Development of scintillation detectors with MRS APD light readout for CBM Muon system and ECAL presh...
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Development of scintillation detectors with MRS APD light readout for CBM Muon system and ECAL preshower. Alexander Akindinov ITEP(Moscow) on behalf of ALICE-ITEP group. Outlook. MRS APD – fast Geiger mode high gain photodetector START – technology

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Alexander Akindinov ITEP(Moscow) on behalf of ALICE-ITEP group

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Development of scintillation detectors with MRS APD light readout for CBM Muon system and ECAL preshower

Alexander Akindinov

ITEP(Moscow) on behalf of ALICE-ITEP group


  • MRS APD – fast Geiger mode high gain photodetector

  • START – technology

  • ALICE CRTF – first implementation for START technology

  • Counters for CBM muon systems

  • Counters for EMCAL preshower

  • Conclusion



MRS APD – fast Geiger mode high gain photodetector

M = C*(U - Ubr)

MRS APD structure

Many other name:


Slope corresponds to elementary micro-cell capacity Q/U.

Q = Ncell*C*(U - Ubr)

Single electron resolution is a result of dispersion of Ubr and Ccell across diode area.

Optical trench(CPTA) – low optical coupling between cells.Acceptable noise rate for reasonable thresholds

Probability to have more

than one pixel fired from a single primary e-h pair

 = (N n+1)/ (N n )

Noise spectrum slope is a result of “red” cross-talks between cells, when avalanche in one cell initiate avalanche in neighboring one via photon.

PDE is optimize for WLS fibers

P.D.E. = Q.E. * g* R

εg – geometrical fill-factor

R – probability to initiate

Geiger avalanche

Q.E. – quantum efficiency


For 4th cell threshold noise count about a few kHz

High geometrical factor

START- (Scintillation Tile with MRS APD Light ReadouT)

MRS APD optimize geometry (d=1.15 mm) for the fiber readout

σ-shape groove for uniform response


in coincidence

“On board” FEE

Mosaic array



Cosmic μ

Polisterol 165 150X150X10 mm

1 groove, 2 rings Y11 and glued

First implementation - ALICE CRTF

Upper plane

10 strips 8 STARTs

in each (80 STARTS)

Bottom plane

10 strips 8 STARTs

in each (80 STARTS)

Up to 5 ALICE TOF modules under the test.

Trigger and monitoring

Simple logic block for trigger configuration and monitoring were connected via USB to LabView

  • !!Monitoring the only by counting rate of individual detector, no any LED system was used.!!!

  • Efficiency was measured as difference in counting rate for 80 pairs.

Long term operation results

First real experiment with 320 new photosensors (CPTA firm MRS APD).

About 3 years of continues operation, all 87 ALICE TOF modules was tested.

Summary of “dead” and replaced diodes

Counters for CBM muon system

“Develop and produce START prototypes adapted for dE/dx measurements. Five detectors of each of two types of START will be produced: tiles sized 100x100x 10 mm3 and strips sized 5x200x10 mm3

INTAS Ref. Nr 06-1000012-8781

Strips 5x200x10 mm3

Tiles with different groove diameters to find optimal uniformity (d = 90, 80, 70, 60, 50 mm)

ROLAND milling machine

!!!Many thanks to our friends from ITEP-CALICE group!!!!

New package to minimize “dead zone” and new connector


New package

Very uniform response (about 8%). Main sources - regions near optical connectors and groove.

New transparent optical connector produced by the same digital milling machine as tiles

Diodes calibration and fiber cut

Each diode after placement into connector was checked (how well diode active area is with connector hole)

Setup to cut fiber with microscope

Setup for diodes test


12 channel board

Diodes calibration and fiber cut

Number of photoelectrons for given light was checked

I-U curve to find out breakdown point

Single cell noise and photoionization (α) coefficient were measured

Detector assembly and electronics

FEE card for tiles

Simple amplifier for strips (10mm width)

Tiles were wrapped in Tyveсk and light shield

FEE for tiles

Ubias сontrol

Test input (50 Ω)

Jumper 2 for


Jumper 1 for



Amplitude 2

(50 Ω)

Amplitude 1

(50 Ω)


Jumper 2 for



Jumper 1 for






+4-+10 V

First task: find optimal geometry for uniform response

D=50 mm









Scans were done using Ru β – source with 2.5 mm collimator. 19x19 points (5 mm step).

New improved MRS APD (2007)

Data was taken from

Photonique SA C.P. 15621211 Geneva-1Switzerland

Reduced thickness of n+ - PDE increased + blue enhanced

2005 – diodes for ALICE CRTF

New diodes 2007

Light yield with old and new diodes

Beam test CERN PS (2x2 cm2 trigger center of tile)

N ≈ 29 ph.e.

N ≈16 ph.e.

N ≈ 22 ph.e.

“43V” old “23V”new


Tile 100x100x10 mm3

Tile 150x150x10 mm3

With this significant improvement can we work with one diode?

Tiles with single diodes

Three reasons to produce tiles with one diode:

To check if we can improve light yield using another glue

Check if we can work with one diode

Make prototype for ECAL preshower

3 tiles were used for test

2 were assembled for cosmic test

100x100x10 mm3 with one output for fiber ( d=80 mm )

So called “half-board” designed for long strips

Other task: to improve gluing

How it’s important

4 grams each time

Accuracy up to 0.01g

Measurements were done before and after gluing with the same diode

Does not depend on plastic type

Since refractive indexes almost the same we can suppose that difference is due to acid type (groove walls “melting” – more uniform and transparent volume). For our milling process – Epo-Tek 301 is the best.

Cosmic ray test one diode





Diode noise

“Soft” and “hard” part of cosmic ray

It works!!! We can use only one diode.

Last task: Strips

3M tape

R.M.S ≈ 12%

4 stripes shows some “oscillating” signals. Reason bad 3M mirror contact. All tiles were reassembled. New test will be done about 20 of October.


  • START detector was adopted for dE/dx measurements

  • Optimal diameter d=80 mm for tile 100x100x10 mm3 response was found (r.m.s < 5.0 %).

  • EPO-TEK 301 glue was found as optimal to increase light yield.

  • 3 types of FEE board were produced (all commercially evaluable)

  • Progress in MRS APD development allows to use only one diode for readout keeping signal/noise ratio almost the same like for two old diodes

  • 4 strips 200x10x5 mm3 were reassembled and will be tested again. Good one has 12% r.m.s.(?)

  • Tools for mass production were produced.

Thank you!


MRS APD calibration

Ubias for given amplification about 106

Thank to Yuri Musienko

from CMS APD lab.

Response and leakage tests

All current is due to intrinsic noise, no significant leakage

Difference – small difference in αand coupling with fiber (epoxy layer share)


Photoionization α

Difference – different field noise contribution to the thermal noise

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