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.