1. 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

2. 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

3. 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

4. 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

5. Pulse Shape Analysis conceptB3 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

6. Pulse Shape Analysis conceptB3 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

7. Pulse Shape Analysis conceptB3 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

8. Pulse Shape Analysis conceptB3 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

9. Pulse Shape Analysis conceptB3 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

10. 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

11. 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

12. 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

13. Doppler correction using PSA results
32 keV
Full statistics used

14. Doppler correction using PSA results
11 keV
32 keV
Full statistics used

15. Doppler correction using PSA results
4.8 keV
11 keV
32 keV
Full statistics used
PSA algorithm: Grid Search

16. Simulation vs Experiment
Recursive Subtraction
Matrix Method
Miniball Algorithm
Grid Search
Results obtained with different PSA algorithm

17. 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

18. 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

19. 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]

20. Imaging setup at LNL AGATA prototype detector
TNT2 Digitizers: 4ch 14bit 100MHz
60Co source

21. Outline of analysis/simulation
DAQ MC
Event selection
Event selection
PSA
Smearing (position resolution)
Image formation
Image formation
Position resolution

22. Comparison to simulation
Simple back-projections MC
MC + E res E ≈
MC + E res + pos res
E,p
Exp ≈

23. 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]

24. 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.

28. Basic implementation of LMML1 20 6

29. 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

30. Compton imaging application