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Micromegas-TPC development for rare event detection

Micromegas-TPC development for rare event detection. Leila Ounalli Neuchâtel University. 3 rd symposium on Large TPCs for low energy rare event detection , Paris, 11-12 December 2006. Restrictive conditions for rare event detection. Big detector mass (high pressure),

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Micromegas-TPC development for rare event detection

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  1. Micromegas-TPC development for rare event detection Leila Ounalli Neuchâtel University 3rd symposium on Large TPCs for low energy rare event detection, Paris, 11-12 December 2006.

  2. Restrictive conditions for rare event detection • Big detector mass (high pressure), • Radioactive background as low as possible (underground laboratory + radio-pure components), • Good energy resolution (FWHM), • High gas gain (collected charge / initial charge).

  3. Cones Sticks Light Optic nerve Brain (analyze, classify, memorize) The eye and the retina

  4. spacers Cathode 1mm Ed~ 200V/cm Conversion + Drift e- Dave Nygren (1970) Micromesh Grid Amplification (> 50 m) Ea~ 40-100kV/cm Woven wires http://www.bopp.ch/ Anode (gamma, RX, UV …) Micromegas « Compact » The TPC and Micromegas  • analyze, • classify, • memorize.

  5. miniTPC(10X20cm) • The source position. • max of count @ dC-g=18cm • The drift electric field choice: • Ed= 200 V.cm-1.bar-1 Edrift The Neuchâtel mini-TPC • The gap dimension (dgrille-anode ): • (75-100-250 µm) • High pressure + low voltages • The quencher choice and %: • - Xe + (CF4, isobutene): • double beta decay • - CF4 + (Xe, Ar): • solar n @ low E

  6. Why we replace the MWPC by the Micromegas micro-pattern?

  7. http://www.bopp.ch Contours of V near the amplification gap Comparison with MWPC’s x10-3 Y-Axis[cm] Y-Axis[cm] x10-3 X-Axis[cm] X-Axis[cm] Circular form: Charge deviation from their trajectories. (RE + ξ ) bad (50% @ 6 keV) rectilinear: E uniform: // of electrons. (RE + ξ ) good (35% @ 6keV with 1 bar of CF4)

  8. C Conversion + Drift Micromesh G Amplification (75, 250) m A How to operate the Micromegas-TPC at higher pressures? The increase of the gap amplification permits a good charge collection at high pressure

  9. 250 µm 104 @ 4 bar 75 µm Why we choose a gap of 250 µm?

  10. How to improve the charge collection in Xe? A small CF4 addition is sufficient

  11. P: 1.00 atm, Ed=200 V.cm-1.atm-1, Gap: 100 µm ■ Xe-CF4 (2, 5, 10, 50%) ▲ Xe-isobutene (2%) ← improves the charge collection. CF4 is the best additive for Xe CF4 addition: • increases the electron • drift velocity in Xe. • reduces longitudinal and • transversal diffusions.

  12. Optimal parameters • Ed= 200 V.cm-1.atm-1. • Gap: 250 µm. • Gas: Xe(98)CF4(2) • Make preliminary tests in the mini-TPC of Neuchâtel (241Am).

  13. 4.00 atm Gas: Xe(98)CF4(2) Ed= 200V.cm-1.atm-1 Source: 241Am (37kBq) 1.05 atm 3.00 atm 1.05 atm 2.01 atm ▲ 8.05 keV Cu-Kα 29.779 keV Xe-Kα 2.01 atm 103 3.00 atm 4.00 atm The Xe(98)CF4(2) gain and the energy resolution @ 60 keV at different pressures

  14. Cu-Kα Cu-Kα 63% @ 8 keV G ≈ 1340 68% @ 8 keV G ≈ 1340 Pulser 36% @ 30 keV G ≈ 1670 Xe-Kα 19% @ 30 keV G ≈ 1670 Pulser Xe-Kα Pulse height spectra of 241Am source in Xe(98)CF4(2) with a Micromegas-TPC 1 bar 3 bar

  15. Radio-pure and radio-active components

  16. Ge (400 cm3) “Vue-des-Alpes” The Germanium detector :gamma spectrometry

  17. Lead. • Copper (TPC+rings+cathode). • Glue (araldite). • Grid (Stainless steel). • insulators (delrin, teflon) Kevlar Radio-pure 2614 • Printed-circuit (resin-epoxy). • Resistances (ceramic). • Solder (210Pb) Resin-epoxy Radio-active x104 2614

  18. Gotthard results

  19. diameter: 50 cm Gap: 250 µm TPC (60X70cm) Micromegas • Gotthard-TPC calibration @ low • energies (241Am, 133Ba). The Gotthard TPC • Estimate the radioactive • background of the TPC. - Find the sources of noise: Measure the radioactivity of components using a Ge detector “Vue-des-Alpes”.

  20. The compact Micromegas is tested before being installed

  21. Micromegas (50 cm of diameter):(Am and Ba) sources effect 81 keV (133Ba) 53% @ 60 keV (241Am) 60 keV (241Am) The Compton plateau (133Ba)

  22. 46 keV 46 keV The behavior of the background registered in the Gotthard TPC 1 bar of P10 gas 3 bar of P10 gas

  23. Conclusions • We improve the energy resolution when we replace the MWPC with a Micromegas. • Xe(98)CF4(2): ideal for double beta search: high gains, good efficiency, good (energy, spatial and time) resolutions. • Increase the gap (amplification): permits a good charge collection in Xe and go up at higher pressures. • Micromegas in compact:(50 cm) showed high efficiency and good energy resolution.

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