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Advanced GAmma Tracking Array
Performance of an AGATA prototype detector estimated by Compton-imaging techniques Francesco Recchia INFN - Legnaro on behalf of the AGATA collaboration
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The g-ray spectrometer AGATA
Rint = 23 cm Rext = 32 cm Design values: 5 mm of position resolution assumed 180 HPGe Efficiency: 43% (Mg=1) 28% (Mg=30) today’s arrays ~10% 5% Peak/Total: 58% (Mg=1) 49% (Mg=30) today ~55% % Angular Resolution: ~1º FWHM (1 MeV, v/c=50%) ~ 6 keV today ~40 keV 180 large volume 36-fold segmented Ge crystals packed in 60 triple-clusters Digital electronics and sophisticated Pulse Shape Analysis algorithms Operation of Ge detectors in position sensitive mode for g-ray tracking Triple cluster
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Ingredients of g-ray tracking
Identified interaction points 1 4 (x,y,z,E)i Highly segmented HPGe detectors Reconstruction of scattering sequence from Compton vertices Pulse Shape Analysis to decompose recorded waves 3 g What has to be done to perform tracking What are the ingredients Detectors highly segmented, encapsulated, cryostats Electronics Digital PSA to extract Energy Time and Position Algorithm development particularly for position Area where effort is required Thorsten Kroell. See him. Tracking algorithms, reconstruction of the events for full array Obtain full energy Many technical development in all areas. 2 Digital electronics to record and process segment signals Reconstructed gamma-rays
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Pulse Shape Analysis concept
(10,10,46) B3 B4 B5 (10,30,46) C3 C4 C5 y C4 B4 CORE measured D4 x A4 E4 F4 791 keV deposited in segment B4 z = 46 mm
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Pulse Shape Analysis concept
B3 B4 B5 (10,10,46) C3 C4 C5 y C4 B4 CORE measured calculated D4 x A4 E4 F4 791 keV deposited in segment B4 z = 46 mm
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Pulse Shape Analysis concept
B3 B4 B5 (10,15,46) C3 C4 C5 y C4 B4 CORE measured calculated D4 x A4 E4 F4 791 keV deposited in segment B4 z = 46 mm
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Pulse Shape Analysis concept
B3 B4 B5 (10,20,46) C3 C4 C5 y C4 B4 CORE measured calculated D4 x A4 E4 F4 791 keV deposited in segment B4 z = 46 mm
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Pulse Shape Analysis concept
B3 B4 B5 (10,25,46) C3 C4 C5 y C4 B4 CORE measured calculated D4 x A4 E4 F4 791 keV deposited in segment B4 z = 46 mm
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Pulse Shape Analysis concept
B3 B4 B5 (10,30,46) C3 C4 C5 y C4 B4 CORE measured calculated D4 x A4 E4 F4 791 keV deposited in segment B4 z = 46 mm
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Pulse Shape Analysis concept
Result of Grid Search algorithm B3 B4 B5 (10,25,46) C3 C4 C5 y C4 B4 CORE measured calculated D4 x A4 E4 F4 791 keV deposited in segment B4 z = 46 mm
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The position resolution required for the AGATA detectors
Simulations suggest that the overall performance depends on the attainable position resolution A test-beam experiment has been performed to measure this parameter in realistic experimental conditions
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Setup of the in-beam experiment
Symmetric triple cluster d(48Ti,49Ti)p BEAM 48Ti 100 MeV TARGET 48Ti + 2H 220 μg/cm2 Si detector DSSSD Thickness: 300 μm 32 rings, 64 sectors AGATA symmetric triple-cluster experiment performed at IKP of Cologne Digitizers: 30 XIA DGF 4c cards 40MHz 14 bit Silicon detector
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Doppler correction using PSA results
32 keV Full statistics used
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Doppler correction using PSA results
11 keV 32 keV Full statistics used
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Doppler correction using PSA results
4.8 keV 11 keV 32 keV Full statistics used PSA algorithm: Grid Search
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Simulation vs Experiment
Recursive Subtraction Matrix Method Miniball Algorithm Grid Search Results obtained with different PSA algorithm
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Why Compton imaging? 15 days of beam-time to perform the test experiment 1 year of analysis PSA will be on-line Need for a simpler procedure Need an prompt feed-back from on-line analysis
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Compton imaging Compton imaging of a radioactive source
In-beam experiment: typical conditions of future use Compton imaging of a radioactive source inverse tracking E1 q E2 target E1 E2 q g-source
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Compton imaging performance
Error on Compton identification of source direction from: Position resolution (axis) Energy resolution (scattering angle) Compton profile (scattering angle) angular error [deg] scattering angle [deg]
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Imaging setup at LNL AGATA prototype detector
TNT2 Digitizers: 4ch 14bit 100MHz 60Co source
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Outline of analysis/simulation
DAQ MC Event selection Event selection PSA Smearing (position resolution) Image formation Image formation Position resolution
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Comparison to simulation
Simple back-projections MC MC + E res E ≈ MC + E res + pos res E,p Exp ≈
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Comparison to MC simulation
q profile of experimental image Experiment q [deg] peak FWHM [deg] 5.2 f [deg] position resolution FWHM [mm] Monte Carlo + 5 mm position resolution f profile of experimental image q [deg] peak FWHM [deg] 4.7 f [deg] position resolution FWHM [mm]
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CONCLUSIONS Position resolution extracted by in-beam experiment and Compton imaging is 5 mm FWHM. This value is in line with the design assumptions of the AGATA spectrometer, confirming the feasibility of g-ray tracking. AGATA will have a huge impact on nuclear structure studies (first phase of AGATA: LNL 2009…) Possible applications of g-ray tracking detectors to imaging.
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Basic implementation of LMML
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Requirements to the next generation g-ray spectrometer
AGATA is the next generation g-ray spectrometer which will be used at radioactive ion beam facilities: High efficiency and P/T ratio. Capability to stand a high counting rate. Good position resolution on the individual g interactions in order to perform a good Doppler correction and measure the linear polarization
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Compton imaging application
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