Requirement for photon-detectors at directional measurement ...
Research Center for Neutrino Science ,Tohoku University
KamLAND Kamioka Liquid Scintillator Anti-Neutrino Dete
KamLAND, constructed at 1000m underground from top of the mountain,has a balloon with a 6.5m radius, filled with 1 kton of Liquid Scintillator ( LS ).
1879 PMTs( 17or20 inch ) are set around the balloon detect scintillation to decide vertex from time difference of signal.
KamLANDs targets : reactor e , geo e , solar e
How to detect?
PMTs detect anti-neutorinos via the inverse -decay reaction in LS. ( Figure1 )
PMTs distinguish some signals of anti-neutrino from backgrounds with Coincidence.
Li-loaded LS is proper.
Li has large neutron-capture cross section, besides generates not -ray but -ray.
-ray doesnt diffuse but stops at once. ( Figure3 )
So we can get directional data. ( Figure4 )
And we can use also coincidence, because Li-loaded LS generates prompt and
at 200s interval
Neutron angle depends on incoming
neutrino direction in low energy.
20 MeV MeV
10 MeV MeV
5 MeV MeV
3 MeV MeV
n<35 2 MeV
We want to know which direction anti-neutrinos
come from better than now.
If we can get directional data of reactor-neutrino,
it will be neutrino-oscillation with individual baseline.
If we can get directional data of geo-neutrino,
we will observe directly the interior of the earth.
Vertex reconstruction using time of flight with PMT
We want directional sensitive photo detectors with gain instead of PMT.
Imaging ( lens + photo detector )
B loaded LS (1.0%)
Li loaded LS (0.15%)
Li loaded LS (1.5%)
at 5s interval
Figure2 : energy dependence
directional data is lost for the neutrons thermal
and -ray diffusion( ~40cm )
the position resolution of PMTs is not too high ( ~10cm at object )
Now we are researching and testing organic solvent for Li. example : EDTA, crown
Figure4 : n event reconstructed point
Test of SCITIC with LS
SCITIC SCIntillation Tracking Image Camera
First aim : imaging cosmic-ray with 1L LS and CCD+I.I.
Plastic Scintillators ( PS ) detect going through LS.
PMT detect it, and open CCDs gate.
CCD records the afterglow at fluorescence plane of
image intensifier ( I.I. ).
CCD send the image to PC.
Requirement for photo detector
Sequent data acquisition at 1s or shorter interval
small data size at one acquisition
Position resolution at object 1cm or better
good time resolution
Position resolution etc. is good compared to PMT.
Active area of MPPC is too small
Can active area of MPPC be larger?
MPPC generates several hundred kHz dark noise at room temperature.
I think dark noise will be reduced by 1/1000 at 200K. So I will test it soon.
The output pulses from the APD pixels pile up with each other,
because all APD pixels are connected to 1 readout channel.
Pixel-size resolution is lost simply because of 1 readout.
Feature of I.I. ( courtesy of KEK )
Active area : 100mm
Gain : ~106
Q.E. : 12% @ 422 nm
Afterglow : a few s ( a few ns pulse incidence )
KamLAND LS + BisMSB
Feature of CCD
number of pixels : 310*5
type : interline
readout rate : 82 frames/s
CCD imaged -track ! ( Figure6 )
Figure6 : track
Next, we want to observe 2-signals from Bi-Po ( Figure7 )
like anti-neutrino signal.
Now, CCD is adapted!
This CCD will be adapted for recording 2-images
at dozens s intervals by HPK. ( Figure8 )
active area efficiency
Feature of PSD is that it is connected to 4 readout channels
to detect the center of gravity of multiple hits.
It means directional data isnt lost.
So data size is small.
And PSD must be combined with some amplifier
because PSD has no gain.
Go to Test of SCITIC with LS!
Figure7 : Bi Po reaction
If MPPC has 4 readout channel, MPPC will be the detector getting t
he center of gravity of multiple hits and with gain !?
I will investigate possibility using PSD+MPPC in KamLAND.
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