A view inside SOLARIS and the accelerator and detectors to the rear. Credit: ArgonneNational Laboratory
How does the universe's building blocks, the chemical elements, come together? For the better part a century, this question has been the heart of nuclear physics.
Scientists discovered at the start of the 20th century that elements had a central core, or nucleus. These nuclei contain a variety of protons as well as neutrons.
Researchers at Michigan State University's Facility for Rare Isotope beams (FRIB), have now developed and tested a device that can provide crucial insights into heavy elements. These are elements with very high numbers of protons or neutrons. This effort was led by Ben Kay, a physicist from the U.S. Department of Energy (DOE), Argonne National Laboratory. FRIB is an DOE Office of Science User Facility.
Kay and his team completed their first experiment with the SOLARRIS device. This stands for Solenoid Spectrometer Apparatus to Reaction Studies. The planned experiments will provide information on nuclear reactions that produce some of the most dangerous elements in the world, such as iron and uranium.
Experiments with exotic isotopes are also planned. Isotopes can be elements with the same number or different numbers of protons. Scientists call certain isotopes exotic because they have different ratios of neutrons to protons than the stable or long-lived elements that are found naturally on Earth. These unstable isotopes are essential for astronomical events.
Kay said, "Exploding stars and the merger of giant collared stars, we now know details about the nuclear reactions that are at the core of these events." "With SOLARIS we can recreate these reactions here on Earth to see them for our own eyes."
This new device follows the HELIOS (the Helical Orbit Spectrometer) at Argonne. Both devices use superconducting magnets that were repurposed from an MRI machine. Both use a beam of particles to target a material within a vacuum chamber. Transfer reactions take place when the particles collide. Depending on the particle and its energies, the protons or neutrons are either removed from the nuclei or added to them in such reactions.
Kay stated that by recording the energy and angle of various particles released or deflected in collisions, Kay can gather information about the structure nuclei in these isotopes. "The SOLARIS design is a novel way to improve our understanding of exotic nuclei."
SOLARIS is unique because it can operate as a dual mode spectrometer. This means it can measure with very high and very low intensity beams. Kay explained that SOLARIS can work in both of these modes. One uses a traditional silicon array in a vacuum. The other uses the gas-filled target from the Active-Target Time Projection Chamber at Michigan State. It is led by Daniel Bazin, a SOLARIS team member and senior FRIB physicist. The AT-TPC was tested in this first experiment. Scientists can use weaker beams to get the results they need with high accuracy using the AT-TPC.
The AT-TPC is basically a large chamber that contains a gas. This serves as both the target and detector medium. This is in contrast to the conventional vacuum chamber, which uses a silicon detector array with a separate, thin target.
Kay stated, "By filling the chamber in gas, you ensure that the smaller, more concentrated particles from the low intensity beam will contact the target material." The scientists then have the opportunity to study the products of these collisions.
Clementine Santamaria, FRIB research associate, was the first to examine the breakdown of oxygen-16, which is the most prevalent oxygen isotope on Earth. This resulted in smaller alpha particles. The eight protons, eight neutrons, and eight nuclei of oxygen-16 were broken down into four alpha particles. Each particle consists of two protons, two neutrons, and one neutron.
Kay explained that by determining the decay of oxygen-16 like this, one can draw comparisons to the 'Hoyle' state, which is an excited state of a carbon Isotope we believe plays a crucial role in the production and distribution of carbon in stars.
Kay and his colleagues recorded more than two million reactions during the experiment. They also observed numerous instances of decay of oxygen-16 into Alpha particles.
SOLARIS' dual functionality will enable scientists to perform more nuclear reactions than ever before and provide new insight into some of the most mysterious aspects of the cosmos.
Continue reading to learn more about the workings of the nucleus