How Seawater Could Corrode Nuclear Fuel

Japan used seawater to cool nuclear fuel at the stricken Fukushima-Daiichi nuclear plant after the tsunami in March 2011 -- and that was probably the best action to take at the time, says Professor Alexandra Navrotsky of the University of California, Davis.

But Navrotsky and others have since discovered a new way in which seawater can corrode nuclear fuel, forming uranium compounds that could potentially travel long distances, either in solution or as very small particles. The research team published its work Jan. 23 in the Proceedings of the National Academy of Sciences.

"This is a phenomenon that has not been considered before," said Alexandra Navrotsky, distinguished professor of ceramic, earth and environmental materials chemistry. "We don't know how much this will increase the rate of corrosion, but it is something that will have to be considered in future."

Japan used seawater to avoid a much more serious accident at the Fukushima-Daiichi plant, and Navrotsky said, to her knowledge, there is no evidence of long-distance uranium contamination from the plant.

Uranium in nuclear fuel rods is in a chemical form that is "pretty insoluble" in water, Navrotsky said, unless the uranium is oxidized to uranium-VI -- a process that can be facilitated when radiation converts water into peroxide, a powerful oxidizing agent.

Peter Burns, professor of civil engineering and geological sciences at the University of Notre Dame and a co-author of the new paper, had previously made spherical uranium peroxide clusters, rather like carbon "buckyballs," that can dissolve or exist as solids.

In the new paper, the researchers show that in the presence of alkali metal ions such as sodium -- for example, in seawater -- these clusters are stable enough to persist in solution or as small particles even when the oxidizing agent is removed.

In other words, these clusters could form on the surface of a fuel rod exposed to seawater and then be transported away, surviving in the environment for months or years before reverting to more common forms of uranium, without peroxide, and settling to the bottom of the ocean. There is no data yet on how fast these uranium peroxide clusters will break down in the environment, Navrotsky said.

Navrotsky and Burns worked with the following co-authors: postdoctoral researcher Christopher Armstrong and project scientist Tatiana Shvareva, UC Davis; May Nyman, Sandia National Laboratory, Albuquerque, N.M.; and Ginger Sigmon, University of Notre Dame. The U.S. Department of Energy supported the project.

Story Source:

The above story is reprinted from materials provided byUniversity of California - Davis.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

---

Journal Reference:

1. C. R. Armstrong, M. Nyman, T. Shvareva, G. E. Sigmon, P. C. Burns, A. Navrotsky. Uranyl peroxide enhanced nuclear fuel corrosion in seawater. Proceedings of the National Academy of Sciences, 2012; DOI:10.1073/pnas.1119758109

New Material to Remove Radioactive Gas from Spent Nuclear Fuel

This illustration of a metal-organic framework, or MOF, shows the metal center bound to organic molecules. Each MOF has a specific framework determined by the choice of metal and organic. Sandia chemists identified a MOF whose pore size and high surface area can separate and trap radioactive iodine molecules from a stream of spent nuclear fuel. (Credit: Image courtesy of Sandia National Laboratories)

Science Daily  — Research by a team of Sandia chemists could impact worldwide efforts to produce clean, safe nuclear energy and reduce radioactive waste.

The discovery could be applied to nuclear fuel reprocessing or to clean up nuclear reactor accidents. A characteristic of nuclear energy is that used fuel can be reprocessed to recover fissile materials and provide fresh fuel for nuclear power plants. Countries such as France, Russia and India are reprocessing spent fuel.The Sandia researchers have used metal-organic frameworks (MOFs) to capture and remove volatile radioactive gas from spent nuclear fuel. "This is one of the first attempts to use a MOF for iodine capture," said chemist Tina Nenoff of Sandia's Surface and Interface Sciences Department.

The process also reduces the volume of high-level wastes, a key concern of the Sandia researchers. "The goal is to find a methodology for highly selective separations that result in less waste being interred," Nenoff said.

Part of the challenge of reprocessing is to separate and isolate radioactive components that can't be burned as fuel. The Sandia team focused on removing iodine, whose isotopes have a half-life of 16 million years, from spent fuel.

They studied known materials, including silver-loaded zeolite, a crystalline, porous mineral with regular pore openings, high surface area and high mechanical, thermal and chemical stability. Various zeolite frameworks can trap and remove iodine from a stream of spent nuclear fuel, but need added silver to work well.

"Silver attracts iodine to form silver iodide," Nenoff said. "The zeolite holds the silver in its pores and then reacts with iodine to trap silver iodide."

But silver is expensive and poses environmental problems, so the team set out to engineer materials without silver that would work like zeolites but have higher capacity for the gas molecules. They explored why and how zeolite absorbs iodine, and used the critical components discovered to find the best MOF, named ZIF-8.

"We investigated the structural properties on how they work and translated that into new and improved materials," Nenoff said.

MOFs are crystalline, porous materials in which a metal center is bound to organic molecules by mild self-assembly chemical synthesis. The choice of metal and organic result in a very specific final framework.

The trick was to find a MOF highly selective for iodine. The Sandia researchers took the best elements of the zeolite Mordenite -- its pores, high surface area, stability and chemical absorption -- and identified a MOF that can separate one molecule, in this case iodine, from a stream of molecules. The MOF and pore-trapped iodine gas can then be incorporated into glass waste for long-term storage.

The Sandia team also fabricated MOFs, made of commercially available products, into durable pellets. The as-made MOF is a white powder with a tendency to blow around. The pellets provide a stable form to use without loss of surface area, Nenoff said.

Sandia has applied for a patent on the pellet technology, which could have commercial applications.

The Sandia researchers are part of the Off-Gas Sigma Team, which is led by Oak Ridge National Laboratory and studies waste-form capture of volatile gasses associated with nuclear fuel reprocessing. Other team members -- Pacific Northwest, Argonne and Idaho national laboratories -- are studying other volatile gases such as krypton, tritium and carbon.

The project began six years ago and the Sigma Team was formalized in 2009. It is funded by the U.S. Department of Energy Office of Nuclear Energy.

Sandia's iodine and MOFs research was featured in two recent articles in the Journal of the American Chemical Societyauthored by Nenoff and team members Dorina Sava, Mark Rodriguez, Jeffery Greathouse, Paul Crozier, Terry Garino, David Rademacher, Ben Cipiti, Haiqing Liu, Greg Halder, Peter Chupas, and Karena Chapman. Chupas, Halder and Chapman are from Argonne.

"The most important thing we did was introduce a new class of materials to nuclear waste remediation," said Sava, postdoctoral appointee on the project.

Nenoff said another recent paper in Industrial & Engineering Chemistry Research shows a one-step process that incorporates MOFs with iodine in a low-temperature, glass waste form. "We have a volatile off-gas capture using a MOF and we have a durable waste form," Nenoff said.

Nenoff and her colleagues are continuing their research into new and optimized MOFs for enhanced volatile gas separation and capture.

"We've shown that MOFs have the capacity to capture and, more importantly, retain many times more iodine than current materials technologies," said Argonne's Chapman.

Story Source:

The above story is reprinted from materials provided by DOE/Sandia National Laboratories, via News wise.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

---

Journal References:

1. Karena W. Chapman, Dorina F. Sava, Gregory J. Halder, Peter J. Chupas, Tina M. Nenoff. Trapping Guests within a Nanoporous Metal–Organic Framework through Pressure-Induced Amorphization. Journal of the American Chemical Society, 2011; 133 (46): 18583 DOI:10.1021/ja2085096
2. Dorina F. Sava, Mark A. Rodriguez, Karena W. Chapman, Peter J. Chupas, Jeffery A. Greathouse, Paul S. Crozier, Tina M. Nenoff. Capture of Volatile Iodine, a Gaseous Fission Product, by Zeolitic Imidazolate Framework-8.Journal of the American Chemical Society, 2011; 133 (32): 12398 DOI: 10.1021/ja204757x

Advanced Supercomputer Models Supplant Real-World Nuclear Weapons Tests

Advanced Supercomputer Models Supplant Real-World Nuclear Weapons Tests | Popular Science@import "/files/css/a1c433465f8fe485195cb11d70c36108.css";@import "/files/css/33f6b7ecb4513ed2fe6c670880a27187.css"; home Login/Register Newsletter Subscribe RSS GadgetsComputersCamerasSmartphonesVideo GamesCarsConceptsHybridsElectric CarsScienceFuture of the EnvironmentEnergyHealthPopSci Eco TourTechnologyMilitaryAviationSpaceRobotsEngineeringDIYProjectsHacksToolsAuto DIYMore From Our Partner: Toolmonger GalleriesVideosColumnsThe GrouseSex FilesGreen Dream Innovation ChallengesHow It WorksFeatures Tweet Digg Advanced Supercomputer Models Supplant Real-World Nuclear Weapons Tests But are they accurate? By Rebecca Boyle Posted 11.02.2011 at 5:41 pm 5 Comments
Trinity Test Jack Aeby / Department of Energy

While our friends Jaguar and Ranger toil to model the Earth’s atmosphere, star formation and battery chemistry, other supercomputers are working on classified national security problems. Namely: What happens when a nuclear weapon explodes? Are we sure our nuclear arsenal would actually work, should, God forbid, we decide to use it?

Related ArticlesJaguar, What Are You Working on Today?Jaguar is Getting a GPU Upgrade, to Make it the World's Fastest Supercomputer AgainOak Ridge Labs Using World's Fastest Supercomputer to Model Next-Gen Nuclear PlantsTagsTechnology, Rebecca Boyle, lawrence livermore national laboratory, military, nuclear tests, nuclear weapons, supercomputer, supercomputersAfter live nuclear testing ended (or at least was supposed to end) in 1992, supercomputers supplanted explosions so scientists could continue studying how they work. The nation’s stockpile stewardship program, run by the National Nuclear Security Administration at three national laboratories, checks the nation’s nukes for any problems. Supercomputers at Los Alamos, Sandia and Lawrence Livermore national labs conduct tests that can in some ways go beyond the detail of any live explosion, as the Washington Post reports.

They have found some good news and some bad news, as Sen. Jon Kyl, R-Ariz., puts it: “The good news is that it tells us a lot more about these weapons than we ever knew before. The bad news is that it tells us the weapons have bigger problems that we realized,” he tells the WaPo.

For example, several years ago scientists at Lawrence Livermore National Laboratory modeled the life cycle of a nuke, from the moment it leaves storage to the instant it impacts its target. They found some fatal flaws that would cause the warhead to “fail catastrophically,” as the Post quotes Bruce T. Goodwin, Livermore’s principal associate director for weapons programs. The military has since fixed the problem, the Post reports.

The flaw lay in the weapon’s ballistics handling, not its explosivity, so this is something that could never have been revealed in a physical test, the Post notes. The power of supercomputers to model these types of things could negate the need for physical testing, some officials say — but Congress has still not ratified the Comprehensive Test Ban Treaty (although the U.S. abides by it). It turns out not everyone trusts supercomputers. Kyl believes while they are helpful, they’re not a substitute for testing, the Post quotes him saying. “That’s why, even though we’re not testing right now, we should not give up the legal right to test,” he said.

Click through to the Post's account for the full story on how supercomputers are helping model the most explosive forces in nature.

[Washington Post]

Previous Article: See The Data-Centric Universe, Then and NowNext Article: What Are You Doing Today, iForge? 5 Comments Link to this comment D13 11/02/11 at 10:52 pm

what further testing of "nukes" is needed?

"Do not try and bend the spoon. That's impossible. Instead... only try to realize the truth. There is no spoon."

Link to this comment trireme 11/03/11 at 1:27 am

@ D13- Brand-new-off-the-assembly-line nukes don't need testing, but the US stockpile has many 30+ year old nukes whose components have been bombarded by radiation for all that time. There is a program to refurbish/replace the components on these older weapons, but there is a backlog. Politicians don't like nuclear testing, but many nuclear experts don't trust the computer simulations.

Link to this comment emneumann 11/03/11 at 7:24 am

Not to mention the spontaneous degredation of the fissile and fusable elements that are the true heart of the bomb. Over time, there is less of the U-235 and Deuterium and or Tritium that would produce a lower yield in the best case or prevent a chain reaction altogether in the worst case.

Link to this comment scientific anomaly 11/03/11 at 8:20 am

well thats not extremely good that when its in mid flight it decides to take out the u.s. military base than the enemies. atleast the terrorrists would be dead in the explosion too

-Knock knock
-Who's there?
-The Doctor.
-Doctor Who?
-Yes

Link to this comment Q 11/03/11 at 8:33 am

D13,
Any and all electronic components as they are stored degrade. Some electronic components simply stop working all together sitting on the shelf. With that said, consider how old the original nuclear bombs, missiles and arsenal are. The active ones we have need to be constantly pulled and the electronics constantly test, simply because they are aging.

Besides, over the course of time as you know, there have been many improvements in electronics and so upgrades are made to the weapons too.

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November 2011: Data Is Power

This month, we examine all the ways information is driving our future, from dating to crime to how we see the world.

Plus: turning your smartphone into a wallet, BMW's electric cars, and a space heater with no fan.

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Pocket Particle Accelerators Like This One Could Bring Safer Nuclear Power to Neighborhoods

Meet EMMA, the Electron Model of Many Applications
EMMA Installation Science and Technology Facilities Council-UK

A wee particle accelerator in the English countryside could be a harbinger of a safer, cleaner future of energy. Specifically, nuclear energy, but not the type that has wrought havoc in Japan and controversy throughout Europe and the U.S. It would be based on thorium, a radioactive element that is much more abundant, and much more safe, than traditional sources of nuclear power.

Some advocates believe small nuclear reactors powered by thorium could wean the world off coal and natural gas, and do it more safely than traditional nuclear. Thorium is not only abundant, but more efficient than uranium or coal — one ton of the silver metal can produce as much energy as 200 tons of uranium, or 3.5 million tons of coal, as the Mail on Sunday calculates it.

The newspaper took a tour of a small particle accelerator that could be used to power future thorium reactors. Nicknamed EMMA — the Electron Model of Many Applications — the accelerator would be used to jump-start fissile nuclear reactions inside a small-scale thorium power plant.

Thorium reactors would not melt down, in part because they require an external input to produce fission. Thorium atoms would release energy when bombarded by high-energy neutrons, such as the type supplied in a particle accelerator.

Providing that stimulus is one obstacle to building small thorium reactors — but a new generation of accelerators like EMMA, and someday potentially even smaller, luggage-sized ones — could do the job.

EMMA is the first non- scaling, fixed-field, alternating-gradient (NS-FFAG) accelerator, qualities that make it easier to operate and maintain, more reliable and compact, more flexible and more efficient, according to British researchers. Other particle accelerators use alternating electric fields, which require special safety measures to guard against microwave exposure, for instance. EMMA’s alternating magnetic field gradients are a more efficient and cheaper way to accelerate particles to higher energies. (Brookhaven National Laboratory explains in more detail here.)

EMMA operates at operates around 20 MeV, or 20 million electronvolts, a paltry amount for an atom accelerator. The Tevatron, for instance, accelerates particles to 1 tera-electron volts. The Large Hadron Collider is designed to speed them to 7 TeV. But thorium reactors would not need such high energies to initiate fusion.

British scientists are already working on a successor called PAMELA, the Particle Accelerator for Medical Applications, which will be used to treat cancer.

Click through to the Mail for a full tour of EMMA, its sister apparatus ALICE (Accelerators and Lasers In Combined Experiments), and a description of British efforts to produce thorium power.

[Mail on Sunday]

View the original article here

GPS stations can detect clandestine nuclear tests

ScienceDaily (June 8, 2011) — At the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), American researchers are unveiling a new tool for detecting illegal nuclear explosions: Earth's global positioning system (GPS).

Even underground nuclear tests leave their mark on the part of the upper atmosphere known as the ionosphere, the researchers discovered, when they examined GPS data recorded the same day as a North Korean nuclear test in 2009. Within minutes on that day, GPS stations in nearby countries registered a change in ionospheric electron density, as a bubble of disturbed particles spread out from the test site and across the planet.

"Its as if the shockwave from the underground explosion caused the earth to 'punch up' into the atmosphere, creating another shockwave that pushed the air away from ground zero," said Ralph von Frese, professor of earth sciences at Ohio State University and senior author on the study.

Jihye Park, a doctoral student in geodetic science at the university, is presenting the results of the study in a poster session at the CTBTO meeting in Vienna, Austria.

International authorities already possess several methods for detecting illegal nuclear tests, Park said. Seismic detectors pick up shockwaves through land, and acoustic sensors monitor for shockwaves through water and the air for tests that happen above ground. Chemical sensors detect airborne radioactive gas and dust as definitive evidence of a nuclear explosion. However, these particles may be lacking if the explosion is contained deeply below ground.

"GPS is a complement to these other methods, and can help confirm that a nuclear test has taken place -- especially when the test was underground, so that its effect in the air is very subtle, and otherwise nearly impossible to detect," she said.

While GPS was designed for location purposes, the technology has always been especially sensitive to atmospheric disturbances, said Dorota Grejner-Brzezinska, a professor of geodetic science at Ohio State and Park's advisor.

"GPS signals must pass from transmitters on satellites high above the planet down to ground-based receivers," Grejner-Brzezinska explained. "Air molecules -- more specifically, the electrons and other charged particles in the ionosphere -- interfere with the signal, generating position error. Part of our research concerns how to compensate for that vulnerability and make GPS work better. Jihye found a way to take that vulnerability and turn it into something useful."

Park wrote computer algorithms that search GPS signals for patterns indicating a sudden fluctuation in atmospheric electron density in specific locations, which is what happens when a shockwave pushes a bubble of air through the atmosphere. As the GPS signal passes through the edge of the bubble, the change in electron density disturbs the signal in a noticeable way.

Park was able to utilize data collected from GPS receivers that the International GNSS Service (IGS) has planted around the globe for research purposes. Five of the IGS receivers scattered in Eastern Asia provided data for this study, as did six receivers belonging to the South Korean GPS network.

When Park analyzed the data from the 11 GPS stations, she detected a sudden spike in atmospheric electron density after the May 25, 2009 underground test, which is believed to have happened just before 1:00 a.m. Coordinated Universal Time that day.

Within 25 minutes, the shockwave had traveled 225 miles to the nearest GPS station in the study, which was located in Inje County, in Gangwon Province, South Korea. That means that it was traveling through the air at 9 miles per minute, or 540 miles per hour. Within that first hour, it had reached all 11 stations.

Based on the timing of the shockwave, the researchers traced the origin of the explosion back to P'unggye, in Hamyong Province, North Korea. This finding agrees with seismic data from the event, which was collected by the CTBTO and the US Geological Survey.

The researchers will continue this work as Park earns her PhD, and they are seeking funding and partnerships to expand it further. In the meantime, they have submitted a paper on the discovery to the journal Geophysical Research Letters.

Collaborators on the study include Yu Morton, professor of electrical and computer engineering at Miami University in Oxford, Ohio, and Luis Gaya-Pique of CTBTO's On-Site Inspection Division.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Ohio State University. The original article was written by Pam Frost Gorder.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

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Nuclear magnetic resonance with no magnets

ScienceDaily (May 19, 2011) — Nuclear magnetic resonance (NMR), a scientific technique associated with outsized, very low-temperature, superconducting magnets, is one of the principal tools in the chemist's arsenal, used to study everything from alcohols to proteins to such frontiers as quantum computing. In hospitals the machinery of NMR's cousin, magnetic resonance imaging (MRI), is as loud as it is big, but nevertheless a mainstay of diagnosis for a wide range of medical conditions.

It sounds like magic, but now two groups of scientists at Berkeley Lab and UC Berkeley, one expert in chemistry and the other in atomic physics, long working together as a multidisciplinary team, have shown that chemical analysis with NMR is practical without using any magnets at all.

Dmitry Budker of Berkeley Lab's Nuclear Science Division, a professor of physics at UC Berkeley, is a protean experimenter who leads a group with interests ranging as far afield as tests of the fundamental theorems of quantum mechanics, biomagnetism in plants, and violations of basic symmetry relations in atomic nuclei. Alex Pines, of the Lab's Materials Sciences Division and UCB's Department of Chemistry, is a modern master of NMR and MRI. He guides the work of a talented, ever-changing cadre of postdocs and grad students known as the "Pinenuts" -- not only in doing basic research in NMR but in increasing its practical applications. Together the groups have extended the reach of NMR by eliminating the use of magnetic fields at different stages of NMR measurements, and have finally done away with external magnetic fields entirely.

Spinning the information

NMR and MRI depend on the fact that many atomic nuclei possess spin (not classical rotation but a quantum number) and -- like miniature planet Earths with north and south magnetic poles -- have their own dipolar magnetic fields. In conventional NMR these nuclei are lined up by a strong external magnetic field, then knocked off axis by a burst of radio waves. The rate at which each kind of nucleus then "wobbles" (precesses) is unique and identifies the element; for example a hydrogen-1 nucleus, a lone proton, precesses four times faster than a carbon-13 nucleus having six protons and seven neutrons.

Being able to detect these signals depends first of all on being able to detect net spin; if the sample were to have as many spin-up nuclei as spin-down nuclei it would have zero polarization, and signals would cancel. But since the spin-up orientation requires slightly less energy, a population of atomic nuclei usually has a slight excess of spin ups, if only by a few score in a million.

"Conventional wisdom holds that trying to do NMR in weak or zero magnetic fields is a bad idea," says Budker, "because the polarization is tiny, and the ability to detect signals is proportional to the strength of the applied field."

The lines in a typical NMR spectrum reveal more than just different elements. Electrons near precessing nuclei alter their precession frequencies and cause a "chemical shift" -- moving the signal or splitting it into separate lines in the NMR spectrum. This is the principal goal of conventional NMR, because chemical shifts point to particular chemical species; for example, even when two hydrocarbons contain the same number of hydrogen, carbon, or other atoms, their signatures differ markedly according to how the atoms are arranged. But without a strong magnetic field, chemical shifts are insignificant.

"Low- or zero-field NMR starts with three strikes against it: small polarization, low detection efficiency, and no chemical-shift signature," Budker says.

"So why do it?" asks Micah Ledbetter of Budker's group. It's a rhetorical question. "The main thing is getting rid of the big, expensive magnets needed for conventional NMR. If you can do that, you can make NMR portable and reduce the costs, including the operating costs. The hope is to be able to do chemical analyses in the field -- underwater, down drill holes, up in balloons -- and maybe even medical diagnoses, far from well-equipped medical centers."

"As it happens," Budker says, "there are already methods for overcoming small polarization and low detection efficiency, the first two objections to low- or zero-field NMR. By bringing these separate methods together, we can tackle the third objection -- no chemical shift -- as well. Zero-field NMR may not be such a bad idea after all."

Net spin orientation can be increased in various ways, collectively known as hyperpolarization. One way to hyperpolarize a sample of hydrogen gas is to change the proportions of parahydrogen and orthohydrogen in it. Like most gases, at normal temperature and pressure each hydrogen molecule consists of two atoms bound together. If the spins of the proton nuclei point in the same direction, it's orthohydrogen. If the spins point in opposite directions, it's parahydrogen.

By the mathematics of quantum mechanics, adding up the spin states of the two protons and two electrons in a hydrogen molecule equals three ways for orthohydrogen to reach spin one; parahydrogen can only be spin zero, however. Thus orthohydrogen molecules normally account for three-quarters of hydrogen gas and parahydrogen only one-quarter.

Parahydrogen can be enhanced to 50 percent or even 100 percent using very low temperatures, although the right catalyst must be added or the conversion could take days if not weeks. Then, by chemically reacting spin-zero parahydrogen molecules with an initial chemical, net polarization of the product of the hydrogenation may end up highly polarized. This hyperpolarization can be extended not only to the parts of the molecule directly reacting with the hydrogen, but even to the far corners of large molecules. The Pinenuts, who devised many of the techniques, are masters of parahydrogen production and its hyperpolarization chemistry.

"With a high proportion of parahydrogen you get a terrific degree of polarization," says Ledbetter. "The catch is, it's spin zero. It doesn't have a magnetic moment, so it doesn't give you a signal! But all is not lost…."

And now for the magic

In low magnetic fields, increasing detection efficiency requires a very different approach, using detectors called magnetometers. In early low-field experiments, magnetometers called SQUID were used (superconducting quantum interference devices). Although exquisitely sensitive, SQUID, like the big magnets used in high-field NMR, must be cryogenically cooled to low temperatures.

Optical-atomic magnetometers are based on a different principle -- one that, curiously, is something like NMR in reverse, except that optical-atomic magnetometers measure whole atoms, not just nuclei. Here, an external magnetic field is measured by measuring the spin of the atoms inside the magnetometer's own vapor cell, typically a thin gas of an alkali metal such as potassium or rubidium. Their spin is influenced by polarizing the atoms with laser light; if there's even a weak external field, they begin to precess. A second laser beam probes how much they're precessing and thus just how strong the external field is.

Budker's group has brought optical-atomic magnetometry to a high pitch by such techniques as extending the "relaxation time," the time before the polarized vapor loses its polarization. In previous collaborations, the Pines and Budker groups have used magnetometers with NMR and MRI to image the flow of water using only the Earth's magnetic field or no field at all, to detect hyperpolarized xenon gas (but without analyzing chemical states), and in other applications. The next frontier is chemical analysis.

"No matter how sensitive your detector or how polarized your samples, you can't detect chemical shifts in a zero field," Budker says. "But there has always been another signal in NMR that can be used for chemical analysis -- it's just that it is usually so weak compared to chemical shifts, it has been the poor relative in the NMR family. It's called J-coupling."

Discovered in 1950 by the NMR pioneer Erwin Hahn and his graduate student, Donald Maxwell, J-coupling provides an interaction pathway between two protons (or other nuclei with spin), which is mediated by their associated electrons. The signature frequencies of these interactions, appearing in the NMR spectrum, can be used to determine the angle between chemical bonds and distances between the nuclei.

"You can even tell how many bonds separate the two spins," Ledbetter says. "J-coupling reveals all that information."

The resulting signals are highly specific and indicate just what chemical species is being observed. Moreover, as Hahn saw right away, while the signal can be modified by external magnetic fields, it does not vanish in their absence.

With Ledbetter in the lead, the Budker/Pines collaboration built a magnetometer specifically designed to detect J-coupling at zero magnetic field. Thomas Theis, a graduate student in the Pines group, supplied the parahydrogen and the chemical expertise to take advantage of parahydrogen-induced polarization. Beginning with styrene, a simple hydrocarbon, they measured J-coupling on a series of hydrocarbon derivatives including hexane and hexene, phenylpropene, and dimethyl maleate, important constituents of plastics, petroleum products, even perfumes.

"The first step is to introduce the parahydrogen," Budker says. "The top of the set-up is a test tube containing the sample solution, with a tube down to the bottom through which the parahydrogen is bubbled." In the case of styrene, the parahydrogen was taken up to produce ethylbenzene, a specific arrangement of eight carbon atoms and 10 hydrogen atoms.

Immediately below the test tube sits the magnetometer's alkali vapor cell, a device smaller than a fingernail, microfabricated by Svenja Knappe and John Kitching of the National Institute of Standards and Technology. The vapor cell, which sits on top of a heater, contains rubidium and nitrogen gas through which pump and probe laser beams cross at right angles. The mechanism is surrounded by cylinders of "mu metal," a nickel-iron alloy that acts as a shield against external magnetic fields, including Earth's.

Ledbetter's measurements produced signatures in the spectra which unmistakably identified chemical species and exactly where the polarized protons had been taken up. When styrene was hydrogenated to form ethylbenzene, for example, two atoms from a parahydrogen molecule bound to different atoms of carbon-13 (a scarce but naturally occurring isotope whose nucleus has spin, unlike more abundant carbon-12).

J-coupling signatures are completely different for otherwise identical molecules in which carbon-13 atoms reside in different locations. All of this is seen directly in the results. Says Budker, "When Micah goes into the laboratory, J-coupling is king."

Of the present football-sized magnetometer and its lasers, Ledbetter says, "We're already working on a much smaller version of the magnetometer that will be easy to carry into the field."

Although experiments to date have been performed on molecules that are easily hydrogenated, hyperpolarization with parahydrogen can also be extended to other kinds of molecules. Budker says, "We're just beginning to develop zero-field NMR, and it's still too early to say how well we're going to be able to compete with high-field NMR. But we've already shown that we can get clear, highly specific spectra, with a device that has ready potential for doing low-cost, portable chemical analysis."

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by DOE/Lawrence Berkeley National Laboratory.

Journal Reference:

T. Theis, P. Ganssle, G. Kervern, S. Knappe, J. Kitching, M. P. Ledbetter, D. Budker, A. Pines. Parahydrogen-enhanced zero-field nuclear magnetic resonance. Nature Physics, 2011; DOI: 10.1038/nphys1986

Note: If no author is given, the source is cited instead.

Disclaimer: This article is not intended to provide medical advice, diagnosis or treatment. Views expressed here do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Nuclear magnetic resonance with no magnets

ScienceDaily (May 19, 2011) — Nuclear magnetic resonance (NMR), a scientific technique associated with outsized, very low-temperature, superconducting magnets, is one of the principal tools in the chemist's arsenal, used to study everything from alcohols to proteins to such frontiers as quantum computing. In hospitals the machinery of NMR's cousin, magnetic resonance imaging (MRI), is as loud as it is big, but nevertheless a mainstay of diagnosis for a wide range of medical conditions.

It sounds like magic, but now two groups of scientists at Berkeley Lab and UC Berkeley, one expert in chemistry and the other in atomic physics, long working together as a multidisciplinary team, have shown that chemical analysis with NMR is practical without using any magnets at all.

Dmitry Budker of Berkeley Lab's Nuclear Science Division, a professor of physics at UC Berkeley, is a protean experimenter who leads a group with interests ranging as far afield as tests of the fundamental theorems of quantum mechanics, biomagnetism in plants, and violations of basic symmetry relations in atomic nuclei. Alex Pines, of the Lab's Materials Sciences Division and UCB's Department of Chemistry, is a modern master of NMR and MRI. He guides the work of a talented, ever-changing cadre of postdocs and grad students known as the "Pinenuts" -- not only in doing basic research in NMR but in increasing its practical applications. Together the groups have extended the reach of NMR by eliminating the use of magnetic fields at different stages of NMR measurements, and have finally done away with external magnetic fields entirely.

Spinning the information

NMR and MRI depend on the fact that many atomic nuclei possess spin (not classical rotation but a quantum number) and -- like miniature planet Earths with north and south magnetic poles -- have their own dipolar magnetic fields. In conventional NMR these nuclei are lined up by a strong external magnetic field, then knocked off axis by a burst of radio waves. The rate at which each kind of nucleus then "wobbles" (precesses) is unique and identifies the element; for example a hydrogen-1 nucleus, a lone proton, precesses four times faster than a carbon-13 nucleus having six protons and seven neutrons.

Being able to detect these signals depends first of all on being able to detect net spin; if the sample were to have as many spin-up nuclei as spin-down nuclei it would have zero polarization, and signals would cancel. But since the spin-up orientation requires slightly less energy, a population of atomic nuclei usually has a slight excess of spin ups, if only by a few score in a million.

"Conventional wisdom holds that trying to do NMR in weak or zero magnetic fields is a bad idea," says Budker, "because the polarization is tiny, and the ability to detect signals is proportional to the strength of the applied field."

The lines in a typical NMR spectrum reveal more than just different elements. Electrons near precessing nuclei alter their precession frequencies and cause a "chemical shift" -- moving the signal or splitting it into separate lines in the NMR spectrum. This is the principal goal of conventional NMR, because chemical shifts point to particular chemical species; for example, even when two hydrocarbons contain the same number of hydrogen, carbon, or other atoms, their signatures differ markedly according to how the atoms are arranged. But without a strong magnetic field, chemical shifts are insignificant.

"Low- or zero-field NMR starts with three strikes against it: small polarization, low detection efficiency, and no chemical-shift signature," Budker says.

"So why do it?" asks Micah Ledbetter of Budker's group. It's a rhetorical question. "The main thing is getting rid of the big, expensive magnets needed for conventional NMR. If you can do that, you can make NMR portable and reduce the costs, including the operating costs. The hope is to be able to do chemical analyses in the field -- underwater, down drill holes, up in balloons -- and maybe even medical diagnoses, far from well-equipped medical centers."

"As it happens," Budker says, "there are already methods for overcoming small polarization and low detection efficiency, the first two objections to low- or zero-field NMR. By bringing these separate methods together, we can tackle the third objection -- no chemical shift -- as well. Zero-field NMR may not be such a bad idea after all."

Net spin orientation can be increased in various ways, collectively known as hyperpolarization. One way to hyperpolarize a sample of hydrogen gas is to change the proportions of parahydrogen and orthohydrogen in it. Like most gases, at normal temperature and pressure each hydrogen molecule consists of two atoms bound together. If the spins of the proton nuclei point in the same direction, it's orthohydrogen. If the spins point in opposite directions, it's parahydrogen.

By the mathematics of quantum mechanics, adding up the spin states of the two protons and two electrons in a hydrogen molecule equals three ways for orthohydrogen to reach spin one; parahydrogen can only be spin zero, however. Thus orthohydrogen molecules normally account for three-quarters of hydrogen gas and parahydrogen only one-quarter.

Parahydrogen can be enhanced to 50 percent or even 100 percent using very low temperatures, although the right catalyst must be added or the conversion could take days if not weeks. Then, by chemically reacting spin-zero parahydrogen molecules with an initial chemical, net polarization of the product of the hydrogenation may end up highly polarized. This hyperpolarization can be extended not only to the parts of the molecule directly reacting with the hydrogen, but even to the far corners of large molecules. The Pinenuts, who devised many of the techniques, are masters of parahydrogen production and its hyperpolarization chemistry.

"With a high proportion of parahydrogen you get a terrific degree of polarization," says Ledbetter. "The catch is, it's spin zero. It doesn't have a magnetic moment, so it doesn't give you a signal! But all is not lost…."

And now for the magic

In low magnetic fields, increasing detection efficiency requires a very different approach, using detectors called magnetometers. In early low-field experiments, magnetometers called SQUID were used (superconducting quantum interference devices). Although exquisitely sensitive, SQUID, like the big magnets used in high-field NMR, must be cryogenically cooled to low temperatures.

Optical-atomic magnetometers are based on a different principle -- one that, curiously, is something like NMR in reverse, except that optical-atomic magnetometers measure whole atoms, not just nuclei. Here, an external magnetic field is measured by measuring the spin of the atoms inside the magnetometer's own vapor cell, typically a thin gas of an alkali metal such as potassium or rubidium. Their spin is influenced by polarizing the atoms with laser light; if there's even a weak external field, they begin to precess. A second laser beam probes how much they're precessing and thus just how strong the external field is.

Budker's group has brought optical-atomic magnetometry to a high pitch by such techniques as extending the "relaxation time," the time before the polarized vapor loses its polarization. In previous collaborations, the Pines and Budker groups have used magnetometers with NMR and MRI to image the flow of water using only the Earth's magnetic field or no field at all, to detect hyperpolarized xenon gas (but without analyzing chemical states), and in other applications. The next frontier is chemical analysis.

"No matter how sensitive your detector or how polarized your samples, you can't detect chemical shifts in a zero field," Budker says. "But there has always been another signal in NMR that can be used for chemical analysis -- it's just that it is usually so weak compared to chemical shifts, it has been the poor relative in the NMR family. It's called J-coupling."

Discovered in 1950 by the NMR pioneer Erwin Hahn and his graduate student, Donald Maxwell, J-coupling provides an interaction pathway between two protons (or other nuclei with spin), which is mediated by their associated electrons. The signature frequencies of these interactions, appearing in the NMR spectrum, can be used to determine the angle between chemical bonds and distances between the nuclei.

"You can even tell how many bonds separate the two spins," Ledbetter says. "J-coupling reveals all that information."

The resulting signals are highly specific and indicate just what chemical species is being observed. Moreover, as Hahn saw right away, while the signal can be modified by external magnetic fields, it does not vanish in their absence.

With Ledbetter in the lead, the Budker/Pines collaboration built a magnetometer specifically designed to detect J-coupling at zero magnetic field. Thomas Theis, a graduate student in the Pines group, supplied the parahydrogen and the chemical expertise to take advantage of parahydrogen-induced polarization. Beginning with styrene, a simple hydrocarbon, they measured J-coupling on a series of hydrocarbon derivatives including hexane and hexene, phenylpropene, and dimethyl maleate, important constituents of plastics, petroleum products, even perfumes.

"The first step is to introduce the parahydrogen," Budker says. "The top of the set-up is a test tube containing the sample solution, with a tube down to the bottom through which the parahydrogen is bubbled." In the case of styrene, the parahydrogen was taken up to produce ethylbenzene, a specific arrangement of eight carbon atoms and 10 hydrogen atoms.

Immediately below the test tube sits the magnetometer's alkali vapor cell, a device smaller than a fingernail, microfabricated by Svenja Knappe and John Kitching of the National Institute of Standards and Technology. The vapor cell, which sits on top of a heater, contains rubidium and nitrogen gas through which pump and probe laser beams cross at right angles. The mechanism is surrounded by cylinders of "mu metal," a nickel-iron alloy that acts as a shield against external magnetic fields, including Earth's.

Ledbetter's measurements produced signatures in the spectra which unmistakably identified chemical species and exactly where the polarized protons had been taken up. When styrene was hydrogenated to form ethylbenzene, for example, two atoms from a parahydrogen molecule bound to different atoms of carbon-13 (a scarce but naturally occurring isotope whose nucleus has spin, unlike more abundant carbon-12).

J-coupling signatures are completely different for otherwise identical molecules in which carbon-13 atoms reside in different locations. All of this is seen directly in the results. Says Budker, "When Micah goes into the laboratory, J-coupling is king."

Of the present football-sized magnetometer and its lasers, Ledbetter says, "We're already working on a much smaller version of the magnetometer that will be easy to carry into the field."

Although experiments to date have been performed on molecules that are easily hydrogenated, hyperpolarization with parahydrogen can also be extended to other kinds of molecules. Budker says, "We're just beginning to develop zero-field NMR, and it's still too early to say how well we're going to be able to compete with high-field NMR. But we've already shown that we can get clear, highly specific spectra, with a device that has ready potential for doing low-cost, portable chemical analysis."

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by DOE/Lawrence Berkeley National Laboratory.

Journal Reference:

T. Theis, P. Ganssle, G. Kervern, S. Knappe, J. Kitching, M. P. Ledbetter, D. Budker, A. Pines. Parahydrogen-enhanced zero-field nuclear magnetic resonance. Nature Physics, 2011; DOI: 10.1038/nphys1986

Note: If no author is given, the source is cited instead.

Disclaimer: This article is not intended to provide medical advice, diagnosis or treatment. Views expressed here do not necessarily reflect those of ScienceDaily or its staff.

View the original article here