Scientists at Los Alamos National Laboratory study what happens when a nuclear weapon detonates.
April 2, 2024
Scientists first witnessed the effects of a nuclear detonation some 210 miles south of Los Alamos, New Mexico, on July 16, 1945. At 5:29 a.m., an ocean of light exploded across the Jornada del Muerto desert. An enormous ball of roiling fire, flashing scarlet, green, and yellow, rose into the sky. Sand swept up into the fireball, fused together, and fell to the ground as radioactive green glass. The tower that had held the nuclear device was gone, vaporized, a shallow crater in its place. The atomic age had begun.
This was the Trinity test—the world’s first detonation of a nuclear device and an important milestone in the Manhattan Project effort to build atomic weapons to help end World War II. During the days leading up to the test, scientists struggled to anticipate the outcome. What would be the explosive power, or yield? How far would its shock wave travel? Physicist Edward Teller even wondered if the detonation would set the atmosphere on fire. (Physicist Hans Bethe squashed this notion after an hour of calculations.)
During the test, physicist Enrico Fermi released slips of paper into the air and measured their motion in the shock wave. With this information, he estimated the device’s yield to be about 10 kilotons. Fermi’s experiment and initial calculations marked the first nuclear weapons effects test.
Eighty years later, scientists at Los Alamos National Laboratory are still studying weapons effects—but not by dropping pieces of paper and not by setting off any nuclear devices. (The United States has been under a nuclear testing moratorium since 1992.)
Instead, scientists rely largely on data from the 1,149 nuclear tests conducted by the United States between 1945 and 1992. This data is incorporated into state-of-the-art computer codes that run on some of the world’s fastest and most advanced supercomputers, which produce high-resolution simulations of nuclear detonations and their effects—such as radiation, electromagnetic pulse, and shock waves in the air, ground, or underwater. Scientists can also simulate second- and third-order effects—things like impacts on people, vegetation, vehicles, structures, and electronics. Additionally, variables including topography, geology, weather, and the aboveground elevation of a detonation can be programmed into computer models to produce simulations that allow decision-makers to consider very specific scenarios both at home and abroad.
“There are lots of circumstances when the details really matter,” says Los Alamos physicist and nuclear engineer Tim Goorley. “Those details support deterrence and keep the nation safe.”
Jim Cooley, who leads the Strategic Analyses and Assessments office at Los Alamos, agrees, adding that the Laboratory’s work in weapons effects is increasingly important. “The changing geopolitical landscape and the fact that the United States is facing a threat spectrum that involves multiple adversaries have led to increased focus on weapons effects research,” he says.
Building on 80 years of research
Whether Goorley, Cooley, and others are briefing government officials or lecturing Air Force cadets, they draw on nearly 80 years of weapons effects research. The 1,149 nuclear tests conducted by the United States—which took place in the atmosphere, underground, underwater, and even in outer space—are the primary sources of data for weapons effects.
“A great advantage that the United States has over almost any other country is that we have more than 1,000 tests worth of data,” says Los Alamos senior historian Alan Carr. “Many different tests generated many different types of data, and we learned something from every test.”
“A key piece of having a credible deterrent is being able to achieve military and political goals on the battlefield.” —Tim Goorley
Much of that data is housed in the National Security Research Center, the Laboratory’s classified library, which contains millions of records. “It’s an amazing repository of real-world test data,” Carr says. “It’s of extreme value. Although the ground-shaking blasts of the past may be history, their technical and political legacies continue to guide scientists and policymakers alike in an ever-changing and ever-dangerous world.”
During these tests, scientists used various types of diagnostic sensors to capture data. As decades passed, technology became more sophisticated, and the measurements and data generated became increasingly complex. By better understanding the variables impacting the detonations and their effects, scientists could refine weapons designs. Although the U.S. nuclear stockpile did grow in size and destructive power during this time, it also became safer as scientists were able to incorporate safety measures.
“Hollywood gets a lot of things wrong.” —Tim Goorley
After the 1992 testing moratorium went into effect, scientists had to rely on computers to model and simulate nuclear detonations and then compare those simulations to past tests. If the comparisons were similar, the computer models were validated.
For more than 30 years, researchers have used high-performance computers and complex multiphysics codes that simultaneously model different aspects of weapons systems and the interactions among them. The result is what’s called high-fidelity simulations—high-resolution 3D representations of processes that allow scientists to virtually explore weapons and weapons effects.
As this computational modeling capability has improved over decades, researchers have refined the tests and gathered more data. “The Lab has had decades of development of high-fidelity modeling tools to provide accuracy and confidence,” Goorley says. “Visualization of these models and their results has also advanced, which makes communicating key concepts far easier.”
Today, modern codes run on extremely large multi-processor computers, such as Crossroads, which was installed at Los Alamos in 2023. High-fidelity simulations typically take from a single day to a month to run, although with recent computer advancements, some can now run in hours.
“Computer simulations provide a way to use high-fidelity mathematical models to study the complex physics of real-world systems and phenomena,” says Scott Doebling, senior director for Advanced Simulation and Computing and division leader for Computational Physics. “Scientists can study the complex interactions of physics across a wide range of time- and length-scales following a nuclear detonation.”
Other, older computer codes, called legacy codes, are engineering-based, creating 1D and 2D simulations that can be generated much faster than the more complex, physics-based simulations that the high-fidelity codes create. Legacy codes can analyze the possible effects of a detonation on thousands of targets in just minutes and can be run on a laptop in the battlefield.
“We continue to work with the legacy codes because they can provide information and predictions quickly,” says Trevor Tippetts, a research and development engineer at Los Alamos. “Although these simulations are less sophisticated than the high-fidelity simulations, they could be invaluable for the military to explore many possible outcomes and optimize for the best case.”
Goorley points out that regardless of the codes used, additional experiments are needed to validate the simulations. That’s where nuclear effects emulators come into play.
“Understanding weapons effects is part of developing a stable, well-defined nuclear strategy policy.”
—Jim Cooley
Nuclear effects emulators are experiments that imitate real-life conditions like those that occur during an actual nuclear blast. Emulators may mimic the extreme heat of thermal radiation or the electromagnetic interference a detonation creates.
One example is the White Sands Solar Furnace at the White Sands Missile Range near Alamogordo, New Mexico. The 45-foot-tall by 100-foot-long facility focuses and concentrates the Sun’s rays using mirrors to generate a temperature of more than 4,500 degrees Fahrenheit, similar to the heat from a nuclear blast some distance away. Other devices such as the Large Blast Thermal Simulator and the Gamma Radiation Facility produce environments that allow researchers to examine specific weapons effects.
“We can look at how military and civilian equipment and hardware and various types of electronics will withstand the intense thermal radiation and powerful shock waves,” Goorley says.
Defending the homeland
Weapons effects simulations and emulations, backed by historic testing data, continue to inform national security policy, particularly for thinking about a nuclear attack on American soil.
After the Soviet Union detonated its first nuclear weapon in 1949, the U.S. military wanted to understand how to fight through the aftermath of a nuclear blast and win on the battlefield. From 1951 to 1957, 30 nuclear detonations in the Nevada desert were accompanied by military exercises. Some units conducted simulated infantry, armored, and airborne assaults with associated live fire to test equipment functionality, while others observed the detonations from a few miles away. The exercises involved extensive testing of equipment, vehicles, and fortifications, as well as assessing the impact of flash blindness from atomic blasts and the amount of radiation protection that armored vehicles provided. Psychologists conducted interviews before and after the exercises to understand the role of training and preparation in enhancing combat capability.
“There are many things we have learned from these tests about how to ensure troops, equipment, and facilities are secured against adversary attack,” Goorley says. “Resilience and survivability matter. A key piece of having a credible deterrent is being able to achieve military and political goals on the battlefield.”
Another rationale behind studying nuclear weapons effects is preparing first responders for the possibility of a nuclear weapons attack. Los Alamos physicist Randy Bos says movies and television have shaped the public’s perception. “When I worked with the Federal Emergency Management Agency on nuclear weapons response strategies, I realized how many myths there are. Understanding the truth about weapons effects is essential for emergency responders and healthcare workers,” he says. “Ultimately, there is lifesaving that can be accomplished by the emergency responders if they understand and plan for the realistic, limited impacts of these detonations.”
U.S. Air Force Lieutenant Colonel James Bevins, of the Defense Threat Reduction Agency’s Nuclear Assessments Division, is a former Los Alamos Air Force Fellow. Bevins points out that many of the injury and damage prevention measures for a nuclear detonation are similar to those implemented to protect people from the effects of conventional weapons. “Understanding how people can be triaged and treated and how modern construction can provide shielding is key,” Bevins says. “Simple measures can go a long way to reduce casualties.”
Another misconception about nuclear weapons effects focuses on a nuclear detonation’s ability to create a powerful wave of electromagnetic energy called an electromagnetic pulse (EMP) that has the potential to disrupt electronics, the power grid, and communications technology. “People tend to think an EMP is going to knock us back into the Stone Age,” Bevins says. “While it is a challenge to predict and work around EMP effects, it won’t knock out all electrical systems. There may be some disruption and damage, but we can build protected and redundant systems thanks to our understanding of EMP effects.”
Computer models and simulations also allow scientists to predict how fires might spread following a detonation. “Nuclear detonation–induced fires could be a major concern for first responders,” Bos says. “Computer simulations allow us to predict how a detonation’s initial thermal pulse will start fires. These fires may then combine with secondary fires caused by broken gas lines and ruptured fuel lines, spreading rapidly and threatening large areas.”
Similarly, simulations provide insight into effects on modern structures and the way trees and similar items deflect and absorb energy. The complex computer codes consider the many factors that shape the impact of a nuclear detonation. Two of those factors are the geographic location and the weather at the time of the detonation. Simulations can provide realistic representations of topographical locations, including canyons, mountains, and cities. The codes can even create simulations of how underground structures would be affected.
Resilient and survivable weapons systems
Weapons effects research is valuable not only for defending the United States but also in the event that the United States deploys a nuclear weapon against an adversary.
“Many people think that a nuclear weapon is just a nuclear weapon. That’s not the case,” says Bob Webster, deputy director for Weapons Programs at Los Alamos. He notes that Los Alamos scientists are working to design and maintain weapons that achieve specific purposes with particular targets. Successfully achieving this goal requires understanding all aspects of weapons effects.
“The point is to ensure that at any moment in time, our nuclear deterrent is fit for the purpose,” Webster says. “In a changing world, you don’t necessarily get to pick that time.”
Webster notes that modern warfare requires a more specialized approach to weapons development. “It is becoming increasingly clear that our adversaries can make certain targets more difficult to attack, so we need a more specialized approach,” he explains. “Truly appreciating the effects of nuclear weapons factors into what weapons’ designs and modifications look like.”
U.S. Air Force Colonel Joshua Henderson, formerly a Los Alamos Air Force Fellow and now the National Nuclear Security Administration's executive action officer to the U.S. Nuclear Weapons Council, explains that robust communication is necessary between the national laboratories (that design the weapons) and the military (that uses the weapons). “This relationship between the armed services and the laboratories allows us to provide the best options and advice to senior leadership,” he says. “By better understanding weapons effects, we can talk more specifically about what designs we need and for what end and purpose. We can say, ‘I want this tool, with this power, by this date.’”
For Goorley, the bottom line is simple. “The Department of Defense [DOD] is the Lab’s end customer. When we design a weapon, we need to be sure it does what they need it to do.”
Modern nuclear weapons can be designed specifically to destroy underground targets, to disrupt electronics and communications systems, to level buildings and infrastructure, or to create casualties. Whatever the goal of a weapons system, experts say the design and the effects always go hand in hand.
“By better understanding weapons effects, we can talk more specifically about what designs we need and for what end and purpose.” —Colonel Joshua Henderson
“The goal is to ensure effectiveness,” Goorley says. “In other words, does the military target get destroyed to the degree it needs to be destroyed?” Weapons designers must also consider more nuanced questions: Can a target be destroyed while minimizing civilian casualties? What does it take to render an airstrip unusable? Goorley notes that “each weapon has its own strengths and weaknesses—for instance, a weapon designed to function underwater for destroying submarines will be different from an air-deployed weapon.” All of these factors must be considered by weapons effects researchers who endeavor to ensure the reliability and effectiveness of the nation’s nuclear deterrent.
An emphasis on effects education
An increased focus on weapons effects recently resulted in a new position at the Laboratory: chief scientist of weapons effects. Goorley was selected for that role in July 2023 and now spends much of his time synchronizing new and ongoing nuclear weapon effects efforts across the Laboratory. Many of these efforts happen at the request of external stakeholders, such as DOD, and require additional expertise from other laboratories, especially sister labs Lawrence Livermore and Sandia, so Goorley finds himself coordinating across a broad spectrum of organizations.
“I’m excited that Los Alamos is placing more emphasis on nuclear weapon effects to address the increasing interest from the National Nuclear Security Administration, DOD, and other interagency partners,” Goorley says. “I believe that the Laboratory is well positioned to not just contribute, but lead, several important nuclear weapons effects topics.”
In addition to helping Los Alamos develop new modeling and simulation capabilities, one of Goorley’s primary objectives is educating people—the public, policymakers, members of the military, and pretty much anyone else he encounters—about weapons effects. Armed with posters and talking points, Goorley is always ready to discuss what really happens when a weapon detonates. He often points out that a nuclear detonation is highly complicated and debunks myths and misunderstandings about nuclear devices. “People tend to believe what they see in TV and movies, but Hollywood gets a lot of things wrong,” Goorley says. “Many movies suggest that a nuclear detonation will destroy most of life on Earth. That’s not the case.”
Bevins agrees that education is paramount because so many people have misconceptions about nuclear weapons. “In the current geopolitical environment, it is essential that we spread the word that Hollywood portrayals of nuclear weapons are often not accurate frames of reference for the threats we face,” he says. “The challenges of operating in nuclear environments are immense but are more tractable than commonly believed.”
Bevins says his goal is to increase what he calls “DOD’s collective nuclear IQ.”
“Examining our knowledge of weapons effects has many benefits,” he says. “The information allows us to create resilient and survivable weapons systems. It helps in the development of battlefield strategies and prepares the military to operate in the face of a nuclear attack, which denies our adversaries the benefits of using nuclear weapons.”
Cooley also stresses the need for Los Alamos scientists to provide military leadership with sufficient information to understand effects and ask the right questions. “Understanding weapons effects is part of developing a stable, well-defined nuclear strategy and policy,” Cooley says.
To facilitate these conversations, Goorley has implemented a Lab-wide forum he calls Nuclear Weapons Effects Community Conversations. Subject matter experts, managers, and leaders from across the Lab gather each month to hear technical talks, program overviews, and policy updates. “All perspectives are welcome,” Goorley says. “Together we can leverage information, achieve synergies, unite experts, and become aware of all capabilities across the Lab.”
Cooley notes that although the study of weapons effects began in 1945 with the first nuclear detonation, the research continues. “The world is a dangerous and complicated place, and the study of weapons effects is part of the science and psychology behind deterrence.” ★
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