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A. Nepomuk Otte MPI für Physik, Munich / Humboldt Universität, Berlin

The Geiger-APD a novel photon detector and its application in astrophysics experiments and positron emission tomography. A. Nepomuk Otte MPI für Physik, Munich / Humboldt Universität, Berlin. Outline. why new photon detectors for experiments in astroparticle physics

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A. Nepomuk Otte MPI für Physik, Munich / Humboldt Universität, Berlin

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  1. The Geiger-APDa novel photon detector and its application in astrophysics experiments and positron emission tomography A. Nepomuk Otte MPI für Physik, Munich / Humboldt Universität, Berlin

  2. Outline • why new photon detectors for experiments in astroparticle physics • the G-APD and some of its characteristics • application of G-APD in: • positron emission tomography (PET) • air Cherenkov telescopes Max-Planck-Institut für Physik / Humboldt Universität Berlin

  3. Many future experiments will use >> 100,000 photon detectors Requirements to be fulfilled by the photon detector candidate: • robust and stable • easy to calibrate • blue sensitive • low cost (+ low peripheral costs) • compact • low power consumption • … • highest possible photon detection efficiency Astroparticle experiments that will use this photon detector Max-Planck-Institut für Physik / Humboldt Universität Berlin

  4. Cosmic Ray Physics from Space • Highest energy cosmic rays > 1020 eV • GZK mechanism • sources of CR • … http://www.euso-mission.org/ Max-Planck-Institut für Physik / Humboldt Universität Berlin

  5. Ground based Gamma Ray Astrophysics Gamma Ray induces electromagnetic cascade relativistic particle shower in atmosphere Cherenkov light fast light flash (nanoseconds) 100 photons per m² (1 TeV Gamma Ray) MAGIC: world largest air Cherenkov telescope http://wwwmagic.mppmu.mpg.de/ Max-Planck-Institut für Physik / Humboldt Universität Berlin

  6. VHE gamma-ray sources: status ICRC 2007 71 known sources factor of 6 increase within 4 years very successful above 100GeV Rowell Max-Planck-Institut für Physik / Humboldt Universität Berlin

  7. pushing to lower energies entering an unexplored energy window between 10 GeV and 100 GeV • extragalactic background light studies • gamma ray bursts • dark matter • tests of quantum gravity • pulsars • … requires: • larger light collectors • high efficiency photon detectors currently used: classical photomultiplier tubes with ~20% QE Max-Planck-Institut für Physik / Humboldt Universität Berlin

  8. The G-APD a promising photon detector concept invented in Russia in the 80’s advantages • sensors with ~60% efficiency become available • internal gain ~105 -106 • compact and robust • … disadvantages • small sizes (<5x5mm²) • optical crosstalk (10%) • high dark count rate (~MHz) • … P. Buzhan et al. http://www.slac-stanford.edu/pubs/icfa/fall01.html Otte et al., IEEE TNS. 53 (2006) 636. SNIC-2006-0018, Apr 2006 Max-Planck-Institut für Physik / Humboldt Universität Berlin

  9. 3x3 mm² G-APD Max-Planck-Institut für Physik / Humboldt Universität Berlin

  10. A look into basic operations of semiconductor photon detectors with internal amplification Max-Planck-Institut für Physik / Humboldt Universität Berlin

  11. Working modes of avalanche photodiodes Geiger Mode Linear/Proportional Mode • Bias: (10%-20%) ABOVE breakdown voltage • Geiger-mode: it’s a BINARY device!! • Count rate limited • Gain: “infinite”!! • Bias: slightly BELOW breakdown • Linear-mode: it’s an AMPLIFIER • Gain: limited < 300 (1000) • High temperature/bias dependence • No single photo electron resolution Max-Planck-Institut für Physik / Humboldt Universität Berlin

  12. Advantages of APDs in Geiger ModeorSingle Photon Avalanche Diodes (SPADs) • Large standardized output signal • high immunity against pickup • High sensitivity for single photons • Excellent timing even for single photo electrons (<<1ns) • Good temperature stability • Low sensitivity to bias voltage drifts • Devices operate in general < 100 V • Complete insensitive to magnetic fields • No nuclear counter effect (due to standardized output) Max-Planck-Institut für Physik / Humboldt Universität Berlin

  13. The principal disadvantage for many applications: It is a binary device One knows: There was at least one electron/hole initiating the breakdown but not how many of them solved in the G-APD concept Max-Planck-Institut für Physik / Humboldt Universität Berlin

  14. Basic unit in a G-APD is a Single Photon Avalanche Diode (SPAD) Breakdown in SPAD is quenched by individual polysilicon resistor (passive quenching) from B. Dolgoshein (ICFA 2001) http://www.slac.stanford.edu/pubs/icfa/ Max-Planck-Institut für Physik / Humboldt Universität Berlin

  15. Bias and Output 1mm 30µm The G-APD typically 100…2000 small SPADs / mm² All SPADs connected in parallel Only one common signal line SPAD quenching resistor small signal replacement circuit Max-Planck-Institut für Physik / Humboldt Universität Berlin

  16. SiPM output is the analog sum of all SPADs Well defined output signal per SPAD  multi pixel resolution Max-Planck-Institut für Physik / Humboldt Universität Berlin

  17. working range from B. Dolgoshein Light06 Dynamic Range Dynamic range naturally limited by number of available SPADs working condition: Number of photo electrons < SPAD cells From probability considerations:  20% deviation from linearity if 50% of cells respond Max-Planck-Institut für Physik / Humboldt Universität Berlin

  18. Photon Detection Efficiency (PDE)orEffective Quantum Efficiency Most important parameter of a photon detector!! limiting factors: • Intrinsic quantum efficiency • Fraction of sensitive area (20% - 80%) • Surface reflection losses • Probability for Geiger breakdown • (depends on electric field) • SPAD recovery time (passive quenching) • Active volume / absorption length W.Oldham, P.Samuelson, P.Antognetti, IEEE Trans. ED (1972) In total: Currently claimed best PDE values are ~60% Max-Planck-Institut für Physik / Humboldt Universität Berlin

  19. Measurement of the Photon Detection Efficiency PDE measurements are not an easy task • optical crosstalk • dependency on bias voltage often a photomultiplier with unknown photoelectron collection efficiency is used as reference  Overestimation of the PDE Max-Planck-Institut für Physik / Humboldt Universität Berlin

  20. A method to measure the PDE use calibrated PiN-diode as reference use integrating sphere with two exit ports (splitting ratio of several thousand) flash PiN-diode and G-APD with pulsed monochromatic light source Otte et al., NIM A 567 360–363, 2006 Max-Planck-Institut für Physik / Humboldt Universität Berlin

  21. Problems: Optical Crosstalk High Dark Count Rate Max-Planck-Institut für Physik / Humboldt Universität Berlin

  22. Optical Crosstalk • SPADs not only detect photons • they also emit photons during • breakdown Emission microscopy picture of a prototype SiPM Max-Planck-Institut für Physik / Humboldt Universität Berlin

  23. Photons can trigger additional cells Sketch from Cova et al. NIST 2003 Workshop on single photon detectors •  Optical crosstalk • Artificial increase in signal • Excess Noise Factor of SiPM can be quite significant Max-Planck-Institut für Physik / Humboldt Universität Berlin

  24. Using optical crosstalk to learn more about the photons emitted in avalanches Max-Planck-Institut für Physik / Humboldt Universität Berlin

  25. Light Emission in Avalanches W. J. Kindt • measured spectra do not show similar behavior • emission mechanisms not well known • very few absolute measurements Max-Planck-Institut für Physik / Humboldt Universität Berlin

  26. optical crosstalk spectrum from dark noise Try to reproduce this distribution with Monte Carlo simulations Max-Planck-Institut für Physik / Humboldt Universität Berlin

  27. SiSi: The SiPM Simulator *Elisabeth ”Sisi” von Wittelsbach was the empress consort of Emperor Franz Joseph of Austria. She was born 1837 in Munich, Bavaria and murdered 1898 in Geneva, Switzerland Max-Planck-Institut für Physik / Humboldt Universität Berlin

  28. SiSi SiSi is an “almost” complete simulator of a SiPM • simulation of avalanche photons: • black body radiation with free parameters: • temperature • intensity • isotropic emission photoelectrons in non-depleted bulk are subject to simple diffusion model; lifetime of electrons is a free parameter Max-Planck-Institut für Physik / Humboldt Universität Berlin

  29. Example of a good match residuals Residuals can be explained by dark counts which are not simulated in SiSi no unique set of model parameters (Temperature and Intensity of photon spectrum) Max-Planck-Institut für Physik / Humboldt Universität Berlin

  30. Characteristics of Photons that cause Optical Crosstalk 2 photon spectra that reproduce the measured crosstalk distributions Crosstalk is only caused by photons within a narrow range of energies FWHM: ~0.2 eV Peak: ~1.26eV energy distribution of photons causing optical crosstalk Intensity (1.15 … 1.40 eV): ~3*10-5 photons / electron (systematic uncertainty of ~2) Max-Planck-Institut für Physik / Humboldt Universität Berlin

  31. Reason for narrow range of photon energies strong dependence of absorption lengths on photon energy not absorbed in G-APD absorption in same cell Max-Planck-Institut für Physik / Humboldt Universität Berlin

  32. Two possible applications for G-APDs: • positron emission tomography (PET) • air Cherenkov telescopes Max-Planck-Institut für Physik / Humboldt Universität Berlin

  33. detectors γ Object containing some quantity of radio-labeled tracer (positron-source) Positron annihilation : two back-to-back 511 keV photons γ The emitted photons are detected by two opposing detectors in coincidence Positron Emission Tomography (PET) Basic principle PET : image distribution of a radio-labeled tracer inside the body Tracer Molecules : Labeled by positron emitting isotopes ( 11C, 13N, 15O, 18F) Max-Planck-Institut für Physik / Humboldt Universität Berlin

  34. The Reconstruction Problem This is... what you are looking for! Max-Planck-Institut für Physik / Humboldt Universität Berlin

  35. G-APDs in PET: the first studies Advantage: very compact, no sophisticated amplifier needed, … • direct coupling of SiPM to crystal • no cooling • Factor 4 area miss match between SiPM and crystal wrapped crystals G-APDs signal readout Otte, et al. NIM A 545 (2005) Max-Planck-Institut für Physik / Humboldt Universität Berlin

  36. G-APDs in PET: the first studies Advantage: very compact, no sophisticated amplifier needed, … • direct coupling of SiPM to crystal • no cooling • Factor 4 area miss match between SiPM and crystal first ever measurement • Energy resolution 22% FWHM • on 22Na coincidence spectrum • Time resolution 1.5 nsec FWHM Things have quite improved since then Otte, et al. NIM A 545 (2005) Max-Planck-Institut für Physik / Humboldt Universität Berlin

  37. Result of measurements with MW-3 (3x3 mm2) Geiger- mode APDs from Dubna (Z. Sadygov) + LYSO crystals (2x2x10 mm3) Energy Resolution: 12% FWHM Time Resolution: 540ps (limited by crystal) MRS diode used Alexey Stoykov, Dieter Renker (PSI) (2006) Max-Planck-Institut für Physik / Humboldt Universität Berlin

  38. Gamma ray • Cherenkov light image of particle shower in telescope camera • fast light flash (nanoseconds) • 100 photons per m² (1 TeV Gamma Ray) Particle shower ~ 10 km ~ 1o Cherenkov light reconstruct: arrival direction, energy reject hadron background ~ 120 m Imaging Air Cherenkov Technique Max-Planck-Institut für Physik / Humboldt Universität Berlin

  39. Figure of Merit Cherenkov spectrum folded with photon detector response Cherenkov spectrum on ground photon detector response Max-Planck-Institut für Physik / Humboldt Universität Berlin

  40. Application of G-APDs in air Cherenkov telescopes Figure of Merit Cherenkov spectrum folded with photondetector response MPPC from Hamamatsu with highest PDE (from data sheet MPPC with 100x100 µm² cells) photomultiplier tubes can hope for factor >2 increase in sensitivity compared to bialkali PMTs Max-Planck-Institut für Physik / Humboldt Universität Berlin

  41. Test on La Palma with MAGIC 4 MPPC-33-050C from Hamamatsu: sensor size: 3x3mm² single cell size: 50x50µm² nominal bias: 70.4V dark rate at nominal bias: ~2MHz gain at nominal bias: 7.5*105 crosstalk at nominal bias: 10% MAGIC Pixel Size Array of 4 MPPCs: light catchers with factor 4 concentration; 6x6mm² onto 3x3mm² peak photon detection efficiency 55% needs to be confirmed Max-Planck-Institut für Physik / Humboldt Universität Berlin

  42. array mounted next to the MAGIC camera for 3 nights for fine tuning and tests G-APDs signals recorded by the MAGIC DAQ with each trigger • array not removed or protected during day • it was raining for one day! Max-Planck-Institut für Physik / Humboldt Universität Berlin

  43. Array mounted onto the MAGIC camera entrance window for two nights Max-Planck-Institut für Physik / Humboldt Universität Berlin

  44. Light recorded from Calibration Runs Pedestal 1 phe UV-LEDs 375nm single phe-resolution degraded because of light from night sky 2 phe 3phe … easy calibration  reduced systematics some recorded showers  Max-Planck-Institut für Physik / Humboldt Universität Berlin

  45. location of MPPC array 2 phe 1 phe 4 phe 1 phe MPPCs 35 phe 70 phe 15 phe 35 phe PMTs Max-Planck-Institut für Physik / Humboldt Universität Berlin

  46. Max-Planck-Institut für Physik / Humboldt Universität Berlin

  47. Max-Planck-Institut für Physik / Humboldt Universität Berlin

  48. Shower Signals: MPPC vs PMT event selection: two PMTs next to MPPCs with more than 15 photoelectrons in each tube ~300 events from ~30 min data signals are correlated counts on average MPPC record a larger signal Max-Planck-Institut für Physik / Humboldt Universität Berlin

  49. ratio of signals MPPC/ (scaled) PMT event by event 100% efficiency assumed for the light catcher in front of the MPPCs  on average 1.6 times more light detected with MPPCs (crosstalk corrected) in reality higher due to non perfect light concentrator Max-Planck-Institut für Physik / Humboldt Universität Berlin

  50. Summary The silicon photomultiplier is a real breakthrough in photon detection!! High photon detection efficiency (>60%) Offers high internal amplification (>105) Fast timing (<nsec) Low power consumption (1…100µW/mm²) It can not be damaged by exposure to strong source of light No aging CMOS like technology  prospects for cheap mass production <10$ per mm² … Max-Planck-Institut für Physik / Humboldt Universität Berlin

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