Hiroyuki Sekiya Jul. 31st 2008, Philadelphia, ICHEP2008

Development of Gaseous Photomultiplierwith GEM/μPIC Hiroyuki Sekiya ICRR, University of Tokyo

E-mail: sekiya@icrr.u-tokyo.ac.jp

Abstract: We are developing a new photon detector with gas amplification devices. A semitransparent CsI photocathode is combined with 10cm×10cm GEM/μPIC for the first prototype which is aimed for the large liquid Xe detectors. Using Ar+C2H6

(10%) gas, we achieved the gas gain of 105 which is enough to detect single photo-electron. We, then, irradiated UV photons from a newly developed solid scintillator, LaF3(Nd), to the detector and successfully detected single photo-electron.

1.MotivationRecently, large area micro pattern gaseous detectors such as GEM, Micromegas, and μPIC have been developed and successfully operated. 30cmGEM30cmμ-PIC

These devices with photocathode can realize a gaseous photomultiplier for future large volume detectors.

Possible features Large areaLow costSmall volume

Position sensitiveLow background

Handling bialkali photocathodes requires special equipments,

therefore, we use the CsI for the first step. In particular, the quantum efficiency of the CsI matches the liquid/gas Xe scintillators; thus, dark matter and neutrino experiments are the targets of this photon detector.

2.Prototype Detector

Window/photocathode

•MgF2 54Φ×5t•Al electrode (edge10mm)

•CsI evaporated by Hamamatsu

GEM

μPIC

10cmGEM

10cmμ-PIC

•Advanced MSGC•PCB technology (Toshiba, DNP)•10cm×10cm•256×256 strips　 merged to 4×4

Structure of μ-PIC

400μm

anode

cathode

•SMASH (plasma etched GEM)

(SciEnergy Co., Ltd.)•100μm Liquid Crystal Polymer•10cm×10cm•140μm pitch, 70μm Φ

2GEMs + μPIC System for suppression ion/photon feedback high gain operationGas: Ar ＋ C2H6 （ 90 ： 10 ） 1atm

6.Conclusions and ProspectsSuccessfully operated with the stable gas gain of 105 .UV lights from LaF3(Nd) were detected. Has enough sensitivity to single photo-electron.The quantum efficiency of this semitransparent photocathode is 2% as expected.To increase the QE, a reflective photocathode (300nm-thick CsI evaporated to one side of GEM ) is tested now.

Many additional tests such as the uniformity, the longtime stability, and the detection efficiency should be conducted.

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4. LaF3(Nd) – VUV source

• For liquid Xe : UV enhanced bialkali photocathode• QE ～ 30%@172nm

Response to the “SLS “

Reference Detector PMT R8778 (Hamamatsu)

•λpeak =172nm •100 photons/MeV(gamma)•100 photons/241Am (5.5MeV α) →”Standard Light Source”

150 160 170 180 190 200 210 220 230 240 250 260

10.90.80.70.60.50.40.30.20.10.0

wavelength(nm)

Newly developed VUV scintillator (Yoshikawa grope, IMPAM, Tohoku Univ.)

Optical spectrum

-1300V gain =2.2x106

wavelength(nm)160 180 200 220 240 260

100

10

1

QE (by Hamamatsu )

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5.Performance for VUV

Typical signal after 1V/pC charge amplifier

“SLS” attached to the MgF2 window of the prototype detector

120mV/1V×1pC/(1.602×10-19pC)/ (2.6×105)

=2.9 p.e signal

gain =2.6x105

spectrum in p.e. spectrum in mV

•Has sensitivity to 1p.e. •QE is about 2% as expected.

3.Electron multiplication The gas gain of the detector was examined with 5.9keV Xray

10 MΩ

20 MΩ

1MΩ

100pF

500MΩ

20μmAl

6mm

2mm

6mm

12mm-HV

20 MΩ

20 MΩ

+HV

-HV

100pF

55Fe

0.3kV/cm

0.3kV/cm

Results

Stable operation with the gain of 2.6 ×105 was achieved without any discharges

The uPIC which is not good one (reused, old product ) limit the gain.

25μm Mylar ® tape window (only for this measurement)

gas gain =10000

Typical Spectrum

[μPIC] A.Takada et al., Nucl. Instr. and Meth A. 573 (2007) 195[GEM/SMASH] SciEnergy Co., Ltd. http://www.scienergy.jp[This detector] H.Sekiya, Proc. of the International Workshop on new Photon-Detectors, Proceedings of Science, PoS(PD07)028

References

30 ％ @172nm

wavelength(nm)

ref. CsI

B.K. Singh et al., NIMA 581(2007) 651

QE

(%)

wavelength(nm)

trans. CsI

172

Hamamatsu catalog

2 ％ @172nm

QE(%)

Au-plated GEM for CsI evaporation

120mV