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Imaging chambers in medicine, biology and astrophysics

Imaging chambers in medicine, biology and astrophysics. F.A.F. Fraga LIP - Coimbra, CFRM and Departamento de Física da Universidade de Coimbra, 3004-516 Coimbra, Portugal. Outline. Imaging gas scintillators The GEM - an active scintillator CCDs Apllications Quality control

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Imaging chambers in medicine, biology and astrophysics

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  1. Imaging chambers in medicine, biology and astrophysics • F.A.F. Fraga • LIP - Coimbra, CFRM and Departamento de Física da Universidade de Coimbra, 3004-516 Coimbra, Portugal

  2. Outline • Imaging gas scintillators • The GEM - an active scintillator • CCDs • Apllications • Quality control • Imaging chamber • Alpha tracking • Neutrons • Radiography • Therapeutic beam monitoring • Other projects • Neutron spectrometer • Thermal neutron imaging • Pollarimeter • Conclusions

  3. Introduction • 2D imaging detectors • Advantages of optical readout • Electronics decoupled from detection media • Insensitive to electronic noise or RF pickup signals • Real multi hit capability with true pixel readouts - complex events • Large areas without dead spaces - optical systems (lenses, mirrors, fibers and tapers) New developments in optical imaging detectors, A. Breskin, NIM A498(1989)457c-468c

  4. Gaseous avalanche chambers with optical readout • 2D gas scintillators with optical readout by PMs or intensified CCDs • Initially used with wires and pure gases • Xe, Kr, Ar and He with the addition of N2 - UVscintillation, innefficient and expensive optics, optical wavelenght shifters • Improvements • continuous amplifying structures (PPAC, grids) • gas mixtures scintillating at > 250 nm The gas proportional scintillation chamber, A.J.P. Policarpo, Space Sci. Instr. 3(1977)77

  5. A few examples • High pressure xenon (up to 20 bar) waveshifter fibers • A. Parsons, B. Sadoulet, S. Weiss, T. Edberg, J. Wilkerson, IEEE TNS 36(1989)931-935 • Multistep, low pressure and high gas gain (light gap ~ 9 mm, light yield up to 3 ph./el.) • A. Breskin, R. Chechik and D. Sauvage NIM A286(1990)251-256 • PPACs at atmospheric preassure light gap ~ 1.5 mm, TEA, TMAE, Penning effect, higher light to charge ratio • G. Charpak, W. Dominik, J.P. Fabre, J. Gaudaen, F. Sauli and M. Suzuki, NIM A269(1988)142-148 • V. Peskov, G. Charpak, W. Dominik and F. Sauli NIM A227(1989)547-556 • TPC with optical readout (multistep, low pressure TEA) • U. Titt, A. Breskin, R. Chechik, V. Dangendorf , H. Schmidt-Böcking and H. Schuhmacher, NIM A416 (1998)85 • Optical imaging with capillary plate, argon-TMA and intensified CCD. • T. Masuda, H. Sakurai, Y. Inoue, S. Gunji and K. Asamura, IEEE TNS 49(2002)553-558

  6. Some limiting features • Low number of emitted photons • image intensifiers - expensive, degrade image resolution, limited size • Large scintillation gaps • degrade position resolution, diffusion, optical depth of field • Technically complicated and expensive • low pressure, high temperature, capillary plates

  7. Luminiscence in microstrips • 1993 A. Oed and P. Geltenbort reported high luminosity from pure gas mixtures • 1998 We used scintillation to perform quality control of microstrips • CCD with Ar2% Xe Microstrip operation in noble gases: an active scintillator, P. Geltenbort and A. Oed, Proceedings of the Workshop on Progress in Gaseous Microstrip Proportional Chambers, Grenoble, 21-23 June 1993 Towards a method for quality control of microstructures for gaseous detectors based on scintillation light, F.A.F. Fraga, M.M. Fraga, R. Ferreira Marques, J.R. Gonçalo, E. Antunes, C. Bueno and A.J.P.L Policarpo

  8. The GEM should be a good candidate for a gas scintillator See http://gdd.web.cern.ch/GDD/ F.Sauli. NIMA386(1997)351

  9. Electric field simulation • Magnitude of the electric field along the center of the GEM channel for equal measured gain in GEMs of different metal hole size • Thin gap, high gain, no blurring

  10. Study of luminiscence of GEMs • Both charge and light signals were digitized

  11. Typical light signal shape using He-40%CF4 • The light signal risetime at the preamplifier output is 39ns

  12. Average rise time of the light and charge signals versus induction field, Ei • 55Fe • Ed=0.5kV/cm • Et= Ei = 2kV/cm • double GEM gain ~ 3.1x103.

  13. Energy resolution

  14. CCD characteristics • CCD camera: QUANTIX 1400 (PHOTOMETRICS) • Number of pixels 1317 x 1035 (6.8 x 6.8 mm pixels) • Read noise (1 MP/s) 18 e RMS • Dark current 0.03 e/p/s (-25ºC, Peltier cooled) • Binning - 2x2 up to 7x7 • less position resolution but lower noise! • Nikon 50mm f1.8 photographic lens with C mount adapter • Quantum efficiency of the Quantix 1400 camera versus wavelengh

  15. What is a CCD? • Pixel type silicon light sensitive detector • High quantum efficiency - up to 90% - but no gain • Integrating type device - exposure time from ms to minutes • Limited range • Low noise - cooling can be needed • Pixel sizes up to 30 x 30 m • High number of pixels up to 4000 x 4000 • Analog-digital serial readout - slow

  16. Why using CCDs for the readout of radiation detectors? • High resolution - up to 4000x4000 pixels • Large area detection using lenses or mirrors • Can be placed away of detection media • Cheap cost • Electrical noise free • Simple interface with computers

  17. CCD readout of GEM scintillation Radiation source Minimum focusing distance~30cm

  18. First images of GEM scintillation • Scintillation image of a GEM foil. The holes of the GEM are seen as emitting dots in the small zone which is shown magnified • Ar-2%Xe

  19. Gas study and optimization Quality control • Increasing the CO2 amount lowers the light emission • A small amount of quencher enhances stability of light emission • Ar-5%CO2 was found to be the optimum mixture for q.c. • Light yield ~ 0.03 photons/secondary electron

  20. Quality control • scintillation is sensitive to electric field configuration • checks GEMs gain uniformity • identification of local defects • finds optically unseen deffects

  21. GEM characteristics • Electrical field can have higher values than in PPACs • Cascaded GEMs • Micro-Pattern Gaseous Detectors, by F. Sauli and A. Sharma, Ann. Rev.Nucl.Part.Sci 49(1999)341 • High gain up to 4 stages, gain up to 105 - 106 • J. Va´vra, A. Sharma, NIM A Vienna 2001 • A. Breskin, PSD6 • Free from ion feedback • Study of ion feedback in multi-GEM structures, A. Bondar, A. Buzulutskov, L. Shekhtman, A. Vasiljev, 2002, submitted to NIM A • Photon screening, free from photon feedback • R. Chechik et al. NIMA419(1998)423 • Large areas (~30 x 30cm) • Gem detectors for COMPASS, by B. Ketzer, S. Bachmann, M. Capeáns, M. Deutel, J. Friedrich, S. Kappler, I. Konorov, A. Placci, K. Reisinger, L. Ropelewski, L. Shekhtman, F. Sauli. IEEEE NSS Lyon, 2000.. • No need to collect the electrons on the induction electrode avoiding breakdown in the last stage

  22. Tracking chamber • Sensitive volume ~250 cm3 • Track lenghts up to 8cm • Cascaded standard double GEM (10x10cm) 30 cm

  23. Tracking chamber views

  24. Data on Ar CF4 gain and relative luminosityEC=0; Ar 5%CO2 shown for comparison • Ar CF4 has greater light emission than Ar CO2 • Good light emission for higher percentage of quencher • Ar-5% CF4 light yield 0.57 photon/secondary electron (>400 nm) • Performance of a tracking device based on the GEM scintillation, F. A. F. Fraga, S. T. G. Fetal, L. M. S. Margato, R. Ferreira Marques and A. J. P. L. Policarpo, Presented at the IEEE 2000 NSS

  25. Nº of photons emitted, between 400 and 1000 nm, per secondary electron, as a function of the effective gain, in Ar-CF4 mixtures. (Measurements performed with the photodiode). Visible and NIR emission spectra of Ar-CF4 mixtures, normalized to the light intensity at 620 nm. The GEM scintillation in He-CF4, Ar-CF4, Ar-TEA and Xe-TEA mixtures, M. M. Fraga, F. A. F. Fraga, S. T. G. Fetal, L. M. S. Margato, R. Ferreira Marques and A. J. P. L. Policarpo, presented at Beaune 2002 conference, submitted to NIM A

  26. Images of alpha tracks taken using the tracking chamber with Ar -5%CF4 VGEM1=VGEM2=400V (Gain~140), ET=5.45KV/cm, EC=5.86KV/cm, Texp.=10ms. (a,b)VGEM1=VGEM2=400V (Gain~140), ET=5.45KV/cm, EC=5.86KV/cm, CCD Binning 4x4, Texp.=10ms; (c,d) VGEM1=VGEM2=430V (Gain~300), ET=5.45KV/cm, EC=0, CCD Binning 7x7, T=10ms.

  27. Bragg curves of 241Am alpha particles Light callibration using full tracks ~ 180 detected photons per deposited keV light yield ~0.6 photons/secondary electron

  28. Projections of alpha tracks Ar-5%CF4 • Triple GEM, VGEM=450V, g=82, ED=1kV/cm, ET=3.4 kV/cm, b=7x7, EC=0, • 241Am alpha particles energy = 5.48 Mev • Range of 241Am alpha particles in Ar = 3.42 cm The length and orientation of the track can be measured using charge or PMT signals Perfomance of a Tracking Device Based on the GEM Scintillation", F.A.F. Fraga, L.M.S. Margato, S. T. G. Fetal, R. Ferreira Marques and A.J.P.L Policarpo, IEEE Trans. on Nucl. Sci. 49, NO.1, February 2002, pg.281- 284

  29. 3He thermal neutron detectors • Thermal neutron capture in 3He • 3He + n  p + 3H + 770 keV • proton range = 4.4 mm, triton range = 1.6mm (1bar CF4) • R.B. Knott, G.C. Smith, G. Watt, J.W. Boldemann, NIM A392(1997)62

  30. Data on charge gain and light emission in CF4 pressures 400mbar, 1, 2 and 3 bar • Gain saturates for smaller holes at lower pressures as reported in NIMA 419(1998)410 • 60 m hole GEMs have higher light yield

  31. Data on CF4 + HeCF4 pressure = 400mbar, He = 0.6 and 3.6 bar Photon yield 0.077 photons/secondary electron at 1 bar He-60%CF4

  32. Closed detector • Clean GEM chamber- stainless steel • GEMs 5 x 5cm • 50mm diameter transparent window • carbon fiber window or aluminum cover

  33. Details of the clean GEM chamber

  34. Images of proton and triton tracks in 3He- 400 mbar CF4 • Triple GEM camera • two 80 m, one 60 m metal hole • absorbtion space 3 mm • ED (drift field) =1KV/cm, • ET (transfer field) = 3.25 kV/cm, • EC (collection field) = 0 • VGEM1 =VGEM2 =350V. • Binning 7x7 • AmBe source with Polyethylene shielding

  35. Images of proton and triton tracks in 3He- 400 mbar CF4 • Projection of the light intensity along the track as measured by the CCD CCD readout of GEM based neutron detectors, F.A.F. Fraga, L.M.S. Margato, S. T. G. Fetal, M.M.F.R. Fraga, R. Ferreira Marques, A.J.P.L Policarpo, B. Guerard, A. Oed, G. Manzini and T. van Vuure, Nucl. Instr. and Meth. In Physics Research A 478 (2002) 357

  36. X-rays radiography Car key (~5 cm) radiography X-ray energy ~8keV Xe-10%CO2 at 1bar absobtion length ~3 mm Plastic gearwheel ~1.5 cm radiography Imaging detectors based on the GEM scintillation light, F.A.F. Fraga, L.M.S. Margato, S. T. G. Fetal, I. Ivaniouchenkov,, R. Ferreira Marques, A.J.P.L Policarpo, presented at the IEEE NSS 1999

  37. High pressure Xe X-ray detector • A 25 mm thick conversion volume at 5 bar Xe will have ~ 90% detection efficiency for 17.5 keV X-rays! • 50 mm will be needed to get 80% efficency at 25 keV • Performance of high pressure Xe/TMA in GEMs for neutron and X-ray detection, R. Kreuger, C. W. E. van Eijk, F. A. F. Fraga, M. M. Fraga, S. T. G. Fetal, R. W. Hollander, L. M. S. Margato, T. L. van Vuure, presented at the IEEE NSS 2001

  38. High pressure Xe / TMA • Xe-TMA strong Penning effect • TMA ion. pot 8.1 eV • Xe metastable pot. 8.3 • Operation at a lower voltage single GEM 60/70/140

  39. Operation of Xe - TMA at 5 bar (light) • Light yield • ~ 0.3 ph/ sec. electron • ~104 ph / keV with gas gain 700 • Scintillators have 20-50 ph/ keV

  40. UV CCD system~40 keuro, CCD chip ~10 keuro

  41. Radiography of a small dog-whelkdouble GEM, 5mm absorption space, Xe-2.5%TMA at 5bar, molybdenium X-ray tube at 40 kV

  42. Radiography of a small snail ~8mmdouble GEM, 5mm absorption space, Xe-2.5%TMA at 5bar, molybdenium X-ray tube at 30 and 40 kV The width of the shell fissure is similar to the GEM picth

  43. Images of a 50 micron slit collimator • X-ray voltage 30kV • Collimator length 25 mm • Collimator slit 50 m •  ~ 65 m CCD readout of high pressure xenon-TMA GEM detectors for X-ray imaging, L. M. S. Margato , F. A. F. Fraga*, M. M. F. R. Fraga*, S. T. G. Fetal*, R. Ferreira Marques*, A. J. P. L. Policarpo*, T.L. van Vuure, R. Kreuger, C.W.E. van Eijk and R.W. Hollander, presented at the SAMBA 2002, Trieste, 2002

  44. Xe-2.5%TMA rise-time at 1 and 3 bar versus collection field

  45. Energy resolution using Xe-2.5% TMA 5bar (light signals)

  46. Recoil detector for fast neutron (1-10 MeV) spectroscopy • Single event energy resolution • Efficiency is expected to be more than two orders of magnitude better than current Li foil detectors (~10-7) • Gaseous media • GEM multiplication • Scintillation read by CCD

  47. Recoil neutron spectrometer • We have to measure • Energy of the recoil • Total light measurement • Angle of the recoil nucleus • ratio between track real length (estimated from the recoil energy) and projection read by the CCD

  48. Gas selection(neutron recoil spectrometer) • Maximal track length should be around 5 cm • Efficient scintillator Experimental measurements with alpha particles are being carried on to estimate the accuracy of the spectrometer Tests will be done at the Democritos (Greece) neutron accelerator facility

  49. GEM2 GEM1 kapton mylar Window window Proton Beam Mirror 3.5 mm 3 mm (E = 150 MeV) L1 L1+L2 ~ 2m L2 Cathode CCD camera A B C D Medical applications • Dose imaging in radioteraphy Dose imaging in radiotherapy with an Ar-CF4 filled scintillating GEM,S. Fetal, C.W.E. van Eijk, F. Fraga, J. de Haas, R. Kreuger, T.L. van Vuure and J.M. Schippers, PSD6, submitted to NIM

  50. Other projects • Thermal neutron imaging • Solid converter detector with GEM active scintillator readout • Groups integrating the TECHNI collaboration • X-ray polarization • GEM polarimeter with optical readout • GEM coating with p-terphenyl

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