Welcome to the
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).
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 see, http://newscenter.lbl.gov/feature-stories/2010/11/12/gretina-cave/ , http://www.lbl.gov/Science-Articles/Archive/sabl/2007/Feb/GRETINA.html and http://lbl.webdamdb.com/albums.php?albumId=182248
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 has been 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 http://nscl.msu.edu/users/equipment.html#gretina, https://people.nscl.msu.edu/~nojis/gretina_s800 and http://www.nscl.msu.edu/features/video-gretina-comes-nscl
GRETINA is currently being installed at Argonne National Laboratory (ANL) with operations to begin in late 2013 and to continue through 2014. This will allow time for experiments in both "standalone" mode and in combination with the FMA, using reaccelerated radioactive beams from CARIBU as well as high intensity stable beams. In this period ongoing efforts on performance measurements and enhancement will continue. Procurement of additional quad cluster modules is continuing with Q8 delivery expected in September 2013 and the order for Q9 is imminent.
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 recent 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 at: Summary of 2007 Richmond meeting
To find out more about the recent history of the project you are invited to browse through our Newsletters and other significant documents. They contain a great deal of information about the progress of the project with many hyperlinks to associated meetings, photographs, and other events of interest.
Newsletter #1 (Jan 2003)
Newsletter #2 (Oct 2003)
Newsletter #3 (July 2004)
Newsletter #4 (Sept 2005)
Newsletter #5 (Nov 2006)
Newsletter #6 (Jan 2008)
Newsletter #7 (March 2009)
Newsletter #8 (Feb. 2010)
Newsletter #9 (Summer 2011)
Newsletter #10 (Winter 2013)
GRETINA/GRETA was not only be strongly endorsed in the 2007 LRP but the 2 previous LRPs too. In preparation for the 2015 LRP GRETA has again been strongly endorsed in the White Paper on Nuclear Astrophysics and Low Energy Nuclear Physics which has been submitted to the NSAC LRP Writing Group, see below.
The original GRETINA Projector Manager from 1994 to the end of 2012 was I.Y. Lee (LBNL). We all owe IY a huge debt of gratitude for his brilliant leadership! Thank you IY! The new GRETINA Projector Manager is Augusto Macchiavelli (LBNL).
The GRETINA-GRETA Advisory Committee (formerly Steering Committee) has worked closely with the Project Manager from the very beginning in the mid-90's and continues to help steer the project forward towards GRETA. Its members are:
Previous members include: Kim Lister (ANL), Doug Cline (Rochester) and Thomas Glasmacher (MSU). We thank them for their magnificent service and contributions."
The chairpersons of the working groups are:
The GRETINA Users Community was formed in 2012 prior to the start of operations of GRETINA at the NSCL and is an organization of scientists interested in the development, and use, of GRETINA. Membership of the Users Group is open to all practicing scientists interested in any or all aspects of gamma-ray tracking. You can sign up on the web at http://lists.physics.fsu.edu/mailman/listinfo/gretina-users
GRETINA Users Executive Committee members are:
The GRETINA User Group Charter is available HERE.
The concept of a gamma-ray tracking detector array was proposed in 1994, and after about ten years of R&D, the technology was in place to construct such a detector. The Department of Energy made the Critical Decision-0 (CD0) for GRETINA in August 2003 to construct a tracking detector covering one-fourth of the total solid angle. Since then the project proceeded according to schedule and was completed in 2011 on time and within budget. The dates of Critical Decision are shown in the following table.
Preliminary Baseline Range
Start Construction of Long Lead Time Items
Start of Construction
Start of Operation
A short summary of the major components of the GRETINA project is given below.
The critical detector technology is the manufacture of two-dimensionally segmented coaxial germanium detectors which provide signals with sensitivity for locating interaction points in three dimensions. In addition, the crystals should have large volume and be shaped into tapered irregular hexagon shapes to allow for close packing into a spherical shell with a high solid angle coverage. We have been working closely with the detector manufacturer to develop such a detector through several prototype stages. The geometric design of GRETINA uses 120 crystals packed in 30 cryostats. The first production 4-crystal detector module was ordered and was delivered at the end of 2006. A picture of the first GRETINA production module is shown below.
Determining the gamma-ray interaction position in three dimensions requires a detailed analysis of the pulse shapes. To accomplish this, the pulse shape from each segment needs to be recorded at a sampling rate of about 100 MHz and with a resolution of 14 bits. To reduce the amount of data that has to be stored on disc, online processing in the digitizer generates energy, time, and trigger information, as well as capturing the relevant portion of the pulse shapes for further signal decomposition by a computer farm in real time. A trigger and timing system will carry out complex trigger decisions and distribute the clock and trigger information to GRETINA and its auxiliary detectors. All of the digitizer and trigger modules were produced and tested in 2008, and some of them are in use.
In order to perform gamma-ray tracking, the positions and energies of the gamma-ray interactions in the Ge crystal must be accurately determined from the signal waveforms. Each gamma-ray typically interacts via several Compton scattering events, followed by photoelectric absorption. The procedure must handle cases where two or more interactions occur within one of the detector segments. An algorithm to perform this "signal decomposition" has been developed, by combining several methods such as Singular Value Decomposition, adaptive grid search, and constrained least-squares. It utilizes calculated signal waveforms, and incorporates such effects as the preamplifier response and two different types of cross talk. We have shown experimentally that this algorithm can achieve an average position resolution of at least 2 mm.
It is important that the signal decomposition be performed in real time, so that large quantities of wave-form data need not be stored. This requirement means that signal decomposition is expected to form the data acquisition bottleneck; computational speed and efficiency of the algorithm are therefore very important. On the current generation of 2 GHz processors, the algorithm requires less than 10 ms of CPU time per hit segment. With advances in processing power from multi-core CPUs, this performance will be sufficient to meet our requirements. The GRETINA's computer farm will consist of 40 eight-core processors.
The tracking process uses the energies and positions of the interaction points produced by the signal decomposition to determine the scattering sequence for a particular gamma-ray. Algorithms have been developed to track events based on Compton scattering, pair-production and photo electric interactions. The tracking efficiencies achieved ranged from ~100% to 50% when gamma-ray multiplicity changed from 1 to 25. The current tracking algorithm needs ~10% of the planned computing power.
The performance of GRETINA with seven quad-crystal modules is shown in the following table.
|Number of Ge crystals1||≥ 28|
|Number of segments||6 longitudinal x 6 transverse|
|Segment Energy resolution||≤ 2.5 keV (FWHM) average, at 1.33 MeV|
|Noise per segment||≤ 7 keV (standard deviation) average at 35MHz bandwidth|
|Time resolution||≤ 10 nsec (FWHM) average, at 1.33 MeV|
|Array peak efficiency||≥ 7.2 % at 1.33 MeV|
|Array peak-to-total ratio||≥ 40% at 1.33 MeV|
|Position resolution||≤ 2 mm (standard deviation) average for Eint > 300 keV|
|Digital Signal Processing Module|
|Digitizer sampling rate||≥ 75 MHz|
|Digitizer resolution 2||≥ 12 bits|
|Final integral nonlinearity3 (in Egamma)||≤ ± 0 .1% over the top 99% of the dynamic range|
|Final differential nonlinearity3 (in Egamma)||≤ ± 1% over the top 99% of the dynamic range|
|Final energy/gain stability3||≤ ± 0.2%/hour gain drift for ≤ ± 5°temperature drift|
|Trigger and Readout|
|Readout speed||≥ 10 MB/s/crystal|
|Additional functionality||Accommodate auxiliary detectors in the trigger and the data stream|
|Data processing rate||≥ 20,000 gamma/s total|
|Data storage rate||≥ 10 MB/s|
|Performance following Signal Decomposition and Tracking|
|Efficiency||≥ 5.4 % at 1.33 MeV|
|Peak-to-total||≥ 55 % at 1.33 MeV|
 Plus one preexisting module with 3 crystals
 Resolution refers to the nominal value, not the effective resolution or effective number of bits
 As measured in the final energy spectrum
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