Toxic Milk Return

Part of an Access Excellence lesson
Modified for PULSE by Christopher Martin
Edited by Stephanie Nardei

Time: One class period
10 minutes

Periodic table
Nuclear Energy Handout

Students will use the finding of radioactive milk far from the Chernobyl site to demonstrate their ability to explain nuclear decay reactions.

Students will be able to:

  1. Write nuclear decay reactions for Alpha and Beta decay of the following:
    • Uranium 235
    • Cesium 137
    • Plutonium 24
    • Iodine 131
  1. Articulate the difference between atomic number and atomic mass.
  2. Use the periodic table to find elements with a specific atomic number.
  3. Define half-life and understand the relationship between time, half-life and mass of radioactive isotope.

National Science Education Standard
CONTENT STANDARD D:The Physical Setting

The structure of Matter
The nucleus of radioactive isotopes is unstable and spontaneously decays, emitting particles and/or wavelike radiation. It cannot be predicted exactly when, if ever, an unstable nucleus will decay, but a large group of identical nuclei decay at a predictable rate. This predictability of decay rate allows radioactivity to be used for estimating the age of materials that contain radioactive substances.

Strand 5: Physical Science
Concept 1: Structure and Properties of Matter

Understand physical, chemical, and atomic properties of matter.
PO 6 Describe the…..
Explain the details of atomic structure (e.g., electron configuration, energy levels, isotopes).

Teacher Background
In 1993, NESTLE LANKA, a subsidiary of the multinational food firm in Sri Lanka, was required by the Sri Lankan Customs officials to return 15 tons of radioactive milk powder imported from Poland.  While the company maintained Geneva-based Societe Generale de Surveillance had certified the milk as having acceptable levels of radioactivity, local tests found that it contained more than the permissible amount of radioactive particles. Customs officials said the discovery was made by the Radio Isotope Centre at the University of Colombo, Sri Lanka. Checks were introduced following the 1984 disaster at the Chernobyl nuclear power plant in the then-Soviet Union, which raised fears that neighboring milk-producing countries could have been affected. You can go to http://newsfromrussia.com/accidents/2005/11/22/68275.html for an article related to the topic.  

Students will need this information for the activities.




Iodine 131

Beta and Gamma

8 days

Cesium 137

Beta and Gamma

30 years

Uranium 235


700 million years

Plutonium 240


6564 years

For extra practice with radioactive decay reactions, go to:

Related and Resource Websites
Chernobyl Resources

CDC Emergency Preparedness & Response: http://www.bt.cdc.gov/radiation/isotopes

PULSE Resource Page on Nuclear Radiation: http://pulse.pharmacy.arizona.edu/resources/chemicals/nuclear.htm
Britannica on Chernybol: http://www.britannica.com/eb/article-9072288/Three-Mile-Island
Brown University of Three Mile Island: http://envstudies.brown.edu/thesis/2003/Jessica_Galante/pages/tmi.html
Pennsylvania Highways on Three Mile Island: http://www.pahighways.com/features/threemileisland.html
Three Mile Island on Wikipedia: http://en.wikipedia.org/wiki/Three_Mile_Island

Periodic Table Resources
Los Alamos National Lab Periodic Table: http://periodic.lanl.gov/default.htm
Pictorial Periodic Table: http://chemlab.pc.maricopa.edu/periodic/periodic.html
WebElements Periodic Table: http://www.webelements.com/
Periodic Table on Wikipedia: http://en.wikipedia.org/wiki/Periodic_table


  1. Display a map of the world on an overhead or on a wall. Using this map explain that it wasn’t only Russia or Europe that were affected by the radiation, but people all over the world.  Have a student identify Chernobyl on the map and identify where Poland is relative to Chernobyl and Russia.  Is it surprising that radiation affected this area? Ask a student to identify Sri Lanka on the map.  Explain while winds may not have carried the same quantities of radiation to this country, it was still affected.  Ask students how else radioactive material from Chernobyl may have reached Sri Lanka, other than by natural weather and climate processes. 
  2. Once students suggest ideas describe events in the teacher background.  Explain today they will be use radioactive isotope knowledge to explain, nearly a decade after Chernobyl, how milk from Poland could still be radioactive.  Ask for suggestions.
  3. Once students make suggestions, ask to review as a group what radioactive isotopes are.  Remind them radioactive isotopes undergo different types of decay:
    • alpha
    • beta
    • gamma

      Refer to the Natural Energy handout to demonstrate the difference between these.
  4. Students will write radioactive decay reactions for I 131, Cs 137, U 235 and Pu 240.
  5. Provide them with the decay half-life chart and give the students the following definition of a half-life;

    The half-life is the amount of time it takes for half of the atoms in a sample to decay”.
  6. Demonstrate half-life using the following example: Iodine has a half-life of 8 days. If you had 4g ofIodine 131, how much would there be after 8 days?  There will be 2g left and after 16 days there will be 1g left.
  7. Starting with 10g of radioactive isotope, students  complete the following chart:
  8. Explain how milk from cows in Poland nine years following Chernobyl might still have radioactive properties. 
    • What type of isotopes might they expect in this milk?
    • What implications does that have for human health?



Mass remaining

# of Half-Life

Iodine 131




Cesium 137

120 years



Uranium 235

1400 million years



Plutonium 240




If Applicable.

Embedded Assessment
Students will write four balanced equations, calculating the atomic masses and atomic numbers of the decay products and using the periodic table to assign symbols to the products. They will be able to use definition of a half-life to calculate mass and time.




PULSE is a project of the Community Outreach and Education Program of the Southwest Environmental Health Sciences Center and is funded by:

NIH/NCRR award #16260-01A1
The Community Outreach and Education Program is part of the Southwest Environmental Health Sciences Center: an NIEHS Award


Supported by NIEHS grant # ES06694

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Last update: March 7, 2007
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