Transcript Surveying the Earth with Neutrinos

Exploring the Geo-reactor
Hypothesis with Neutrinos
Jelena Maričić
KamLAND Collaboration
March 24th 2007
DOANOW Workshop
University of Hawai’i
Outline
• The geo-reactor hypothesis
• Limits on the geo-reactor hypothesis
with KamLAND experiment
• Prospects of verifying the georeactor hypothesis with future
Hanohano experiment
• Summary and conclusion
Uranium in the Core?
•
•
•
•
•
Radical hypothesis
If it is there, it may undergo fission.
Natural nuclear reactor with power up to
10 TW operating in the center of the
Earth, proposed by M. Herndon as the
energy source of geo-magnetic field
(geo-magnetic field reversals and higher
ratios of 3He/4He observed in volcanic
plumes in some places).
Although not a mainstream theory, not
ruled out by any evidence.
If the geo-reactor exists, its antineutrino flux is visible in KamLAND
and Hanohano in future!
Why do we Care about Verifying a Radical
Hypothesis such as Geo-reactor Sitting in the
Earth’s Core?
It is a freebie.
It can be verified with existing experiments and
future planned experiments
Geo-reactor
Discovered:
- revolutionize geology
Does not exist
or/and too small:
- independent check that
there are no surprises in
the energy region where
we do not expect them
Differentiating between Geo-neutrinos
and Geo-reactor Neutrinos
Inv.  reaction:
e p+  e+ + n
Inverse
β-decay
energy
threshold
1.8 MeV.
- Geo-neutrinos emitted in the
decay chains of 40K, 232Th,
238U and can have energies up
to 3.4 MeV
- Geo-reactor neutrino’s energy
spectrum approximately
resembles the spectrum of a
typical commercial nuclear
reactor and these neutrinos
may have energies that extend
all the way to 9 MeV
- Any positive signal above 3.4
MeV limit for geo-neutrinos
must be attributed to reactor
like neutrinos
No geo-neutrinos
above 3.4 MeV
Geo-reactor
Search with KL
• KamLAND detects reactor antineutrinos
• The possible surplus of detected
events implies that there may be
another source of anti-neutrinos
that have not been accounted for.
• Proposed 3-10 TW georeactor
if exists would produce antineutrino signal of 4-14% of the
KamLAND signal.
• The goal is to set an upper limit
on the power of the hypothetical
geo-reactor.
Is it there and if so, how large is it?
Motivation for Geo-reactor Search
Survival probability
Large error!
KamLAND
•
•
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Incoming daily flux varies due
to nuclear reactors varying work
regime.
Rate from the putative geo-reactor
very small!
It is assumed that geo-reactor power
is constant on the data taking time
scale.
90% C.L.
Time integrated
plot
Small positive offset of 0.03e/day
with VERY LARGE ERROR
may be present, for 0 ev/day
expected!
Phys.Rev.Lett.94:081801,2005
Confidence Levels on
the Geo-reactor Power
Very wide minimum
The best fit value is 6 TW
and 90% C.L. limit is 19 TW
Based on 515 days of livetime
0.0102 events/TW·day
Comparison of the Best Fit
Result with Geological Data
Simulation of the Improving Limits on the
Geo-reactor Power with 2.5 more data
•
•
Simulations with 2.5 more data!
Value of the geo-reactor power treated as a free parameter.
Rate only
No parameter
constraints
R0 = (-6  10) TW
R0 = 14 TW at 90%C.L.
90%
68%
Rate only
+ parameter
constraints
R0 = (-4  5) TW
R0 = 9 TW (90%C.L.)
90%
68%
Expectation
With 2.5 more
data
R0 = (0  4) TW
R0 = 7 TW (90%C.L.)
Rate + shape
+ parameter
constraints
90%
68%
Tightest
limit
Geo-reactor Search with KamLAND
Summary
• 90% C.L. is 19 TW.
• Simulations with 2.5 times more data shows that there
will be improvement in the limits, but it is still
insufficient to give any final say about the geo-reactor.
Based on the simulation:
– 90 % C.L. limit will be lowered to 7 TW.
– The best fit will be lowered: (0  4) TW
• Final result is greatly influenced by:
– Error on the input neutrino mixing parameters that will not
improve greatly in near future
– Background from man-made nuclear reactors that is 10-20 times
larger than geo-reactor signal
– Detector backgrounds will be decreased by a new radioactive
source calibration measurement at KamLAND
• KamLAND size detector far away from nuclear reactors
needed for high confidence (>99.99%) measurement.
• Hawaii presents an excellent choice for a definite
geo-reactor measurement (
).
Making a more decisive
measurement of
geo-neutrinos with future
Hanohano experiment
Hano Hano - KamLAND in Ocean
• Hano Hano = Hawaii Antineutrino
Detector
- Hanohano = Hawaiian for “glorious,
Distinctive”
• Basic Idea:
- KamLAND-style
anti-neutrino detector in the ocean
@ 4km depth
- Design: measurement of 238U and 232Th
in the mantle - 25% measurement of mantle geoneutrinos (U/Th) - Will be able to distinguish between
different geological models of the Earth.
- Will be able to detect geo-reactor neutrinos from the
1 TW or larger geo-reactor if one exists with > 4 C.L.
Planned Detector Design and Location
- Designed as 10 kton liquid
Pier construction
scintillator detector.
constraint!
- Detection reaction:
Oahu
Hanohano
4 km depth
Big
Island
 e  p  e  n
Why Hawaii Represents Such a Good
Location for Geo-reactor Detection
Commercial nuclear reactor background
• Japan presents one of
the worst locations for
the geo-reactor detection
while Hawaii presents one
of the best locations for
geo-reactor detection.
Commercial nuclear reactor background
Japan
Hawaii
Significance and Signals for
the Geo-reactor Detection
• Signal significance: σ = S / √(S+B)
• Background rate:
30 events per 10 kT-y (3.4 < Eν(MeV) < 9.3)
• 1 TW geo-reactor signal
38 events per 10 kT-y (3.4 < Eν(MeV) < 9.3)
• If the goals for backgrounds are
achieved:
 = 4.6 C.L. for 1 TW geo-reactor discovery

Summary and
Conclusion

• Current upper limit on the power on the
hypothetical geo-reactor has been set at 19
TW at 90% C.L.
• Simulations with larger data set show
improvements but insufficient to give any final
say about the existence of geo-reactor.
• Destiny of the geo-reactor will be far better
resolved with Hanohano detector.


Geo-reactor
Pros
and
Cons
…can explain the following unresolved
question:
- provide the energy source for
driving the Earth’s magnetic field
(0.02-10 TW of power running for
more than 3 billion years!!!).
- perhaps explains reversals of
the geo-magnetic field
(171 reversals recorded in the
last 70 million years).
- provide explanation for the up to
40 times higher measured ratios
(comparing to average
atmospheric ratio) of 3He/4He
observed in volcanic plumes in
Hawaii, Iceland some other places.
…requires substationally different
inner core content:
Traditional Model (BSE):
content of the inner core based
on meteorites called
carbonaceous chondrites. As a
result, U and Th are in the form
of oxides, act as lithophiles and
can exist in the crust and mantle
only.
Nuclear Earth Model (by M.
Herndon): content of the inner
core based on rare type of
meteorites called enstatite
chondrites. U and Th are alloyed
with Fe or S, act as siderophiles
and due to high density can exist
in the inner core and particularly
the Earth’s center.