Science at NSCL

The primary goal of our scientific endeavor is to unravel the mysteries that reside at the center of atoms, in atomic nuclei. These compact structures are ten thousand-times smaller than the atom they reside in but they contain more than 99.9 percent of its mass.

There are 115 known elements in the universe, each defined by its own unique number of protons inside its nucleus. However, the number of neutrons in the nucleus is not set in stone, resulting in more than 330 known isotopes that can be found here on Earth.

Though much has been learned during the last century about these nuclei, at least 3,100 rare isotopes exist in the vast universe. But because they sometimes exist for only a fleeting moment inside of stars and supernovae – the cosmic cauldrons in which elements are created – little or nothing about them is known.

Yet thousands of these isotopes are continually created and play a fleeting though important role in the cosmos. The evolution of stars from birth to often cataclysmic death is intertwined with the nuclear reactions that occur inside stars and are responsible for the formation of many elements. The resulting elemental abundances influenced the processes that formed our solar system and ultimately led to life on Earth. Inadequate knowledge of important nuclear properties limits understanding of these important astrophysical processes, which today is rudimentary, at best.

Scientists at NSCL work at the forefront of the research into these rare nuclei. Using superconducting cyclotrons, they accelerate stable isotopes to half the speed of light before smashing them into other nuclei in order to make and study the rare isotopes that cannot be found on Earth.

Chart of the nuclides. Different elements are shown as the chart goes up on the y-axis, while each elements known and predicted isotopes stretch out on the x-axis.

Learn more about the specific disciplines studied at NSCL below, or by exploring the NSCL Welcome brochure and Research pamphlet. Also, browse our collection of interesting science stories and discoveries in our Golden Science Nuggets section.

Nuclear Science

Talk about getting to the core of an issue. To probe the mysteries of an atom's nucleus is to seek answers to some of the most fundamental of questions about how the elements were formed and why atoms exist at all. But to push the boundaries of science’s current understanding, large, complex, and advanced equipment, vast computing power, and often specially designed tools that have no duplicate elsewhere in the world are needed.

This is because in order to truly understand the complexities involved in nuclear science, researchers must probe the very limits of atoms. How many neutrons can an atom have? What is the heaviest element that can exist? Going to the extremes inflates and highlights formerly minor effects, allowing nuclear scientists to gain a more complete understanding of the forces involved.

Nuclear science deals with the inner workings of the core of an atom.

Typically, experiments can only hone in on a couple of properties at a time. One experiment might seek to catch a nucleus decaying into a more stable form by emitting gamma rays, beta rays, neutrons or protons, for example, and reconstruct the original nucleus. Another might knock a proton out of a nucleus by hitting it with a neutron. Seeing the properties of the ejected particle gives insight into how the original nucleus was put together.

Nuclear science seeks to answer these questions and many others, including what tools do we need to understand the smallest complex objects in nature? Can we find evidence for new particles, or new forces of nature in the study of atomic nuclei? How has the universe changed over time? Where did the atoms in our body originate? Why do stars sometimes explode?

But this is not all. Nuclear science often goes beyond the study of atoms and their nuclei. Another branch of nuclear science deals with nuclear systems heated to billions of degrees, scientists study the collision of two nuclei at high energies, where the individual protons and neutrons can collide many times. This increases the “temperature” of the nuclear system just as the temperature of water is increased by an increase of the collisions of the water molecules. If you increase the temperature by increasing the velocity of the projectile, the nucleus boils off (evaporates) nucleons. At even higher temperatures the nucleus can explode completely and break into smaller nuclear fragments and many protons and neutrons. By measuring the remnants of the compression and explosion of a nuclear collision, one can infer the densities and pressures that can be created within the nucleus.

In this way, scientists study matter under the most extreme conditions found in nature. This helps us understand exotic objects like neutron stars and search for new states of matter.

The quest to push this frontier leads into nuclear realms that have never before been explored. New possibilities yield new opportunities and always new surprises. This search, rather than for new lands or planets, is for new territories more than a billion-billion times smaller. We hope you will join in our voyage of discovery. Stay tuned.

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Nuclear Theory

Like every branch of the physical sciences, the backbone of nuclear science is theory. Every experiment, calculation, result and prediction starts and ends with nuclear theory. The fundamental laws that describe how particles and forces interact within a nucleus can all be expressed as a group of equations; the crux of nuclear theory.

Nuclear theory has many facets. One involves working to construct models that more accurately describe the structure of large nuclei. How protons and neutrons interact, and how those interactions affect properties like its shape, size or radioactive decay, are examples of questions that theorists are constantly trying to create models to answer. Though fairly accurate descriptions of the properties of nuclei with 12 or fewer nucleons have been created, computational limitations make such treatments unfeasible for heavier nuclei and additional approximations are necessary.

Theory also is essential for understanding how particles interact during a reaction experiment and making sense of the results. This branch is called reaction theory. Being able to detect particles and the products of a nuclear reaction is only valuable if the nuclear theory is good enough to reconstruct what happened.

Experimental results also are used to update, improve and validate the framework that nuclear scientists work within. The new information then comes full circle by helping to determine which experiments are conducted next. By knowing where the gaps in knowledge about the way a nucleus works are – where nuclear theory needs more information – scientists can better decide which questions to ask and which experiments to run next.

Additionally, a few theorists at NSCL are involved in questions being experimentally addressed outside the laboratory’s walls. For example, effective field theory attempts to unite the models of a nucleus with the interactions and structure of quarks and gluons (Quantum Chromodynamics QCD). Some in our group are concerned with high density matter and develop theory relevant to experiments at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC).

These are just a few of the examples of what theorists are up to at NSCL.

To learn more, visit the NSCL Theory Group's website.

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Nuclear Astrophysics

Astrophysics and nuclear physics are intimately connected fields. Nuclear processes, for example, shape much of the visible universe. Unstable rare isotopes play a critical role in cosmic explosions and in neutron stars, but their study in experiments here on Earth is very difficult. However, advances at NSCL have put some of these experiments within reach. Among the open questions to be addressed, three important ones stand out:

What is the origin of the heavy elements?

It is believed that half of the elements heavier than iron were created in extremely energetic astronomical phenomena like exploding stars or gamma-ray bursts. But which one of these phenomena is responsible and what exactly the nuclear processes are is not understood. Creating in the lab and studying these same rare isotopes that exist briefly in these extreme environments before decaying into stable nuclei is one of the lab’s goals.

Graphic representation of an event consisting of a rare isotope smashing with a probe nucleus.

How do stars explode?

There are many types of explosive events in the cosmos, including X-ray bursts, core-collapse supernovae, thermonuclear (Type Ia) supernovae, and novae. Experiments at NSCL seek to answer lingering questions about the mechanisms involved in each.

What is the nature of dense nuclear matter in neutron stars?

The crust of neutron stars links observations of neutron star surface phenomena such as X-ray bursts or cooling behavior to the interior properties of the star. It is composed of rare neutron rich isotopes that are unstable on earth, but become stabilized by the high density in neutron stars. Again, though little is known about these exotic nuclei and their reactions in neutron star crusts, experiments at NSCL can produce and study the very same nuclei and help to unlock the mysteries of the densest objects in the universe.

Accelerator Physics

Accelerators are the workhorses of nuclear physics research — the ones with the muscle to smash atoms so the aftermath can be studied. Although the language of accelerator physics sometimes may sound more like auto racing, it is the cornerstone of understanding the origins of the universe.

Yet, even with such lofty goals, accelerators can be engineered to come in all sizes — from a tabletop to a small city. As a general rule, bigger accelerators pack more power, but new technologies developed at NSCL and other laboratories help to reduce their size and cost.

Ion Source Research

Cassiopeia: A supernova remnant.

In order to accelerate a particle beam, one must use electromagnetic fields. Electromagnetic fields can accelerate only particles with an electric charge. Therefore, if the particles are neutral, like a typical atom balanced by its numbers of protons and electrons, one must first ionize them, converting them into charged particles (ions). This is done by removing electrons from the atoms in devices called ion sources.

Beam Dynamics

Most particle accelerators increase the energy of charged particles in several steps. In circular accelerators — such as cyclotrons, and synchrotrons — the particles are guided in circular orbits and forced to pass by the same radio frequency (RF) high voltage system many times. At every pass of the RF system, the energy of the particle is increased. In linear accelerators — which will be used in FRIB and ReA3 — multiple RF systems are lined up one behind the other to provide an energy boost to the particles that traverse them only once. In all cases, it is necessary to manipulate the beam to keep it from increasing in size and hitting the wall of the vacuum pipe in which it moves. Special care must be taken to keep the beam in perfect timing with the accelerating RF field. When intense beams are accelerated, the internal forces between the beam particles (space charge forces) can become important since particles of the same electric charge will repel each other and tend to increase the size of the beam. Beam dynamics is the study of all these effects.

Lattice Design

Lattice design research is the study of beam containment and focusing through beam transport systems, linear and circular accelerators, and experimental devices such as NSCL’s S800 magnetic spectrograph or the A1900 fragment separator.

Magnet Research

Various magnetic devices are needed to manipulate beam particles or analyze the outcome of experiments. As nuclear science continues to advance, increasingly powerful magnets are required. This demands new approaches to meet the challenges inherent in magnets. For one, material properties limit how high a magnetic field can be pushed before the magnet self destructs. Also, magnets are damaged by high levels of radiation, such as those that occur in advanced nuclear physics experiments. Thus, the science of magnetics is focused on extending present technology to new limits.

A supernova; the interstellar birthplace of the heavy elements.

Superconducting RF

Radio frequency (RF) cavities are used to accelerate charged particles to high speeds. The electric field inside the cavity can deliver kinetic energy to a charged particle passing through it. A large speed is attained after the particle travels through many cavities lined up together in a series. A typical cavity generates a potential of over 1 million volts.

A conventional copper cavity requires a lot of power to produce this high potential. The power being dissipated in the cavity walls can be as high as 1 million watts. As a result, copper cavities cannot operate continuously at high potential; superconducting radio frequency (SRF) cavities must be used for this purpose. The power dissipation in an SRF cavity is about 100,000 times smaller than in a copper cavity. Special materials and extremely cold temperatures are needed to make a cavity superconducting. An SRF cavity made of niobium is operated at a temperature of about -456 °F or 2 Kelvin (K).

SRF research is aimed at improving the performance of SRF cavities and extending SRF technology to new applications.

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Practical Applications

Much of the knowledge gleaned from the lab’s experiments has applications in day-to-day life. For example, experiments in condensed matter physics have applications in nanotechnology and the quest for quantum computers and quantum optics. The mathematics behind describing the interaction of protons and neutrons in a nucleus have applications in chemistry, biology and nanoscience. The software programs written to collect data from the experiments have been adopted by more than 20 institutions that perform experiments in areas ranging from atomic and nuclear physics to health care research. Applications exist in basic physics research and related technologies, including nuclear theory, applied superconductivity, and accelerators designed for cancer therapy. And recent NSCL graduates now work in nuclear medicine, airport security, environmental protection, weapons stewardship, national security, nuclear fusion, and areas related to the radiation safety of space travel.

But above and beyond these and other practical applications, the science performed at NSCL is fundamental basic research. While the ultimate goal of studying the structure of atomic nuclei is to understand the underlying nature of the world and derive a benefit from it, scientists must first ask the "gee-whiz" questions like "Why is magnesium-32 deformed?" By first asking the simple, but seemingly uninteresting questions and then answering them, a foundation of knowledge is built that is critical to advancing to more difficult questions.

This knowledge enhances our understanding of nature and the universe in which we exist. Its results will be beneficial to society by laying the foundation for new technologies and applications beyond our own imaginations. Yet it is the realized dreams of the few dedicated students, staff and scientists working together at NSCL that will take all of us there.

Learn more about the specific disciplines studied at NSCL below, or by exploring the NSCL Welcome brochure and Research pamphlet. Also, browse our collection of interesting science stories and discoveries in our Golden Science Nuggets section.

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