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Towards sealed GEM-based flame detectors
G. De Cataldo1,2, G. Volpe1,2, V.Peskov1,2,3
1CERN
2Bari University
3Inst for Chem.Phys., RAS
In fire safety it is very important to record appearance of a flame
on its early stage
EU standard:The highest sensitivityClass 1: ~30x30x30cm3 flame on ~20m in 20sec
There are various commercial flame detectors on the market
An example of the Class-1 detector
It is a digital device, it cannot distinguish between a single photon and a spark
Hamamatsu UVtronis used in some sensors produced by other companies
UV light from flamesCreate photoelectronsfrom the metal cathodeand they trigger a glow discharge. The latter isquenched by an externalresistor
Ours idea-CsI coating to enhance the QE
.. the spin of ALICE and COMPASSapproach for Cherenkov photons detection
Laboratory prototype
First sealed detector (industrial prototype)
The detector showed stable operation for 12 years, The sensitivity was 100 times higher than Hamamatsu(the QE loss was due to the exposure to air). The detector was demonstrated in operation at CERN open days
The history of manufacturing:
Miranda evaporated theCsI photocathode at CERN ona inner surface of the tube.
It was put then to a plastic bag and sent to Oxford Instr., wherethe detector was filled with the gas and sealed
CsI was exposed to air for one week
Immediate gain in sensitivity 1000 times
It is excellent for indoor applications, however in direct sunlight ”noise” pulses appear
Alternative approach
-photosensitive vapour. In this case the sensitivity to direct sunlight is practically zero
Ethylferrocene
TMAE
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Efficiency vs. temperature
TMAE
CsI
EF
Temperature (C)
Mea
n c
ou
nti
ng
rate
(H
z)
Detectors with photosensitive gases are efficient at room and elevated temperatures
Signals from invisible sparks
All these detectors were exploitedin proportional mode,so they can distinguish betweensingle photons and sparks
This why we are consideringnow a GEM-based approach
It offers several advantages, for example:
Compact flat-panel geometry
Large area-herefore, higher sensitivity
Single wire detectors: in the past the cost of sealed X-ray counter was low, around 100 Euro,(Hamamatsu is around 50 Euro), including HV supply and electronics.
However, nowadays they are not produced anymore (solid state detectors took over)To start their production is not easy and require a considerable investment
We started of course, with flushed detectors (this part of work was done in collaboration with A. Di Mauro and P. Martinenego and was supported by the CERN Technology Transfer office )
In this work we try to learn the difficulties in this approach
Examples of optimizations made in flush mode:
choice grift region geometry
Choice of THGEM and RETGEM geometries: t=0.8, d=0.6, s=1,h=0.1mmand
t=0.4, d=0.5, s=0.9,h=0.1mm
Example of some results:efficiency vs radius
Conclusion : there ae some losses, but the construction is simpler
Break due to windows geometry
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Chart Title
Series1 Series2 Series3
In principle, one can gain sensitivity further with the window size increase
From:Di Mauro, P. Martinego, V. PeskovReport to CERNTech. Transfer office
Comparison with Hamamatsu
Sealed detectors
In the case of CsI thedrift was 10 mmIn the case of photosensitive gases it was 80 mm
Teflon pieces were changed to ceramics
In first experiments we used heating tapes wrapped in Al foil 150-180, pumped for7-10 days, the vacuum was better 10-6 Torr
Later a more advanced, more convenient, setup was developed
Heating cabinet(in collaboration with A. Di Mauro)
Vacuum, 1 cm
CsI, 1 cm, Ne+5%CH4
TMAE, 80mm Ne+5%CH4
EF, 80mm, Ne+5%CH4
Ionization chamber measurements
Cu
rren
t (n
A)
Voltage (V)
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Ne as a cleanness probeCurrent measurements
Double THGEMt=0.4, d=0.5, s=0.9,h=0.1mm
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10
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Effe
ctiv
e ga
in
Voltage (V)
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No
rmal
ized
gai
n a
t 3
25
VTime (days)
In TMAE THGEMs become noisy even if we introduce its vapours
below the saturation value
Original idea expressed in CERN PatentApplication.Authors:R. Oliveira, Di Mauro, P. Breule, V. Peskov
Oxide Cu (0.2 mm thick)
Ceramic
First prototypes were developed byelectronic Workshop in Ecole des Mine,
St. Etienne, France
Latest prototype-Ragent-(a photonic branch of theInst. for Chem. Phys. RAS)
Later a similar detector was developed and successfully tested by the Inst of Nucl. Phys. RAS
0.4 mm
Hols 0.4mm
Special THGEM design for TMAE(to avoid leakage current)
Gain and stability in other gases
The method:Stabilization at low gain and step by step increase
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TMAE, THGEM
EF
Effe
ctiv
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in
Voltage (V)
CsI
TMAE, Wall-less
Time (days)
Cu
rren
t (n
A)
TMAE, Wall-less
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TMAE, THGEM
CsI
EF
Note: adding a sun-blocking filter reduce the efficiency of the CsI THGEM four times
Comparison sealed GEM-based detectors with Hamamatsu
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Distance (m)
Co
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g ra
te (
Hz)
In contrast to Hamamatsu GEM-based detectors are capable to detect sparks
Stability with temperature
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Temperature (C)
Mea
n c
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nti
ng
rate
(H
z)
However, the necessity to use filters create some problems,e.g:
size,price
The most attractive are GEM-based detectors with CsI photocathodes:
they operate stably in wide temperature interval
Pilot studies progress:CsI surface coating as an incorporated filter
(in collaboration with Di Mauro, P. Martinengo and P. Breul)
CERN Techn.Transfer office filed a patent application
Conclusions
• GEM approach offers the possibility to manufacture compact ,but large area, high sensitivity flame detectors
• CsI detectors the most attractive , but require filters for outdoor applications
This increase the cost
• GEMs with photosensive vapours practically are not sensitive to the direct Sunlight, but have high QE only at temperatures more than 15C. So they are good either for indoor application or for outdoor applications in warm countries (Greece, Israel, Italy, California etc)
• It will be attractive to coat CsI with a incorporated filter
Our nears effort will be focused on optimization of these layers
• We are also working on imaging version of GEM-based flame detectors
Probably we will be able to present some results on one of the RD51 meetings
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