The Gamma-Ray Energy Tracking Array (GRETA), a powerful new detector for studying atomic nuclei, has completed its primary construction phase. 

A collaborative team led by the US Department of Energy’s (DOE) Lawrence Berkeley National Laboratory has finished building the key components, which are multiple germanium detector modules, the electronics system, the instrument’s mechanical frame and infrastructure, and the computing systems..

Once running, GRETA’s expected to be 10 to 100 times more sensitive than previous detectors, allowing scientists to study the core of atoms in greater detail than ever before.

“Our goal was to make the best high-resolution, high-efficiency gamma-ray detector we possibly could,” said Paul Fallon, GRETA’s project director from Berkeley Lab.

Using a particle beam

To see inside a nucleus, researchers will use a particle beam to hit a target placed at the center of GRETA. This collision creates unstable, energetic nuclei. As these nuclei return to a more stable state, they release energy as gamma rays. GRETA’s spherical array of detectors is designed to track the path and energy of these gamma rays.

“The excited states and gamma rays are a fingerprint for each isotope,” explained Heather Crawford, a scientist at Berkeley Lab. “GRETA is the world’s most powerful microscope to examine these fingerprints.”

This “fingerprint” data will help scientists answer several fundamental questions. For instance, it’ll provide insights into how elements heavier than iron are created in stars and what the limits are for how many protons and neutrons can be held together in a nucleus. The research will also help explore why the universe is made of matter instead of antimatter.

Providing maximum sensitivity

GRETA is an expansion of an earlier detector, GRETINA. It’ll eventually combine GRETINA’s 12 detector modules with 18 new ones, for a total of 30 modules that form a complete sphere. Each module contains four crystals of ultra-pure germanium cooled to approximately -300°F for maximum sensitivity.

Argonne National Laboratory played a key role by designing the detector’s trigger system, which is essential for sorting through the enormous amount of data and identifying important events. 

The research team is also applying artificial intelligence (AI) to improve the software that reconstructs the gamma-ray paths, making the instrument even more powerful. 

“GRETA is also a potential first use case for an accelerated data pipeline called DELERIA, a new software platform for streaming enormous amounts of data at high speeds,” said the researchers in a press release.

Decoding nuclear synthesis

In recent tests, GRETA’s systems processed up to 511,000 gamma-ray interactions per second, exceeding its design goals.

GRETA will be shipped to the Facility for Rare Isotope Beams (FRIB) at MSU this fall. After installation, its first experiments are scheduled to begin in 2026.

The instrument is designed to be mobile and will eventually operate at both FRIB and Argonne’s ATLAS facility to take advantage of different types of particle beams.

“This research is exciting for nuclear physicists and has implications for astrophysics and understanding of nuclear synthesis,” said Dariusz Seweryniak, an experimental physicist at Argonne.