Towards Nuclear Spectroscopy using a Position Sensitive Avalanche Photo Diode

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

2. 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). < 200 m thick Si ANL User Workshop

3. Phase I – Circuit Board Layout & Preamps ANL User Workshop

4. 6 MeVa 140 keV FWHM PSAPD – Phase I – Operating Parameters composite spectrum 1000 V 1100 V 1200 V Bias HV Operating Bias HV 1300 V 1400 V 1500 V

5. a-source PSAPD – Phase I – Position resolution mask 7 x 7 matrix 1/16” (1.6 mm) pitch 1/64” (0.4 mm) dia holes

6. 1.6 mm 0.5 mm PSAPD – Phase I – Position resolution pincushion distortion

7. 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

8. A B D C 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 ANL User Workshop

9. 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. ANL User Workshop

10. 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 ANL User Workshop

11. a PSAPD g q GeDSSD Towards Nuclear Spectroscopy Alpha-Gamma Angular Correlation PSAPD-GeDSSD Compact geometry, large solid angle coverage GeDSSD @ 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 ANL User Workshop

12. S zα z Alpha-Gamma Angular Correlation fully aligned, strong anisotropy in a-g m=0 g a a g Zα = 13mm Z = 42mm On-Axis Geometry

13. Phase II tests • Uncorrelated Distribution • Angle Reconstruction • Measured vs Expected • Large angle coverage • Sensitivity to source position ANL User Workshop

14. 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. ANL User Workshop

15. 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 ANL User Workshop

16. 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 ANL User Workshop