Towards Earth Antineutrino Tomography

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• Towards Earth Antineutrino Tomography
• (EARTH)

R.J. de Meijer, F.D. Smit, F.D. Brooks, R.W.
Fearick, H.J. Wörtche (EARTH Collaboration)
Neutrino Geophysics Conference, Honolulu , 14-16
December, 2005
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How does the Earth work?

• Surface phenomena (e.g. magnetism and heat flow)
  are caused by processes deep in the Earth motored
  by heat transport.

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Earths Interior
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New Earth model
CMB may contain 40 of Earths K,Th and U
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Motivation

• The CMB is a very dynamic part of the Earth. It
  is a thin (200km thick) interface between the
  core and the mantle
• Due to subduction of crust and oceanic magma the
  CMB may contain 40 of the Earth radionuclides
  and hence radiogenic heat sources.
• Mapping of these heat sources therefore requires
  high resolution (3) antineutrino tomography.

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Seismic Tomography
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EARTH
The Earth AntineutRino TomograpHy programme aims
at making a tomographic image of the radiogenic
heat sources in the Earths interior by a system
of ten geoneutrino telescopes with a combined
angular resolution of 3. Geoneutrinos are (at
present) the only tool to probe these sources!!
Anticipated spatial resolution dimension is 3,
corresponding to about 300km for the centre of
the Earth 150km at the CMB.
Each telescope will contain 4ktonnes of detection
material and will have a angular resolution of
10 and consist of many modules
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Sensitivity

• Assuming 20TW homogeneously produced in the
  mantle and 5TW as a localised source at the core
  boundary at 30 S and 69W.
• Both sources have radionuclide ratios according
  to BSE.
• What count rates will we observe at Curaçao
  (12N 69W) with a 4kton detector, with an
  efficiency of 0.5 and including flavour change
  and how much false events can we tolerate?

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Sensitivity and Background

• 160/year from homogeneous (scaled from LENA
  calculation)
• 80/year from the localised source.
• 500/year from the crust.
• Two real events per day.

Expected false event according to KamLAND
1kHz/ktonnes. For TeleLENS 100 events/year
requires a reduction factor of 1010.
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Dimensions

• Each EARTH telescope is designed to have 4kton of
  scintillator three times the mass of KamLAND.
• With 4cm2 diameter, 1m long detectors, 10 million
  detector units are required!
• Ten telescopes comprise a mass of 40kton twice
  Superkamiokande

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Detector design

• Antineutrinos are detected by capture on protons,
  leading to positrons (energy info) and neutrons
  (direction info).
• Neutrons are detected indirectly but by ?-rays (H
  or Gd) or by a-particles (10B or 7Li).
• Range of ?-rays is much larger than of neutrons
  (few cm) therefore loss of direction information
  is unavoidable.
• Direction sensitive detection is only feasible
  with small diameter detectors that preserve
  direction information and are incorporated in a
  modular system of large mass.

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B-Loading

• a-particles are stopped instantaneous and hence
  preserve directionality. High capture cross
  section reduces neutron scattering (and direction
  information loss) before capture.
• 10B allows a higher loading factor.

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Neutron distribution
2 MeV
4 MeV
10 MeV
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Principle and first results
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Axial/Radial Eff. Ratio
(Neutrons only)
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Double Pulse Events
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Delayed coincidences
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Pulse Shape Discrimination
NE213 Scintilator (no B) Am Be Source
Pulse Shape
Neutrons
Gammas
Pulse Height
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Background reduction

• Delayed coincidence (106)
• Position control (102)
• Pulse shape (101-2)
• Constant a-pulse (101-2)
• (Anti-)coincidence (102-3)

Expected range1011-1015
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Conclusions

• Various geophysics models exist for the engine
  of the Earth, especially for the CMB.
• Antineutrinos provides novel information, but
  this tool has not yet been exploited.
• To exploit this tool, direction sensitive
  detection of antineutrinos is imperative.
• Presently this only seems feasible by large
  volume, modular detector systems.
• Simulations indicate detector diameters of a few
  cm2 diameter.
• EARTH is an ambitious, long-term programme,
  focused on 3D tomographic mapping of radiogenic
  heat sources with a combined angular resolution
  of 3, dictated by the CMB.
• Initial detector development indicates the
  feasibility, but not straightforwardly.

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remember Pauli
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Activity overview (1)
EARTH-Detector
Electronics
New materials
Read-out
Koeberg-tests
Housing
Proof of Principle
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Scintillator Materials forFast Neutron Detection

• 6Li, 10B loaded liquid scintillators
• BC501A, BC523, BC523A, NE213, NE320
• good ?/n separation
• strong quenching of capture signals
• chemical critical, complex handling
• 6Li, 10B loaded plastic scintillator
• BC414, BC45, plastic fibers
• no sufficient ?/n separation
• quenching of capture
• simplified handling
• Plastic scintillators (no moderation capture)
• BC418, BC422, (silicon chemistry)
• problems ?/n separation
• cost effective

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Scintillator MaterialsProposed Developments

• Focus on plastic scintillators, two development
  lines
• reduce quenching for loaded (slow) scintillators
• i.e. promote energy levels in triplet states
• investigate options by (extremely) fast
  scintillators
• to detect scintillation from single knock-on
  protons
• (neutron tracking)
• Polymer chemistry ?
• Potential features for spin-offs
• simplified handling
• directional sensitive fast neutron detection
  tracking
• cost efficient.

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Photonics Scintillator Readout

• Readout exclusively by photomultipliers
• Characteristics depending on approach,
• cross features
• amplifications exceed 106
• for HVs exceeding 1.3 - 1.5 kV
• rise-times of order 1 - 2 ns
• quantum effeciencies of order 20

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Photonics Requests

• Characteristics matching photo multiplier
  features
• improved energy efficiency
• possibly compact
• possibly robust
• channel-plate technology ?

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Readout Electronics

• NIM, CAMAC, VME based electronics
• (direct) current signals preamplified signals
• for capture gated measurements
• two analog branches with low/high
  amplification
• digital signal analysis by digital scopes or
• dedicated integrated electronics
• (8-bit, up to 500 MS/s)
• signal shape charge content, no timing
• variety of digital algorithms.

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Readout Electronics Proposed Development

• integrated analog digital electronics
• parallel signal branches with different
  characteristics
• increased dynamics and sensitivity
• signal timing handled in analog section
  alternatively
• implementation of 12-bit sampling with 200 MS/s
• signal analysis in the frequency domain
• Potential features for spin-offs
• integrated readout and data processing
  electronics
• for scintillator based detectors with high
  flexibility and
• Self-sustained functionality

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Milestones for first Go/Nogo

• Exploratory simulations and experiments with
  available electronics. (completed at iThemba)
• Comparision of B-loaded plastic scintillators
  with iThemba results.
• Building a 200 litre detector module and test it
  at Koeberg.
• Design a chip for the electronics.