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DEVELOPMENT OF PHOTODETECTION SYSTEM BASED ON MULTIPIXEL AVALANCHE GEIGER PHOTODIODES WITH WLS FOR LXE LOW-BACKGROUND DETECTORS D.Yu. Akimov, A.V. Akindinov, I.S. Alexandrov, A.A. Burenkov, M.V. Danilov, A.G. Kovalenko, V.N. Stekhanov University Department, State Scientific Centre of Russian Federation Institute for Theoretical and Experimental Physics (ITEP), 25 Bolshaya Cheremushkinskaya str., Moscow, Russia DARK MATTER EXPERIMENTS Xenon10,100 at Gran Sasso XMASS at Kamioka All detectors utilizes PMTs for detection of the LXe VUV light. ZEPLIN III at Boulby mine LUX at SUSEL At present, PMTs (even low-background) are the most radioactive elements of detector. Search for a replacement of PMTs for the future detectors is actual. THE AIM OF THIS STUDY The aim of the current work is to demonstrate experimentally: The possibility of the use of MPGP (Multi Pixel Geiger Photodiode) for detection of the LXe luminescence light together with a wavelength shifter To estimate the global PDE of such a system MULTIPIXEL AVALANCHE GEIGER PHOTODIODE Readout -Voper Scheme of MRS APD View of matrix cells Structure of 1 cell MULTIPIXEL AVALANCHE GEIGER PHOTODIODE Multiplication: M = C*(U - Ubr) Charge: Q = e*Ncell*C*(U - Ubr) Photon Detection Efficiency: PDE= Q.E.*RG*ε geom Typical PDE for CPTA 2x2 mm2 CPTA “green” – blue, green, IR CPTA “blue” – blue, green, IR WAVELENGTH SHIFTER LXe emission, p-terphenyl absorption and emission spectra and PDE of “blue” CPTA photodiode EXPERIMENTAL SETUP LXe LXe 1 1 2 2 3 3 4 7 4 5 6 5 8 a) b) Scheme of measurements. a) The p-terphenyl deposited layer between two optical windows, b) p-terphenyl is coated by a poly-para-xylylene film. 1 – PMT Hamamatsu R7200, 2 – αsource 241Am, optical window (sapphire), 4 – p-terphenyl, 5 – MRS APD, 6 – optical 2 x32- mm, 1584 pixels window, 7 – Ar gas between the window, 8 - poly-para-xylylene film. Photo of assembled constructions (Ar gas between the windows) EXPERIMENTAL SETUP Photo multiplayer MRS APD k Scheme of measurements EXPERIMENTAL SPECTRUMS noise CPTA “blue” PMT α peak pedestal 1 cell 2 cells Pulse area, V·ns RESULTS & PDE CALCULATION 84 cells RESULTS & PDE CALCULATION Sapphire Ω2 Ω1 WLS MRS APD 1 4 PDE N cells 2 f N 0 10 0 N cells 1 2 N0 f , 4 4 N0=Eα/w, were Eα= 5.486 MeV is the energy of alpha particle w = 16.3 ± 0.3 eV f - total attenuation coefficient of the light in the windows η - efficiency of transformation of the VUV light to the visible region ξ - photo detection efficiency of the photodetector in the wave range of WLS emission 2 PDE 4 1 2 10 1 4 4 4 2 RESULTS & PDE CALCULATION Series of measuremts Ncells µ f Figure 1a) 24±0.5 0.74 0.68 Ω 1.35*10-3 Figure 1b) 72±1.5 0.17 0.75 1.99*10-2 P. Benetti, et al., Nucl. Instr. Meth. A505, 89 (2003). For a blue sensitive PMT (QE ≈20%) with WLS. PDE0 ,% 9.7 ±1.2 8.4 ±1.1 FUTURE PLANS MGPD matrix WLS Electroluminescence, detected by MGPD GEM/THGEM Gaseous Xe Electroluminescence, detected by PMTs LXe surface Grid e- LXe Fig. 2. Possible design of high precision detection system for two-phase noble gas detectors with THGEM + WLS +MGPD. CONCLUSION • • • The capability of operation of WLS in LXe with protection has been shown. Poly-para-xylylene film is good protection items in LXe. The results of experiment allow one to build a detection system based on WLS. Type of construction WLS PDE, % p-terphenyl is sealed between two optical windows p-terphenyl is coated by a poly-paraxylylene film. 9.7±1.2 8.4±1.1 One can build a system with low radioactive background for a two-phase detector sensitive to very low ionization.