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
ZEPLIN III at Boulby mine
XMASS at Kamioka
LUX at SUSEL
All detectors utilizes PMTs for detection of the LXe VUV light.
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 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
The aim of the current work is to demonstrate experimentally:
MULTIPIXEL AVALANCHE GEIGER PHOTODIODE
-Voper
Readout
Structure of 1 cellScheme of MRS APD
View of matrix cells
MULTIPIXEL AVALANCHE GEIGER PHOTODIODE
CPTA “green” – blue, green, IR CPTA “blue” – blue, green, IR
Typical PDE for CPTA 2x2 mm2
Charge: Q = e*Ncell*C*(U - Ubr)
Multiplication: M = C*(U - Ubr)
Photon Detection Efficiency:PDE= Q.E.*RG*ε geom
LXe emission, p-terphenyl absorption and emission spectra and PDE of
“blue” CPTA photodiode
WAVELENGTH SHIFTER
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 – α-source 241Am, 3 - optical window (sapphire), 4 – p-terphenyl, 5 – MRS APD, 6 – optical window, 7 – Ar gas between the window, 8 - poly-para-xylylene film.
LXe
3
58
LXe 1
2
3
4
65
7
1
2
4
a) b)
EXPERIMENTAL SETUP
Photo of assembled constructions(Ar gas between the windows)
2 x 2 mm, 1584 pixels
EXPERIMENTAL SETUP
Scheme of measurements
Photo multiplayerMRS APD
k
Pulse area, V·ns
CPTA “blue”
PMT
EXPERIMENTAL SPECTRUMS
noise
α peak
1 cell
2 cells
pedestal
RESULTS & PDE CALCULATION
84 cells
RESULTS & PDE CALCULATION
,44
210
fNNcells
PDE 4
2
2
1
444
0121
010
0 4
2
1
NfNPDE cells
WLSSapphire Ω1
Ω2
N0=Eα/w, were Eα= 5.486 MeV is the energy of alpha particle w = 16.3 ± 0.3 eVf - total attenuation coefficient of the light in the windowsη - efficiency of transformation of the VUV light to the visible regionξ - photo detection efficiency of the photodetector in the wave range of WLS emission
MRS APD
RESULTS & PDE CALCULATION
Series of measuremts
Ncells µ f Ω PDE0 ,%
Figure 1a) 24±0.5 0.74 0.68 1.35*10-39.7
±1.2
Figure 1b) 72±1.5 0.17 0.75 1.99*10-28.4
±1.1
P. Benetti, et al., Nucl. Instr. Meth. A505, 89 (2003).For a blue sensitive PMT (QE ≈20%) with WLS.
MGPD matrix
WLS
GEM/THGEM
LXe surface
Grid
LXee-
Electroluminescence, detected by MGPD
Electroluminescence, detected by PMTs
Gaseous Xe
Fig. 2. Possible design of high precision detection system for two-phase noble gas detectors with THGEM + WLS +MGPD.
FUTURE PLANS
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
9.7±1.2p-terphenyl is coated by a poly-para-
xylylene film. 8.4±1.1
One can build a system with low radioactive background for a two-phase detector sensitive to very low ionization.