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, December, 2005

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.

Earth’s Interior

New Earth model CMB may contain 40% of Earth’s K,Th and U

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.

Seismic Tomography

The Earth AntineutRino TomograpHy programme aims at making a tomographic image of the radiogenic heat sources in the Earth’s 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!! EARTH Each telescope will contain 4ktonnes of detection material and will have a angular resolution of ~10° and consist of many modules Anticipated spatial resolution dimension is ~3°, corresponding to about 300km for the centre of the Earth; 150km at the CMB.

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 (12˚N; 69˚W) with a 4kton detector, with an efficiency of 0.5 and including flavour change and how much false events can we tolerate?

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

Dimensions Each EARTH telescope is designed to have 4kton of scintillator: three times the mass of KamLAND. With 4cm 2 diameter, 1m long detectors, 10 million detector units are required! Ten telescopes comprise a mass of 40kton: twice Superkamiokande

Antineutrinos are detected by capture on protons, leading to positrons (energy info) and neutrons (direction info). Neutrons are detected indirectly but by γ-rays (H or Gd) or by α-particles ( 10 B or 7 Li). Range of γ-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. Detector design p n e + p n e e + PMT e p n e + p n e e + PMT e

B-Loading α-particles are stopped instantaneous and hence preserve directionality. High capture cross section reduces neutron scattering (and direction information loss) before capture. 10 B allows a higher loading factor. 5% 10 B No B

Neutron distribution 2 MeV4 MeV10 MeV

Principle and first results p n e + p n e e + PMT e p n e + p n e e + PMT e

Axial/Radial Eff. Ratio (Neutrons only)

Double Pulse Events t(ns) a b gamma + phototube after-pulse (a) n-p scatter + 10 B(n, α) (b)

Delayed coincidences

NE213 Scintilator (no B) : Am Be Source Pulse Height Pulse Shape Neutrons Gammas Pulse Shape Discrimination

Background reduction  Delayed coincidence (~10 6 ); Position control (~10 2 ); Pulse shape ( ~ ); Constant α-pulse (~ ); (Anti-)coincidence (~ ); Expected range:

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 cm 2 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.

… remember Pauli

Activity overview (1) EARTH-Detector Koeberg- tests New materials Read- out Electronics Housing Proof of Principle

Scintillator Materials forFast Neutron Detection 6 Li, 10 B loaded liquid scintillators BC501A, BC523, BC523A, NE213, NE320 good  /n separation strong quenching of capture signals chemical critical, complex handling 6 Li, 10 B 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

Scintillator Materials Proposed 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-off’s simplified handling; directional sensitive fast neutron detection & tracking cost efficient.

Photonics Scintillator Readout Readout exclusively by photomultipliers Characteristics depending on approach, cross features: amplifications exceed 10 6 for HV’s exceeding kV rise-times of order ns quantum effeciencies of order 20 %

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

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.

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-off’s: integrated readout and data processing electronics for scintillator based detectors with high flexibility and Self-sustained functionality

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.