Transcript Sensitivity of SK to Reactor Neutrinos

A Water-Based Neutron and AntiNeutrino Detector
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Neutron Detection – Fast Neutrons
“Fast” neutrons are those with kinetic energy above
a few 10’s of keV
m
energetic nuclear decays
fission
fusion
high energy interactions on nuclei
nucleus
N
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fast neutron
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Fast Neutron Detection
N
P
recoil proton
g
capture
gamma
N
thermalization
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nucleus
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Anti-Neutrinos
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Nuclear Reactors
Supernovae
Beta decay of neutron-rich nuclei
accelerator beams
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Anti-Neutrino Detection
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n
e+
Eion
e+
p
g
511 keV
e-
p
g
n
511 keV
g
n
~200 ms
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p
2.2 MeV
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Liquid Scintillator
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Organic liquid scintillator sensitive to both
recoil protons, capture gammas, and positron
annihilation – that’s good. Used since 1950’s.
These liquids which are often toxic and many
common ones are flammable - that’s bad.
Example is pseudocumine.
Disposal and environmental concerns always a
problem, even for less flammable and toxic
compounds
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Liquid Scintillator
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Expensive for detectors in the kton or larger range.
Most scintillators have capture time of ~200 ms – this is
often too long due to backgrounds
2.2 MeV gamma is near 208-Tl 2.6 MeV gamma – from
natural thorium chain
solution – dope with high-cross section, high capture
energy additive. Gadolinium is most popular due to
extremely high cross-section for capture and 8 MeV
gamma cascade.
metal doping makes most scintillators chemically
unstable and/or very sensitive to environmental
conditions.
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Water Cherenkov Detectors
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charged particles moving
faster than speed c/1.33
give off broadband
“Cherenkov” radiation
water is cheap, nontoxic, non-flammable
(except in Cleveland)
2.2 MeV capture
gammas Compton scatter
off atomic electrons – too
low energy to see!
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Super-Kamiokande
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Water Cherenkov
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tracking detectors
not sensitive to fast
neutrons below few
GeV
good for thermalizing
fast neutrons – just
can’t see them when
they capture
Why Not Dope With
Gd Also?
Why would we like to see neutrons?
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Galactic Supernovae
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SN1987A
Massive stars end their life by
collapse into a neutron
star or black hole. In this process they give off 99% of
the collapse energy (which is huge) in neutrinos of all
types.
The spectrum and time evolution of the neutrinos is of
great scientific interest as it is the only way to directly
observe this process
Cross-section for antielectron-neutrinos is much higher
than others by factor of 20-30. Only they give off
neutrons. If these can be removed we can pull out the
specta of the other types, which come from deeper
inside the baby neutron star.
Understanding these violent explosions gives a direct
handle on how heavy elements are synthesized.
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Relic Supernovae
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It is expected that
there is a
cosmological
background of
relic SN neutrinos
Sensitive to
history of star
formation in
universe
Major background
limiting SK do not
have coincident
neutrons
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Super-K
Theories
of stellar
formation
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Reactor Safeguards
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LLNL and SNL have a joint project to develop
antineutrino detectors for use in measuring
plutonium content in running reactors in situ
A prototype detector is now running at San
Onofre Nuclear Generating Station (SONGS)
These detectors must be located right outside
the reactor containment vessel
Concern with safety
Concern with stability of detector sensitivity
over many years. Also very temperature
sensitive.
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Other Possibilities
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Potential for very large neutron-sensitive
neutrino detectors
could detect reactors from long distances
KamLAND can just see Kashiwazaki power
plant 180 km away with 0.5 ktons. We
could go much larger.
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Who Are We?
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R.Svoboda: many years experience in neutrino
detection (SN1987A, Solar Neutrinos, Reactor
Neutrinos). Former Navy Nuclear Power Officer.
Hank Sobel: professor at UCI with similar
experience
Mark Vagins: Researcher at UCI, published
original concept
Steven Dazeley: visiting postdoc from LSU
William Coleman: grad. student visitor that this
proposal would help support for a summer visit.
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What Do We Want to Do?
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We have done some preliminary work on
evaluating this concept via an Office of
Science ADR Grant. Final report submitted
last month.
No “Show Stoppers”, but some problems
uncovered
There are still potential “Show Stoppers”
we would like to test for by making a
small test detector here at LLNL
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ADR Study
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Will adding GdCl3 to water cause
corrosion problems for detector
components?
Will Gd-loaded water still be transparent
at the 100-m scale?
How can Gd-loaded water be cleaned?
Empirically, this continuous cleaning is
required in large detectors, but the
reasons are not understood
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Initial Corrosion Test
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1 year soak
test in high
GdCl3
concentration
(~30 years)
50 materials,
most are OK
some
problems
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Tank Steel
Weld points
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What is Happening?
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Water has dissolved oxygen – this is likely
the culprit
need to do test in sealed, de-oxygenated
water tank
also need to test full Photomultiplier
Assembly (basic component of all Water
Cherenov Detectors) due to worries about
galvanic corrosion
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Cleaning Concepts
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Working with a local California small business
(South Coast Water) UCI has worked out on test
bench a concept for cleaning water with GdCl3
Not possible to determine effectiveness with
typical small (10 cm) photospectrometer – need
larger test bed
Also – can we determine why we have to clean
the water at all?
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Test Tank at LLNL
3.5 m
photodetector
UV laser
Cleaning system
Test bed
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Goals
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Measure water transparency over 3.5m
(maybe 7m) baseline as a function of
GdCl3 concentration up to 1.0%
Test for corrosion after 6 mos exposure in
de-oxygenated water at 1% (~5 years)
See if water cleaning effective, try out
new ideas
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Instrument for
measuring the
transparency of GdCl3
doped water at LLNL
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Tuneable dye laser
will be injected and
reflected back. Gd
concentration is
Variable.
A “micro-SuperK”
is also being built
to test anti-corrosion
schemes.
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