1. 1 Plasma Panel Sensors for Particle & Beam Detection (N31-7) Peter S. Friedman Integrated Sensors, LLC / Ottawa Hills, Ohio, USA / 419-536-3212 (peter@isensors.net / www.isensors.net)peter@isensors.netwww.isensors.net R. Ball, J. W. Chapman, C. Ferretti, D. S. Levin, C. Weaverdyck, B. Zhou University of Michigan / Dept of Physics / Ann Arbor, Michigan, USA Y. Benhammou, E. Etzion, N. Guttman, M. Ben Moshe, Y. Silver Tel Aviv University / School of Physics & Astronomy / Tel Aviv, ISRAEL James R. Beene and Robert L. Varner Jr. Oak Ridge National Laboratory / Holifield Radioactive Ion Beam Facility / Oak Ridge, TN, USA E. H. Bentefour Ion Beam Applications S.A. / Louvain La Neuve, BELGIUM 2012 IEEE Nuclear Science Symposium & Medical Imaging Conference, Anaheim, November 1, 2012 ntegrated ensors™ Transforming radiation detection

2. 2 Plasma-TV / PDP (Plasma Display Panel) ntegrated ensors™ Transforming radiation detection For detector mode, remove specific elements: No phosphors No MgO layer No dielectric layers (or ribs?) Add a quench resistor to pixels that terminates the discharge

3. 3 Plasma Panel Sensor (PPS) Concept ntegrated ensors™ Transforming radiation detection The PPS was conceived as a high performance, low cost, radiation detector that could leverage off of a mature, plasma display panel (i.e. PDP-TV or plasma-TV) technology and manufacturing infrastructure. PDPs have a 45 year history and sell (with profit) for ~ $0.03 / cm 2 including drive electronics. They are probably the lowest cost (per area), highly pixelated, highly integrated, digital device ever developed. PDPs are hermetically sealed devices with a demonstrated lifetime of hundreds-of-thousands of hours (i.e. decades of service life). PDPs are inherently digital, high gain (i.e. Geiger mode), radiation damage resistant, stable devices, operable over a wide range of environmental conditions and unaffected by external magnetic fields.

4. 4 Plasma Panel Detector Inherits many operational and fabrication principles common to PDPs: –A dense micro-array of gas discharge cells or pixels –Pixels bias for gas electrical discharge - Geiger mode operation –Pixels are enclosed in hermetically-sealed glass panel –Uses non-reactive, radiation-hard materials: glass substrates, refractory metal electrodes, inert gas mixtures High gain and inherently digital device with 2D readout Potential for: ntegrated ensors™ Transforming radiation detection Low power consumption Large area with low cost Ultra-low mass structure < 1 ns response times High granularity Position resolution < 100 µm

5. 5 PPS Configurations Each pixel operates like an independent micro-Geiger counter and is activated either by direct ionization in the gas, or indirect ionization in a conversion layer. Our development focus has been on PPS device structures configured primarily for direct ionization. PPS ionization radiation detectors can have a variety of configurations, but we have focused on modified DC type columnar-discharge PDP structures. ntegrated ensors™ Transforming radiation detection

6. 6 Commercial DC-PDP Structure ntegrated ensors™ Transforming radiation detection Concept drawing of columnar-discharge, 2-electrode panel structure. Orthogonal SnO2 or Ni electrodes are separated by a few hundred micron gas layer. Dark band around perimeter is a hermetic glass seal

7. 7 Modified-PDP Commercial Panel ntegrated ensors™ Transforming radiation detection Modified-PDP columnar-discharge (PPS) test panel with “refillable” gas capability. Each HV-cathode line (i.e. column electrode) has a current-limiting quench resistor.

8. 8 Columnar-Discharge PPS ntegrated ensors™ Transforming radiation detection dielectric Cathodes + + + + + + + - - - Discharge Gap glass Anodes glass COMSOL Simulation of Single Cell E-field No E-field E-field is localized Measurements of background signal and response to radioactive sources with different gases. Columnar-discharge PPS (pixels at intersections of orthogonal electrode array)

9. 9 PPS aims to inherit PDP features ntegrated ensors™ Transforming radiation detection Small cell size & fast response  high spatial & temporal resolution Low cost and scalable panel size  from ~ 1 cm 2 to 1 m 2 Hermetically sealed volume & long lifetime  no gas flow Using modified plasma-TV technology for radiation detectors

10. 10 PPS Radiation Sources of Interest Sources demonstrated to date: Cosmic-Ray Muons (relativistic energies ≥ GeV) Beta Particles (max. electron energy): 137 Cs (1.2 MeV), 90 Sr (2.3 MeV), 106 Ru (3.5 MeV) Gamma-Rays: 57 Co (122 keV), 99m Tc (143 keV) Proton Beam: 226 MeV (for proton beam cancer therapy) Sources planned for future demonstration Muon Beams: GeV range (for high energy physics research) Radioactive Ion Beams: 1-100 MeV/u (for nuclear physics research) X-Ray Beams: 6-8 MeV (for X-ray cancer therapy & homeland security ) Electron Beams: 4 - 18 MeV (for electron beam radiation therapy) Neutrons: Thermalized neutrons (for homeland security) ntegrated ensors™ Transforming radiation detection

11. 11 PPS Technology & Projections Pixels/cells act as independent, parallel collectors (~ 10 3 − 10 4 cells/cm 2 ) Inherently digital, highly linear, particle/photon counting devices Localized pulses  minimal discharge spreading Low background noise  no cooling Small drift regions & gas gaps  minimally affected by magnetic fields Amorphous & non-reactive materials  radiation damage resistant Wide detection range  keV to TeV (i.e. X-rays to colliders) Avalanche response  large signals (~ 10 7 gain for 1 mm cell) Targeted cell size ~ 100 - 200 µm  spatial resolution ~ 50 µm Fast cell response  rise time ≤ 1 ns Low energy consumption  ~ 1 nJ per event discharge (200 µm cell) Low power consumption  ~ 20 µW/cm 2 at “hit” rate of 20 kHz/cm 2 ntegrated ensors™ Transforming radiation detection

12. 12 PPS Measurements with Beta Sources ntegrated ensors™ Transforming radiation detection DAQ includes: 4 channels 5 GHz digitizer Simulated 90 Sr β-spectrum in panel 106 Ru

13. 13 ntegrated ensors™ Transforming radiation detection Two-fold coincidence hodoscope / trigger measurement with 106 Ru beta-source in PPS (1% CO 2 in 99% Ar at 600 torr. The same PPS has been successfully demonstrated with several other particle sources, including: 90 Sr (beta source), medical proton beams (226 MeV), and cosmic ray muons (≥GeV). The PPS response appears about the same for all of the charged particle sources tested. Rise Time: 1.2 ns (20-80%) Pulse Duration: 1.9 ns (FWHM) “Typical” Pulse Rise Time & Duration

14. 14 Rate Measurements Using β-Source ntegrated ensors™ Transforming radiation detection Ar CO2 (1%) 600 torr @ 815 V HV line=110, RO=3-6 Response to Source vs. 1/R quench Very high R quench (high RC time constant)  causes pixel to saturate at low Hz Moderate R quench  no rate dependence & rate is ~100 Hz, low bkg Low R quench  regeneration can occur resulting in inflated high Hz signals

15. 15 PPS Discharge Spreading Example ntegrated ensors™ Transforming radiation detection Triple-coincidence hodoscope measurement with 106 Ru beta-source. The adjacent anode wires (i.e. channels 6, 7 & 8) appear as the black, red and green lines, and show no indication of any discharge spreading.

16. 16 Detection Setup of Cosmic-Ray Muons ntegrated ensors™ Transforming radiation detection PMT1 PMT2 PMT-1 PMT-2 Ionizing Particle Panel tested with CF 4 or SF 6 at 600 & 200 torr Scaler & waveform digitizer Events triggered with 3-fold coincidence Signals collected with DRS-4 fast waveform digitizer

17. 17 Cosmic-Ray Muon Detection ntegrated ensors™ Transforming radiation detection About 8% of all muon triggers associated with signal from the panel To further improve performance we are investigating panels with different structures and higher resolutions (i.e. smaller pixels with higher fill-factors and different discharge geometries) Pixel active area ~ 1.7 mm 2 Total 4x4 matrix (16 pixels) active area ~ 27 mm 2 Hodoscope triggering area ~ 250 mm 2 Geometric acceptance for muons ~ 11% Our initial estimate of the PPS muon detection efficiency, when taking into account the geometric acceptance for the active cell area, is on the order of ~ 70%

18. 18 Arrival Time Measurement of Cosmic-Ray Muons ntegrated ensors™ Transforming radiation detection Time arrival distribution for 197 cosmic-ray muons detected in a PPS with SF 6 at 500 torr & operating at 1530 V. Both pure CF 4 and SF 6 gases show a signal with a very fast response time. Arrival time is defined with respect to the hodoscope trigger (the offset reflects residual cable delays). Timing jitter (σ) is 5 ns.

19. 19 Side view Sr 90 top Ru 106 bottom Top view HV=815V RO lines Response to 2 Simultaneous Sources - Setup

20. 20 ntegrated ensors™ Transforming radiation detection RO 24 RO 1 HV lines  1 20 100 110 128 Pickoff card 100X attenuation HV=815V R=400 MΩ VPA 600 Torr 99%Ar/1%CO 2 Filled Feb 15, 2012 Discriminator -150 mV OR Scalar 106 Ru 90 Sr RO lines 3-6 Expectation: rate with two sources = sum of the two rates in single mode until the sources starts (partially) overlapping Response to 2 Simultaneous Sources - Setup

21. 21 Response to 2 Simultaneous Sources - Results ntegrated ensors™ Transforming radiation detection Result: Panel responds independently to each source until they nearly overlap and saturate a line.

22. 22 Beta Scattering Simulation* with GEANT4 ntegrated ensors™ Transforming radiation detection Graphite Collimator (1.2 mm slit) 106 Ru Beta Source PPS Glass Substrates (2.25 mm) Betas (orange) Generated X-rays (yellow) Ar at 1 atm 0.44 mm Gap * 10 6 tracks simulated (10 3 tracks shown)

23. 23 106 Ru Example ntegrated ensors™ Transforming radiation detection Graphite Collimator (1.2 mm slit)

24. 24 PPS Position Resolution Experiment ntegrated ensors™ Transforming radiation detection Translation of “collimated” 106 Ru beta-source through a 1.25 mm wide graphite slit (20 mm thick) in 0.5 mm increments across the PPS sense electrodes (anodes). Plot shows the Gaussian means vs. source position. RMS position resolution is ~ 0.7 mm, in panel with a 2.5 mm electrode pitch. Panel has 1% CO 2 in 99% Ar, at 600 torr, and 890V. slope = 0.39 ± 0.01 per mm

25. 25 PPS Proton Beam Accelerator Test ntegrated ensors™ Transforming radiation detection PPS Panel

26. 26 Proton Beam Position Scan ntegrated ensors™ Transforming radiation detection Position scan of 226 MeV proton beam (1 mm diameter). Plot of position centroid of “hit” map for 16 runs in which PPS was shifted by increments of ~ 1 mm relative to the proton beam from an IBA-C235 medical accelerator.

27. 27 Modeling and Simulations ntegrated ensors™ Transforming radiation detection COMSOL: –Electric field and charge motion –Estimate capacitance of cells SPICE: –Electrical characteristics of PPS cell signals –Role of stray capacitance & inductances GEANT4: –Passage of particles through matter

28. 28 Modeling with SPICE and COMSOL ntegrated ensors™ Transforming radiation detection Capacitive coupling to neighboring cells is critical ! Stray capacitance, self-inductance & line resistance included Cell parameters generated from COMSOL

29. 29 Particle Scattering Simulations ntegrated ensors™ Transforming radiation detection  Principal tool is GEANT4 CERN developed tool, similar to MCNPx Simulates particle scattering in materials Particle production mechanisms Coulomb scattering Nuclear scattering Very general geometry and materials Widely used in nuclear physics Gives event-by-event or summary output for later analysis Open source, easily available for researchers  Cases 106 Ru and 90 Sr production and propagation PPS Collimators Trigger detectors Neutron capture in Gd Photosensor in a Compton Telescope

30. 30 106 Ru Example ntegrated ensors™ Transforming radiation detection 106 Ru β-energy spectrum Glass PPS Gas Hodoscope detectors Source

31. 31 106 Ru Example 1.30 MeV Beta 2.83 MeV Beta( 90 Sr)3.54 MeV Beta 1.30 2.83 3.54

32. 32 Summary Modified, off-the-shelf, commercial plasma panels have demonstrated: 1) Low-cost PDP-based technology can be modified to detect ionizing radiation 2) Sensitivity to charged particles – betas, protons and muons 3) Devices produce fast, self-terminating, self-contained, high-gain pulses 4) Inherently digital, particle counting, non-proportional Geiger-mode operation 5)Can be hermetically sealed & fabricated with inherently rad-hard materials – e.g. panels sealed with gas 9 years ago (2003) work similar to new panels 6)Panel “sealed” with shut-off valve & vac fittings still operating after 8 months ntegrated ensors™ Transforming radiation detection

33. 33 Summary 7)Good timing jitter using triggered muons (~ 5 ns) 8)Fast cell response (≤ 1 ns) 9)Sensitivity to independent, separate sources 10)Position sensitivity to high intensity sources (~ 1 MHz of protons / mm) 11)Spatial resolution commensurate with high granularity of electrode pitch – can detect a stream of particles with sub-millimeter separation. 12)Low background noise 13)New generation of PPS devices being fabricated with projected higher performance capability ntegrated ensors™ Transforming radiation detection

34. 34 Backup ntegrated ensors™ Transforming radiation detection

35. 35 Single pixel: Principles of operation Muon track (-) High Voltage cathode anode 50-100 

36. 36 Single pixel: Principles of operation Muon track (-) High Voltage cathode Charged particle creates ion-pairs clusters Cluster formation dictated by Poisson Cluster statistics: n i >1 ion-pair. Avg = 3, with long exponential tail anode 50-100 

37. 37 Single pixel: Principles of operation Muon track (-) High Voltage cathode - ---- + ++++ ++ + Electron drift & acceleration initiates avalanche. High E–fields lead to streamers. Gas breakdown (discharge potential) according to Paschen’s Law: P= pressure d= gap size V=voltage a,b = gas specific parameters anode 50-100 

38. 38 Minimum voltage occurs when Wikipedia: Paschen entry. A.K. Bhattacharya, GE Company, Nela Park, OH  Phys. Rev. A, 13,3 (1975) Small variations in Penning gas mixtures can dramatically affect breakdown voltage Paschen discharge potential

39. 39 Discharge cell: Important gas processes primary ionization metastable generation Excitation Penning ionization Image from: Flat Panel Displays and CRTs (Chapter 10), L. Tannas, Jr, photon emission Metastable ejection ion ejected electron

40. 40 R quench R term C pixel Electrical description During discharge cell becomes conductive The E field drops, discharge self-terminates HV Supply cathode - + anode The quench resistance on each pixel (or pixel chain): 1) Impedes E-field rise until ions and meta-stables are neutralized 2) Maintains HV on all other cells so that they are enabled for hits 3) Signal amplitude set by cell capacitance: C pixel signal start with simplified schematic of single PPS discharge cell

41. 41 {ResNi} More realistic cell model C pixel Include stray capacitances, line resistance, self inductance

42. 42 Full Schematic