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
The g-ray spectrometer AGATA
Rint = 23 cm
Design values:
5 mm of position resolution assumed
Rext = 32 cm
180 HPGe
Efficiency: 43% (Mg=1)
28% (Mg=30)
Peak/Total: 58% (Mg=1)
49% (Mg=30)
today
40%
today’s arrays ~10%
~55%
5%
Angular Resolution: ~1º
FWHM (1 MeV, v/c=50%) ~ 6 keV
today


Triple
cluster

~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
Ingredients of g-ray tracking
1
Highly segmented
HPGe detectors
Identified
interaction points
(x,y,z,E)i
·
··
Pulse Shape Analysis
to decompose
recorded waves
4
Reconstruction of
scattering sequence from
Compton vertices
·
··
g
3
2
Digital electronics
to record and
process segment
signals
Reconstructed
gamma-rays
Pulse Shape Analysis concept
A3
A4
A5
(10,10,46)
B3
B4
B5
(10,30,46)
C3
C4
C5
y
C4
CORE
B4
measured
D4
791 keV deposited in segment B4
A4
E4
F4
z = 46 mm
x
Pulse Shape Analysis concept
A3
A4
A5
B3
B4
B5
(10,10,46)
C3
C4
C5
y
C4
CORE
measured
calculated
791 keV deposited in segment B4
B4
D4
A4
E4
F4
z = 46 mm
x
Pulse Shape Analysis concept
A3
A4
A5
B3
B4
B5
(10,15,46)
C3
C4
C5
y
C4
CORE
measured
calculated
791 keV deposited in segment B4
B4
D4
A4
E4
F4
z = 46 mm
x
Pulse Shape Analysis concept
A3
A4
A5
B3
B4
B5
(10,20,46)
C3
C4
C5
y
C4
CORE
measured
calculated
791 keV deposited in segment B4
B4
D4
A4
E4
F4
z = 46 mm
x
Pulse Shape Analysis concept
A3
A4
A5
B3
B4
B5
(10,25,46)
C3
C4
C5
y
C4
CORE
measured
calculated
791 keV deposited in segment B4
B4
D4
A4
E4
F4
z = 46 mm
x
Pulse Shape Analysis concept
A3
A4
A5
B3
B4
B5
(10,30,46)
C3
C4
C5
y
C4
CORE
measured
calculated
791 keV deposited in segment B4
B4
D4
A4
E4
F4
z = 46 mm
x
Pulse Shape Analysis concept
A3
B3
A4
B4
A5
B5
Result of
Grid Search
algorithm
(10,25,46)
C3
C4
C5
y
C4
CORE
measured
calculated
791 keV deposited in segment B4
B4
D4
A4
E4
F4
z = 46 mm
x
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
Setup of the in-beam experiment
Symmetric triple cluster
d(48Ti,49Ti)p
BEAM
48Ti
TARGET
48Ti
100 MeV
220 μg/cm2
+ 2H
Thickness: 300 μm
Si detector
DSSSD
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
Doppler correction using PSA
results
32 keV
Full statistics used
Doppler correction using PSA
results
11 keV
32 keV
Full statistics used
Doppler correction using PSA
results
4.8 keV
11 keV
32 keV
Full statistics used
PSA algorithm:
Grid Search
Simulation vs Experiment
9
Recursive
Subtraction
8
Miniball
Algorithm
Grid Search
peak FWHM [keV]
Matrix Method
7
6
5
4
Results
obtained with
different PSA
algorithm
3
2
0
1
2
3
4
5
6
7
8
9
10
position resolution FWHM [mm]
11 12 13
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
Compton imaging
 In-beam
experiment:
 typical conditions
of future use
E1
 inverse tracking
E2
target
 Compton imaging
of a radioactive
source
q
E1
g-source
q
E2
Error on Compton identification
of source direction from:
 Position resolution (axis)
 Energy resolution (scattering
angle)
 Compton profile
(scattering angle)
angular error [deg]
Compton imaging performance
scattering angle [deg]
Imaging setup at LNL
AGATA prototype
detector
TNT2 Digitizers:
4ch 14bit 100MHz
60Co
source
Outline of analysis/simulation
DAQ
MC
Event
selection
Event
selection
PSA
Smearing
(position resolution)
Image
formation
Image
formation
Position resolution
Comparison to simulation
Simple back-projections
MCE+ E res
MC
≈
MC + E,p
E res + pos res
Exp
≈
q profile
of experimental image
Experiment
peak FWHM [deg]
q [deg]
Comparison to MC simulation
position resolution FWHM [mm]
f profile
of experimental image
Monte Carlo +
5 mm position resolution
peak FWHM [deg]
q [deg]
f [deg]
f [deg]
5.2
4.7
position resolution FWHM [mm]
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.
Basic implementation of LMML
0
1
20
6
Compton imaging application