A Water-Based Neutron and Anti-Neutrino Detector

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A Water-Based Neutron and Anti-Neutrino Detector
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Neutron Detection Fast Neutrons
Fast neutrons are those with kinetic energy
above a few 10s of keV - energetic
nuclear decays - fission - fusion
- high energy interactions on nuclei
nucleus
m
fast neutron
N
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Fast Neutron Detection
N
recoil proton
P
g
capture gamma
N
thermalization
nucleus
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Anti-Neutrinos

• Nuclear Reactors
• Supernovae
• Beta decay of neutron-rich nuclei
• accelerator beams

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Anti-Neutrino Detection
g
_
511 keV
Eion
n
e
e
e-
Prompt
p
p
g
511 keV
n

g
n
2.2 MeV
p
200 ms
Delayed
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Liquid Scintillator

• Organic liquid scintillator sensitive to both
  recoil protons, capture gammas, and positron
  annihilation thats good. Used since 1950s.
• These liquids which are often toxic and many
  common ones are flammable - thats bad. Example
  is pseudocumine.
• Disposal and environmental concerns always a
  problem, even for less flammable and toxic
  compounds

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Liquid Scintillator

• 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

• charged particles moving faster than speed
  c/1.33 give off broadband Cherenkov radiation
• water is cheap, non-toxic, non-flammable (except
  in Cleveland)
• 2.2 MeV capture gammas Compton scatter off
  atomic electrons too low energy to see!

Super-Kamiokande
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Water Cherenkov

• tracking detectors
• not sensitive to fast neutrons below few GeV
• good for thermalizing fast neutrons just cant
  see them when they capture
• Why Not Dope With Gd Also?

Why would we like to see neutrons?
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Galactic Supernovae
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
Super-K

• 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

Theories of stellar formation
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Reactor Safeguards

• 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

• 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?

• 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?

• 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

• 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

• 1 year soak test in high GdCl3 concentration
  (30 years)
• 50 materials, most are OK
• some problems

Tank Steel
Weld points
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What is Happening?

• 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

• 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
photodetector
3.5 m
UV laser
Cleaning system Test bed
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Goals

• 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.