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Image of photographer taking photographs of atomic bomb detinations.
Daring Aerial Photographer, Atomic Bomb Test Bikini Atoll, July 1946

Launching Units with Primary Sources: Operation Crossroads

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This post is by Jacqueline Katz, the 2022-2023 Albert Einstein Distinguished Educator Fellow at the Library of Congress.

Have you considered using primary sources as launching phenomena in your classroom? Primary sources often present a puzzle that needs to be solved; the content related to your discipline can help put the pieces together. For example, in a chemistry classroom starting a unit on gas laws or nuclear reactions, students can observe images of Operation Crossroads, a terrifying but interesting pair of nuclear weapons tests conducted by the United States at Bikini Atoll in July 1946. In addition to learning about gas laws, students might consider the human impacts of such tests.

Present students with these images of mushroom clouds from the nuclear tests that were part of Operation Crossroads and support them in comparing and contrasting by creating a Venn Diagram. Both Figure 1, “Test Baker,” and Figure 2, “Test Able,” were attempting to study the effects of nuclear explosions on warships. Students will likely identify a difference in the height and shape of the mushroom clouds, but may recognize that both clouds are forming over water. Create a class Venn Diagram, so students can add their observations and share their thinking. Then ask students, “What is responsible for the differences of these two mushroom clouds?” This can serve as the driving question for the unit.

Mushroom cloud with ships below during Operation Crossroads nuclear weapons test on Bikini Atoll, July 1946. Also described as “Test Baker”.


Mushroom cloud with ships below during Operation Crossroads nuclear weapons test on Bikini Atoll, July 1946


Provide students time to harness their prior knowledge and list possible responses to this driving question. These thoughts can be posted around the classroom throughout the unit to show how the class’s thinking changes. To explain the phenomenon of the Operation Crossroads mushroom clouds, focus students on the reaction that occurs when a plutonium bomb detonates and the effect on the surrounding fluid. Activities that address how temperature affects the properties of a gas and liquid, including density and buoyancy, will help students to construct a response to the driving question.

Once students understand the scientific reasoning for mushroom cloud formation, they can start proposing ideas to explain the factors that might change the characteristics of the cloud. Students should provide evidence from the images and activities from the unit to support their claims. These scientific arguments can serve as an end of unit assessment or you may reveal that Test Baker involved a plutonium bomb detonated under water. Students can then explain the characteristics of the Baker mushroom cloud using the knowledge gained throughout the unit, considering how the gas bubble that causes the mushroom cloud would behave differently in water.

Continue the conversation by asking students to assess the pros and cons of this type of nuclear testing. By searching “Operation Crossroads” in Chronicling America, limiting to the years 1945-6, students will find that these tests were widely publicized events; journalists were invited to observe the detonations. What do your students think of this? How about the fact that the inhabitants of Bikini Atoll were removed from their homes prior to the testing and were never able to return? What ethical obligations do scientists and researchers have to the population at large? How has our knowledge surrounding nuclear weapons changed since the 1940s?

Primary sources, such as the images of Operation Crossroads, can provide launching phenomena that challenge students to learn new content, reflect on scientific practices, and be reminded of the constructive nature of science.

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