A newly powered-up particle accelerator could reveal rare forms of matter

A newly powered-up particle accelerator could reveal rare forms of matter

Just a few hundred feet from where we sit is a large metal chamber, devoid of air and covered with the wires needed to operate the instruments inside. A beam of particles passes silently through the interior of the chamber at about half the speed of light until it smashes into a solid piece of material, causing a burst of rare isotopes.

All this happens in Rare Isotope Beam Facility, or FRIB, which is operated by Michigan State University for the US Department of Energy’s Office of Science. Starting in May 2022, national and international teams of scientists gathered at Michigan State University and began conducting scientific experiments at FRIB to create, isolate and study new isotopes. The experiments promised to provide new insights into the fundamental nature of the universe.

By accelerating heavy ions – electrically charged atoms of elements – FRIB will allow scientists like us to create and study thousands of never-before-seen isotopes.

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

The accelerator at FRIB started out at low power, but when it finishes ramping up to full power, it will be the most powerful heavy ion accelerator on Earth. By accelerating heavy ions – electrically charged atoms of elements – FRIB will allow scientists like us to create and study thousands of never-before-seen isotopes. A community of approx 1,600 nuclear scientists from around the world waiting a decade to start doing science, thanks to the new particle accelerator.

The first experiments at FRIB were completed in the summer of 2022. Although the facility is currently operating at only a fraction of its full capacity, numerous scientific collaborations working at FRIB have already produced and about 100 rare isotopes have been discovered. These early results are helping researchers learn about some of the rarest physics in the universe.

Rare isotopes are radioactive and decay over time as they emit radiation – visible here as streaks coming from the small piece of uranium in the center.

What is a rare isotope?

Most isotopes require incredibly large amounts of energy to produce. In nature, heavy rare isotopes are produced during the cataclysmic deaths of massive stars called supernovae or during merger of two neutron stars.

To the naked eye, two isotopes of each element look and behave the same – all isotopes of the element mercury would look exactly like 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 how long they live, what type of radioactivity they emit, and in many other ways.

FRIB can accelerate any naturally occurring isotope — whether it’s as light as oxygen or as heavy as uranium — to roughly half the speed of light.

For example, some isotopes are stable and do not decay or emit radiation, so they are common in the universe. Other isotopes of the same element can be radioactive, so they inevitably decay as they turn into other elements. Because radioactive isotopes decay over time, they are relatively rarer.

However, not all breakups happen at the same rate. Some radioactive elements – such as potassium-40 – emit particles by decaying at such a low rate that a small amount of the isotope can last for billions of years. Other, more highly radioactive isotopes such as magnesium-38 exist for only a fraction of a second before decaying into other elements. Short-lived isotopes, by definition, do not survive long and are rare in the universe. So if you want to study them, you have to do them yourself.

Creating isotopes in a laboratory

While only approx 250 isotopes occur naturally on Earththeoretical models predict that approx 7000 isotopes must exist in nature. Scientists have used particle accelerators to produce approx 3000 of these rare isotopes.

The FRIB accelerator is 1,600 feet long and is made of three segments folded roughly into the shape of a paper clip. Within these segments are numerous, extremely cold vacuum chambers that alternately pull and push the ions using powerful electromagnetic pulses. FRIB can accelerate any naturally occurring isotope—whether it’s as light as oxygen or as heavy as uranium—to approx half the speed of light.

To create radioactive isotopes, you only need to smash this beam of ions into a solid target such as a piece of beryllium metal or a spinning disc of carbon.

The impact of the ion beam on the fragmentation target breaks the nucleus of the stable isotope into parts and produces many hundreds of rare isotopes simultaneously. To isolate the interesting or new isotopes from the others, a separator is placed between the target and the sensors. Particles with the correct momentum and electrical charge will pass through the separator while the rest are absorbed. Only a a subset of the desired isotopes will reach many instruments built to observe the nature of particles.

The probability of creating a particular isotope during a single collision can be very small. The odds of creating some of the rarer exotic isotopes can be on the order of 1 in a quadrillion — roughly the same odds as winning back-to-back Mega Millions jackpots. But the powerful ion beams used by FRIB contain so many ions and produce so many collisions in one experiment that the team can reasonably expect they find even the rarest isotopes. According to calculations, the FRIB accelerator should be able to produce approximately 80% of all theorized isotopes.

FRIB’s first two science experiments

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

The FDSi device records the time each ion arrives, what isotope it is, and when it decays. Using this information, the collaboration deduced the half-lives of the isotopes; the team already has reports five previously unknown half-lives.

The second FRIB experiment began on June 15, 2022, led by a collaboration of researchers from Lawrence Livermore National Laboratory, ORNL, UTK and MSU. The facility accelerated a beam of selenium-82 and used it to produce rare isotopes of the elements scandium, calcium and potassium. These isotopes are commonly found in neutron stars, and the purpose of the experiment was to better understand what type of radioactivity these isotopes emit as they decay. Understanding this process can shed light on how neutron stars lose energy.

FRIB’s first two experiments were just the tip of the iceberg of the capabilities of this new facility. In the coming years, FRIB is set to investigate four big questions in nuclear physics: First, what are the properties of atomic nuclei with a large difference between the number of protons and neutrons? Second, how are the elements formed in space? Third, do physicists understand the fundamental symmetries of the universe, such as why there is more matter than antimatter in the universe? Finally, how can information from rare isotopes be applied to medicine, industry, and national security?

Sean Liddickassociate professor of chemistry, Michigan State University and Artemis Spiruprofessor of nuclear physics, Michigan State University

This article was republished by The conversation under a Creative Commons license. Read on original article.

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