The Gamma-Ray Energy Tracking Array (GRETA) project is advancing quickly towards the Critical Decision 4A (CD-4A) milestone, which marks the completion of the majority of the project scope, and will be followed by delivery of the array to the Facility for Rare Isotope Beams (FRIB) this summer.
A critical step in the preparation for CD-4A is to demonstrate that all of the key performance parameters (KPPs) defined for the project, which capture the required capabilities of the system, have been achieved. These included delivery of at least 6 GRETA Quad Detector Modules, and the electronics systems to instrument fully all 30 GRETA Quad Modules which will comprise the complete array. With the support of the LBNL survey and alignment group, the project has also confirmed that the GRETA mechanical support structures can hold the load of all 30 Quad Modules with the required precision and can be aligned such that the location of all detectors is known at the level of better than 1mm.
Computing performance was also verified in January with the demonstration of the GRETA computing cluster’s capacity to perform “signal decomposition”, or the localization of gamma-ray interactions within a HPGe crystal. This computationally-expensive calculation was demonstrated at 511,000 signal decompositions per second, exceeding the specified 480,000 for which the array was designed.
Finally, the integrated systems performance was confirmed through measurement of a gamma-ray calibration source with 6 Quad Modules installed in the GRETA array at Building 88 onsite at LBNL. Pictured in Figure 1, the Quad Modules were installed in a close-packed configuration and fully instrumented with all of the GRETA electronics and support systems. The system KPP required the energy resolution to be less than 3.0 keV for the 1.33 MeV transition using a 60Co source – the project achieved a resolution of 2.39 keV, exceeding the required performance.
GRETA is a $58M project funded by the DOE Office of Nuclear Physics and led by the LBNL’s Nuclear Science Division (NSD). The project team that includes staff from NSD, ESNET, and Engineering Division at LBNL, and from Argonne National Laboratory, Oak Ridge National Laboratory and FRIB, are now preparing for the CD-4A review of the project to take place later this Spring.
