Department Responds to Global Helium Shortage


Assistant Professor N. Peter Armitage makes adjustments to the new helium reliquefier system.

Early in the fall semester, researchers and faculty members installed a helium recovery system and liquefier in the Bloomberg Center. Condensed matter physicists and astronomers in the department use liquefied helium to create extremely cold research conditions (often just a few degrees above absolute zero). When helium gas is released into the air, whether from a party balloon or from liquid helium vaporized in a research cryostat, it dissipates into the atmosphere, never to be utilized again. The new system, which captures used helium from labs throughout the department and then purifies and re-cools it back to the liquid state, serves as a much-needed recycler of this nonrenewable resource. It can store 500 liters of liquid helium.

“The liquefier delivers helium to researchers at a greatly reduced cost,” explains Assistant Professor N. Peter Armitage, who spearheaded the liquefier’s acquisition and installation. “The price of helium had increased about 30 percent in the five years or so leading up to when we decided to buy a liquefier last year, and the price has gone up about another 40 percent just in this year alone. And we can’t even get it reliably. Helium is becoming more expensive and less available.”

The current scarcity of helium could have significant implications for the space, high-tech, and medical industries.

“It’s just wasteful not to have a liquefier,” says Armitage. The liquefier creates a nearly closed loop of helium usage within Bloomberg, and by enabling a stable and affordable supply of liquid helium for the department, it will provide critical infrastructure for research from superconductivity and nanoscience to cosmology for years to come.

WMAP Team Scores Big with Gruber Cosmology Prize and World's Most Cited Paper


Professor Charles Bennett and the Wilkinson Microwave Anisotropy Probe (WMAP) space mission science team were awarded this year’s Gruber Cosmology Prize.

Bennett and the 26-member WMAP team were recognized for their unprecedented study of ancient light dating back to the infant universe. The WMAP team, led by Bennett, was able to determine a much more precise age, shape, composition, and history of the universe. The WMAP team also discovered that the first stars formed when the universe was only about 400 million years old.

The annual Gruber Cosmology Prize recognizes “fundamental advances in our understanding of the universe.” It is co-sponsored by the Gruber Foundation and the International Astronomical Union and aims to acknowledge and encourage further exploration.

“It is tremendously exciting to be recognized with the Gruber Cosmology Prize,” says Bennett, the Alumni Centennial Professor of Physics and Astronomy. “I have been very fortunate to work with the talented and fine people of the WMAP team, and I am particularly delighted that our entire science team has been honored with this prestigious award.” Bennett and the team shared the $500,000 prize, and Bennett was given a gold medal in August at the International Astronomical Union meeting in Beijing.

In addition to winning the Gruber Cosmology Prize, the research conducted by Bennett and the WMAP team resulted in production of the three most highly cited scientific papers in the world in 2011, according to Thomson Reuters’ Science Watch. Papers from the WMAP mission have made it to the top of the list in previous years (2003, 2007, 2009), but this is the first time they have taken the top three spots.

Milestone: The Judd-Ofelt Theory Turns 50


No one would have guessed that in 1962, rare earth metals would become a staple of modern living in less than 50 years time. Likewise, few would have guessed that 31-year-old physicist Brian Judd was on the verge of publishing seminal research on rare earth metals that his colleagues would cite well into the 21st century—becoming more popular and relied upon as decades came and went.

Brian Judd became fascinated by the rare earth ions in crystalline materials or liquids while studying at Oxford in the 1950s. He was particularly interested in the paramagnetic resonance of these 15 elements’ electrons, an effect akin to the nuclear magnetic resonance used in medical imaging devices.

The study of rare earth metals was advancing thanks in part to interest in crystals stimulated by radar and microwave research. But these metals and their ions were still puzzling researchers because, despite their similarities, they produced strikingly different signatures when analyzed with a spectrograph.

“They were just a big mystery,” says Judd, the Gerhard H. Dieke Professor Emeritus in the Department of Physics and Astronomy. And few researchers have done more to try to unravel that mystery than he has.

As late as the early 1960s, physicists struggled to find a mathematical language to describe the behavior of these elements at the sub-atomic level, where classical physics breaks down and quantum theory takes over.

What no one knew 50 years ago was that one day rare earth doped materials would play a crucial role in fiber optic communications, and make it possible to produce miniaturized electronic components for everything from laptop computers and mobile phones to hybrid cars and lasers.

Judd’s key scientific contribution to the field came in 1962, when he published a paper titled “Optical Absorption Intensities of Rare-Earth Ions,” that proposed a mathematical method for predicting how the f electrons in rare earths behave when they jump from one energy level to another while orbiting the atom’s nucleus.

Brian R. Judd, Gerhard H. Dieke Professor Emeritus

Judd, then at the University of California at Berkeley, used the mathematical theory of Lie groups to simplify the calculations needed to describe the behavior of rare earth electrons, without sacrificing accuracy.

His paper was published the same day as a structurally similar work on f electrons by George Ofelt, a graduate student of Brian Wybourne at Johns Hopkins University, which did not include Judd’s detailed numerical comparisons between theory and experiment for the radiation intensities of the electrons. The approach came to be known as the Judd-Ofelt Theory.

“The reason that the article I wrote was so successful was that it dealt directly with experiment,” Judd, now 81, said in an interview. “I remember that the British physicist Maurice Pryce told me never to get seduced by the mathematics. It’s very easy to be first of all amazed by how the mathematics is beautiful in a funny kind of way, by the surprises you get when you work out the mathematics.

“But Pryce said, ‘Never be seduced.’ And in fact when I wrote the article it was strictly calculations with the idea of describing only what an experimentalist would find useful.”

The Judd-Ofelt Theory quickly became a standard work, frequently cited in papers by other researchers. Its citation rate accelerated sharply in the early 1990s, after the invention of erbium-doped optical fiber amplifiers, critical for long-range optical fiber communications, and is now being referenced over 200 times per year.

In August, Judd and Ofelt were honored at a chemistry and physics conference in Udine, Italy, where a series of speakers celebrated the 50th anniversary of the publication of their work.

“It’s really defined the whole field for the people who study the spectroscopy of these rare earth elements,” says Daniel Reich, chair of the department.

The late physicist Brian Wybourne, who studied rare earth elements at Hopkins in the early 1960s, wrote in 2004 that the Judd-Ofelt papers “represent a paradigm that has dominated all further work on the intensities of rare earth transitions in solutions and solids up to the present time.”

Judd came to Hopkins in 1966, not long after authoring his groundbreaking research paper, and he would remain on the Homewood campus for the rest of his career. Today he is retired and living in Baltimore with his wife, Josephine Gridley, but keeps in touch with his former graduate students and maintains an office at the Homewood campus.

Even in retirement, Judd remains fascinated by the mathematical challenges posed by elements 57 through 71 of the periodic table. “There’s a whole pile of mysteries, to my mind, in the mathematics of rare earths,” he said.

“Everything can be calculated according to quantum mechanics. And everything works out well.” But certain complicated electron configurations produce results that still puzzle him, and he is still trying to understand them.

“If you get too interested in the mathematics, you can spend a lifetime working it out,” he says. “And in fact that’s what happened to me. I’ve become seduced by the mathematics.”

Faculty and Students Instrumental in LHC Breakthrough


 

Members of the department played important roles in this summer’s discovery of a new particle that contains qualities consistent with the Higgs boson—arguably the most important particle physics breakthrough in decades.

“We do not yet know where it will lead us. But it may have profound implications.”

For most of 2012, Associate Professor Andrei Gritsan, post-doctoral fellow Sara Bolognesi, and graduate student Andrew Whitbeck traveled back and forth from Baltimore to the Large Hadron Collider (LHC) in Geneva, Switzerland. The trio was part of a large, world-wide team of physicists working on the Compact Muon Solenoid (CMS), one of two massive particle detectors used to analyze the LHC’s proton-proton collisions in the search for the long-predicted Higgs boson.

Gritsan and his team focused their search for the Higgs boson on a specific form of decay of the Higgs into two Z bosons. They developed an array of very specific variables designed to indicate the presence of a new particle over the course of billions of individual collisions. And the presence of a new particle is precisely what they and their colleagues found.

But what particle? Much more research is needed to identify the new particle and confirm if it is, in fact, the Higgs boson. Such a confirmation would help explain how massless particles acquired mass in the very early history of the universe and add more legitimacy to the Standard Model. “We do not yet know where it will lead us,” explains Gritsan, who has been working at the LHC since 2005. “But it may have profound implications.”

Regardless of the particle’s true identity, Gritsan, Bolognesi, and Whitbeck contributed to its discovery and were front-and-center at the LHC during the exciting early days of July, when the revelation was announced. “It was a huge discovery that will influence my research for the rest of my career,” says Whitbeck.

Using Physics to Help Protect the Military


Robbins has brought his experience in bridging the gaps between atomic and macroscopic scales to the new Hopkins Extreme Materials Institute (HEMI). Housed in JHU’s Whiting School of Engineering, HEMI is headed by K. T. Ramesh, the Alonzo G. Decker, Jr. Professor of Science and Engineering. Its first project was launched in April 2012 with up to $90 million in funding over 10 years from the U.S. Army.

Robbins is part of that project, a collaborative endeavor called Materials in Extreme Dynamic Environments, which is a major component of President Obama’s Materials Genome Initiative. He and his colleagues are conducting fundamental research into protective materials, developing new predictive models for how well they will absorb energy in an attack.

“We want to understand and predict how every aspect of material structure from atomic bonds to macroscopic shape affects the behavior of materials at high strain rates,” Robbins says. “The central vision of the Materials Genome Initiative is that this type of capability will revolutionize the development of future materials.”