Radioactive Material Detected Remotely Using Laser-induced Electron Avalanche Breakdown

New method developed by UMD researchers could be scaled up to improve security at ports of entry

Physicists at the University of Maryland have developed a powerful new method to detect radioactive material. By using an infrared laser beam to induce a phenomenon known as an electron avalanche breakdown near the material, the new technique is able to detect shielded material from a distance. The method improves upon current technologies that require close proximity to the radioactive material.

With additional engineering, a new method to detect radioactive material, developed by physicists at the University of Maryland, could be scaled up to scan shipping containers at ports of entry—providing a powerful new tool for security applications. Image credit: USDA/APHIS (Click image to download hi-res version.)With additional engineering, a new method to detect radioactive material, developed by physicists at the University of Maryland, could be scaled up to scan shipping containers at ports of entry—providing a powerful new tool for security applications. Image credit: USDA/APHIS (Click image to download hi-res version.)

With additional engineering advancements, the method could be scaled up and used to scan trucks and shipping containers at ports of entry, providing a powerful new tool to detect concealed, dangerous radioactive material. The researchers described their proof-of-concept experiments in a research paper published March 22, 2019 in the journal Science Advances.

“Traditional detection methods rely on a radioactive decay particle interacting directly with a detector. All of these methods decline in sensitivity with distance,” said Robert Schwartz, a physics graduate student at UMD and the lead author of the research paper. “The benefit of our method is that it is inherently a remote process. With further development, it could detect radioactive material inside a box from the length of a football field.”

As radioactive material emits decay particles, the particles strip electrons from—or ionize—nearby atoms in the air, creating a small number of free electrons that quickly attach to oxygen molecules. By focusing an infrared laser beam into this area, Schwartz and his colleagues easily detached these electrons from their oxygen molecules, seeding an avalanche-like rapid increase in free electrons that is relatively easy to detect.

“An electron avalanche can start with a single seed electron. Because the air near a radioactive source has some charged oxygen molecules—even outside a shielded container—it provides an opportunity to seed an avalanche by applying an intense laser field,” said Howard Milchberg, a professor of physics and electrical and computer engineering at UMD and senior author of the research paper. “Electron avalanches were among the first demonstrations after the laser was invented. This is not a new phenomenon, but we are the first to use an infrared laser to seed an avalanche breakdown for radiation detection. The laser’s infrared wavelength is important, because it can easily and specifically detach electrons from oxygen ions.”

This short animation illustrates a new method, developed by physicists at the University of Maryland, to detect concealed radioactive material by using an infrared laser beam to induce an electron avalanche breakdown near the material. Credit: R. Schwartz/H. Milchberg/U. of Maryland (Click image to download hi-res version.)This short animation illustrates a new method, developed by physicists at the University of Maryland, to detect concealed radioactive material by using an infrared laser beam to induce an electron avalanche breakdown near the material. Credit: R. Schwartz/H. Milchberg/U. of Maryland (Click image to download hi-res version.)

Applying an intense, infrared laser field causes the free electrons caught in the beam to oscillate and collide with atoms nearby. When these collisions become energetic enough, they can rip more electrons away from the atoms.

“A simple view of avalanche is that after one collision, you have two electrons. Then, this happens again and you have four. Then the whole thing cascades until you have full ionization, where all atoms in the system have at least one electron removed,” explained Milchberg, who also has an appointment at UMD’s Institute for Research in Electronics and Applied Physics (IREAP).

As the air in the laser’s path begins to ionize, it has a measurable effect on the infrared light reflected, or backscattered, toward a detector. By tracking these changes, Schwartz, Milchberg and their colleagues were able to determine when the air began to ionize and how long it took to reach full ionization.

The timing of the ionization process, or the electron avalanche breakdown, gives the researchers an indication of how many seed electrons were available to begin the avalanche. This estimate, in turn, can indicate how much radioactive material is present in the target.

“Timing of ionization is one of the most sensitive ways to detect initial electron density,” said Daniel Woodbury, a physics graduate student at UMD and a co-author of the research paper. “We’re using a relatively weak probe laser pulse, but it’s ‘chirped,’ meaning that shorter wavelengths pass though the avalanching air first, then longer ones. By measuring the spectral components of the infrared light that passes through versus what is reflected, we can determine when ionization starts and reaches its endpoint.”

The researchers note that their method is highly specific and sensitive to the detection of radioactive material. Without a laser pulse, radioactive material alone will not induce an electron avalanche. Similarly, a laser pulse alone will not induce an avalanche, without the seed electrons created by the radioactive material.

While the method remains a proof-of-concept exercise for now, the researchers envision further engineering developments that they hope will enable practical applications to enhance security at ports of entry across the globe.

“Right now we’re working with a lab-sized laser, but in 10 years or so, engineers may be able to fit a system like this inside a van,” Schwartz said. “Anywhere you can park a truck, you can deploy such a system. This would provide a very powerful tool to monitor activity at ports.”

###

In addition to Milchberg, Schwartz, and Woodbury, UMD-affiliated co-authors of the research paper include Phillip Sprangle, professor of physics and electrical and computer engineering with an appointment at IREAP, and Joshua Isaacs, a physics graduate student.

The research paper, “Remote detection of radioactive material using mid-IR laser-driven avalanche breakdown,” Robert Schwartz, Daniel Woodbury, Joshua Isaacs, Phillip Sprangle and Howard Milchberg, was published in the journal Science Advances on March 22, 2019.

This work was supported by the Defense Threat Reduction Agency (Award No. HDTRA11510002), the Air Force Office of Scientific Research (Award Nos. FA9550-16-10121 and FA9550-16-10259), the Office of Naval Research (Award No. N00014-17-1-2705) and the Department of Energy (Award No. DE-NA0003864). The content of this article does not necessarily reflect the views of these organizations.

Media Relations Contact: Matthew Wright, 301-405-9267, This email address is being protected from spambots. You need JavaScript enabled to view it.

University of Maryland
College of Computer, Mathematical, and Natural Sciences
2300 Symons Hall
College Park, MD 20742
www.cmns.umd.edu
@UMDscience

About the College of Computer, Mathematical, and Natural Sciences

The College of Computer, Mathematical, and Natural Sciences at the University of Maryland educates more than 9,000 future scientific leaders in its undergraduate and graduate programs each year. The college's 10 departments and more than a dozen interdisciplinary research centers foster scientific discovery with annual sponsored research funding exceeding $175 million.

Ion experiment aces quantum scrambling test

scrambling blackhole linke monroe gallery

 

Researchers at the Joint Quantum Institute have implemented an experimental test for quantum scrambling, a chaotic shuffling of the information stored among a collection of quantum particles. Their experiments on a group of seven atomic ions, reported in the March 7 issue of Nature, demonstrate a new way to distinguish between scrambling—which maintains the amount of information in a quantum system but mixes it up—and true information loss. The protocol may one day help verify the calculations of quantum computers, which harness the rules of quantum physics to process information in novel ways.

“In terms of the difficulty of quantum algorithms that have been run, we’re toward the top of that list,” says Kevin Landsman, a graduate student at JQI and the lead author of the new paper. “This is a very complicated experiment to run, and it takes a very high level of control.”

The research team, which includes JQI Fellow and UMD Distinguished University Professor Christopher Monroe and JQI Fellow Norbert Linke, performed their scrambling tests by carefully manipulating the quantum behavior of seven charged atomic ions using well-timed sequences of laser pulses. They found that they could correctly diagnose whether information had been scrambled throughout a system of seven atoms with about 80% accuracy.

“With scrambling, one particle’s information gets blended or spread out into the entire system,” Landsman says. “It seems lost, but it’s actually still hidden in the correlations between the different particles.”

Quantum scrambling is a bit like shuffling a fresh deck of cards. The cards are initially ordered in a sequence, ace through king, and the suits come one after another. Once it’s sufficiently shuffled, the deck looks mixed up, but—crucially—there’s a way to reverse that process. If you kept meticulous track of how each shuffle exchanged the cards, it would be simple (though tedious) to “unshuffle” the deck by repeating all those exchanges and swaps in reverse.

Quantum scrambling is similar in that it mixes up the information stored inside a set of atoms and can also be reversed, which is a key difference between scrambling and true, irreversible information loss. Landsman and colleagues used this fact to their advantage in the new test by scrambling up one set of atoms and performing a related scrambling operation on a second set. A mismatch between the two operations would indicate that the process was not scrambling, causing the final step of the method to fail.

That final step relied on quantum teleportation—a method for transferring information between two quantum particles that are potentially very far apart. In the case of the new experiment, the teleportation is over modest distances—just 35 microns separates the first atom from the seventh—but it is the signature by which the team detects scrambling: If information is successfully teleported from one atom to another, it means that the state of the first atom is spread out across all of the atoms—something that only happens if the information is scrambled. If the information was lost, successful teleportation would not be possible. Thus, for an arbitrary process whose scrambling properties might not be known, this method could be used to test whether—or even how much—it scrambles.

The authors say that prior tests for scrambling couldn’t quite capture the difference between information being hidden and lost, largely because individual atoms tend to look similar in both cases. The new protocol, first proposed by theorists Beni Yoshida of the Perimeter Institute in Canada, and Norman Yao at the University of California, Berkeley, distinguishes the two cases by taking correlations between particular particles into account in the form of teleportation.

“When our colleague Norm Yao told us about this teleportation litmus test for scrambling and how it needed at least seven qubits capable of running many quantum operations in a sequence, we knew that our quantum computer was uniquely-suited for the job,” says Linke.

The experiment was originally inspired by the physics of black holes. Scientists have long pondered what happens when something falls into a black hole, especially if that something is a quantum particle. The fundamental rules of quantum physics suggest that regardless of what a black hole does to a quantum particle, it should be reversible—a prediction that seems at odds with a black hole’s penchant for crushing things into an infinitely small point and spewing out radiation. But without a real black hole to throw things into, researchers have been stuck speculating.

Quantum scrambling is one suggestion for how information can fall into a black hole and come out as random-looking radiation. Perhaps, the argument goes, it’s not random at all, and black holes are just excellent scramblers. The paper discusses this motivation, as well as an interpretation of the experiment that compares quantum teleportation to information going through a wormhole.

“Regardless of whether real black holes are very good scramblers, studying quantum scrambling in the lab could provide useful insights for the future development of quantum computing or quantum simulation,” Monroe says.

By Chris Cesare

In addition to Landsman, Monroe and Linke, the new paper had four other coauthors: Caroline Figgatt, now at Honeywell in Colorado; Thomas Schuster at UC Berkeley; Beni Yoshida at the Perimeter Institute for Theoretical Physics; and Norman Yao at UC Berkeley and Lawrence Berkeley National Laboratory.

 

APS Outstanding Referees Program Recognizes Three Faculty Members

OutstandingPin squareH. Dennis Drew, Howard M. Milchberg, and Jay Deep Sau have been recognized by the Americal Physical Society as Outstanding Referees for their contributions to the Physics community.

Each year, about 150 of the over 70,000 indivudal referees who help review manuscripts for publication in APS journals are recognized by APS for their efforts in maintaining the high standards of their journals. This is a lifetime award that has been carried out since 2008. 

Drew, Milchberg and Sau join these UMD Physics faculty who were recognized by the Outstanding Referees Program in previous years:

2016       Sarah Eno           

2013       Alessandra Buonanno   

2013       Jayanth Banavar              

2012       Thomas D. Cohen            

2011       James F. Drake 

2010       R. N. Mohapatra              

2009       Andrew Elby      

2009       Christopher Jarzynski    

2009       Edward Ott        

2009       John D. Weeks 

2009       O. W. Greenberg            

2009       S. M. Bhagat      

2009       Steven Rolston 

2009       T. R. Kirkpatrick

2009       Ted Jacobson    

2008       Dieter Brill          

2008       Hans R. Griem  

2008       J. Robert Dorfman          

2008       Michael E. Fisher             

2008       Sankar Das Sarma           

2008       Stephen J. Wallace          

2008       Theodore L. Einstein

 

More about the Outstanding Referees Program and a list of all members at https://journals.aps.org/OutstandingReferees.

 

Zohreh Davoudi Receives 2019 Sloan Research Fellowship

Zohreh Davoudi, an assistant professor of physics at the University of Maryland, has been awarded a 2019 Sloan Research Fellowship. Granted by the Alfred P. Sloan Foundation, this award identifies 126 early-career scientists every year based on their potential to contribute fundamentally significant research to the wider academic community. Zohreh Davoudi, an assistant professor of physics at the University of Maryland, has been awarded a 2019 Sloan Research Fellowship. Image credit: Faye Levine Zohreh Davoudi, an assistant professor of physics at the University of Maryland, has been awarded a 2019 Sloan Research Fellowship. Image credit: Faye Levine

Davoudi, a theoretical nuclear physicist who studies how complex phenomena in nature connect to the Standard Model of particle physics, will use the fellowship to further her research into properties of matter—especially in cases where matter is used in laboratories to detect new particles and interactions not currently accounted for by the Standard Model.

“It is a great honor to be selected as a Sloan Fellow,” said Davoudi, who also has an appointment at the Maryland Center for Fundamental Physics. “Knowing that a committee of esteemed physicists saw promise in my research plan provides further motivation to continue addressing fundamental questions in nuclear physics. It encourages me to keep doing what matters to me scientifically and academically.”

Davoudi’s research seeks to bridge the gap between the theory of quantum chromodynamics—a specialized part of the Standard Model that explains the interactions between quarks and gluons, two elementary particles that make up larger particles such as protons and neutrons—and observations that lie within and beyond the boundaries of current scientific knowledge. Her work could make important contributions to physicists’ understanding of a range of phenomena, such as the nature of dense matter in the interiors of neutron stars; fusion reactions that occur in the hearts of stars; and neutrinoless double beta decay, an exotic process that violates the tenets of the Standard Model.

“On paper, quantum chromodynamics provides a relatively simple picture of fundamental particles and interactions. However, a wealth of complexities arise in nature from these interactions,” Davoudi explained. “So far, physicists haven’t been able to fully build the connection between these complexities and the underlying theory. One of the main thrusts of my research has been to define pathways between computer simulations of nuclear systems and the properties of these systems as observed in nature.”

Much of Davoudi’s research applies a method called lattice quantum chromodynamics (LQCD). By restricting quantum chromodynamics to be defined by a set of discrete points in finite space and time, researchers can use LQCD to reduce big, intractable problems into smaller pieces that a supercomputer can handle. Davoudi’s research shows how to remove these restrictions to make reliable predictions about complex systems. Working with her collaborators, Davoudi has applied these methods to perform accurate simulations. For example, Davoudi and her colleagues were the first to calculate the rate of proton fusion and the beta decay of tritium, a radioactive isotope of hydrogen. The researchers described their findings in a research paper published in 2017 in the journal Physical Review Letters

With the Sloan Research Fellowship, Davoudi plans to continue pushing the boundaries of LQCD and other related techniques into new and exciting areas. As part of this effort, she plans to expand her research group to accelerate the pace of creating and testing new ideas. Davoudi is particularly excited about creating new collaborations with researchers at the Joint Quantum Institute, a partnership between UMD and the National Institute of Standards Technology, to use quantum computing to address computationally complex problems in nuclear physics.  

Davoudi has authored more than 20 peer-reviewed journal articles. Before joining UMD, she was a postdoctoral researcher at the Massachusetts Institute of Technology’s Center for Theoretical Physics from 2014 to 2017. During this time, she also was a visiting researcher at the Kavli Institute for Theoretical Physics at the University of California, Santa Barbara and a visiting researcher and program organizer at the Institute for Nuclear Theory in Seattle. 

Davoudi earned her bachelor’s and master’s degrees in physics from the Sharif University of Technology in Tehran, Iran, in 2007 and 2009, respectively. She earned her doctoral degree in theoretical physics from the University of Washington in 2014. In 2018, she was awarded the Kenneth G. Wilson Award for Excellence in Lattice Gauge Theory, one of the highest distinctions for a junior researcher in her field. Davoudi is also a fellow of the RIKEN Nishina Center for Accelerator-Based Science.

Davoudi joins the list of 40 current UMD College of Computer, Mathematical, and Natural Sciences faculty members who have received Sloan Research Fellowships.

The two-year, $70,000 Sloan Research Fellowships are awarded to U.S. and Canadian researchers in the fields of chemistry, computer science, economics, mathematics, computational and evolutionary molecular biology, neuroscience, ocean sciences, and physics. Candidates must be nominated by their fellow scientists and winning fellows are selected by independent panels of senior scholars on the basis of each candidate’s independent research accomplishments, creativity and potential to become a leader in his or her field.

“Sloan Research Fellows are the best young scientists working today,” said Adam Falk, president of the Alfred P. Sloan Foundation. “Sloan Fellows stand out for their creativity, for their hard work, for the importance of the issues they tackle, and the energy and innovation with which they tackle them. To be a Sloan Fellow is to be in the vanguard of twenty-first century science.” 

###

The research paper, “Proton-Proton Fusion and Tritium β Decay from Lattice Quantum Chromodynamics,” Martin Savage, Phiala Shanahan, Brian Tiburzi, Michael Wagman, Frank Winter, Silas Beane, Emmanuel Chang, Zohreh Davoudi, William Detmold and Kostas Orginos, was published August 10, 2017 in the journal Physical Review Letters

Media Relations Contacts: Matthew Wright, 301-405-9267, This email address is being protected from spambots. You need JavaScript enabled to view it. 

University of Maryland
College of Computer, Mathematical, and Natural Sciences
2300 Symons Hall
College Park, MD 20742
www.cmns.umd.edu
@UMDscience

About the College of Computer, Mathematical, and Natural Sciences

The College of Computer, Mathematical, and Natural Sciences at the University of Maryland educates more than 9,000 future scientific leaders in its undergraduate and graduate programs each year. The college's 10 departments and more than a dozen interdisciplinary research centers foster scientific discovery with annual sponsored research funding exceeding $175 million.