a square array approximately 3 feet apart and give each student two balls. Take a ball for yourself and to begin the activity, throw your ball up into the air or at a student. Any student that is hit with this ball throws their two balls straight up into the air. Any student hit by these balls then throws their balls into the air. The reaction continues until there are no more balls in the air. The first time, the reaction will probably die out quickly, this is called subcritical.

Repeat the process, but place the students only 1 foot apart this time and carry out the activity. This time, the reaction should be self-sustaining. This is called critical and a critical reactor is running at a steady state.

Repeat the process a final time, but place the students in a tight array without any space between them. This time, there should be lots of balls in the air at one time. This represents a supercritical mass, or when a reactor is increasing its power level.

Variation

Replace the students with mousetraps and place them in an array. Set the traps and place a ping pong ball on each one. Be careful not to get your fingers caught in the traps, as sometimes they will go off when you set the ball on them. Then drop a ball on the array and watch the ball bounce around, setting off more traps. View demo here.

Optional Exercise:

In a nuclear reactor, the reaction is controlled by control rods. These are special rods that go in between groups of fuel rods (which have fuel pellets stacked in them) inside the reactor. The control rods help to start (when they are removed), stop (when they are fully inserted), increase or decrease (when they are partially removed or inserted) the fission process.

Explain that students will now demonstrate a controlled reaction. Use the same students to be atoms or select a new group. Choose one (or more) additional student(s) to be a control rod. Their job is to stand inside the “atoms” group and try to grab or bat away the falling balloons before they hit a student. Since there are now control rods in your demonstration, the first balloon may have to be thrown several times before it hits a student. After all the balloons are thrown, discuss what happened. Fewer students should have been hit because the control rods intercepted some of the “neutrons.” Students can see how the rods slow down and can even stop a chain reaction. When that happens, the fission process will stop very quickly.

NGSS Guided Inquiry:

Split students into small groups and give each student two balls. Have students design an experiment to model nuclear fission and critical mass with the balls acting as neutrons in a reactor.

Student Procedure

• Hold a ball in each hand.
• If you are hit by a ball, throw your balls straight up into the air without aiming directly at your fellow students.
• Time and record how long each reaction lasts, which is when the last ball is thrown in the air.

Post Discussion

Questions:

What happened during each trial and why?

Assessment Ideas

• Have students discuss the differences between subcritical, critical, and supercritical masses.
• Have students discuss how the different arrangements of students affect the reactor reaching subcritical, critical, and supercritical masses.

Enrichment Question

How do you think nuclear power plant operators use this concept to power up or power down?

Further Resources:

http://www.atomicarchive.com/Fission/Fission3.shtml

http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/moder.html