Directions: After students read the Science News article “Radioactive cloud traced to Russia,” ask them to answer the questions that follow.

1. The article describes “a nuclear whodunit.” What is the mystery that researchers are trying to solve?

A radioactive cloud appeared over Europe in September and October 2017, but no one knows for sure where the cloud came from or what caused it.

2. What data alerted scientists to the mystery and what about that data causes concern?

A network of sensors that monitor the atmosphere across Europe detected small amounts of ruthenium-106 in the skies. This isotope is not found naturally on Earth.

3. Some scientists believe they have solved the mystery. What is their conclusion about the origin and cause of the mystery?

Some scientists believe the Mayak Production Association, a nuclear facility near Ozersk in Russia, was the source. These scientists argue that the cloud was released when the facility attempted to make a material for an experiment looking for subatomic particles called neutrinos.

4. Name the three most important pieces of evidence that support the conclusion.

Students answers will vary, but should come from this list:

 -The cloud shape suggested it didn’t originate in Romania
-The cloud was moving west as it passed over Romania, and simulations suggest it could have traveled from Mayak
-The type and ratio of radioactive material detected matched what might be expected from fuel processing at Mayak related to the neutrino experiment
-An e-mail between experiment leaders referred to “unexpected problems”
-Concentrations of ruthenium across the cloud were not consistent with another possible explanation, that a satellite with a radionuclide battery burned up when it entered Earth’s atmosphere

5. If the scientists’ conclusion is correct, the events below preceded the cloud’s detection. Put the events in chronological order.

-Ruthenium-106 was released into the atmosphere. (3)
-The Mayak facility in Russia attempted to create that source from recently spent fuel. (2)
-Scientists working on a neutrino experiment in Italy needed a radioactive source that produced neutrinos. (1)
-The neutrino experiment was canceled. (5)-The cloud of ruthenium was carried over parts of Europe. (4)

6. Look at the graphic titled “European traveler” in the online version of the story (www.sciencenews.org/article/2017-radioactive-plume-europe-russia-plant-neutrino-experiment). What pattern is shown in the animated graphic? (Include what the circles and colors indicate in your answer.)

The graphic shows where detectors in Romania picked up ruthenium-106 from September 28 through October 5. Circles show detector locations. Red circles indicate that ruthenium-106 was spotted by the detector; white shows where no ruthenium-106 was measured. Red circles appear to be generally moving from an east to west direction as the days pass. 

7. What conclusions can and cannot be drawn from the graphic?

Since the detectors shown are only in Romania, we cannot determine the origin or final destination of the cloud. Within Romania, the cloud of ruthenium-106 first appeared over the eastern side of the country and then spread to the west. It either moved over other countries or dissipated in northwest Romania.

8. According to the article, does everyone agree that the mystery is solved? Why or why not?

No. The Russian state atomic energy corporation says that there was no accident at Mayak that would have led to the radioactive cloud.

9. Do you think the evidence is strong enough to say the mystery is solved? If yes, why? If not, what additional evidence could help solve the mystery?

Student answers will vary. If students answer yes, they should explain why the evidence outweighs the Russian denial. If students answer no, they might suggest new forms of data, including interviews with Russian officials or nuclear workers, or with the leaders of the neutrino experiment. Students might brainstorm other ways to gain environmental data, such as through satellites, or suggest further simulations.