Towards Nuclear Spectroscopy using a

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Towards Nuclear Spectroscopy using a Position
Sensitive Avalanche Photo Diode
S. Lakshmi University of Massachusetts Lowell
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PSAPD Phase I
four-corner design
charge fractionation
(RMD, Inc.)
14
mm
14 mm
K.S. Shah et al., IEEE Trans. Nucl. Sci.49(4),
1687 (2002).
lt 200 ?m thick Si
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Phase I Circuit Board Layout Preamps
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PSAPD Phase I Operating Parameters
composite spectrum
1000 V
1100 V
1200 V
Bias HV
Operating Bias HV
1300 V
1400 V
1500 V
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PSAPD Phase I Position resolution
mask
7 x 7 matrix
1/16 (1.6 mm) pitch
1/64 (0.4 mm) dia holes
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PSAPD Phase I Position resolution
pincushion distortion
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PSAPD Phase II

• Larger PSAPD (28 mm X 28 mm)
• Redesigned circuit board
• Detector centered in cylindrical chamber
• Preamps separated for better heat dissipation
• New mask, 7 x 7 matrix, 1/8 pitch, 1/64 dia
  holes

8th Aug 2009
ANL User Workshop
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Distortion Corrections
Average (I II)/2
I
II

• Less distortion and better separation of spots
• Determine X Y centroids in distorted space
• Create calibration grid to correct distortions
  event-by-event

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Position Reconstruction

• Distorted matrix of centroids fitted to 2nd order
  polynomials in x and y
• Fitted parameters used to generate calibration
  curves on a finer grid.
• Calibration grid used event-by-event to map onto
  undistorted space.

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Corrected Position Spectrum

• Centroids lie on an undistorted grid
• Event-by-event discrepancies greater near corners
  and edges
• Distortion corrections acceptable if events
  restricted to a smaller effective area

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Towards Nuclear Spectroscopy
Alpha-Gamma Angular Correlation PSAPD-GeDSSD
Compact geometry, large solid angle coverage
GeDSSD _at_ ANL
90 x 90 x 20 mm, 5mm strips Electronically
segmented 14 horizontal strips (B) 14 vertical
strips (Li)
Pixel Efficiency source 42 mm from face
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Alpha-Gamma Angular Correlation
fully aligned, strong anisotropy in a-g
m0
a
g
a
g
Za 13mm Z? 42mm
On-Axis Geometry
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Phase II tests

• Uncorrelated Distribution
• Angle Reconstruction
• Measured vs Expected
• Large angle coverage
• Sensitivity to source position

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Phase III In progress
Preamps outside vacuum chamber Cooler preamps
reduce noise, gain shifts
Longer statistics run being set up at Lowell with
precise source positioning.
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Summary and Future
Summary

• PSAPD successfully tested for charged particle
  detection
• Excellent position resolution with few
  electronics channels
• Algorithms being improved to remove position
  distortion
• Compactness and position sensitivity of PSAPD and
  GeDSSD being exploited
• Table-top source measurements of alpha-gamma
  angular correlation in progress
• Event by event angle reconstruction tested with
  uncorrelated distributions

Future

• In-beam tests with other charged particles and
  heavy ions
• Tests of count rate capability
• Tests of radiation hardness
• A PSAPD mini-array (box, wall, )
• PSAPD coupled to scintillator as a
  photomultiplier substitute
• Charged particle veto box near target
• Position sensitive counter at the back of recoil
  separator

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Collaborators
University of Massachusetts Lowell P.
Chowdhury S. K. Tandel Argonne National Lab C.J.
Lister S. Gros Radiation Monitoring Devices,
Inc. K.Shah M. McClish R. Farrell