AGATA detector characterization: Quick 3D scanning system

1
AGATA detector characterizationQuick 3D
scanning system

• N. Saito and J. Gerl
• GSI

2
Concept
Side detector

• Reduce a time to scan by taking data for all
  required positions at same time
• Define directions of g-ray by measuring one of
  511 keV g-rays from a 22Na source
• Define interaction position in Ge by measuring a
  scattering g-ray on the side detector and
  energy deposit in Ge.

511 g
Ge
Collimator (slits)
511 g
Collimator (holes)
22Na g source
Scinti. Fiber
3
Simulation
4.5 cm
5 cm

• GEANT4
• Ge cylindrical shape
• Radius 4 cm, length 9cm
• 6x6 seg. (1, 1, 1.75, 1.75, 1.75, 1.75 cm )
• Collimator surrounding Ge
• Pb cylinder
• Slits width 2 mm length 5 cm
• Inner r. 4.5 cm
• Side detector
• Scintillator (Plastic, NaI, or BGO)
• Source collimator
• Pb ball inner r. 4 cm, thickness 2cm
• 9 x 6 holes, f 1 mm
• Scint. Fiber
• f 0.82 mm, 5 -10 cm length
• Edge 4cm from the source (correspond f 2 mm at
  the Ge surface)

10 cm
Slits 2 mm
4 cm
Fiber f 0.82 mm
4
Position distribution XY plane for each Ge layer
5
Position distribution XZ plane for each Ge layer
6
Rate estimation
Condition

• 10MBq 22Na source
• Detector efficiency from the simulation
• Side detector 12 x 6 BGO (EuroBall inner ball)
• Fiber length 5 cm
• Threshold on Fiber energy 100 keV 0.69
• Energy gate for Ge 220 keV to reduce
  multi-interaction events

Rate
Ge Layer Coincidence events on a reference
position / day
1 270 2 170 3 100 4 61 5 26 6 12

7
Investigation

• Multiple interaction in a Ge segment
• 33 without energy gate on Ge
• 15 with energy gate on Ge
• 7 with energy gate on Ge and side detector
  divided
• Multiple hit on Fiber detectors
• 0.5 with a Pb ball thickness of 1 cm
• 0.4 with a Pb ball thickness of 2 cm
• 0.1 with a Pb ball thickness of 5 cm
• Side detector
• Side detector efficiency (relative to BGO case)
  65 NaI, 26 Plastic
• Energy above 50 keV 99 BGO, 85 NaI, 56
  Plastic

8
Discussion

• Reference points
• 3 rings (q 4, 8, 12 deg)
• Side 1 or 2 ?
• Source position
• 10 cm away from detector
• Side detectors
• BGO or NaI

Radii at surface 7, 14, 21 mm
9
Discussion

• Reference points
• 3 rings (q 4, 8, 12 deg)
• Side 1 or 2 ?
• Source position
• 10 cm away from detector
• Side detectors
• BGO or NaI

Radii at surface 7, 14, 21 mm
10
Discussion

• Reference points
• 3 rings (q 4, 8, 12 deg)
• Side 1 slit for each sector
• Up and down for detailed scanning (4 or 5 steps)
  ?
• Source position
• 10 cm away from detector
• Side detectors
• BGO or NaI

Radii at surface 7, 14, 21 mm