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Imaging Nuclear Reactions

Imaging Nuclear Reactions. Zhon Butcher 2006 REU Program Cyclotron Institute Mentor: Dr. Robert Tribble. Applications of Nuclear Imaging. Space Telescopes – Cosmic radiation identification and direction of origin. Imaging reactions in the nuclear physics laboratory.

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Imaging Nuclear Reactions

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  1. Imaging Nuclear Reactions Zhon Butcher 2006 REU Program Cyclotron Institute Mentor: Dr. Robert Tribble

  2. Applications of Nuclear Imaging • Space Telescopes – Cosmic radiation identification and direction of origin. • Imaging reactions in the nuclear physics laboratory.

  3. How Imaging Works in the Lab • Several detectors are placed around the reaction site covering a given solid angle. • Detectors determine particle identity and position. • The resulting image gives a picture of the reactions that took place in the chamber.

  4. Particle Identification • Telescopes: Front detector and rear detector. • Front detector picks up energy loss as the particle passes through. • Rear detector picks up residual energy. • Particle identification determined by:

  5. Methods for Position Determination • Many small detectors coupled with a large amount of electronics (clustering). • Resistive strip detectors. • Double sided strip detectors. • Resistive sheets.

  6. Q1 Q2 Qtot 1-D Position Sensitive Detector

  7. Resistive Strip Detectors • Consist of many resistive strips placed alongside one another. • Good resolution in the X direction, poor resolution in the Y direction (or vice versa depending on orientation).

  8. PSSDs

  9. Double Sided Strip Detectors • Two sheets of strips placed one in front of the other so the strips form a grid. • Results in better position resolution • Washington University team had detectors with 32 strips in each direction. • 64 strips per detector x 4 detectors = 256 channels for position reconstruction

  10. Double sided PSSDs

  11. Resistive Sheets • A single resistive sheet spans the entire active area of the detector. • Advantages • Fewer signals to process. • Less electronic equipment. • Detector Types: • Duo-lateral: Generates two signals from each face of the detector, two from the front and two from the back. • Tetra-lateral: Generates five signals, one from each corner of the resistive side, and one signal from the back.

  12. Bias 1 MW 10 kW 10 kW 10 kW 10 kW 10 kW 10 kW Schematic diagram of the detector 10 kW 10 kW Tetra Lateral Detectors Particle impinging position calculated by:

  13. Signal Processing ADC Preamplifier Spectroscopy Amplifier Preamplifier Spectroscopy Amplifier Detector Computer Preamplifier Spectroscopy Amplifier Preamplifier Spectroscopy Amplifier Gate Generator Preamplifier Timing Amplifier Discriminator Rear signal

  14. How Silicon Detectors Work

  15. Current Through Semiconductor

  16. Doped Semiconductor What is doping? • Doping is the integration of impurities into the lattice structure of the semiconductor. • This allows extra electron and hole energy levels which will increase the conductivity of the semiconductor.

  17. Experiment • To characterize the Micron Semiconductors tetra-lateral detectors in terms of energy and position resolution as well as non-linearity in position reconstruction. • Three tetra-lateral type PSDs were investigated. One 200 mm and one 400 mm thick detectors with a resistive strip around the active area, and one 200 mm without a resistive strip. • Optimal strip resistance is approx. 1/10th the resistance of the detector active area.

  18. Setup • The detectors were placed in a vacuum chamber with a radioactive source. (241Am and 228Th were used) • The distance between the source and the detector was approx 25cm for 241Am and 10cm for 228Th

  19. Two masks were used to cover the detectors. Calibration Masks

  20. Without resistive strip: With resistive strip: Position Reconstruction 200mm Position reconstruction of impinging alpha particles for the 200 mm thick detector with and without a resistive strip.

  21. Without mask: Slit mask: Holes mask: Position Reconstruction 400 mm Position reconstruction of impinging alpha particles with and without a mask for the 400 mm thick detector with a resistive strip.

  22. Energy Resolution • Energy Spectrum of alpha decay from 228Th with 400mm detector: Energy Resolution: Approx 10%

  23. Results • The position resolution was determined to be around 3-4 mm and energy resolution of 8% for both the 400 mm and 200 mm thick detectors with the resistive strip. • The resistive strip has a major contribution in reducing the position reconstruction distortion.* *For more information see T.Doke et.al. NIM A261 (1987) 605

  24. Conclusion • The position resolution for the tetra-lateral PSDs strongly depends on the resistivity of the resistive sheet, electrode termination resistors, the filter components of the preamplifiers, and the shaping times of the amplifiers. • The measurements done were employing the use of Indiana University preamplifiers and CAEN amplifiers (3 ms shaping time). Further investigation of these dependencies is ongoing.

  25. Acknowledgements Special thanks to: • Dr. Robert Tribble • Dr. Livius Trache • Dr. Adriana Banu • Matthew McCleskey

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