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Xe-based d etectors: recent work at Coimbra

Xe-based d etectors: recent work at Coimbra. C.A.N.Conde, A.D. Stauffer, T.H.V.T.Dias, F.P.Santos , F.I.G.M.Borges , L.M.N.Távora, R.M.C. da Silva, J.Barata, P.N.B.Neves, J.M.Escada, L.P.M.M.Carita, S.do Carmo, A.Trindade, J.Mariquito, P.J.B.M.Rachinhas.

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Xe-based d etectors: recent work at Coimbra

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  1. Xe-based detectors: recent work at Coimbra C.A.N.Conde, A.D. Stauffer, T.H.V.T.Dias, F.P.Santos, F.I.G.M.Borges, L.M.N.Távora, R.M.C. da Silva, J.Barata, P.N.B.Neves, J.M.Escada, L.P.M.M.Carita, S.do Carmo, A.Trindade, J.Mariquito, P.J.B.M.Rachinhas Workshop on Xenon-Based Detectors 16-18 Nov 2009, Berkeley

  2. Electron diffusion in Xe, vs Xe-CH4 & Xe-CF4 Summary Discontinuities in energy resolution & linearity of Xe detectors Energyresolutiondegradation: driftelectric-fieldeffects Detector gas filling: Xe vs Xe-CH4 & Xe-CF4 Electroluminescence fluctuations in Xe, vs Xe-CH4 & Xe-CF4 New detectors developed at Coimbra: Tertiary-ScintillationGasProportionalScintillationCounter Multi-Grid HP Gas Proportional Scintillation Counter The Gridded Gas Proportional Ionization Counter 2/21

  3. Discontinuities in energy resolution Monte Carlo Xe MC simulation experimental M F and w-value are discontinuous L Xenon filled detectors exhibit sudden increases in energy resolution whenever a new Xe atomic-shell becomes available for photoionization 3/21

  4. Discontinuities in Fano factor and w-value Monte Carlo sph ■ MC □ experimental w sph F • w-value and Fano factor F • are Exr dependent • Reflect photoionization XS sph 4/21

  5. Discontinuities in energy linearity & w=Exr/n Is n proportional to Exr ? Monte Carlo Mean number n of primary (sub-ionization) electrons produced in Xe as a function of absorbed x-ray energy Exr 5/21

  6. Energy resolution and Energy linearity Monte Carlo Xe L3 binding energy = 4782 eV • Exr > 4782 eV • distributions shift to lower n: discontinuity in w & linearity. • distributions broaden: discontinuity in F & Rint n Exr < 4782 eV (L3 ): M shell vacancy; M-photoelectron (~3500 eV) dominates; Exr > 4782 eV (L3 ): inner vacancy (L); photoelectron(few eV); variousAuger electrons (30eV to ~4000eV). 6/21

  7. ElectrondiffusioninXe, vs Xe-CH4 & Xe-CF4 Research topics Discontinuitiesinenergyresolution & linearityofXedetectors Energyresolutiondegradation: driftelectric-fieldeffects Detector gasfilling: Xe vs Xe-CH4 & Xe-CF4 ElectroluminescencefluctuationsinXe, vs Xe-CH4 & Xe-CF4 New detectors developed at Coimbra: Tertiary-ScintillationGasProportionalScintillationCounter Multi-Grid HP Gas Proportional Scintillation Counter The Gridded Gas Proportional Ionization Counter

  8. Energy resolution degradation: drift electric-field effects • High E0: • Photoelectrons • carry most of the photon energy E0 • are scattered mostly forward. • have long trajectories in the gas • Long trajectories in the gas: energy gain/loss • from the drift field is not negligible. • Deposited energy is higher (or lower) than E0. 7/21

  9. Energyresolutiondegradation:driftelectric-fieldeffects Intrinsic curve : accounts for fluctuations in # of primary (sub-ionization) electrons (FXe=0.17; wXe=E0/n=21.5 eV). Distributions (PENELOPE): for E/p=0.1 to 0.8 Vcm-1Torr-1: Spreads Г vary with drift field (d-function @field=0). 60 keV x rays Driftfieldeffects: Fluctuationsincreasewith 200 keV x rays • drift field • photon energy 8/21

  10. Electron diffusion in Xe, vs Xe-CH4 & Xe-CF4 Research topics Discontinuitiesinenergyresolution & linearityofXedetectors Energyresolutiondegradation: driftelectric-fieldeffects Detector gas filling: Xe vs Xe-CH4 & Xe-CF4 ElectroluminescencefluctuationsinXe, vs Xe-CH4 & Xe-CF4 New detectors developed at Coimbra: Tertiary-ScintillationGasProportionalScintillationCounter Multi-Grid HP Gas Proportional Scintillation Counter The Gridded Gas Proportional Ionization Counter

  11. Electron scattering cross sections in Xe and CH4 9/21 sion sexc

  12. Electron scattering cross sections in Xe and CF4 10/21

  13. Electron drift velocities in Xe, Xe-CH4 and Xe-CF4 Monte Carlo Addition of CH4 or CF4 to Xe • increases drift velocity 11/21

  14. Electron diffusion in Xe, Xe-CH4 and Xe-CF4 Monte Carlo Addition of CH4 or CF4 to Xe • increasesdriftvelocity • decreases longitudinal andtransverseelectrondiffusion where 12/21

  15. Electron diffusion in Xe, Xe-CH4 and Xe-CF4 Monte Carlo Addition of CH4 or CF4 to Xe • increasesdriftvelocity • decreases longitudinal andtransverseelectrondiffusion where 13/21

  16. ElectrondiffusioninXe, vs Xe-CH4 & Xe-CF4 Research topics Discontinuitiesinenergyresolution & linearityofXedetectors Energyresolutiondegradation: driftelectric-fieldeffects Detector gas filling: Xe vs Xe-CH4 & Xe-CF4 Electroluminescence fluctuations in Xe, vs Xe-CH4 & Xe-CF4 New detectors developed at Coimbra: Tertiary-ScintillationGasProportionalScintillationCounter Multi-Grid HP Gas Proportional Scintillation Counter The Gridded Gas Proportional Ionization Counter

  17. Electroluminescence fluctuations in Xe vs Xe-CH4, Xe-CF4 Monte Carlo The addition of CH4 or CF4 to Xe • decreases EL (n. of excitations, i.e. sc.photons, produced per electron in sc. gap) • increases EL fluctuations (CF4 has catastrophic effect …) 5 cm drift, 1 atm ↔ 5 mm, 10 atm 5 cm drift, 1 atm ↔ 5 mm, 10 atm 14/21

  18. Electroluminescence fluctuations in Xe vs Xe-CH4, Xe-CF4 Monte Carlo 15/21

  19. ElectrondiffusioninXe, vs Xe-CH4 & Xe-CF4 Research topics Discontinuitiesinenergyresolution & linearityofXedetectors Energyresolutiondegradation: driftelectric-fieldeffects Detector gasfilling: Xe vs Xe-CH4 & Xe-CF4 ElectroluminescencefluctuationsinXe, vs Xe-CH4 & Xe-CF4 New detectors developed at Coimbra: Tertiary-ScintillationGasProportionalScintillationCounter Multi-Grid HP Gas Proportional Scintillation Counter The Gridded Gas Proportional Ionization Counter

  20. Tertiary-Scintillation GasProportionalScintillationCounter TS-GPSC prototype 16/21

  21. TS-GPSC Results G Typical spectrum 109Cd source R • Best results obtained for • scintillation electric fields just • above Xe ionization threshold • voltage across GEM-structure • below charge multiplication. FWHM 8.2% 17/21

  22. ElectrondiffusioninXe, vs Xe-CH4 & Xe-CF4 Research topics Discontinuitiesinenergyresolution & linearityofXedetectors Energyresolutiondegradation: driftelectric-fieldeffects Detector gasfilling: Xe vs Xe-CH4 & Xe-CF4 ElectroluminescencefluctuationsinXe, vs Xe-CH4 & Xe-CF4 New detectors developed at Coimbra: Tertiary-ScintillationGasProportionalScintillationCounter Multi-Grid HP Gas Proportional Scintillation Counter The Gridded Gas Proportional Ionization Counter

  23. MultigridHighPressureXe GPSC • primary electrons are produced • in the absorption/drift region • primary electrons produce • secondary scintillation VUV photons along gap between G1 and G2 • VUV photons release electrons • from CsI photocathode • at backplane of detector • electrons are collected at G4 • giving the detector signal (Indicated voltages are ideal values) 18/21

  24. Multigrid High Pressure Xe GPSC – Experimental results Charge gain vs E/p in scintillation gap V3<V4 V3>V4 5.4 bar 5 bar 3 bar Gain 1.5 bar Pulse amplitude vs G3-G4 potential barrier (DV34 ) E/p (Vcm-1Torr-1) 19/21

  25. ElectrondiffusioninXe, vs Xe-CH4 & Xe-CF4 Research topics Discontinuitiesinenergyresolution & linearityofXedetectors Energyresolutiondegradation: driftelectric-fieldeffects Detector gasfilling: Xe vs Xe-CH4 & Xe-CF4 ElectroluminescencefluctuationsinXe, vs Xe-CH4 & Xe-CF4 New detectors developed at Coimbra: Tertiary-ScintillationGasProportionalScintillationCounter Multi-Grid HP Gas Proportional Scintillation Counter The Gridded Gas Proportional Ionization Counter

  26. The gridded GPIC: definition of multiplication volume Grid around the anode: ideal to define multiplication volume However, grid diameter too small, unfeasible at 1 atm. Solution: planar microstructure where PIC conventional anode is hemmed in by a close second anode. 20/21

  27. The gridded GPIC - Experimental results @5.9 keV M M R R 21/21

  28. Experimental results with gridded GPIC

  29. Energyresolutiondegradation:driftelectric-fielddiscontinuitiesatatomicedgesEnergyresolutiondegradation:driftelectric-fielddiscontinuitiesatatomicedges Intrinsic discontinuity At the atomic absorption edges, an electric-field triggered discontinuity may become noticeable as the ejected photoelectron tends to have much lower energy after a new atomic shell becomes photoionizable than before. However this non-linearity is only about 4% of the intrinsic non-linearity.

  30. Drift velocities for electrons in Xe and Xe-CH4 Monte Carlo Addition of CH4 or CF4 to Xe • increases drift velocity

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