GRETA is led by scientist in the nuclear science division, working with engineers from the Lab and teams at Argonne and Oak Ridge national labs and Michigan State University. It will provide new insight about the nature of matter and how stars create elements. Its first phase is expected to be completed in 2023, with the final completion in 2025. It builds on the existing GRETINA instrument, completed in 2011, which has fewer gamma-ray-detecting high-purity germanium crystals. GRETINA will be installed at FRIB facility when it begins operations in 2022. GRETINA is equipped with 12 detector modules and 48 detector crystals. Later, GRETA will replace it, bringing new electronics and 18 more detector modules, for a total of 30 modules and 120 crystals.

Figure 2. Side view of a simplified CAD model of a GRETA Quad Detector Module, illustrating the location of the four crystals (and cold FETs), warm FETs and preamplifier compartments, Radiall multi-pin connectors and the liquid nitrogen (LN) dewar.

GRETA will be key to many experiments at FRIB. Among its uses will be to study the most neutron-rich forms of isotopes, found along the so-called neutron “drip line.” GRETA will also be used to identify nuclei that exhibit pear-like shapes. Such experiments will help scientists learn the limits for the most extreme properties of atomic nuclei, provide key data on their creation, and identify new nuclei that test our understanding of nature’s fundamental interactions.

GRETA will be constructed, assembled, and tested at Berkeley Lab before being shipped to FRIB. Berkeley Lab led the development of the detectors for the project and are responsible for overseeing their delivery, and also leads the design and fabrication of GRETA’s signal-processing electronics, computing, and mechanical systems; Argonne National Lab is developing the electronics related to its trigger and timing systems; Michigan State University is responsible for characterizing the performance of its detectors; and Oak Ridge National Lab is responsible for the real-time signal processing to locate the gamma-ray interactions within the GRETA crystals.

After GRETA is completed, Berkeley Lab will not only play leading roles in the experimental program at FRIB, but will also maintain, reconfigure and upgrade the detectors, in order to benefit the international nuclear physics community. About 25 Berkeley Lab scientists and engineers are involved in the GRETA project.