detector characterisation groupagata.pd.infn.it/documents/week9152003/andrewboston.pdf ·...
TRANSCRIPT
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Detector Characterisation Group
A. Boston, D. Cullen, J. Gerl, A. Görgen, S. Gros, K. Hauschild, T. Kröll, J. Ljungvall, N. Saito,
C. Santos, J. Simpson
What is characterisation?
• Specification of AGATA symmetric/asymmetric crystals• Calculation of reference pulse shapes
– Calculation of E-fields– Simulation of interaction points
• Full characterisation of prototype crystals– Detailed source scans
• Define how to characterise detectors– Define reference points
• Standardise scanning set-ups
With contributions from D. Bazzacco, P. Medina and C. Santos
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Why do we need?
• Charge pulse response characteristics for a closed-end coaxial geometry.
• Pulse shape response of each capsule needs to be understood.• Impurity
concentration• Lattice orientation• Surface passivation
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Highly segmented Ge Detectors
16
543
2A B C D
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Segmented Clover detectors
• s
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Automated Scanning Tables
Liverpool System
• Parker linear positioning table• Pacific scientific stepper motors• 0.3mCi 137Cs/0.2mCi 57Co• 1-2mm collimator• Singles/coincidence system
Precise position calibration
GSI / CSNSM Orsay
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Eurisys Mesures 6x6 Segmented Detector
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Charge pulse response
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Detector scan results
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6x6 Risetime Analysis
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Mirror Charge Asymmetry Analysis
rl
rl
QQQQ
A+−
=
• Ql and Qr are magnitudes of mirror charge signal in the left and right neighbour.
• The asymmetry cancels out the radial contribution and yields information regarding the azimuthal position of the main interaction.
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Image charge asymmetry results
1 3
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Energy Calibrated spectra of sector 1
A1 B1 C1 D1
152Eu source, GASP ACQ, high statistics (0.3 MEvs)
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Add-back spectra (all segments)
F1 F2 F3 F4
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F1 F2 F3 F4
0
1
2
3
4
5
6
1 2 3 4 5 6 7Number of Segments
FWH
M (k
eV)
1392
1394
1396
1398
1400
1402
1404
1406
1408
1410
1 2 3 4 5 6 7Number of Segments
Peak
Ene
rgy
(keV
)
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Energy calibration of CC
Using one energy calibrationderived from total CC spectrum
Using 25 energy calibrationsderived from CC spectra incoincidence with segments
If more than one segment fired, CC amplitude is a weighted average of the different calibrations
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Energy correlation between segments
1
65
4
32
A B C D
Front
Front-segments: A1-A2
(A1+A2) · (A1-A2)(A1) · (A2)
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Position-dependent (?) energy-losses
344 keV1408 keV
244 keV
122 keV
∆Emax ~ 12%(z-scale is logarithmic)
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roup AGATA prototype triple cluster
90 × 40 mm10º tapering angle
• Prototype symmetric triple cluster• Ordered from EM• Requirement to define segmentation scheme of detector• Database of calculated pulse shapes constructed for
consideration.
Courtesy of A. Görgen and T. Kröll
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Pulse shape database
• Two databases constructed utilising program to generate pulse shapes written by Th. Kröll
• Segmentation schemes considered:– 6 : 10 : 18.5 : 18.5 : 18.5 : 18.5– 10 : 10 : 17.5 : 17.5 : 17.5 : 17.5
• Uniform impurity concentration 1010
• -4kV operating voltage• Centre contact radius 5 mm (16mm depth)• GRETA segmentation scheme (for comparison):
– 10 : 12 : 16 : 18 : 20 : 14– Core depth 9mm
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Calculation of pulse shapesCalculation of pulse shapes
FEM-modelof detector
• Calculation of the signals induced on the contacts using the weighting field method
Calculate weightingfields
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Calculation of pulse shapesCalculation of pulse shapes
1.130.940.63
0.310.0
z[cm]
0˚ 7.5˚ 15˚ 22.5˚27˚
ϕ
A 0.55B 1.0
r [cm]
C 1.45D 1.9
E 2.35F 2.8
G 3.25H 3.7
net charge signals
-0.2
0
0.2H
GF
E
D C B A
-0.2
0
0.2
100 200 300
rel.
am
plitu
de
100 200 300t [ns]
-1
-0.75
-0.5
-0.25
0
A
BCDEF
GH
-1
-0.75
-0.5
-0.25
0
100 200 300
rel.
am
plitu
de
100 200 300t [ns]
∗
transient signals
•
•
•
•
•
•
• •
••
•
••••
••
•••••••
• •
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Pulse shape database
• A 1mm grid was used to evaluate the pulse shapes.
• Following cylindrical symmetry arguments interactions only in seg. B → 25,000 grid points were used.
• Net and image charge considered.• 662 keV photons from 137Cs
considered.
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Sensitivity
• Total average sensitivity:
• χ < 1 : Difference in signal is less than noise• χ = 1 : Difference in signal is noise• χ > 1 : Difference in signal is well above noise
2z
2y
2xS χ+χ+χ=
∑ ∑= σ
δ−=χ
i
Tp
0t2
2tt2
x2
))z,y,x(,q)z,y,x(i,q(
Charge collected at time t in segment i for interaction (x,y,z)
Segment that collects net charge and eight direct neighbours
Integration over time in steps of 1ns
Noise factor 1% of total charge
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Sensitivity
• Pulse shapes produced with 1ns precision:– SHOW EXAMPLES
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Sensitivity
• Demonstration of sensitivity: the position sensitivity peaks at the (effective) segment borders
• Regions near the outer surface between segment borders have the poorest sensitivity
total
dz
dy
dx
high
low
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Sensitivity: Conclusions
• Problematic zones:– front corners– back surface
• Very thin front segment reduces effective size of this segment only slightly:
• depth: 6 mm → effective volume 26,000 mm3
• 10 mm → 32,000 mm3
• Second segment can be made larger without significant loss of performance
• Reasonable compromise for segmentation in depth: – 8, 13, 15, 18, 18, 18 mm
• GRETA segmentation scheme (for comparison):– 10 : 12 : 16 : 18 : 20 : 14– Core depth 9mm
http://www-dapnia.cea.fr/Sphn/Deformes/Agata/local/index.shtml
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Design of detectorDesign of detector
• Layout of segments:• Enhance amplitudes of transient
signals• Counting rates per segment• Capacitance of segments• Equalise mean charge collection
times • Folding Algorithm
• Shape of front part of detector• Length of inner hole• We would prefer a more semi-
spherical shape of the front part of the crystal!
(Liverpool/Milano/CSMSM Orsay)
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AGATA capsuleAGATA capsule
• The impact of effective segmentation
0 1 2 3 3.8 0 1 2 3 3.80
10
0 1 2 3 3.80
10
z [cm]
0 1 2 3 3.80
10
tapering angle = 8° r [cm]
geometrical segmentation
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TIGRE simulations
• TIGRE e-drift velocity simulation
Liverpool, Strasbourg, Upsalla collaboration
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TIGRE simulations
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TIGRE simulations
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Conclusions
Status as of today:
• Specification of AGATA symmetric/asymmetric crystals• Calculation of reference pulse shapes
– Calculation of E-fields– Simulation of interaction points
• Full characterisation of prototype crystals– Detailed source scans existing/new detectors
• Define how to characterise detectors– Define reference points
• Standardise scanning set-ups