Archive for May, 2013:

Half-Life : Licorice

Description: With the Half-Life Laboratory, students gain a better understanding of radioactive dating and half-lives. Students are able to visualize and model what is meant by the half-life of a reaction. By extension, this experiment is a useful analogy to  radioactive decay and carbon dating. Students use licorice to demonstrate the idea of radioactive decay. This experiment is best used by students working in pairs.

licorce

Grade Level
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

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 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

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 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

Radtown USA

The U.S. Environmental Protection Agency’s student-focused radiation website, RadTown, has launched with a new look and feel. This interactive, virtual community provides information for students  and teachers about different radiation sources, links to additional information and all new graphics and content. Please visit the all new RadTown USA at www.epa.gov/radtown/.

A new addition to RadTown is EPA’s Radiation Education Activities for middle and high school students (grades 6-12) which includes lesson plans covering radiation basics, sources of radiation, radiation protection, exposure versus contamination, uranium mining methods, radon and more. All educational activities are aligned with the Next Generation Science Standards and the Vocabulary Materials are aligned with the Common Core State Standards. Please visit the all new RadTown USA at www.epa.gov/radtown/.

radtown

 

Source Energy Equivalents Pellet Card

Grade Level: 7-12

A simulated uranium fuel pellet is attached to this card.  The quantity of energy that can be released from this amount of nuclear fuel is compared to three major energy sources: oil, coal, and natural gas.  With a graphic illustration of source equivalents, this card is a useful resource for public information exhibits, discussion groups, students, scout groups, etc.

The reverse side of the card provides text and illustrations which show how pellets are placed in fuel rods and bundles for use in a nuclear reactor.  The text explains current planning for geological disposal of spent nuclear fuel.  There is brief reference to transportation from a reactor site to a geological depository.

Full color postcard.  3 1/2″ x 5 1/2″.

$2.00 each ($1.80 for American Nuclear Society members). To order item #750027 please visit the ANS Store.

The Source Energy Equivalents infographic is a great complementary piece to the pellet card.

April / May 2013

2013-04-05

 

Update:

On October 8, 2013, the 2013 Nobel Prize in Physics was awarded to François Englert of the Université Libre de Bruxellesand and Peter Higgs of the University of Edinburgh “for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle, by the ATLAS and CMS experiments at CERN’s Large Hadron Collider”.  To learn more about their research, please visit the American Institute of Physics – 2013 Physics Nobel Prize Resources.

December 2012 / January 2013

2013-12-1

September / October 2012

2012-09-10

December 2011

2011-12

May 2010

2010-05

October 2006

2006-10

May 2006

2006-05


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