8 th Aug 2009 ANL User Workshop Towards Nuclear Spectroscopy using a Position Sensitive Avalanche Photo Diode S. Lakshmi University of Massachusetts Lowell

8 th Aug 2009 ANL User Workshop 14 mm < 200  m thick Si 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

8 th Aug 2009 ANL User Workshop Phase I – Circuit Board Layout & Preamps

1500 V 1400 V 1300 V 1200 V 1100 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

8 th Aug 2009 ANL User Workshop  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 PSAPD – Phase II

8 th Aug 2009 ANL User Workshop D AB C Distortion Corrections III Average (I + II)/2  Less distortion and better separation of spots  Determine X & Y centroids in distorted space  Create calibration grid to correct distortions event-by- event

8 th Aug 2009 ANL User Workshop Position Reconstruction  Distorted matrix of centroids fitted to 2 nd 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.

8 th 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

8 th 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 strips Electronically segmented 14 horizontal strips (B) 14 vertical strips (Li) ANL Pixel Efficiency: source 42 mm from face

  Z α = 13mm Z  = 42mm Alpha-Gamma Angular Correlation  m=0 fully aligned, strong anisotropy in  On-Axis Geometry zαzα zz S

8 th Aug 2009 ANL User Workshop Phase II tests  Uncorrelated Distribution  Angle Reconstruction  Measured vs Expected  Large angle coverage  Sensitivity to source position

8 th Aug 2009 ANL User Workshop 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.

8 th Aug 2009 ANL User Workshop  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 Summary and Future Summary 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

8 th Aug 2009 ANL User Workshop 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