The BGO matrix readout for
the 2009 Test Beam
Guido & Alessandro
BGO in 2008
•
A lot of time was spent to recover the BGO
crystals and to design and build the matrix
•
The readout was relatively simple: 4 PMTs
looking at the BGO light through UG11
filters
•
Coupling by means of a diffusing light-guide,
with unfortunately non-optimal diffusing
properties in the near-UV range – this lightguide should have acted as a light mixer
•
No tests could be performed before the
test beam period
•
After preliminary checks it was decided to
couple directly the 4 PMTs to the small side
of the matrix, the only solution that allowed
the readout of some light from the matrix
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G. Ciapetti, A. Cardini
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BGO matrix in 2008
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BGO matrix in 2008
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Improvements for 2009
• Purchased Photonis XP3392B PMTs,
to cover the large side of the
matrix. We currently own 12 such
PMTs + dividers
• Couple the PMTs to the BGO matrix
by means of a UV-transparent
plexiglass adapter (see next slides)
• UG11 filters in front of each PMT
windows
• Use of an optical elastomer for a
proper optical coupling (or use an
optical grease, to be decided)
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Coupling PMTs to the BGO matrix
A. Zullo design
UV-transparent plexiglas
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A. Zullo design
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A. Zullo design
Matrix rotated to increase Cerenkov light yield
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UV-transparent Plexiglas
Another UV-transmitting
plexiglas type (GS-218)
also exist
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Plexiglas Transmission Curve (from Franco)
1
0.1
Anti UV plexig.
UV transp. Plexig.
T30 quartz
T40 quartz
Cerenkov light
0.01
0
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Elastomer
~1mm thick cook1ie measured in Cagliari
(absolute normalization could be wrong)
Very good transparency properties
in the 300-400nm range
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Optical grease
• “Saint-Gobain Crystals BC-630 is a clear, colorless,
silicone optical coupling compound which features
excellent light transmission and low evaporation and blend
at 25°C. It has a specific gravity of 1.06 and an Index of
Refraction of 1.465”
• I was unable to found transmission property – found a
>79% for 1cm thick layer (in the visible range): ???
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Other possibilities
• Use Richard R8900 PMTs to readout the other side of
the matrix with a different granularity (n.b.: the other
side could also be the larger side)
• No Plexiglas but only a thicker layer of optical
elastometer. Could be built in-situ by pouring the
elastometer on the matrix before polymerization –
feasibility to be tested
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Working plan
• Purchase RT-601 silicon rubber and measure optical properties of a
thick (10mm-20mm) layer
• Verify thick UV-transparent Plexiglas optical properties – but
difficult to find 20mm-30mm thick plates
• Verify optical grease transmission properties
• Purchase 16 (+ spares) 76mm x 76 mm UG11 filters
• Test XP3392 PMTs, measure photocathode non-uniformities
• Finalize readout options and design and build mechanics
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