Development of Gaseous Photomultiplier with GEM/ μ PIC

1. Development of Gaseous Photomultiplierwith GEM/μPIC 120mV 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. w 1.Motivation 4. LaF3(Nd) – VUV source Recently, large area micro pattern gaseous detectors such as GEM, Micromegas, and μPIC have been developed and successfully operated. Newly developed VUV scintillator (Yoshikawa grope, IMPAM, Tohoku Univ.) Optical spectrum • λpeak =172nm • 100 photons/MeV(gamma) • 100 photons/241Am (5.5MeV α) • →”Standard Light Source” 30cmGEM 30cmμ-PIC These devices with photocathode can realize a gaseous photomultiplier for future large volume detectors. wavelength(nm) • Reference Detector PMT R8778 (Hamamatsu) • Response to the “SLS “ • Large area • Low cost • Small volume Possible features QE (by Hamamatsu ) • Position sensitive • Low background • For liquid Xe : UV • enhanced bialkali • photocathode • QE～30%@172nm -1300V gain =2.2x106 • 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. w 5.Performance for VUV “SLS” attached to the MgF2 window of the prototype detector 2.Prototype Detector • Typical signal • after 1V/pC charge amplifier 2GEMs + μPIC System for suppression ion/photon feedback high gain operation Gas: Ar＋C2H6（90：10）1atm 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 120mV/1V×1pC/(1.602×10-19pC) / (2.6×105) =2.9 p.e signal • Window/photocathode 150160 170 180 190 200 210 220 230 240 250 260 • MgF2 54Φ×5t • Al electrode (edge10mm) • CsI evaporated by Hamamatsu • spectrum in mV • spectrum in p.e. 100 10 1 • Has sensitivity • to 1p.e. • QE is about 2% • as expected. gain =2.6x105 • μPIC 10cmμ-PIC anode • GEM 160 180 200 220 240 260 10cmGEM wavelength(nm) 400μm cathode • Advanced MSGC • PCB technology • (Toshiba, DNP) • 10cm×10cm • 256×256 strips • merged to 4×4 6.Conclusions and Prospects Structure of μ-PIC • SMASH (plasma etched GEM) • (SciEnergy Co., Ltd.) • 100μm Liquid Crystal Polymer • 10cm×10cm • 140μm pitch, 70μm Φ • Successfully 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. 3.Electron multiplication The gas gain of the detector was examined with 5.9keV Xray 25μm Mylar ® tape window (only for this measurement) • Typical Spectrum 55Fe gas gain =10000 0.3kV/cm 12mm 20μmAl -HV Hamamatsu catalog B.K. Singh et al., NIMA 581(2007) 651 QE(%) ref. CsI 6mm -HV 20 MΩ QE(%) 0.3kV/cm 2mm 10 MΩ 20 MΩ • Results 2％@172nm 100pF 6mm 30％@172nm 20 MΩ trans. CsI 100pF Au-plated GEM for CsI evaporation 1MΩ 500MΩ wavelength(nm) +HV 172 wavelength(nm) • 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. References [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