This accelerator can reveal rare forms of the substance

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This accelerator can reveal rare forms of the substance

A few hundred feet away is a large metal chamber devoid of air and draped with the wires required to control the instruments inside. A beam of particles moves silently through the chamber’s interior at around half the speed of light until it collides with a solid piece of material, resulting in a burst of rare isotopes.

This is all happening at Michigan State University’s Facility for Rare Isotope Beams, or FRIB, which is run by the US Department of Energy’s Office of Science. National and international scientific teams converged at Michigan State University in May 2022 and began running scientific experiments at FRIB with the goal of creating, isolating, and studying new isotopes. The experiments were supposed to reveal new information about the fundamental nature of the universe.

We are two nuclear chemistry and nuclear physics professors who study rare isotopes. Isotopes are different flavors of an element that have the same number of protons but different numbers of neutrons in their nucleus.

The accelerator at FRIB began at low power, but once fully operational, it will be the most powerful heavy-ion accelerator on the planet. FRIB will enable scientists like us to create and study thousands of previously unseen isotopes by accelerating heavy ions—electrically charged atoms of elements. For the past decade, a community of approximately 1,600 nuclear scientists from around the world has been waiting to begin doing science enabled by the new particle accelerator.

The first FRIB experiments were completed in the summer of 2022. Despite the fact that the facility is currently only operating at a fraction of its full capacity, multiple scientific collaborations working at FRIB have already produced and detected approximately 100 rare isotopes. These preliminary findings are assisting researchers in learning about some of the universe’s most unusual physics.

What exactly is a rare isotope?

Most isotopes require enormous amounts of energy to produce. Heavy rare isotopes are produced in nature during the cataclysmic deaths of massive stars known as supernovas or during the merger of two neutron stars.

To the naked eye, two isotopes of any element appear and behave identically—all isotopes of mercury would appear identical to the liquid metal used in old thermometers. However, because the nuclei of isotopes of the same element have different numbers of neutrons, they differ in terms of how long they live, the type of radioactivity they emit, and many other characteristics.

Some isotopes, for example, are stable and do not decay or emit radiation, so they are abundant in the universe. Because other isotopes of the same element can be radioactive, they will inevitably decay as they transform into other elements. Because radioactive isotopes decay over time, they are becoming increasingly scarce.

However, not all decay occurs at the same rate. Some radioactive elements, such as potassium-40, emit particles at such a slow rate that a small amount of the isotope can last for billions of years. Other, more radioactive isotopes, such as magnesium-38, only exist for a fraction of a second before decaying into other elements. Short-lived isotopes, by definition, do not last long and are therefore uncommon in the universe. As a result, if you want to study them, you must create them yourself.

In a laboratory, isotopes are created.

While only about 250 isotopes occur naturally on Earth, theoretical models predict that approximately 7,000 isotopes should exist in nature. Scientists used particle accelerators to create approximately 3,000 of these rare isotopes.

The FRIB accelerator is 1,600 feet long and is composed of three segments folded in the shape of a paperclip. Within these segments are numerous, extremely cold vacuum chambers that use powerful electromagnetic pulses to alternately pull and push the ions. FRIB can accelerate any naturally occurring isotope to approximately half the speed of light, whether it is as light as oxygen or as heavy as uranium.

To make radioactive isotopes, simply smash this ion beam into a solid target, such as a piece of beryllium metal or a rotating disk of carbon.

powerful linear accele 1
The Facility for Rare Isotope Beams was designed to allow researchers to create rare isotopes and measure them before they decay. Credit: Facility for Rare Isotope BeamsCC BY-ND

The impact of the ion beam on the fragmentation target fractures the nucleus of the stable isotope, producing hundreds of rare isotopes at the same time. A separator is placed between the target and the sensors to separate the interesting or new isotopes from the rest. Particles with the appropriate momentum and electrical charge will pass through the separator, while the remainder will be absorbed. Only a subset of the desired isotopes will make it to the numerous instruments designed to study the nature of the particles.

The likelihood of producing any particular isotope during a single collision is extremely low. The chances of producing some of the rarer exotic isotopes are on the order of one in a quadrillion—roughly the same odds as winning two Mega Millions jackpots in a row. However, the FRIB’s powerful ion beams contain so many ions and produce so many collisions in a single experiment that the team can reasonably expect to find even the most rare isotopes. Calculations show that FRIB’s accelerator should be capable of producing approximately 80% of all theorized isotopes.

FRIB’s first two scientific experiments

On May 9, 2022, a multi-institutional team led by researchers from Lawrence Berkeley National Laboratory, Oak Ridge National Laboratory (ORNL), the University of Tennessee, Knoxville (UTK), Mississippi State University, and Florida State University, along with MSU researchers, launched the first experiment at FRIB. The researchers fired a 1 kW beam of calcium-48—a calcium nucleus with 48 neutrons instead of the usual 20—at a beryllium target. Even at a quarter of the facility’s maximum power of 400 kW, approximately 40 different isotopes passed through the separator to the instruments.

The second FRIB experiment, led by researchers from Lawrence Livermore National Laboratory, ORNL, UTK, and MSU, began on June 15, 2022. The facility used an accelerated beam of selenium-82 to create rare isotopes of scandium, calcium, and potassium. These isotopes are commonly found in neutron stars, and the experiment’s goal was to learn more about the type of radioactivity these isotopes emit as they decay. Understanding this process may help us understand how neutron stars lose energy.

The first two FRIB experiments were only the tip of the iceberg in terms of the capabilities of this new facility. FRIB plans to investigate four major questions in nuclear physics in the coming years: To begin, what are the properties of atomic nuclei with a large number of protons and neutrons? Second, how do elements form in the universe? Third, do physicists understand the universe’s fundamental symmetries, such as why there is more matter than antimatter in the universe? Finally, how can rare isotope information be used in medicine, industry, and national security?


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