r.svoboda, u.c. davis /llnl this work was performed under the auspices of the u.s. department of...
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R.Svoboda, U.C. Davis /LLNL
This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-
Eng-48.
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Improved neutron detection antineutrino tagging (Super-K, SONGS) active neutron shield (LUX) national security (LLNL Portal Monitoring Project)
Improved light collection antineutrino spectral measurements reduce required PMT coverage
Unwanted additives what makes good water go bad?
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• Viable: • GdCl3 relatively inexpensive• Small concentrations of Gd in water improve neutron
capture significantly• Gd capture signature (8 MeV γ- cascade) easily
detectable
• Workable?• What is GdCl3 effect on transparency?• What are the physical effects of GdCl3 caused by
extended exposure to SK detector components?
Optimal?
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Injection andMeasurement
Optics
Storagetank
PMT tank DeionizingFiltering
Sterilization
Alignmentmirror
Nitrogen purge and relief valve
Nitrogen purge
Recirculationpump
drain mixing tankand pump
Light transmission arm
Baffled joints
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Light transmission
arm
Acrylicwindow
reflectedbeamintegrator primary
beamintegrator
beam splitter
PMT
PMT lightintegrator
Lawrence Livermore National Laboratory
9.54 meters
Not shown: collamators, baffles, filters
LLNL Test Set-Up
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337 N2 Laser
w/ dye attachement
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primary
reflected
ns
V
Typical Waveform for 337nm
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By putting filters of known transmittance (<1% uncertainty) into theinjected primary beam, the system is seen to be linear towithin 2% over a 40% variation in transmission
The system is also stable to variations in PMT gain to better than 1%
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0.650
0.670
0.690
0.710
0.730
0.750
0.770
0.790
0.0 50.0 100.0 150.0 200.0 250.0 300.0 350.0 400.0
Hrs
R/P
Sto
ppe
d re
circ
+/- 2%
pure water fall offin transparency overtime (337 nm)
0.9 %/day
Preliminary
Stability…
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0.180
0.230
0.280
0.330
0.380
0.430
0.480
0.530
0.580
0.630
0.0 50.0 100.0 150.0 200.0
Hrs
R/P
Ad
de
d 0
.2%
Gd
Cl3
Inje
cte
d m
ixin
g t
an
kW
ate
r a
nd
filt
ere
d
Inje
cte
d m
ixin
g t
an
kW
ate
r a
nd
filt
ere
d
Removed GdCl3
Test of GdCl3Addition at 337 nm
~13%/day
Preliminary
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Ad
de
d 0
.2%
Gd
Cl3
Injected Pure Water @ 8 MOhm
Test of GdCl3Addition at 400 nm
Preliminary
Injected Pure Water @13 MOhm
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Ad
de
d 0
.2%
Gd
Cl3
Injected Pure Water@ 8 MOhm
Injected Pure Water @ 13 MOhm
Test of GdCl3Addition at 420 nm
Preliminary
~8.5% /day
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ResultsPure water in stainless steel slowly looses
transparency at 337, 400 and 420 nm. For 337nm measurements, the water was
deoxygenated via nitrogen bubbler to 0.9 ppm (typical air is 8-9 ppm) as measured by dissolved oxygen measurement.
For 400nm & 420nm measurements, initial dissolved oxygen was measured at .15 ppm.
Addition of GdCl3 makes the water transparency drop much faster (factor of 15).
Injection of water from polypro tank shows that water stored there suffered no/little degradation in transparency.
Loss of transparency directly from GdCl3 very small (consistent with 0 at all three wavelengths).
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Conclusion:
GdCl3 is not a suitable additive for detectors with steel walls. May be OK for other materials.
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Super-Kamiokande water must be continuouslyand cleaned – else transparency drops slowly
similar behavior seen in IMB (plastic walls)
and SNO (acrylic walls – but much slower degradation)
REDUCING THE REQUIREMENT FOR RECIRC WILLLOWER COST OF MEGATON SCALE DETETOR
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Test with FeCl3 10 ppm Fe+3 ion makes water look like ice
tea. Clearly very low levels can affect transparency
next week we will test 0.1 ppm slowly raise concentration to measure molar
attenuation coefficient test Ni, Cr metal ions for similar behavior
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Future Change steel pipe for acrylic one use polypro tank for materials testing of
HDPE and other potential plastic liners for LUX and future detectors
Investigate coatings for steel for cryostat treatment
monitor Water SONGS for stability (acrylic sides)
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lower tank (6 sides)- 3/8” thick UVT acrylic,-Gd-water fill -5 side external Tyvek wrap
8 ea. 8” PMTs (1 cm spacing in both directions)
Upper tank (5 sides)3/8” thick UVT acrylic4 sides external Tyvek wrapPure water fill to 10 cm
Water SONGS1 cm black Delryn lid
100 cm
50 cm
15 cm
0.2% wt. GdCl350 cm
- total external dimensions = 100 cm x 50 cm w x 80 cm ht
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The antineutrino interacts with a proton producing…
– A 0-7 MeV positron (+ annihilation gammas)
– A neutron which thermalizes, captures and creates a delayed 8 MeV gamma cascade
– mean time interval ~30 μsec ~ capture time of neutron
Both energy depositions and the time interval are measured
The time since the most recent muon is also measured
Antineutrino Detection
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_𝜈e + p = n + e+
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BackgroundAntineutrinos are not the only particles that produce our
coincident signalCosmic ray muons produce fast neutrons, which scatter
off protons and can then be captured on GdImportant to tag muons entering the detector
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