Takeshi Fujiwara, Hiroyuki Takahashi, Kaoru Fujita, Naoko Iyomoto Department of Nuclear Engineering and Management, The University of Tokyo, JAPAN Study on transparent electrode ITO-MSGC for Gas Proportional Scintillation Counter MPGD’09 June 13 th Greece

Outline  Introduction  Multi-Grid MSGC (M-MSGC)  Active scintillation method  Fabrication of transparent M-MSGC (ITO)  Test results in X-ray  Summary

1. Introduction

J-PARC (Japan Proton Accelerator Research Complex) 400MeV Lineac Mercury target 3GeV synchrotron MLF MLF (Material and Life Facility) Facility for material analysis and life science Overview

MLF spectrometers And more is being developed

MLF spectrometers A facility to analysis materials with reflection of neutrons Mirror Target Detector Neutron beam (Various wave length) Diffraction Diagrammatic sketch of Refelctrometer Θ

2. Multi-Grid MSGC (M-MSGC)

Anode Cathode Micro-strip electrodes patterned on glass plate <100µm between anode & cathode Up to 1600V between each strips Electron is multiplied with avalanche and produces charge Charge division readout method for 1D position detection 2D position detection by layering 2 plates Diagrammatic sketch MSGC (Micro Strip Gas Counter) Avalanche Electron

Charge up causes decrease of gas gain Damage caused by sudden discharge Bad in stability High count rate Low cost Could be used with high pressure gas MSGC (Micro Strip Gas Counter) Good Bad AnodeCathode

AnodeCathode... Separation of two strong electric fields Small surface charge Low surface resistance Grid1 Grid2 Multi-grid-type MSGC (M-MSGC) Avoid charge-up and sudden discharge Charge up causes decrease of gas gain Damage caused by sudden discharge Bad in stability Bad V anode > V grid1 > V grid2 > V cathode

A G1 G2 G3 G4C 4 cm x 4 cm active area Anode width: 5 µm 4 grids(20,25,35,42.5µm) and 10 µm gaps 4 cm x 4 cm active area Anode width: 5 µm 4 grids(20,25,35,42.5µm) and 10 µm gaps 400  m A test plate consists of 4 grids + anode + cathode

Obtained energy resolution was 14.6% FWHM. (Gas gain =3000) 6keV Ar escape Pulse Height Spectrum for 6keV X-rays Experiment is done with 6keV X-ray Photon Factory) 0.1mm ϕ beam, 400cps/mm 2 Ar(30) + CH 4 (70%) ＠１ atm

Neutron Image by Floating Pad Charge Division Method 6mm 1mm Spatial resolution 0.6mm FWHM

3. Active scintillation

Active scintillator method (proposed in MILAND) Incident neutron MSGC Photo Multiplier Electron drift Primary light Position Measurement at T=Gap/V drift d Primary light signal enables to calculate the depth of interaction information, and reduce parallax error T charge signal T primary light

Problems of conventional method Photo Multiplier Unwanted diffraction Incident neutron Stop Primary light Position Measurement at T=Gap/V drift MSGC Incident neutron Since neutrons have to go through the MSGC, unwanted diffractions and stops can be caused.

Problems of conventional method Photo Multiplier MSGC Incident neutron In order to avoid unwanted diffraction or stop, MSGC should be under the conversion area. However, since ordinary MSGC’s are not transparent, primary light cannot get to PMT. Primary light Electron drift

Problems of conventional method Photo Multiplier MSGC Incident neutron But if the MSGC is transparent…, Primary light Electron drift

Problems of conventional method Photo Multiplier MSGC Incident neutron Primary light Electron drift But if the MSGC is transparent…, primary light signal enables to calculate the depth of interaction information, and reduce parallax error without worrying about the unwanted diffraction d

4. ITO - The transparent MSGC

ITO MSGC  ITO(Indium Tin Oxide) is known as a transparent conductive material used for LCD display.  Optical transmission is 80-90%.  We fabricated a multi-grid-type MSGC using ITO.  OA10 glass substrate  170nm thick ITO layer  Use with Ar/CF 4 gas for efficient GSPC

This is ITO MSGC If you have super excellent eyes, may be you can see…

Picture of ITO MSGC ITO version of M-MSGC Electrode pattern is same as our conventional M-MSGC

Transmissivity of ITO

5. Test results with X-rays

Experimental Setup Ar(70%) + CH 4 (30%) ＠１ atm HV(2ch out put) ORTEC 456 Tektronix DPO 4034 Oscilloscope - 800V PMT Hamamatsu R5600U 55 Fe 3mm PMT or ANODE Pocket MCA 8000A PC Chamber inside Cathode Anode ORTEC 570 HV (4ch out put) ORTEC 710 Socke t E5780 PMT R5600U Sensitive Area 300nm ～ 650nm Anode Cathode Grid 1 Grid 2 Active area 2.7 cm 3.0cm  8.0mm Optical Signal Charge Signal

Test of operation as a proportional counter ANODE signal CATHODE signal Ar 70% + CH 4 30%

LIGHT CHARGE 100ns

Obtained energy spectra ITO M-MSGC FWHM 25.4% FWHM 27.4% Charge Light

ANODE HV AMPLITUDE Gas gain & PMT Spectra

5.2. Position Scan with 6keV X-ray beam

Test of position readout Experimental setup HV(2ch out put) ORTEC 456 Tektronix DPO 4034 Oscilloscope V Hamamatsu R PSPMT 3mm PMT or ANODE MPA PC Chamber inside Cathode Anode ORTEC 570 HV (4ch out put) ORTEC 710 PS PMT R-2486 Sensitive wave length 300nm ～ 650nm Ar(90%) + CF 4 (10%) ＠１ atm Position Readout ORTEC 464 6keV X-ray Optical Signal Charge Signal

Position measurement Hamamatsu R PSPMT ITO-MSGC X1 X2 Y2 Y1 Ar/CF4 90:10 PS Module ORTEC 464

Schematic of Hamamatsu PS-PMT R

5mm Position scanned result obtained with PSPMT Channel 6keV collimated X-ray beam (scanned in 25mm * 25mm area) Count 5mm ≈2.5mm(FWHM) Experiment is done with 6keV X-ray Photon Factory) 0.1mm ϕ beam, 400cps/mm 2 Hamamatsu PS-PMT R Ortec 464 Position Detection module

Results of position scan by 5mm 5mm Y Axis (Peak channel) X Axis (Peak channel) Experiment is done with 6keV X- ray Photon Factory) 0.1mm ϕ beam, 400cps/mm 2 Hamamatsu PS-PMT R Ortec 464 Position Detection module

Future work ITO- MSGC SiPM array ITO-MSGC Charge signal (Y) Normal PMT Light signal (X) Optical mask (position modulation) He3 + CF 4 Use both of charge/optical signal for position detection Transmissivity

Future work He3 + CF 4 Anger camera ITO- MSGC PMT

Summary  ITO M-MSGC has been fabricated and tested with 6keV X-rays.  Position sensing by optical signal has been demonstrated.  Active scintillation could be a solution for higher spatial resolution  Optics for better light collection should be considered.

Thank you Takeshi Fujiwara

2D Multi-Grid-Type MSGC by induced charge sensing  Place FLOATING pads close to cathode  Positive Ions stay on pads  Pad charge can be read out through substrate A G Pad C Readout Strips Charge stay on pads Avalanche region