Here’s what you’ll learn when you read this story:

• Understanding the nuances of nuclear fallout—whether from a nuclear weapon or accident—could help save countless lives.
• A new study from scientists at Lawrence Livermore National Laboratory have recreated a portion of the nuclear fireball process to understand how elements like uranium, cesium, and cerium interact and condense as they cool after an explosion.
• Understanding these “thermal histories” can help scientists create more accurate fallout models for when disaster strikes.

In a nuclear accident, the explosion usually isn’t the deadliest side effect—it’s the fallout. While two workers tragically died from the initial explosion at Chernobyl in April of 1986, upwards of 6 million people were potentially impacted by the subsequent radioactive fallout. Having a nuanced understanding of how fallout behaves following an explosion or accident could potentially save millions of lives, but current models treat materials—whether they be uranium or some other radioactive element—as separate components that rarely interact with the environment or other materials.

Now, a new study led by scientists at the Lawrence Livermore National Laboratory (LLNL) in California has created miniature nuclear fireballs in the lab to see how three elements—uranium, cerium, and cesium—vaporize, react and condense in a controlled environment. The hope is that better understanding the mechanics of nuclear fallout will help improve models at a time when they are desperately needed. The results of the study were published in the journal Analytical Chemistry.

“These particles preserve a record of how they formed,” Rakia Dhaoui, lead author of the study, said in a press statement. “By studying these processes in a controlled system, we can replace assumptions with measurements, improve the models used to interpret nuclear debris, and support decision-making when it matters most.”

Dhaoui and her team used a plasma flow reactor to study these nuclear fireballs—specifically, how hot vapor cools and condenses into particles. With this reactor, scientists can add specific mixtures, crank up the temperature to turn the elements into a plasma, and then vaporize them. As the vapor moves through the tube, the reactor continuously collects the material at multiple points so scientists can see exactly how particles change over time.

The team explored two scenarios, known as “thermal histories.” In the first, temperatures drop continuously along the tube. In the second, temperatures remain steady for longer before cooling rapidly.

“Historical fallout studies indicate that the path materials take as they cool is important,” Dhaoui said in a press statement. “Cooling rate and time at elevated temperature can alter chemical speciation and particle formation.”

Uranium and cesium seem like obvious candidates for this research. Uranium, after all, is the atom that typically splits during fission, whereas cesium-137 is a byproduct of that reaction. Cerium, at first glance, might seem like a bit of a headscratcher, but this element is often used as a safe substitute for plutonium in laboratory settings. That’s because it’s a nonradioactive element behaves like a radioactive one chemically and physically, including how quickly it condenses after being vaporized.

Because it’s less volatile, uranium condensed the fastest, along with cerium. But cesium condensed much later, allowing it more time to mix with other materials in the system. This provides crucial information for updating fallout models—the vital thing isn’t just when an element condenses, but how it interacts with other elements while cooling.

While this first study has now established baseline measurements for tracking how radioactive elements condense and interact over time, the team hopes that future studies will include more common elements, hopefully taking us a step closer to analyzing potential fallout effects of a real-world nuclear explosion in a laboratory setting.