Geoneutrinos

1
Geoneutrinos

• Nikolai Tolich
• University of Washington

2
Introduction

• Total measured heat flow at the surface of the
  earth is 44?1TW (87mW/m2).
• Based on chondritic meteorite measurements the U,
  Th, and K concentrations in the Bulk Silicate
  Earth (BSE) results in heat production of 8TW,
  8TW, and 3TW, respectively, totaling 19TW.
• This radiogenic heat is believed to be the most
  significant heat source in the earth and is
  therefore an important component in understand
  mantle convection.
• Electron anti-neutrinos from U, Th, and K decay
  allow us to directly measure the concentration of
  these nuclei.

3
Geoneutrino signal
Neutron inverse beta decay threshold
4
U and Th in the Earth

• U and Th are thought to be absent from the core
  and present in the mantle and crust.
• U and Th concentrations are highest in the
  continental crust.
• Th/U ratio of 3.9 is known better than the
  absolute concentrations.

5
Georeactor

• It has been hypothesized that a blob of uranium
  is located at the center of the Earth.
• This could then form a natural nuclear reactor
  produce up to 6TW of heat powering the Earths
  dynamo.
• This could explain the observed anomaly in the
  3He/4He ratio.
• The only way to test this hypothesis directly is
  to observe the neutrinos produced by this reactor.

6
Results from KamLAND
Data from March, 2002 to October, 2004.
Nature 436, 499-503 (28 July 2005)
Expected total
Expected total background 127 13
Candidate data 152 events
Expected (?,n) 42 11
Expected reactor 80.4 7.2
Measured Accidental 2.38 0.01
Expected U 14.8 0.7
Expected Th 3.9 0.2
7
How many geoneutrinos?
Expected ratio from chondritic meteorites
Best fit 3 U geoneutrinos 18 Th geoneutrinos
Expected result from reference Earth model
Central value 28
8
Geoneutrino flux
Homestake geoneutrino flux 50 larger than at
KamLAND 54 per 1032 target protons per
year
50 kton
1 kton
1 kton
0.3 kton
10 kton

• www.fe.infn.it/fiorenti

9
Future experiments

• Needs to be located away from nuclear reactors
  and have a significant overburden.
• Measurement located on oceanic crust can measure
  U and Th content in the mantle. Important for
  mantle convection.
• Measurement located on continental crust can
  measure U and Th content in the crust.
• Important to perform multiple measurements to
  test variation.

10
Reactor Background
Homestake

• Distances to the closest reactors are similar to
  the distance between the Korean reactors and
  KamLAND
• The Korean reactors contribute 2 of KamLANDs
  reactor background

11
Expected signal
U geoneutrinos
Th geoneutrinos
6TW georeactor
Commercial reactors
12
Detector Requirements

• Expected geoneutrino flux has
• 9 error due to neutrino oscillations
• 7 error due to global crustal variation
• 3 error due to local crustal variation (at
  KamLAND)
• Should attempt to make a 10 measurement of the
  geoneutrino flux, this requires exposure of
  2.3?1032 proton years.
• 2-3 year measurement with KamLAND sized
  detector.
• To observe a 6TW reactor at the Earths core at 3?
  would require exposure of 0.8?1032 proton years

13
How Can We Improve

• Scintillator technology studying better
  scintillators and additives, doping for neutron
  detection and directional sensing.
• Water doping studying Gd and other additives,
  and possible scintillators.
• Detector studies depth and backgrounds,
  shielding requirements,
• Photodetectors increased collection, response,
  imaging possibilities,....
• Studies for 40K neutrino detection