GRETA Project Organization

GRETA received CD-0, or 'Mission Need' from the U.S. Department of Energy, Office of Science on September 15, 2015, as the first step toward the realization of a full 4π γ-ray tracking detector.  

GRETA Conceptual Design

Planned as a key instrument for the Facility for Rare Isotope Beams (FRIB), the Gamma-Ray Energy Tracking Array (GRETA) is the realization of a full 4π γ-ray tracking detector, capable of reconstructing the energy and three-dimensional position of γ-ray interactions within a compact sphere of high-purity germanium crystals. It consists of a total of 120 highly segmented large-volume, coaxial germanium crystals, with four crystals combined to form a total of 30 Quad Detector Modules, designed to cover the total solid angle with a close-packed spherical geometry. Each crystal is electrically segmented into 36 individual elements and a core contact, and read out over custom designed, digital electronics. The detector signals are analyzed to reconstruct γ-ray energies and interaction points in a dedicated high performance computing cluster of commercially available CPUs. GRETA, with its unprecedented combination of high efficiency, good background rejection, and excellent energy and position resolution,will be needed to achieve the full scientific potential at FRIB.

The technology and the scientific impact of a γ-ray tracking array have already been demonstrated. Between 2003 and 2011, the US low-energy nuclear physics community constructed GRETINA, a 1π tracking detector optimized for fast-beam nuclear physics experiments and employing the same segmented detector and signal decomposition technology as GRETA. Building on the success of GRETINA, and following the strong support expressed by the U.S. nuclear physics community in the 2015 Long Range Plan, GRETA received CD-0 approval in September 2015.

The overall objective of the GRETA project is to deliver all necessary subsystems required to expand the existing GRETINA array to subtend the currently envisioned (and previously proposed) full 4π coverage of γ-ray tracking detectors. The project scope comprises the procurement of 18 Quad Detector Modules, as well as the design and fabrication of the data acquisition, computational processing, data storage, and mechanical infrastructure for the full 30 Quad Module Array. Project completion is aligned to FRIB operations, with baseline completion in 2026 and early finish in 2024.

The Conceptual Design Report (available here) was presented as a part of the GRETA CD-1 DOE Review in April 2017. The report presents the underlying principles behind the GRETA technology, the science reach of the array and a description of the technical performance, conceptual design and implementation.