A new lab to explore quantum mysteries
Filled with tunneling particles, electron sinks, charmed quarks and zombie cats, quantum mechanics takes everything Sir Isaac Newton taught about physics and throws it out the window.
Every day, researchers uncover new details about the laws that govern the smallest building blocks of the universe. These details not only increase scientific understanding of quantum physics, but they also have the potential to unlock a host of technologies, from quantum computers to lasers to next-generation solar cells.
But there is one area that remains a mystery even in this most mysterious science: the quantum mechanics of nuclear fuels.
EXPLORE THE FRONTIERS OF QUANTUM MECHANICS
Until now, most basic scientific research in quantum mechanics has focused on elements such as silicon because these materials are relatively inexpensive, easy to obtain, and easy to work with.
Now, researchers at the Idaho National Laboratory plan to explore the frontiers of quantum mechanics with a new synthesis lab capable of working with radioactive elements such as uranium and thorium.
An announcement about the new lab appears online in the journal Nature Communication.
Uranium and thorium, which are part of a larger group of elements called actinides, are used as fuels in nuclear reactors because they can undergo nuclear fission under certain conditions.
However, the unique properties of these elements, in particular the arrangement of their electrons, also mean that they could exhibit interesting quantum mechanical properties.
In particular, the behavior of particles in special extremely fine materials made from actinides could improve our understanding of phenomena such as quantum wells and quantum tunneling (see box).
To study these properties, a team of researchers built a laboratory around molecular beam epitaxy (MBE), a process that creates ultra-thin layers of materials with a high degree of purity and control.
“The MBE technique itself is not new,” said INL scientist Krzysztof Gofryk. “It is widely used. What is new is that we apply this method to actinide materials – uranium and thorium. Currently, this capability does not exist anywhere else in the world that we know of.
The INL team conducts fundamental research, science for knowledge, but the practical applications of these materials could allow significant technological advances.
“At this point, we are not interested in building a new qubit. [the basis of quantum computing], but we are thinking about materials that might be useful for that,” Gofryk said. “Some of these materials could be potentially interesting for new memory banks and spin-based transistors, for example.”
Both memory banks and transistors are important components of computers.
EPITAXY BY MOLECULAR BEAM
To understand how researchers make these very fine materials, imagine an empty bullet pit in a fast food restaurant. Blue and red balls are thrown into the pit one at a time until they form a single layer on the ground. But this layer is not a random assortment of balls. Instead, they organize themselves according to a pattern.
During the MBE process, the empty ball pit is a vacuum chamber and the balls are very pure elements, such as nitrogen and uranium, which are heated until individual atoms can escape in the bedroom.
The floor of our imaginary ball pit is, in reality, a charged substrate that attracts individual atoms. On the substrate, the atoms order themselves to create a plate of very thin material – in this case, uranium nitride.
THIN MATERIAL SANDWICHES MAKE HETEROSTRUCTURES
Back in the ball pit, we created a layer of blue and red balls arranged in a pattern. Now we make another layer of green and orange balls on top of the first layer.
To study the quantum properties of these materials, Gofryk and his team will join two dissimilar slices of material into a sandwich called a heterostructure. For example, the thin layer of uranium nitride could be joined to a thin layer of another material such as gallium arsenide, a semiconductor. At the junction between the two different materials, interesting quantum mechanical properties can be observed.
“We can make sandwiches of these materials from a variety of items,” Gofryk said. “We have a lot of flexibility. We’re trying to think about what new structures we can create with maybe some predicted quantum properties. »
“We want to look at electronic properties, structural properties, thermal properties, and how electrons are transported through layers,” he continued. “What will happen if you lower the temperature and apply a magnetic field? Will this cause the electrons to behave in a certain way? »
INL ONLY SUITABLE FOR ACTINIDE RESEARCH
INL is one of the few places where researchers can work with uranium and thorium for this type of science. The amounts of radioactive material – and the resulting safety issues – will be comparable to the radioactivity found in an everyday smoke alarm.
“INL is the perfect place for this research because we are interested in this type of physics and chemistry,” Gofryk said.
Ultimately, Gofryk hopes the lab will achieve breakthroughs that will help attract the attention of potential collaborators and recruit new employees for the lab.
“These actinides have such special properties,” he said. “We hope to be able to discover new phenomena or new physics that have not been discovered before.”
SIDEBAR: WHAT IS QUANTUM MECHANICS?
In 1900, German physicist Max Planck first described how light emitted by heated objects, such as the filament of a light bulb, behaves like particles.
Since then, many scientists – including Albert Einstein and Niels Bohr – have explored and developed Planck’s discovery to develop the field of physics known as quantum mechanics. In short, quantum mechanics describes the behavior of atoms and subatomic particles.
Quantum mechanics is different from ordinary physics, in part because subatomic particles simultaneously have particle and wave characteristics, and their energy and motion occur in discrete quantities called “quanta.”
More than 120 years later, quantum mechanics plays a key role in many practical applications, especially lasers and transistors, a key component of modern electronic devices. Quantum mechanics also promises to serve as the basis for the next generation of computers, known as quantum computers, which will be much more powerful at solving certain kinds of calculations.
WHY URANIUM AND THORIUM ARE DIFFERENT
Uranium, thorium and the other actinides have one thing in common that makes them interesting for quantum mechanics: the arrangement of their electrons.
The electrons do not revolve around the nucleus like the earth revolves around the sun. On the contrary, they move somewhat haphazardly. But we can define areas where there is a high probability of finding electrons. These probability clouds are called “orbitals”.
For smaller atoms, these orbitals are simple spheres surrounding the nucleus. However, as atoms get bigger and contain more electrons, the orbitals begin to take on strange and complex shapes.
In very large atoms like uranium and thorium (92 and 90 electrons, respectively), the outermost orbitals are a complex assortment of party balloon, jelly bean, dumbbell, and hula hoop shapes. The electrons in these orbitals are of high energy. While scientists can guess their quantum properties, no one knows for sure how they will behave in the real world.
QUANTUM TUNNELING: WHEN THE IMPOSSIBLE BECOMES IMPROBABLE
Quantum tunneling is a key component of a number of phenomena, including nuclear fusion in stars, mutations in DNA, and diodes in electronic devices.
To understand quantum tunneling, imagine a toddler rolling a ball down a mountain. In this analogy, the ball is a particle. The mountain is a barrier, probably a semiconductor material. In classical physics, there is no chance that the ball has enough energy to go over the mountain.
But in the quantum realm, subatomic particles have both particle and wave properties. The peak of the wave represents the highest probability of finding the particle. Thanks to a quirk of quantum mechanics, while most of the wave bounces off the barrier, a small part of that wave passes through if the barrier is thin enough.
For a single particle, the low amplitude of this wave means that there is very little chance that the particle will cross to the other side of the barrier.
However, when a large number of waves move towards a barrier, the probability increases and sometimes a particle passes through. This is the quantum tunnel effect.
QUANTUM WELLS: WHERE ELECTRONS ARE STUCK
Quantum wells are also important, especially for devices such as light-emitting diodes (LEDs) and lasers.
Like quantum tunneling, to build quantum wells you need alternating layers of very thin material (10 nanometers) where one layer is a barrier.
While electrons normally travel in three dimensions, quantum wells trap electrons in two dimensions inside a barrier that is, for practical purposes, impossible to overcome. These electrons exist at specific energies – say the precise energies needed to generate specific wavelengths of light.
About the Idaho National Laboratory
Battelle Energy Alliance manages INL for the US Department of Energy’s Office of Nuclear Energy. INL is the national center for nuclear energy research and development and also conducts research in each of the DOE’s strategic areas: energy, national security, science, and the environment. For more information, visitwww.inl.gov. Follow us on social networks:Twitter,Facebook,instagramandLinkedIn.