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Geo-Neutrinos : a new probe of Geo-Neutrinos : a new probe of

Earth’s interiorEarth’s interior What is the amount of U, Th and What is the amount of U, Th and 4040K in the K in the

Earth?Earth? Determine the radiogenic contribution to Determine the radiogenic contribution to

terrestrial heat flowterrestrial heat flow Get information about the origin of the Get information about the origin of the

Earth.Earth. Test a fundamental geochemical paradigm: Test a fundamental geochemical paradigm:

the Bulk Sylicate Earththe Bulk Sylicate Earth

(I’ll concentrate on U and Kamioka)(I’ll concentrate on U and Kamioka)

gianni fiorentini, ferrara univ. @ NOW-2004

**based on work with Carmignani, Lasserre, Lissia Mantovani Ricci Schoenert Vannucci

Neutrino flowNeutrino flow

Heat flowHeat flow

22

Geo-neutrinos: anti-neutrinos from the EarthGeo-neutrinos: anti-neutrinos from the Earth Uranium, Thorium and Potassium in the Earth release heat Uranium, Thorium and Potassium in the Earth release heat

together with anti-neutrinos, in a well fixed ratio: together with anti-neutrinos, in a well fixed ratio:

Earth emits (mainly) antineutrinos, Sun shines in neutrinos.Earth emits (mainly) antineutrinos, Sun shines in neutrinos. Geo-neutrinos from U and Th (Geo-neutrinos from U and Th (not not from K) are above treshold for inverse from K) are above treshold for inverse

on protonson protons Different components can be distinguished due to different energy Different components can be distinguished due to different energy

spectra: anti-spectra: anti- with highest energy are from Uranium with highest energy are from Uranium

MeVnep 8.1

33

Probes of the Probes of the Earth’s Earth’s interiorinterior

Deepest hole is Deepest hole is about 12 km.about 12 km.

The crust (and the The crust (and the upper mantle only) upper mantle only) are directly are directly accessible to accessible to geochemical geochemical analysis. analysis.

Seismology Seismology reconstructs density reconstructs density profile (not profile (not composition) composition) throughout all earth.throughout all earth.

crust

Upper mantle

•Geo-neutrinos can bring information about the chemical composition (U,Th and K) of the whole Earth.

44

Uranium in the Earth: Uranium in the Earth: observational data observational data on the cruston the crust

•Crust is the tiny envelope of the Earth, distinguished from the underlying mantle by a clear (Moho) seismic discontinuity.

•Continental and oceanic crust have different origin and U abundance.

•By combining data on Uranium abundances from selected samples with geological maps of Earth’s crust one concludes:

mmCC(U)=(0.3-0.4)10(U)=(0.3-0.4)101717kgkg

•Most of the uncertainty from the lower portion of the crust

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The amount of Uranium in the Earth: The amount of Uranium in the Earth: cosmo-chemical argumentscosmo-chemical arguments

• The material form which Earth formed is generally believed to have same composition as CI-chondrites.

•By taking into account losses and fractionation in the initial Earth one builds the “Bulk Silicate Earth” ((BSEBSE),), the standard geochemical paradigm which predicts:

m(U)=(0.7-0.9) 10m(U)=(0.7-0.9) 101717kgkg

•Remark: The BSE is grounded on solid geochemical + cosmochemical arguments, it provides a composition of the Earth in agreement with most observational data, however it lacks a direct observational test.

BSE

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Where is the rest of Uranium?Where is the rest of Uranium?

•According to BSE, crust contains about one half of the total Uranium amount

•Uranium is a lithophile elements, believed (by geochemists) to be absent from the core.

•So the remaining half should be in the mantle:

•A) according to geochemists, mainly in the lower part.

•B) geophysics, indicating a globally homogeneous mantle, suggests an uniform distribution within the mantle.

Geo-chemistry

Geo-physics

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Heat released from Heat released from the Earththe Earth

•The tiny flux of heat coming from the Earth ( 60 mW/m 60 mW/m22)) when integrated over the Earth surface gives a total flow:

HHEE = (30- 45)TW = (30- 45)TW

•It is equivalent to 104 nuclear power

plants.•Warning: the classical 44TW (Pollack 93) recently revised to the “old” 31 TW (Hofmeister &Criss 04)

•What is its origin?What is its origin?

88

Global heat flow estimates range from 30 to 44 TW … Estimates of the radiogenic contribution ,… based on cosmochemical considerations, vary from 19 to 31 TW. Thus, there is either a good balance between current input and output, as was once believed … or there is a serious missing heat source problem, up to a deficit of 25 TW…

20042004

•Determination of the radiogenic component is importantDetermination of the radiogenic component is important.

BSE

99

•For each elements there is a well fixed relationship between heat presently produced and its mass:

where units are TW and 1017kg.• Since m(Th) : m(U):m(40K)=4:1:1 one has:•Present radiogenic heat production cannot exceed heat released from Earth:

m(U)<1.8 10m(U)<1.8 101717kgkg

HR = 9.5 m(U) + 2.7 m(Th) + 3.6 m(40K)

How much Uranium can be tolerated by How much Uranium can be tolerated by Earth energetics?Earth energetics?

HR = 24 M(U)

1010

From m(U) one immediately derives the geo-neutrino From m(U) one immediately derives the geo-neutrino luminosity L, and an estimate for the flux luminosity L, and an estimate for the flux ≈L/4≈L/4RREarthEarth

22 Fluxes are of order 10Fluxes are of order 1066 cmcm-2-2 s s-1 -1 ,, same as same as 88B.B. From spectrum and cross section one gets the signal:From spectrum and cross section one gets the signal:

Signal is expressed in Signal is expressed in Terrestrial Neutrino Units:Terrestrial Neutrino Units:

1 TNU = 1event /(101 TNU = 1event /(1032 32 prot prot .. yr) yr)

(1kton LS contains 0.8 10(1kton LS contains 0.8 1032 32 prot )prot )

Order of magnitude estimate for the signalOrder of magnitude estimate for the signal

132126

)10

)(10

(2.13

yr

N

scmS par

[TN

U]

1111

½ of the signal ½ of the signal

from within 200 kmfrom within 200 km This requires a detailed This requires a detailed

geochemical & geophysical geochemical & geophysical study of the area.study of the area.

It is unsensitive to m(U) It is unsensitive to m(U)

The geo-neutrino signal and the Uranium mass: The geo-neutrino signal and the Uranium mass: the strategythe strategy

The remaining ½ from the The remaining ½ from the rest of the world.rest of the world.

It this part that brings It this part that brings information on m(U)information on m(U)

•Goal is in determining m(U) from geo- neutrino measurements. •Signal will also depend on where detector is located:•For m(U)=mBSE we expect at Kamioka:

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The rest of the world.The rest of the world.•Signal depends on the value of Uranium mass and on its distribution inside Earth.•For a fixed m(U), the signal is maximal (minimal) when Uranium is as close (far) as possible to to detector:

•Given m(U), the signal from the rest of the world is fixed within ±10%

SignalSignal U in the U in the CrustCrust

U in the U in the MantleMantle

LowLow PoorPoor RetreatedRetreated

High High Rich Rich Homog.Homog.[T

NU

]

Full Rad.min

Contributed Signal from Rest of the world

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The region near KamiokaThe region near Kamioka

Kamioka

Use a geochemical study of Use a geochemical study of the Japan upper crust the Japan upper crust (scale ¼ (scale ¼ 00x ¼ x ¼ 00) and ) and detailed measurements of detailed measurements of crust depth.crust depth.

Use selected values for LCUse selected values for LC Take into account:Take into account:

--(3(3) errors on sample activity ) errors on sample activity measurementsmeasurements--Finite resolution of geochemical Finite resolution of geochemical studystudy--Uncertainty from the Japan sea Uncertainty from the Japan sea crust characterizationcrust characterization--Uncertainty from subducting plates Uncertainty from subducting plates below Japan below Japan --Uncertainty of seismic Uncertainty of seismic measurementsmeasurements

In this way the In this way the accuracy on the local accuracy on the local contribution can be contribution can be matched with the matched with the uncertainty of the uncertainty of the global estimate.global estimate.

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Geo-neutrino signal at Kamioka and Uranium Geo-neutrino signal at Kamioka and Uranium mass in the Earthmass in the Earth

1) Uranium measured in 1) Uranium measured in the crust implies a the crust implies a signal of at least signal of at least 18 18 TNUTNU

2) Earth energetics 2) Earth energetics implies the signal implies the signal does not exceed does not exceed 46 46 TNUTNU

3) 3) BSEBSE predicts a signal predicts a signal between between 23 and 31 23 and 31 TNUTNU

Geo-neutrino detection can provide a direct test of BSE prediction.

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•KamLAND already provided a first glimpse S(U+Th)=(82±52stat.) TNU

•KamLAND is analyzing data for geo-neutrinos now…

•Need to subtract reactor events, may be 10 times as many as geo-neutrino events.

•Borexino at Gran Sasso will have smaller mass but better geo/reactor .

•At Baksan Mikaelyan et al. are considering 1Kton detector, again far from nuclear reactors.

•LENA in Finland envisages a 30Kton LS detector

S [TNU]

•At SNO there are plans of moving to liquid scintillator after physics D20 is completed. With low reactor background, well in the middle of Canadian shield (an “easy “geological situation) it will have excellent opportunitiesexcellent opportunities.

“Se son rose, fioriranno…”

Looking forward to new dataLooking forward to new data