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1) Production of secondary electrons
Widening of the
fluorescence
volume : 2 mm
Negligible impacton electron length
Atm. pressure : 99 % of electronshave E ≤ 5 keV
2) Diffusion on the lead
Influence on the electron spectrumsimulated :
3) Retro-diffusion on the scintillator
Only 10-9 effect :negligible
Gas circulation
Switch
Principle of the DAQ
Calibration : how do the PMTs work ?
electron-PMT :μ ~ 2 000 pe
integral & spectro PMT :μ ~ 0.02 pe
• P(0) = 0• Efficiency ~1
• P(0) = 0.98, P(1) ~ 0.02• single photoelectron mode
!
)exp()(
NNP
N Poisson law :
Pure single pe in PMTs
Analog signal
ADC channel
Photonis XP2020Q« 0 » / « 1 » ~ 50
Pure single pe in PMTs
ADC channel
Analog signal
Pure single pe in PMTs
Detectioninefficiency
integral-PMT : 3.76 %spectro-PMT : 3.85%
Analog signal
ADC channel
Efficiency measurement process
1. X-Y mapping2. Absolute efficiency in (x0, y0)
3. Normalization of the map
New method in 3 stepsuncertainty < 2 %CNRS patent application
1) Mapping
1) Mapping
integral-PMT spectro-PMT
1) Mapping
spectro-PMT
2) Absolute efficiencyAbsolute comparison with something known calibrated source or photodetector
spatial distribution of light~10 % accuracyNO
gain ~1when PMT have gain ~107
2) Absolute efficiency
Integrating spheres AND diaphragms
2) Absolute efficiency
Integrating Sphere
NIST photodiode
2) Absolute efficiency
everything stays thesame but the PMT
2 Spheres+
3 diaphragms
Flux reduction2.42 × 106
3) Normalization of the map
18.5 %1.7 % uncertainty
Effi
cie
ncy
(%)
integral-PMT
Result for integral-PMT
Absolute efficiency measured (377 nm)Integral-PMT response adjusted to measurementUlrich’s fluorescence spectrumAbsolute efficiency of fluorescence detection
0.178 ± 0.004Uncertainty : 2.2 %
wavelength (nm)
Effi
cie
ncy
Integral measurementQuantity Uncertainty
Detection inefficiency, scaler dead time
negligible
geometry (Le and solid angles) 1.5 %
Transmission of the quartz window
1 %
Efficiency of the PMT 2.2 %
TDC 4 %
Statistics 0.2 %
TOTAL 4.91 %
4.23 ± 0.22 photons / m
After normalizations (P, T, E) : 5 %
G. Lefeuvre et al, to be published (NIM A)
Spectral measurement
3.9 ± 0.8 ph/m
(Ulrich, Airlight workshop, 2003)
wavelength (nm)
yie
ld (
ph
oto
ns /
m)
Spectral measurement
Our results
Ulrich’s spectrum,convoluted with our 3 nm resolution
wavelength (nm)
yie
ld (
ph
oto
ns /
m
)
Conclusion
Bahcall & Waxman hep-ph/0206217 v5
Fly’s Eye
Extra-Galactic + GalacticGalacticNo GZKHiResFly’EyesYakutskAGASA
10201019
E (eV)
1018
J x E
2,6
1 (
eV
1,6
1/m
2 . s
r . s)
Still much to measure...
• Pressure & Temperature dependences
• Impurities
• Spectrometer + CCD + light intensifier
• Reduction of the TDC uncertaintyFlash-ADC
Thank you