Download vlvnt2011_7

VLVnT11 Workshop – Erlangen, 12-14 October 2011
VSiPMT for underwater
neutrino telescopes
Daniele Vivolo
INFN – Section of Naples
Outline
Overview
Overview
Čerenkov light
muon
PMTs
To date, a crucial role in this kind of experiments has been
played by
(PMTs).
However they suffer of many
:
• fluctuations in the first dynode gain make single photon
counting
Moreover
thedifficult;
next generation of experiments will require further
• the linearity inis photon
stronglydetectors
related to the gain and decreases as
improvements
the latter increases;
New generation of photodetectors, based on inverse p–n junction:
• the transit time spreads over large fluctuations;
PINmechanical
photodiodes:
no gain;
•• the
structure
is complex and expensive;
•• sensitivity
avalanche
to photodiodes
magnetic fields;
(APD): gain of few hundreds;
•• the
need ofphotodiodes
voltage dividers
increases
failure (GMrisks,
avalanche
in linear
Geiger-mode
complexity
in the
experiments
APD, or SiPM):
gain of
105 – 106. designs and power
consumption.
Structure of SiPM/1
Very high electric field
(noise source of the device)
(useful
signal)
Structure of SiPM/2
Structure of SiPM/3
the output signal is the
of the Geiger mode
signals of microcells.
SiPM
(at present silicon wafer costs and the thermal dark current
limit the dimensions of the SiPM photo detector at few mm2)
Our Purpose
Hemispherical vacuum glass PMT standard envelope composed by:
• a
for
Such
a device acts both
photon-electron
asconversion
a
and as an
with
• an electric
field
that
5
6
gains of 10 - 10 , similar
accelerates and focuses
to all
the
dynode chain of a
the photoelectrons to a
classical
small photomultiplier
Preliminary work
•
•
•
.
In this work I will describe the most relevant results of the
first phase and I will present the results of our simulations.
Characterization/1
Characterization/2
Characterization/3
The charge corresponding to different numbers of fired pixels
shows well separated peaks.
Gain
b = (906 ± 9) 102 V-1
By changing the bias voltage we measured:
••• Moreover,
since:
by
the value
of slope
for the
electron
charge
the multiplying
difference
in
the
• the
charge
of the
signal
we get an estimation
capacitance:
amplitudes
of signalsofofjunction
2 corresponding to the initial
1 p.e., 3 - 2 p.e. and 4 - 3 p.e.
number of photoelectrons.
•weThe
estimated
of the quenching
is therefore:
estimated,
byvalue
extrapolating
from theresistor
gain line
the voltage
value corresponding to G=0,
Dynamic Range
The dynamic range is limited by the condition that:
The signal
when Nph≈ Nmc
If Nph x PDE << Nmc
the signal is fairly
Backscattering
• Backscattering coefficient
• Range in Si
• Total released energy
• Backscattering energy fraction
• Average energy loss in Si
The quartz window has an anti-reflective function:
Backscattering coefficient is
with quartz layer and
without it
Backscattering coefficient
Backscattering coefficient
Backscattering coefficient
E [keV]
Incidence angle [°]
Backscattering energy fraction
Backscattering energy fraction
Backscattering energy
fraction
E [keV]
Incidence angle [°]
Total released energy [keV]
Total released energy [keV]
Total released energy
E [keV]
Incidence angle [°]
Average energy loss in Si [MeV/cm]
Average energy loss in Si [MeV/cm]
Average energy loss in Si
E [keV]
Incidence angle [°]
Range in Si [mm]
Range in Si [mm]
Range in Si
E [keV]
Incidence angle [°]
Conclusions
50% at 75°
14.2% without anti-reflection
quartz window
68% at 75°
Conclusions