Researchers have completed a major milestone in the construction of the Gamma-Ray Energy Tracking Array (GRETA), a cutting-edge detector designed to probe the mysteries of atomic nuclei.
Built through a collaboration led by the United States Department of Energy’s Lawrence Berkeley National Laboratory, with support from Argonne, Oak Ridge, and Michigan State University, GRETA represents the next leap forward in nuclear physics.
For decades, understanding how atomic nuclei behave has fuelled technological advances ranging from MRI scans that detect disease to nuclear power that lights millions of homes.
Yet scientists acknowledge that our picture of the nucleus – the dense heart of the atom – remains incomplete.
GRETA is set to change that by providing an unprecedented view into the forces that hold matter together.
Building the world’s most sensitive nuclear microscope
The GRETA project has now completed its core components, including 30 ultra-pure germanium detector modules, precision electronics, a finely engineered support structure, and high-performance computing systems.
When fully operational, GRETA will be between 10 and 100 times more sensitive than its predecessors, enabling researchers to see faint nuclear structures never observed before.
Each module is built from four hexagonal germanium crystals, carefully manufactured and cooled to cryogenic temperatures.
These crystals are so specialised that only a few can be produced each year, making GRETA a long-term engineering triumph.
The detectors will surround the nucleus in a complete sphere, maximising their ability to track gamma rays – tiny bursts of light emitted when atomic nuclei shed energy.
Unlocking the secrets of rare isotopes
GRETA will soon be shipped to the Facility for Rare Isotope Beams (FRIB) at Michigan State University, where scientists will collide particle beams with target materials to create exotic isotopes.
Many of these isotopes exist for only fractions of a second, but GRETA’s sensitivity will allow researchers to measure their properties in detail.
By examining the gamma rays emitted as excited atomic nuclei settle into stable forms, scientists can uncover their shapes, binding limits, and pathways of decay.
This includes studying the extreme edges of nuclear stability, where neutrons or protons begin to ‘drip’ away because they can no longer be held inside the nucleus.
Probing the Universe’s fundamental mysteries
The implications of GRETA’s discoveries extend far beyond the laboratory. At FRIB and Argonne’s ATLAS facility, researchers will use GRETA to study pear-shaped atomic nuclei that may reveal subtle violations of fundamental symmetries in physics.
Such work could help explain one of the deepest mysteries in science: why our Universe is made predominantly of matter rather than antimatter.
In addition, GRETA will allow scientists to replicate the processes that take place inside stars, where heavy elements are forged.
By recreating stellar conditions on Earth, nuclear physicists hope to gain a better understanding of how elements heavier than iron were formed in cosmic events such as supernovae and neutron star collisions.
A marriage of engineering and computing power
Behind GRETA’s remarkable capabilities lies an intricate blend of engineering precision and computational muscle.
The detector’s aluminium frame was built to tolerances of less than a millionth of an inch, ensuring its two halves align perfectly when enclosing a target.
The electronics system, designed with significant input from Argonne scientists, can process up to 511,000 gamma-ray interactions per second, surpassing initial design goals.
GRETA also integrates a powerful trigger system that filters through the flood of signals to capture only meaningful data.
Artificial intelligence and advanced tracking algorithms are being applied to sharpen GRETA’s performance even further, ensuring the instrument can keep pace with the enormous data streams it generates.
From GRETINA to GRETA
GRETA expands upon an earlier project known as GRETINA, which used 12 germanium modules to track gamma rays.
Those detectors, currently in use at Argonne, will be incorporated into GRETA to complete its 30-module spherical array.
This transition will vastly improve the ability of researchers to reconstruct the 3D paths of gamma rays and assemble a clearer picture of nuclear behaviour.
By catching more gamma rays in real time, GRETA will not only improve accuracy but also accelerate the pace of discovery. Experiments that once took weeks to gather enough data could now yield results in days.
Preparing for first experiments
Installation of GRETA at FRIB is scheduled to be completed in 2026, with the first experiments to follow shortly after.
Over the next decade, the instrument will travel between facilities to take advantage of different particle beams and experimental conditions.
Argonne’s ATLAS accelerator is expected to host GRETA by 2028 or 2029, providing complementary opportunities for nuclear structure studies.
GRETA may also become one of the first tools to utilise DOE’s new DELERIA data pipeline, which will stream vast datasets to supercomputing facilities in real time.
This would allow scientists to adjust experiments on the fly, dramatically improving efficiency and maximising discovery potential.
The next frontier of atomic nuclei research
With GRETA’s arrival, nuclear physicists are poised to answer some of the most fundamental questions about atomic nuclei and the forces that govern them.
From explaining how matter in the Universe came to exist, to exploring the limits of nuclear stability, GRETA promises insights that could reshape our understanding of nature at its deepest level.
As the most advanced gamma-ray detector of its kind, GRETA is not just an instrument – it is a powerful new lens through which humanity can explore the hidden structure of matter, unlocking the secrets of the atomic nucleus one gamma ray at a time.