Past is Prologue with Wigner Energy Nuclear Forensics

By Mark Wolverton
MIT Spectrum

IN SCIENCE AS IN LIFE, the seeds of good ideas can lie fallow. Michael Short ’05, SM ’10, PhD ’10 found one such seed in the form of a neglected memo from more than 70 years ago that led him to the scientific question that now drives most of his work.

Short, the Norman C. Rasmussen Career Development Professor in the Department of Nuclear Science and Engineering and an affiliate researcher of LNSP, is fascinated by the fundamental definition of material damage at the atomic level. “We don’t have a way to measure radiation damage right now,” he says. “That makes it awfully hard to quantify.” Put a piece of metal into a nuclear reactor, he says, and despite any existing tests you might run on the material afterward, “you can’t tell me how much damage is left behind.”

Such damage—invisible, but with major implications for nuclear reactor technologies and a host of other applications—comes from high-energy particles like neutrons or ions knocking atoms out of place from the ordered atomic lattice of a material, a phenomenon that scientists generally describe using the term DPA (displacements per atom). But DPA doesn’t give the complete picture, as Short explains: “It’s a measure of how many times each atom gets knocked around by ionizing radiation, but it’s not a measure of damage, because most of the atoms pop back into place like nothing ever happened. Very few of them remain as defects.” Another problem is that DPA calculations are approximations rather than precise measurements. “I always ask experts in the field why we use the DPA, and their candid answer is, well, it’s not that good, but it’s the best we’ve got.”

Short decided there had to be a better way. Unexpectedly, he found the inspiration for one in a World War II–era memo. In it, Manhattan Project physicists Eugene Wigner and Leo Szilard were discussing a phenomenon that came to be known as Wigner energy or the Wigner effect, in which certain materials exposed to ionizing radiation might actually store energy in some way.

Short first learned of the memo from his nuclear science and engineering colleague, associate professor Scott Kemp. Short also spoke with Ronaldo Szilard, a distant relative of Leo Szilard, who is a nuclear engineer at the Idaho National Laboratory. Using stored energy as a way to quantify damage had occurred to Short and his collaborators, but until hearing about Wigner and Szilard’s speculations, he’d found little encouragement to support such an idea. “We thought we were crazy until we realized this Nobel Prize–winning guy [Wigner] and this other couch-surfing theoretical physicist [Szilard] thought about it earlier.” Kemp showed Short a book noting the document’s location deep in the research library of the DuPont Corporation, where Short’s uncle, Cyril Milunsky, happened to work. “I was like, hey Uncle Cyril, go find this memo!”

Short realized that the stored energy concept could be expanded to encompass not only radiation damage in metals, but any sort of damage in materials. “Damage is defects, and it takes energy to make those defects,” he says. “Usually when you want to get rid of the defects in a material, you anneal it—you heat it up to a high temperature for a long time. If those defects go away, they should release the energy that it took to make them. That’s the crux of it, really.”

Recent data from Short’s group shows the energy released or absorbed once irradiated stainless steel is heated. Features in heat flow for the irradiated steel (red), compared to an unirradiated piece (blue), support Short’s premise that radiation creates a “stored energy fingerprint” in materials. Two unexpected energy absorption spikes above 400 degrees Celsius helped Short and his collaborators in Kazakhstan identify another, previously undocumented effect that could assist in identifying damage: some materials become magnetic when irradiated. 

Short’s insight is that the energy is released as heat in a particular pattern—what he calls a “stored energy fingerprint.” Measured with exquisite precision with a nanocalorimeter, this energy fingerprint can provide a sharp picture of the defects in the material and the specific events that created them. This ability, applied to radiation damage and nuclear technology, has startling implications both for civilian and military uses.

“Scott Kemp has called this ‘radiation forensics,’ using radiation in different ways to reconstruct the historical usage of things,” says Short. “He and I are working together on using stored energy to reconstruct historical uranium enrichment. Scott and I think we can take, say, the centrifuges in Iran, and measure the stored energy in the walls of the devices and figure out how many bombs they’ve made.” That would provide a means of technical verification for international inspectors assessing nuclear deal compliance. For nuclear reactors used to generate energy, Short envisions a “cheek swab test” to check the health of steel reactor vessels, correlating the stored energy fingerprint to embrittlement and other important material parameters, and thus providing the technical reassurance required for extending the life of existing nuclear plants.

After a year of intense simulations, the project is now moving ahead to the dedicated experimental phase, using MIT’s research reactor and other facilities. For example, with funding from the MIT International Science and Technology Initiatives, Short is working with the research group of Oleg Maksimkin at the Institute for Nuclear Physics in Almaty, Kazakhstan, a collaboration he describes as indispensable, the 14-hour flights between continents notwithstanding. Maksimkin’s group has provided some of the theoretical explanations required to interpret Short’s calorimetric findings, confirming the measurements by their own magnetic techniques.

As a nuclear scientist, Short’s main focus at present is defining a standard unit for radiation damage, but he’s actively exploring other possibilities for the stored energy idea. “Let’s say you have a piece of steel that looks fine, but isn’t on the inside, and you can’t just cut it open and look at it because that would destroy it. Can you scoop out a microgram-sized sample of material and make a stored energy measurement to figure out what’s going on?” If Short’s work is successful, the possible applications range far beyond nuclear science to practically all areas of engineering.

For Short, the project has proven not only that good ideas are planted in unexpected ways and places, but also the value of persistence. “I’ve spent pretty much my whole life until now”—including 17 consecutive years at MIT, as a student and then a researcher—“thinking of things and finding out that somebody else has already thought them through,” he says. “Finally, after four years on the MIT faculty, I have an idea that no one else had already!”

Scott Kemp is a Fellow of the American Physical Society

Today the American Physical Society named LNSP founder R. Scott Kemp a Fellow of the society. Each year, no more than one half of one percent of the society membership is recognized by their peers for election to the status of Fellow.

Kemp was elected "for innovative applications of physics to arms control verification, and pivotal scientific contributions to nuclear nonproliferation diplomacy and the understanding of technology-policy interactions in international security."

The APS fellowship program was created to recognize members who have made advances in physics through original research and publication, or made significant innovative contributions in the application of physics to science and technology. A complete list of Fellows is available at the APS Fellows Archive.

Brian Henderson: Experimenting with physics and policy

By Elizabeth Dougherty

As a graduate student in MIT’s Laboratory of Nuclear Science (LNS) in the Department of Physics, Brian Henderson applied his skills in physics to study sub-atomic particles, such as protons. He is now the first Stanton Fellow in Nuclear Science and Security in the Laboratory for Nuclear Security and Policy in the MIT Department of Nuclear Science and Engineering (NSE). His job is to put his experience in experimental particle physics to work in the realm of nuclear weapons detection, with an eye for making sure nuclear weapons policies are scientifically plausible.

“No one wants me to come here and just build experiments,” says Henderson. “My role is to have a broader perspective, which is very appealing. I’m interested in finding ways for my skills to be useful to society.”

Henderson’s projects are related to nuclear weapons detection. In one, he is exploring potential ways to solve the difficult problem of patrolling United States ports for nuclear materials that may be concealed among the tens of thousands of containers arriving in U.S. ports each day. “Cargo containers are generally considered the easiest way to smuggle a nuclear weapon into a populated area,” says Henderson. The strategy may appear simple — scan the cargo and flag containers that could potentially contain a nuclear weapon or weapons material — but it is scientifically tricky. To get a good picture of what’s inside a container, a scanning system must deliver a high dose of radiation. So Henderson and his advisor Areg Danagoulian, assistant professor of NSE, are experimenting with ways of interrogating the cargo with the least amount of radiation possible.

The second project is related to a nuclear weapons verification project that supports nuclear disarmament. The technology aims to allow an inspector overseeing a treaty-driven nuclear weapons dismantlement process to authenticate a weapon with confidence yet still have no access to the classified information about that weapon’s design. Henderson’s first job is to help put together an experimental setup that mimics a real warhead in need of verification. He is also working with scenarios involving fake nuclear weapons designed to defy the system.

“I joined this group to bring my experimental experience to these problems,” says Henderson. “The plans in place are sound on paper, but what we need to do now is build an experiment.”

As an undergraduate at Rice University, Henderson majored in physics and mathematics and participated in several undergraduate research projects in particle physics. Experiences working at Brookhaven National Laboratory and at Cornell University convinced him that his role in particle physics was as an experimentalist — working with particle detectors and accelerators and simulations of particle interactions — and not as a theorist.

Henderson wanted to continue work on particle physics in graduate school, but he didn’t want to participate in the very large experiments, such as those at the Large Hadron Collider. Experiments there often have thousands of physicists participating and writing papers together. “I wanted to work on a small team experiment,” he says.

There are few to choose from, but he found one at MIT’s Laboratory for Nuclear Science. He studied hadronic physics and focused on particles like protons and neutrons. He worked on an experiment called OLYMPUS with a goal of learning more about the composition of protons. It is understood that protons are not elemental particles; they are made of other particles. But it isn’t clear how those particles are distributed within the proton.

OLYMPUS, like most experiments in particle physics, is designed to uncover more about the composition of the proton by shooting things at it. “It’s a bit like having a hard object in a paper bag and shooting BBs at the bag to try to learn more about what’s inside,” says Henderson. “It’s the same with a proton, but we’re probing at a much smaller scale.”

These types of experiments inform theories about protons and neutrons and also about how most of the mass we experience in the world arises, which is still somewhat of a mystery. Henderson’s work was narrowly focused. He contributed to a specific test of a single hypothesis about two competing methods of making the same measurement. The two methods produce different results, underscoring a gap in physicists’ understanding of the underlying physics. Henderson’s project was part of an effort to close that gap.

Instead of pursuing a career with a continued focus on such fundamental science, when Henderson completed his PhD in 2016, he wanted to apply his skills more broadly. He found a match at NSE. “I’m working on bigger questions not only from a scientific perspective, but also from a societal perspective,” he says.

Jayson Vavrek: turning particle detectors into weapons detectors

By Elizabeth Dougherty

Department of Nuclear Science and Engineering (NSE) graduate student Jayson Vavrek got his start in high-energy particle physics looking for the smallest forms of matter in the universe. Now at MIT, he uses the same tools and principles to verify nuclear weapons.

The system Vavrek is developing with his advisor, NSE Assistant Professor Areg Danagoulian, is called physical cryptography. It’s designed to precisely identify a nuclear warhead, but without revealing the weapon’s inner-workings. The goal is to allow inspectors to verify that actual nuclear weapons are being marked for disposal during a disarmament process without revealing the weapons’ internal secrets.

The work is being done in MIT’s Laboratory of Nuclear Security and Policy (LNSP), a collection of experts in physics, nuclear engineering, and public policy. “We have great people who I can talk to about anything, from nitty-gritty physics details to the loftier goals of getting this implemented in the political future,” says Vavrek.

As an undergraduate in physics at the University of Alberta in Canada, Vavrek studied particle physics, the kind of work that led to the discovery of the Higgs boson in 2012. But Vavrek also had a chance to work on a more practical project that involved looking for neutrino emissions from nuclear reactors as a way to detect nuclear material. Neutrinos can’t be shielded, says Vavrek, “So they’re an obvious signal.”

He used a detector called a liquid scintillator that detects high-energy charged particles. When neutrinos pass through the detector, their interactions create charged particles as a by-product that can be measured. “I found it interesting because it was using all the same tools as pure particle physics, but in an applied sense,” Vavrek says.

When it came time to apply to graduate school, Vavrek wasn’t sure he wanted to pursue particle physics. Experiments in this field often involve thousands of collaborators. “The chance to contribute something meaningful is really small,” he says.

But when he came across the MIT Department of Nuclear Science and Engineering, he remembered his project working with neutrinos and thought that a more applied path might be a good fit. “The skills weren’t all that different,” he says.

On day one of his arrival at MIT in 2014, he began work on physical cryptography. The research aims to develop a technology which would enable an inspector overseeing a treaty-driven nuclear weapons dismantlement process to authenticate a weapon with confidence yet still have no access to the classified information about that weapon’s design. Current arms reduction treaties are hampered by the absence of such technology.

The concept that Vavrek is researching involves shooting beams of photons through a weapon, producing a signal that is highly sensitive to the weapon’s makeup. Instead of being measured directly, however, the signal undergoes physical encryption first. The transmitted beam interacts with special materials called encrypting foils that produce a secondary, encrypted signal for detectors to measure.

Different materials create different encryptions, and it is impossible to decode the signal without knowing the composition of the foil materials. As a result, the foils act as virtual “notches” on a cryptographic “key.”

During an inspection, an inspector needs only to determine if the encrypted signal from a weapon undergoing verification matches that from another, previously authenticated weapon.

One of Vavrek’s goals is to determine whether or not it would be possible for a weapon owner to trick the system. A hoax would allow a weapons owner to dismantle fake weapons while claiming that they are compliant with the treaty.

Vavrek has to rely on his own creativity and the expertise of his advisor to simulate potential hoaxes because almost all nuclear weapons specifications are classified. He was able to run simulations using a simplified model of a nuclear weapon from the open literature. He also simulated potential hoaxes involving substitutions and rearrangements of weapons materials in ways intended to produce the same foil as a real weapon. As predicted, his skills from particle physics transferred over seamlessly. “Literally,” he says. “It’s the same simulation software we used in pure particle physics.”

Vavrek is still working on simulations, and he is also working to determine the system’s probability of producing false positives or false negatives or if it could leak information. Within the next year or so, Vavrek hopes to collaborate with the United States National Labs, which have access to weapons grade material.

Looking back on his decision to apply physics to real-world problems, Vavrek is satisfied. He’s already published a paper in the Proceedings of the National Academy of Sciences as one of four equally contributing authors. “I’m happy with the contribution I’ve been able to make,” he says.

Scott Kemp Named Sloan Fellow in Physics

From: MIT News Office

R. Scott Kemp, the Norman C. Rasmussen Assistant Professor of Nuclear Science and Engineering at MIT and director of the MIT Laboratory for Nuclear Security and Policy, is among the 23 American and Canadian researchers awarded the 2016 Sloan Research Fellowship in physics, the Alfred P. Sloan Foundation announced today.

Awarded annually since 1955, the Sloan Research Fellowships are given to early-career scientists and scholars whose achievements and potential identify them as rising stars among the next generation of scientific leaders. 126 awards are made across seven disciplines. This year's recipients are drawn from 52 colleges and universities across the United States and Canada.

“Getting early-career support can be a make-or-break moment for a young scholar,” said Paul L. Joskow, president of the Alfred P. Sloan Foundation, in a press release. “In an increasingly competitive academic environment, it can be difficult to stand out, even when your work is first rate. The Sloan Research Fellowships have become an unmistakable marker of quality among researchers. Fellows represent the best-of-the-best among young scientists.”

Administered and funded by the foundation, the fellowships are awarded in eight scientific fields: chemistry, computer science, economics, mathematics, evolutionary and computational molecular biology, neuroscience, ocean sciences, and physics. To qualify, candidates must first be nominated by fellow scientists and subsequently selected by an independent panel of senior scholars. Fellows receive $50,000 to be used to further their research.

Since the beginning of the program, 43 Sloan Fellows have earned Nobel Prizes, 16 have won the Fields Medal in mathematics, 68 have received the National Medal of Science, and 15 have won the John Bates Clark Medal in economics.

For a complete list of this year’s winners, visit the Sloan Research Fellowships website.