1 / 14

GEANT4 simulations for a new generation of g -ray detector : AGATA

GEANT4 simulations for a new generation of g -ray detector : AGATA (Advanced Gamma Tracking Array) J. Roccaz, K. Hauschild, A. Korichi, A. Lopez-Martens, S. Mohammadi, S. Siem Nuclear Structure Group, CSNSM Orsay, CNRS-IN2P3, France.

lucius-ramirez
Download Presentation

GEANT4 simulations for a new generation of g -ray detector : AGATA

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. GEANT4 simulations for a new generation of g-ray detector : AGATA (Advanced Gamma Tracking Array) J. Roccaz, K. Hauschild, A. Korichi, A. Lopez-Martens, S. Mohammadi, S. Siem Nuclear Structure Group, CSNSM Orsay, CNRS-IN2P3, France Geant 4 Workshop, CERN (Geneva) November 11th-15th, 2002

  2. Outline • Introduction to superdeformation • An example of a current array : EUROBALL • Limits of actual generation • The new generation : AGATA  Description of the project  Work to be performed with GEANT4 V. Summary

  3. Superdeformation (SD) • Definition : • a state of the nucleus • shape of a rugby ball : long axis/short axis = 2 How can we explain the existence of SD nuclei? : Experimental signature : A rotational spectrum Regular spacing of -rays DEg ~ 40keV (~50keV) A~190 (~150) Nucleus quantal object b(elongation) Appearance of a second minimum which stabilizes the nucleus in a SD state

  4. Production & deexcitation of SD nuclei • Fusion-evaporation : • production of compound nucleus at high angular momentum (l >30ћ) and E* ~ 50MeV • deexcitation via particle emission (n, p, a) which removes a lot of energy (~ 10MeV/n) • emission of g rays when no more particles can be emitted •  average emission : 30 g • SD nuclei are rare events : 1% of the reaction channel!! • fusion-evaporation , s=100mb for 36S+160Gd at 159MeV • SD transitions = 1% = 1mb • high sensitive detection device is needed : EUROBALL

  5. EUROBALL @ Vivitron (Strasbourg) beam 239 Ge detectors cooled by liquid N, surround the target Another material is used : BGO (calorimeter, anti-Compton shields surrounding each Ge) Photopeak efficiency : 6.5% Resolution (Ge) : 2.1 keV Peak/Total (related to Signal/Noise) : 40% at 1.3MeV Mg=30

  6. Anti-Compton shields : Why? Totally absorbed  = good event Scattered  = background BGO Ge Signal from Ge + signal from BGO=> rejected event 60Co source

  7. Composite detectors Goal : to reduce -ray broadness due to Doppler effect Dq   DE 

  8. Limits of the current generation Search for hyperdeformation (long axis/small axis=3)  s=few nbarns (expected)!! With EB we can study weak SD structures :  = 10µb Limits of current Ge arrays with AC shields EUROBALL: ~40%, e=6.5%, P/T=40% for Mg=30 Need to replace shields by active material (Ge) to increase solid angle • AGATA : • ~80%, e=25%, P/T=50% for Mg=30 • We are interested in the individual energies in cascade, so we need tracking • To do tracking : Crystal segmentation and digital electronics are necessary

  9. Segmentation and Pulse Shape Analysis (PSA) • Interaction in segment 2: • PSA on 2 : height of signalenergy • rise time radius • precision ~1cm • PSA on 2+1+3  precision ~ few mm • Development of digital electronics Miniball segmented crystal  (E,x,y,z) for each interaction point

  10. 1 1 0 0 2 2 Principle of Tracking b) a) a b source 1 : (e1,x1,y1,z1) 2 : (e2,x2,y2,z2) ( Measured) e’1 E=e1+e2 e’2 a or b i=1, 2 Smallest ² = path followed by the photon

  11. Eg = 1.33 MeV Mg = 30 bad good Principle of tracking for AGATA • Partly escaped • Partly absorbed • First hit 30 + 4 interactions/ (1MeV)= 1031 possible combinations  previous method cannot be used algorithms of reconstruction must be developed Example : Cluster algorithm to group points into candidate events (clusters) Application to an ideal Ge shell 27 g detected ~ 23 photopeaks 16 reconstructed ~ 14 photopeaks World map representation Reconstruction efficiency : 60 % (14/23) Total Photopeak Efficiency : 47% (14/30)

  12. Geometry of AGATA 2 examples of possible geometry : • Planar geometry • 72 cryostats : a stack of4 planar detectors • Each detector • is segmented into 16 • segments •  ~4800 electronic channels • Geometry with 190 coaxial Ge detectors each Ge is segmented into 36 segments  ~7000 electronic channels

  13. Work to be performed with GEANT4 Work started using GEANT3. We will use GEANT4 because of its lower energy threshold  1 keV < interactions < 10keV are not lost • Simulations in order to compare , P/T… between the different geometries and also between GEANT3 and GEANT4 •  optimization of geometry • Creation of a database containing interaction points  test and develop the algorithms of tracking and the PSA

  14. Summary • Current arrays better knowledge of the structure of the atomic nucleus (e.g. superdeformation) • We need a more powerful array : AGATA hyperdeformation • A lot of work still has to be done : • Simulations with GEANT • Pulse Shape Analysis • Tracking algorithms • Prototype detectors testing ... • First experiment with AGATA in 2007-2008 • (if all goes well…)

More Related