Hiroyuki Sekiya Jul. 31 st 2008, Philadelphia, ICHEP2008 Development of Gaseous Photomultiplier with GEM/μPIC Hiroyuki Sekiya ICRR, University of Tokyo 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+C 2 H 6 (10%) gas, we achieved the gas gain of 10 5 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.Motivation Recently, large area micro pattern gaseous detectors such as GEM, Micromegas, and μPIC have been developed and successfully operated. 30cmGEM 30cmμ-PIC These devices with photocathode can realize a gaseous photomultiplier for future large volume detectors. Possible features Large area Low cost Small volume Position sensitive Low 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 MgF 2 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 operation Gas: Ar ＋ C 2 H 6 （ 90 ： 10 ） 1atm 6.Conclusions and Prospects Successfully operated with the stable gas gain of UV lights from LaF 3 (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. w w 4. LaF 3 (Nd) – VUV source For liquid Xe : UV enhanced bialkali photocathode QE ～ Response to the “SLS “ Reference Detector PMT R8778 (Hamamatsu) λ peak =172nm 100 photons/MeV(gamma) 100 photons/ 241 Am (5.5MeV α) →”Standard Light Source” wavelength(nm) Newly developed VUV scintillator (Yoshikawa grope, IMPAM, Tohoku Univ.) Optical spectrum -1300V gain =2.2x10 6 wavelength(nm) QE (by Hamamatsu ) w w 5.Performance for VUV Typical signal after 1V/pC charge amplifier “SLS” attached to the MgF 2 window of the prototype detector 120mV/1V×1pC/( 1.602× pC) / (2.6×10 5) =2.9 p.e signal gain =2.6x10 5 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 +HV -HV 100pF 55 Fe 0.3kV/cm Results Stable operation with the gain of 2.6 × 10 5 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. [This detector] H.Sekiya, Proc. of the International Workshop on new Photon- Detectors, Proceedings of Science, PoS(PD07)028 References 30 wavelength(nm) ref. CsI B.K. Singh et al., NIMA 581(2007) 651 QE(%) wavelength(nm) trans. CsI 172 Hamamatsu catalog 2 QE(%) Au-plated GEM for CsI evaporation 120mV