The Gamma-Ray Energy Tracking In-beam Nuclear Array (GRETINA) is the pre-cursor to the full GRETA 4pi array. Originally planned to consist of seven quad modules (28 crystals), GRETINA was funded by the U.S. Department of Energy, Office of Nuclear Physics, and built by a collaboration of US institutions led by LBNL. The array received CD4 (DOE project completion) in Spring 2011, and has since run physics campaigns at NSCL and ANL. A timeline of the GRETINA history from the beginning of the project through current operations is included below. More information is available at the GRETINA website, hosted by Florida State University.
GRETINA is a new type of gamma-ray detector to study the structure and properties of atomic nuclei. It is built from large crystals of hyper-pure germanium and uses the recently developed concept of gamma-ray energy tracking. GRETINA consists of 28 highly segmented coaxial germanium crystals. Each crystal is segmented into 36 electrically isolated elements and four crystals are combined in a single cryostat to form a quad-crystal module. The original design was for 7 modules in total. The modules are designed to fit a close-packed spherical geometry that covers one quarter of a sphere. GRETINA is the first stage of the full 4Π Gamma-Ray Energy Tracking Array (GRETA).
A Brief History
Construction of the gamma-ray tracking array GRETINA was completed at Lawrence Berkeley National Laboratory (LBNL) in March 2011 and operations began in April 2011 with a period of system integration, testing, and commissioning runs carried out at the LBNL 88-Inch Cyclotron. For more information and photos of GRETINA at LBNL check out the following links: GRETINA first quad in Cave 4C; GRETINA in Cave 4C; and GRETINA installed at the BGS.
In April 2012, the array was moved to the National Superconducting Cyclotron Laboratory at Michigan State University (NSCL/MSU) and installed at the target location of the S800 spectrometer for a campaign of experiments using "fast rare-isotope beams". Experiments at NSCL began in June 2102 and continued through June 2013. GRETINA's science campaign at NSCL was a great success: 23 PAC approved experiments, 3366 hours of beam time, involving more than 200 users from over 20 institutions worldwide. For more information of GRETINA at NSCL, including photos and videos, see GRETINA @ NSCL; GRETINA installed at NSCL (courtesy of S. Noji); and GRETINA being installed at NSCL.
Following the physics campaign at NSCL, GRETINA was installed at Argonne National Laboratory (ANL) with operations beginning in late 2013 and continuing through June 2015. The campaign included a range of experiments with the array coupled to auxiliary devices such as CHICO2 and the WashU Phoswich Wall, using both reaccelerated radioactive beams from CARIBU as well as high intensity stable beams. Procurement of additional quad cluster modules is continuing with Q8 delivered and operational at ANL, and the delivery of Q9 imminent in late summer 2015.
On March 1-2, 2013 a workshop on "Future GRETINA Science Campaigns" was organized by the GRETINA Users Executive Committee (GUEC) and hosted by the Physics Division at ANL. The focus of the meeting was two-fold: To discuss and exchange information on the upcoming GRETINA science and operation at ANL, as well as the ongoing campaign at NSCL, and to discuss science opportunities and future siting of GRETINA beyond the ANL campaign. It was unanimously agreed that GRETINA would move to NSCL for a second campaign of experiments beginning in 2015 for approximately 12 months that builds on the successful first campaign and uses fast beams of rare-isotopes in conjunction with the S800 spectrograph. In parallel, the GRETINA user community will begin preparing the plan for 2016 and beyond.
The details of the initial rotation plan of GRETINA between the national laboratories may be found in the "Report on the GRETINA Users Workshop on Future GRETINA Science Campaigns" while the original rotation plan of GRETINA between the national laboratories an be found in the Summary of 2007 Richmond Meeting.
Figure 1: Gamma-ray resolving power as a function of time in low-energy nuclear spectroscopy. Each development in the field has led directly to improvements in the sensitivity of measurements and the experimental reach possible.