8th Aug 2009 ANL User Workshop

Towards Nuclear Spectroscopy using aPosition Sensitive Avalanche Photo Diode

S. LakshmiUniversity of Massachusetts Lowell

8th Aug 2009 ANL User Workshop

14 mm

< 200 m thick Si

)(

)()(

)(

)()(

DCBA

DCBAY

DCBA

DACBX

four-corner design

charge fractionation

14 mm

K.S. Shah et al., IEEE Trans. Nucl. Sci.49(4), 1687 (2002).

(RMD, Inc.)

PSAPD – Phase I

8th Aug 2009 ANL User Workshop

Phase I – Circuit Board Layout & Preamps

1500 V

1400 V

1300 V

1200 V1100 V

1000 V

Operating Bias HV

6 MeV 140 keV FWHM

composite spectrum

Bias HV

PSAPD – Phase I – Operating Parameters

mask

-source

1/16” (1.6 mm) pitch

7 x 7 matrix

1/64” (0.4 mm) dia holes

PSAPD – Phase I – Position resolution

pincushion distortion

1.6 mm

0.5 mm

PSAPD – Phase I – Position resolution

8th Aug 2009 ANL User Workshop

Larger PSAPD (28 mm X 28 mm)Redesigned circuit boardDetector centered in cylindrical chamberPreamps separated for better heat dissipationNew mask, 7 x 7 matrix, 1/8” pitch, 1/64’’ dia holes

PSAPD – Phase II

8th Aug 2009 ANL User Workshop

DCBA

D)(CB)(AY

DCBA

D)(AC)(BX

4cos(πCA

CΑ4sin(π

DB

DBY

)4/sin(CA

CA)4/cos(

DB

DBX

D

A B

C

Distortion Corrections

I II Average(I + II)/2

Less distortion and better separation of spotsDetermine X & Y centroids in distorted spaceCreate calibration grid to correct distortions event-by-event

8th Aug 2009 ANL User Workshop

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.

8th Aug 2009 ANL User Workshop

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

8th Aug 2009 ANL User Workshop

Towards Nuclear Spectroscopy

PSAPD

GeDSSD

Alpha-Gamma Angular Correlation PSAPD-GeDSSD Compact geometry, large solid angle coverage

90 x 90 x 20 mm, 5mm stripsElectronically segmented 14 horizontal strips (B)14 vertical strips (Li)

GeDSSD @ ANL

Pixel Efficiency: source 42 mm from face

0

0.5

1

1.5

2

0 20 40 60 80 100 120 140 160 180

angle

counts

Zα = 13mmZ = 42mm

Alpha-Gamma Angular Correlation

m=0

fully aligned, strong anisotropy in

On-Axis Geometry

zα z

S

8th Aug 2009 ANL User Workshop

Phase II tests

Uncorrelated Distribution

Angle Reconstruction

Measured vs Expected

Large angle coverage

Sensitivity to source position

8th Aug 2009 ANL User Workshop

Phase III: In progress

Preamps outside vacuum chamberCooler preamps reduce noise, gain shifts

Longer statistics run being set up at Lowell with precise source positioning.

8th Aug 2009 ANL User Workshop

PSAPD successfully tested for charged particle detectionExcellent position resolution with few electronics channelsAlgorithms being improved to remove position distortionCompactness and position sensitivity of PSAPD and GeDSSD being exploitedTable-top source measurements of alpha-gamma angular correlation in progress Event by event angle reconstruction tested with uncorrelated distributions

Summary and Future

Summary

FutureIn-beam tests with other charged particles and heavy ionsTests of count rate capabilityTests of radiation hardnessA PSAPD mini-array (box, wall, …)PSAPD coupled to scintillator as a photomultiplier substituteCharged particle veto box near targetPosition sensitive counter at the back of recoil separator

8th Aug 2009 ANL User Workshop

Collaborators

University of Massachusetts LowellP. ChowdhuryS. K. Tandel

Argonne National LabC.J. ListerS. Gros

Radiation Monitoring Devices, Inc.K.ShahM. McClishR. Farrell