Frequently Asked Questions

Here are some basic answers to questions we commonly hear at the laboratory. If you don't see your question answered here, please don't hesitate to contact us!

About the Laboratory

The Science of Nuclear Physics

The Tools of Nuclear Physics

About the Laboratory

How long did it take to build the NSCL’s cyclotrons and other equipment?

See the history section of the “About NSCL” webpage to read a detailed history of the lab along with an easy-to-follow timeline of major events.

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How do people get to do experiments at NSCL?

Scientists must send in an application proposing an experiment. An international committee reviews all of the proposals and awards beam time to experiments with the highest scientific merit and greatest chance of success.

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How long does an experiment take?

The average time allotted for an experiment is 120 hours. Experiments run 24 hours-a-day, 7 days-a-week. The facility is not always running. Sometimes it is shut down for maintenance; however, the lab ran for over 4,000 hours in the last year alone. After all, time not spent experimenting is time lost.

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How much does an experiment cost?

It costs $5000 per hour to operate the NSCL. However, the experimenters do not pay to do research. The National Science Foundation funds our operating budget, so beam time is free to researchers. MSU contributes as well, and of course many outside users are funded by grants from the Department of Energy, NASA, NSF and other scientific bodies.

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How much radiation is produced in the vault when the cyclotron is on?

It depends on the nuclei being accelerated. In a typical high-energy beam like Oxygen-16, lots of neutrons can be generated. Levels of at least 7+ R/hr neutron flux at a time have been seen, which means in about one hour someone in the vault would exceed the legal occupational limit for trained radiation workers.

To put it in perspective, mild radiation sickness typically starts at 50 R and certain death starts between 600-1000 R. So to even begin to get sick, someone would have to be exposed to the radiation caused by one of our most energetic beams for at least seven hours. Even if it were possible to be in the vault with the beam on – which it’s not – there would be ample time for someone to notice the missing person.

For more information about radiation and safety at the lab, visit the Safety section of the “About NSCL” webpage.

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The Science of Nuclear Physics

What are some examples of research projects conducted at the lab?

The laboratory conducts many kinds of experiments including – but not limited to – resistance to radiation damage for NASA electrical equipment destined to leave Earth’s atmosphere, the masses of rare isotopes never before seen on Earth, searches for new isotopes and processes that are important to transforming one element into another in supernovae. To learn more, visit the science section of the “About NSCL” webpage.

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What discoveries have been made at NSCL?

Besides pioneering the use of superconducting cyclotrons – including a miniaturized version for neutron therapy at Harper Hospital in Detroit – the lab is discovering how the r-process creates heavier elements in exploding stars, the nature of nuclear reactions inside neutron stars and even brand new isotopes like the heaviest form of silicon ever detected by humans.

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Why is this research important? How will it affect my daily life?

Most of the research conducted at the laboratory is basic, fundamental science. It searches for answers to the questions of how the universe works. Though there may not be obvious ways for this research to translate to the public’s day-to-day life, many inventions and innovations have sprung from basic research.

For example, as J.J. Thomson, discoverer of the electron, wrote in 1916 on the discovery of x-rays and their use in medical imaging, “It was not the result of a research in applied science to find an improved method of locating bullet wounds. This might have led to improved probes, but we cannot imagine it leading to the discovery of the X-rays. No, this method is due to an investigation in pure science, made with the object of discovering what is the nature of Electricity.”

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In what kinds of experiments at NSCL would a chemist be interested?

The main “chemistry” connection is the nuclear magnetic resonance (NMR) measurements that determine the magnetic properties of nuclei far from stability. NMR is one of the main characterization tools used by chemists. This process allows scientists to measure the magnetic moments of exotic nuclei, providing insight into their complicated structure.

Additionally, the Low Energy Beam and Ion Trap (LEBIT) conducts measurements for the molecular formation of isotopes in the gas phase. The NSCL gas cell cools and slows down the fast beams for use in the LEBIT Penning Trap. Not only are these measurements chemically important, the mere process of stopping beams moving at half the speed of light involves a lot of chemistry.

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How does research at NSCL lead to new ways to treat cancer?

See applications of nuclear science research on the NSCL website.

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How do exploding stars make the elements and how does NSCL contribute to this research?

There is more than one type of exploding star, each making a different mix of elements and operating in a different way. The very nature of an explosion, however, gives the various scenarios some common properties. Some are faster than others, but all are fast when compared to the timescale for standard nuclear burning in stars.

Because the processes are fast, it becomes likely that the unstable product of one reaction will participate in another reaction before it returns to stability. In fact, large portions of key reaction sequences take place away from stability involving rare-isotopes. These processes are not yet fully understood, in large part because the properties of many of these isotopes are unknown. We need new data for nuclei far from stability and improved nuclear theories to develop accurate models of these astrophysical phenomena.

The NSCL is one of only a few facilities in the world that can study many of the rare-isotopes important to key explosive burning processes, which produced much of the current elemental abundances, especially those of heavy elements.

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How does research at NSCL keep astronauts safe in space?

Cosmic rays are much more intense in orbit and in space than they are on the surface of the earth. Standard electronic components function differently under bombardment by these high-energy particles. Your computer memory may start functioning like a particle detector. What should be a zero becomes a one after a heavy ion streams through. Components to be used in space are tested at the NSCL under the impact of individual high-energy heavy ions to make sure that astronauts can depend on them.

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The Tools of Nuclear Physics

What are the advantages of a cyclotron over a linear accelerator?

The three pole tips in our cyclotrons can be used to accelerate the same nuclei again and again. This translates to a major savings in cost and space.

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Then what are the advantages of linear accelerators, such as FRIB?

Linear accelerators can get to higher energies by adding length, while cyclotrons are limited by their set diameter. As a nucleus increases in speed, its momentum causes it to revolve in a wider and wider circle. Eventually, the strength of the cyclotron’s magnet is no longer enough to keep it within its walls, and maximum velocity has been reached. However, LINACs do not require magnetic fields to constrain the particle to a circular path, which also results in synchrotron radiation and loss of energy. So they are capable of producing beams of higher energy so long as there is space to build enough individual accelerators in a long line.

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How many accelerators are there in the world? Where are they? Who is your competition?

There are many cyclotrons in the world with more being built every year for industrial and commercial uses, such as making rare isotopes and medical treatments. In fact, there are some 30,000 accelerators worldwide, though most are small and used for medicinal or industrial purposes.

There are so many because there are different types and sizes. For example, some accelerate electrons like the linear accelerator at the Stanford Linear Accelerator Center. Others accelerate protons like the Large Hadron Collider at CERN. And a few like those at NSCL accelerate entire nuclei in order to study the forces at work inside of a nucleus.

The physically largest of this kind is the 56-foot-wide TRIUMF in Vancouver, Canada. The K1200 right here at NSCL produces the second-highest energy. Our closest competitors in rare isotope research are RIKEN in Wako, Japan, which uses three cyclotrons including one that was recently completed and now has the highest energy in the world. Also, Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, Germany, uses a linear accelerator and synchrotron to conduct similar research.

Additionally, here in the U.S., similar research is conducted at Oak Ridge National Laboratory located in Tennessee, Thomas Jefferson National Laboratory in Virginia, Argonne National Laboratory located outside of Chicago, Lawrence Berkeley National Laboratory in Berkeley, California, Florida State University, the University of Washington, Texas A&M, Duke University and Yale University.

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What does the "K" value associated with the cyclotrons mean?

Labels such as K50 and K500 refer to the strongest magnetic fields a cyclotron can run. Specifically, the K value represents the energy of a proton beam that could be accelerated by the same field. Thus, a proton accelerated in the K500 could get up to 500 MeV. However, since the lab accelerates entire nuclei filled with many protons and neutrons, the resulting energies are much lower.

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Why do the cyclotrons have three "dees"?

There are three dees – individual magnetic fields responsible for accelerating the nuclei, which happen to be shaped like the letter D – in both the K500 and K1200 cyclotrons. The three pinwheel-shaped ridges inside are charged to create this field.

The reasons for the three dees are threefold. The first is mechanical fit. There is just enough space in the three valleys between the ridges to install three dees with enough space around them to hold the required voltage without creating giant bolts of electricity.

Secondly, having three instead of two or one provides more accelerating gaps. Because the ions get an accelerating kick every time they cross the gap between the dee and the ridge, they particles gain more energy from six separate accelerations per turn. Actually, the cyclotron would work just fine with one dee, but there would be only one-third the energy gain per turn, so the ion would have to make three times as many turns to reach the final speed. If the voltage could be tripled on that one dee, it would compensate for this effect, but this is not practical.

Last but not least, the three dees evenly spaced out provides symmetrical forces on the particles. If they were not evenly spaced, the ions would be pushed off center and enter an elliptical orbit. With only one dee, the particles would get two kicks 60 degrees apart on its path and would coast the rest of the way around before repeating the process. You can imagine how this asymmetry in the pattern of forces would tend to push the orbit off center, toward the side of the cyclotron where the dee is. Such errors in the centering of the orbit can damage the beam by causing it to increase in cross sectional area, even to the point where it will hit the dees, losing many particles before they accelerate to full speed.

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How are the cyclotrons powered?

The K500 is powered similarly to the K1200. The radio frequency amplifiers that produce the AC power that accelerates the ions inside of the K1200 require 20,000 volts of DC, or 300 kilowatts of power for each of the three dees. The lab’s transformer takes the 13,200 kilovolt, three-phase AC power from the electric power line and uses a transformer to produce the correct voltage, convert it to DC and deliver it to the amplifier. Because the resonant copper cavity surrounding each dee is exactly tuned to the frequency of the incoming signal, it takes this voltage and increases it to 140,000 volts over many cycles. This is the voltage that creates the electromagnetic fields that accelerate the ions.

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Why couple the cyclotrons together?

How fast the nuclei are accelerated depends on how many electrons can be stripped away from them. The ion sources that inject charged nuclei into the K500 can only strip away a few electrons. But by accelerating the particles and pushing them through a device that strips away even more electrons, we can inject these into the K1200 with a higher level of charge. This allows for more efficient acceleration, faster beams, higher beam currents and higher energies.

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How many nuclei are in the beam?

Beam density is measured in current. Our ion source can produce varying amounts of ions depending on the desired element. One example is a “primary beam” from the source of oxygen-16. The ion source can reliably produce 100 pnA (particle nano-amps) of this element, which equates to between 10 billion and 100 billion particles per second.

Once the coupled cyclotron facility has fragmented the primary beam and produced a filtered rare isotope beam, it represents a tiny fraction of the initial current. Beams made of isotopes near stability will contain millions of particles per second, while extremely unstable/rare isotopes could be produced at the rate of one per hour or even less!

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How long does it take for a nucleus to get from the ion source to a detector?

Total travel time is less than one hundred microseconds, 350 times shorter than the blink of an eye, dominated by the time it takes to accelerate from the ion source through both cyclotrons. Total travel length is almost three miles.

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Where does NSCL get the isotopes for the ion source?

MosMany of the lab’s beams are created using monoisotopic elements, which are elements that naturally have a lot of the specific isotope that is required, such as uranium-238 or calcium-40. For these beams, we purchase materials from common domestic chemical suppliers, such as Alfa Aesar in Massachusetts. Most of our enriched isotopes used to produce beams, such as calcium-48 or krypton-78 come, from Russia through either U.S. or Canadian distributors. The U.S. has an inventory of these isotopes at Oak Ridge National Laboratory, but does not actively produce them anymore. Also, the competitive commercial culture in Russia makes them substantially more economical in supplying our needs.

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Why choose beryllium-9 as the target?

For a fragmentation target it is good to use material with a low element number. The process needs nucleons for fragmentation, but at the same time it needs to have a small electron density. Electrons in the target material only slow down and degrade the beam. They don’t trigger the production of rare isotopes. Besides having a good balance of nucleons and electrons, beryllium also has very good thermal properties. With the combination of low density, a relatively high melting point, and very good thermal conductivity, the beryllium targets can be used with a high power deposition in the target without melting. Beryllium is the best material available under these considerations.

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How do you "wind" a coil of superconducting wire to make magnets?

The wire that we use for dipole and quadrupole magnets is between .04” and .08” in diameter, which is somewhat smaller than the S800 or K1200 wire. The copper to superconductor ratio is around five to one, making it fairly pliable. While winding the pliable wire, technicians have to be careful not to kink or abruptly bend the wire to prevent breaks in the superconducting filament. They use devices like air and magnetic particle clutches to maintain a consistent tension on the wire while winding. The winding table uses pulleys and springs to keep the wire from breaking and there is a digital readout that is linked to a linear resistor to monitor the predetermined wire tension, which is the most critical factor while winding. If it is too much, the wire will break and if it is too low, the coil has loose wires and there is not enough room to fit it all in the curing form. After winding, the technicians record resistance, dissipation, inductance and a quality factor, which together determines how good the coils are.

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Where does niobium come from, and why is it important to the magnets and cyclotrons?

Niobium is not found free in nature, rather as part of minerals such as columbite and pyrochlore, and costs about as much as silver per ounce. The main quality that makes it so important to NSCL is that a niobium-titanium alloy remains superconducting below 9.2 K under high current and magnetic field, which makes the superconducting magnets at NSCL possible.

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How do you keep the magnets below 9.2 K?

Liquid helium flows to the superconducting magnets inside coaxial, vacuum-jacketed stainless steel pipes. There are multiple layers of insulation inside the vacuum space separating the inner and outer pipes, which keeps the liquid helium insulated from the outside world. Often, there is also a liquid nitrogen-cooled copper shield between the 4.5 K helium pipe and the 300 K outside world.

Many of the beam line magnet connections do not use stainless steel for the helium lines. They use a special alloy called Invar, known generically as FeNi36 or 64FeNi in the United States. This is a nickel-steel alloy notable for its uniquely low coefficient of thermal expansion. This way, when the beam line magnet connections are cooled down, they do not contract and break the welds between them. Also, there are no liquid helium pumps keeping the substance flowing. Instead, the lab pushes the cryogenic fluids around with pressure differentials.

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What are the advantages of reaccelerated beams?

The lab currently is working on a system to cool and slow down the fast particle beams and then reaccelerate them. Our fragmentation process produces a fast beam of rare isotopes, but certain experiments can’t be performed on a beam traveling half the speed of light. Just try weighing something traveling 335 million miles per hour! Many astrophysical events such as stellar nuclear reactions occur at a much lower energies and so it is useful to replicate those conditions. Reaccelerated beams also offer higher beam quality and access to many experimental techniques that were developed for low-energy beams, such as LEBIT.

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How does LEBIT actually "weigh" a nucleus?

While the nucleus is confined in the Penning trap - a combination of a strong magnetic field and a static electric quadrupole field - one can tune a separate radio frequency field to find a frequency that matches the rate at which the ion orbits the center. This is determined by a handy-dandy equation. Since we know the charge, frequency and field strength, the equation gives the mass.

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Does the A1900 Fragment Separator use the same technique as that for uranium enrichment?

The short answer is yes because you can separate ionized U-235 and U-238 with a magnetic field, but there are more methods of enrichment that are much more efficient. While this technique was employed during WWII, it essentially has become obsolete.

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Where do the unused isotopes go?

These nuclei get stopped in the beam stopper or in the magnets.

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Where were the S800 Dipoles built?

The steel came from Japan, the conductor from Italy and the coil bobbins from Colorado. Everything else was procured locally. The complete dipoles were built here in the S3 pit and the East High Bay.

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