Researchers have completed a major milestone in the construction of Gamma Ray Energy Tracking Array (GRETA), a state-of-the-art detector designed to investigate the mysteries of the nucleus.
Built through a collaboration led by the U.S. Department of Energy’s Lawrence Berkeley National Laboratory, with support from Argonne, Oak Ridge and Michigan State University, Greta represents the next leap in nuclear physics.
For decades, understanding how nuclei behaved has fueled technological advances ranging from MRI scans to detect diseases to nuclear capabilities to illuminate millions of homes.
However, scientists acknowledge that the painting of the nucleus – the dense heart of the atoms – remains incomplete.
Greta is set to change it by offering an unprecedented view of the power that unites matter.
Build the world’s most sensitive nuclear microscope
The GRETA project has completed core components including 30 ultra-piergermanium detector modules, precision electronics, finely designed support structures, and high-performance computing systems.
When fully operational, Greta is 10-100 times more sensitive than its predecessor, allowing researchers to see faint nuclear structures that were not previously observed.
Each module is constructed from four hexagonal germanium crystals, carefully manufactured and cooled to cooling temperatures.
These crystals are so specialized that they can only produce a few of them each year, making Greta a long-term engineering victory.
The detector surrounds the nucleus with a complete sphere, maximizing its ability to track gamma rays. A small burst of light emitted when the nucleus flows energy.
Unlocking the secrets of rare isotopes
Greta will soon be shipped to Michigan State University’s Rare Isotope Beam (FRIB) facility, where scientists will collide with the target material to create exotic isotopes.
Many of these isotopes exist only in fractions of a second, but Greta’s sensitivity allows researchers to measure their properties in detail.
By examining the gamma rays emitted when the excited nucleus settles into a stable form, scientists can uncover their shape, binding restriction, and pathways of decay.
This includes studying the extreme edges of nuclear stability. Nuclear stability and protons cannot be retained within the nucleus, causing neutrons or protons to “drip down.”
Investigating the basic mysteries of the universe
The meaning of Greta’s discovery goes far beyond the lab. At the Atlas facility in Frib and Argonne, researchers use Greta to study pear-shaped nuclei that could reveal subtle violations of fundamental symmetry in physics.
Such works could help explain one of the deepest mysteries in science. Why is our universe made up of problems rather than antimatter?
Additionally, Greta allows scientists to replicate the processes that take place inside the star.
Nuclear physicists hope to better understand how heavier elements than iron were formed in cosmic events such as supernovae and neutron star collisions by recreating the conditions of stars on Earth.
The marriage of engineering and computing power
Behind Greta’s outstanding capabilities is a complex blend of engineering accuracy and computational muscles.
The detector’s aluminum frame was built to accommodate a tolerance of less than a million inches, with the two halves perfectly aligned when surrounding the target.
Designed with key inputs from Argonne scientists, the electronic system can exceed initial design goals and handle up to 511,000 gamma-ray interactions per second.
Greta also integrates a powerful trigger system that filters through flooding signals to capture only meaningful data.
Artificial intelligence and advanced tracking algorithms have been applied to enable the equipment to accommodate the vast streams of data generated by Greta to further sharpen performance.
From Gretina to Greta
Greta extends a previous project known as Gretina, using 12 germanium modules to track gamma rays.
These detectors currently used in Argonne are incorporated into Greta to complete a spherical array of 30 modules.
This transition greatly improves the ability of researchers to reconstruct gamma ray 3D paths and construct clearer pictures of nuclear behavior.
By catching more gamma rays in real time, Greta not only improves accuracy, but also accelerates the pace of discovery. An experiment that once took weeks to collect sufficient data could produce results in days.
Preparation for the first experiment
The installation of Greta on FRIB is expected to be completed in 2026, with the first experiment being carried out soon after.
Over the next decade, the equipment will travel between facilities and utilize a variety of particle beams and experimental conditions.
Argonne’s Atlas Accelerator is set to host Greta by 2028 or 2029, providing complementary opportunities for nuclear structural research.
Greta could also be one of the first tools to utilize DOE’s New Delaria data pipeline.
This allows scientists to coordinate their experiments on the spot, dramatically improving efficiency and maximize discovery potential.
Next frontier in nuclear research
With Greta’s arrival, nuclear physicists are poised to answer some of the most basic questions about the nuclei and the forces that govern them.
From explaining how the material in the universe came to exist, to exploring the limits of nuclear stability, Greta promises insights that can change our understanding of nature at its deepest level.
As this kind of cutting-edge gamma ray detector, the Greta is more than just an instrument. It is a powerful new lens that allows humanity to explore the hidden structure of matter and unleash the secrets of atomic nucleus one gamma rays at once.
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