Micro Pixel Chamber 3 , , - PowerPoint PPT Presentation

大面積 Micro Pixel Chamber の開発 3 京都大学 永吉 勉 谷森達 , 窪秀利 , 身内賢太朗 , 竹田敦 , 折戸玲子 , 植野優 , 高田淳史 , Espoo-Vantaa O. Bouianov Institute of Technology CSC-Scientific Computing M. Bouianov 日本物理学会 2003 年秋季大会 @ 宮崎ワールド コ ンベンショ ンセンタ ー・ サミ ッ ト 2003 年 9 月 10 日

Contents 1. Micro Pixel Chamber ( µ -PIC) 2. Optimization of electrode structure • Simulation of electron drift • New manufacture technique 3. Basis for MeV gamma-ray imaging • CF 4 gas • Gas vessel 4. Summary

1.1 Micro Pixel Chamber ( µ -PIC) Printed Circuit Board (PCB) technology •Large area •Low cost polyimide substrate (prepreg) • 400 µ m pitch electrodes • 256 anodes and 10cm 256 cathodes Detection area = 100cm 2

1.2 Performances X-ray imaging gas gain 10 4 1mm Gas: Ar/C 2 H 6 (80/20) 10 3 slits Source: 55 Fe (5.9keV) •Gas: Xe/C 2 H 6 (70/30) •Drift: 3mm (500V/cm) •Gas gain ~ 15,000 (max) Position resolution •Stable operation (>1000h) σ ~ 160 µ m @ gas gain ~ 5000 (knife edge test)

2.1 Drift simulation ~ For the best electrode ~ 3D simulation Drift end points (Maxwell + Garfield) (simulation) RKF meth. MC meth. collected 30% 314 µ m 65% 20 µ m near pin 5% 100 µ m gap 260 µ m Drift paths of electrons Top of anode electrodes Collection efficiency ~ 30% are below substrate.

2.2 Drift simulation Anode height = +10 µ m Anode diameter = 50 µ m Cathode width = 314 µ m Higher anode Cathode diameter = 260 µ m � Higher efficiency collected fraction fraction Thicker substrate substrate Current µ -PIC � Higher efficiency near pin Collection efficiency ~ 97% collected Gas gain: × 3 near pin gap 100 400 gap substrate thickness [ µ m] 0 10 Substrate > 200 µ m … difficult anode height [ µ m] Current µ -PIC Anode = 10 µ m … possible!! ( -20 µ m )

Drift end points Substrate = 5 µ m Substrate = 200 µ m

3 µ 4 0 2.3.1 New µ -PIC m Electrode formation process 100 µ m •Current type … normal plating (“bottom-up”) Coming soon!! •New type Detection area … plating and etching (“top-down”) 30cm × 30cm 1. Electroless plating 3. Surface etching substrate 2. Via-fill plating 4. Electrode etching cathode anode

2.3.2 New µ -PIC 30 × 30 cm 2 detector Edge region Center region Beautiful! 10 × 10 cm 2 : Available for performance test some offset … 30cm

V A = 560V 2.3.3 New µ -PIC Gain map Anode • 10 × 10cm 2 detection area • Bad electrode < 0.1% • Leakage current < 2nA @800V (in air) 10 4 Cathode New µ -PIC × 3 •uniform anodes Gas gain •anode height = cathode thickness Former µ -PIC •gas gain ~ 9000 @V A = 600V 10 3 •gain uniformity ( σ ) ~ 7%

3.1 Gamma-ray imaging γ φ ψ Pre-amp δ µ -PIC NaI + PMTs α e γ ’ Reconstructed image Compton scattering •Electron tracking � Full reconstruction •Cross section σ ∝ number of electrons 133 Ba (356keV) Balloon experiment in 2006

3.2.1 Gas study ~ Ar vs. CF 4 ~ Ar • Number of electrons = 18 Standard gas • W value = 26 eV/pair for gas detectors • (dE/dx) min = 2.44 keV/cm CF 4 • Number of electrons = 42 Good properties • W value = 54 eV/pair for MIPs! • (dE/dx) min = 7 keV/cm • Fast drift (~9cm/ µ s), small diffusion

3.2.2 Operation test 3 × 3cm 2 µ -PIC Operation test with CF 4 gas Dependence on … •Mixture ratio (C 2 H 6 ) •Pressure (1 – 2.5atm) Gas vessel Source: 55 Fe (5.9keV)

3.2.3 Operation test pure CF 4 CF 4 / C 2 H 6 (80/20) 10 4 10 4 Gas gain Gas gain 1atm 1atm 2atm 2atm 10 3 10 3 2.5atm 2.5atm 1300 800 1000 1200 700 1000 Anode voltage [V] Anode voltage [V] • Maximum gas gain ~ 3500 (80/20 mixture) • Gas gain > 10 3 @ 2.5atm

3.3 Gas vessel Flexible boards for read-out • Available for 30 × 30 cm 2 detector • Vacuum ~ 4atm (?) µ -PIC in gas vessel

4 Summary • 3D simulation of µ -PIC – Higher anode � high efficiency ( > 90%) • A new manufacture technology – Anode height = cathode thickness – Gas gain ~ 9000 – Uniformity: σ ~ 7% • CF 4 gas – Stable operation @ gas gain > 1000 • Gas vessel for 30 × 30cm 2 detector – Pressure-resistant test is in progress

3.2.1 Drift and diffusion ~ Simulation by Magboltz ~ Drift velocity Diffusion 10 3 Drift velocity [cm/ µ s] Diffusion [ µ m for 1cm drift] 10 10 2 Pure CF 4 4 CF 4 / C 2 H 6 (80 / 20) CF 4 / C 2 H 6 (60 / 40) Ar / C 2 H 6 (80 / 20) 500 2000 500 2000 E field [V/cm] E field [V/cm] • Drift: × 2 faster than Ar • Diffusion: 1/4 smaller than Ar