Okay folks, half of the Earth’s
heat energy is now unaccounted for.
Careful measurement has eliminated a lot of the uncertainty in our
calculations and we now know that the only understood heat source is good for half
of the observed output. Primordial heat
sounds good and is plausibly the heat of Newtonian assemblage which is still
far too little and has likely long ago been largely dissipated.
So we now have a real problem in explaining
the source of all that heat. I will step
beyond that. There is little evidence of
decay either as we peer backwards in geological time. We are producing heat and it appears almost
sustainable.
This discrepancy is so huge no
hand wave will postpone its confrontation.
So long as we were unable to properly account for the nuclear component,
that hand wave stood.
My first thought and it would be
since I have a unique perspective on particle physics, is that we may well be
working here with dark energy provided that dark energy is capable of reacting
and producing heat.
Better still, we have the Rossi
Focardi reactor to inform us. It is nickel
based and it engages in fusion reactions quite able to produce the heat. Since we can now do just that in the lab with
at least a fifteen times unity heat production, it is obvious that exactly this
form of heat generation is a plausible candidate.
Quite simply, in terms of popular
jargon, the heat deficit is made up by ‘cold fusion’ which has now been
definitively demonstated.
What keeps the Earth cooking?
by Staff Writers
A main source of the 44 trillion watts of heat that flows from the
interior of the Earth is the decay of radioactive isotopes in
the mantle and crust. Scientists using the KamLAND neutrino detector in Japan Lawrence Berkeley
What spreads the sea floors and moves the continents? What melts iron in
the outer core and enables the Earth's magnetic field? Heat. Geologists have
used temperature measurements from more than 20,000 boreholes around the world
to estimate that some 44 terawatts (44 trillion watts) of heat continually flow
from Earth's interior into space. Where does it come from?
Radioactive decay of uranium, thorium, and potassium in Earth's crust
and mantle is a principal source, and in 2005 scientists in the KamLAND
collaboration, based in Japan
"As a detector of geoneutrinos, KamLAND has distinct
advantages," says Stuart Freedman of the U.S.
Department of Energy's Lawrence Berkeley
National Laboratory (Berkeley Berkeley Lab's Nuclear Science Division and a professor in
the Department of Physics at the University
of California at Berkeley ,
leads U.S.
"KamLAND was specifically designed to study antineutrinos. We are
able to discriminate them from background noise and detect them with very high
sensitivity."
KamLAND scientists have now published new figures for heat energy from
radioactive decay in the journal Nature Geoscience. Based on the improved
sensitivity of the KamLAND detector, plus several years' worth of additional
data, the new estimate is not merely "consistent" with the
predictions of accepted geophysical models but is precise enough to aid in
refining those models.
One thing that's at least 97-percent certain is that radioactive decay
supplies only about half the Earth's heat. Other sources - primordial heat left
over from the planet's formation, and possibly others as well - must account
for the rest.
Hunting for neutrinos from deep in the Earth
Antineutrinos are produced not only in the decay of uranium, thorium, and potassium isotopes but in a variety of others, including fission products in nuclear power reactors.
In fact, reactor-produced
antineutrinos were the first neutrinos to be directly detected (neutrinos and
antineutrinos are distinguished from each other by the interactions in which
they appear).
Because neutrinos interact only by way of the weak force - and gravity,
insignificant except on the scale of the cosmos - they stream through the Earth
as if it were transparent. This makes them hard to spot, but on the very rare
occasions when an antineutrino collides with a proton inside the KamLAND
detector - a sphere filled with a thousand metric tons of scintillating mineral
oil - it produces an unmistakable double signal.
The first signal comes when the antineutrino converts the proton to a
neutron plus a positron (an anti-electron),
which quickly annihilates when it hits an ordinary electron - a process called
inverse beta decay. The faint flash of light from the ionizing positron and the
annihilation process is picked up by the more than 1,800 photomultiplier tubes
within the KamLAND vessel.
A couple of hundred millionths of a second later the neutron from the
decay is captured by a proton in the hydrogen-rich fluid and emits a gamma ray,
the second signal. This "delayed coincidence" allows antineutrino
interactions to be distinguished from background events such as hits from
cosmic rays penetrating the kilometer of rock that overlies the detector.
Says Freedman, "It's like looking for a spy in a crowd of people
on the street. You can't pick out one spy, but if there's a second spy
following the first one around, the signal is still small but it's easy to
spot."
KamLAND was originally designed to detect antineutrinos from more than
50 reactors in Japan, some close and some far away, in order to study the
phenomenon of neutrino oscillation. Reactors produce electron neutrinos, but as
they travel they oscillate into muon neutrinos and tau neutrinos; the three
"flavors" are associated with the electron and its heavier cousins.
Being surrounded by nuclear reactors means KamLAND's background events
from reactor antineutrinos must also be accounted for in identifying
geoneutrino events. This is done by identifying the nuclear-plant antineutrinos
by their characteristic energies and other factors, such as their varying rates
of production versus the steady arrival of geoneutrinos. Reactor antineutrinos
are calculated and subtracted from the total. What's left are the geoneutrinos.
Tracking the heat
All models of the inner Earth depend on indirect evidence. Leading models of the kind known as bulk silicate Earth (BSE) assume that the mantle and crust contain only lithophiles ("rock-loving" elements) and the core contains only siderophiles (elements that "like to be with iron"). Thus all the heat from radioactive decay comes from the crust and mantle - about eight terawatts from uranium 238 (238U), another eight terawatts from thorium 232 (232Th), and four terawatts from potassium 40 (40K).
KamLAND's double-coincidence detection method is insensitive to the
low-energy part of the geoneutrino signal from 238U and 232Th and completely
insensitive to 40K antineutrinos. Other kinds of radioactive decay are also
missed by the detector, but compared to uranium, thorium, and potassium are
negligible contributors to Earth's heat.
Additional factors that have to be taken into account include how the
radioactive elements are distributed (whether uniformly or concentrated in a
"sunken layer" at the core-mantle boundary), variations due to
radioactive elements in the local geology (in KamLAND's case, less than 10
percent of the expected flux), antineutrinos from fission products,
and how neutrinos oscillate as they travel through the crust and mantle.
Alternate theories were also considered, including the speculative idea
that there may be a natural nuclear reactor somewhere deep inside the Earth,
where fissile elements have accumulated and initiated a sustained fission
reaction.
KamLAND detected 841 candidate antineutrino events between March of
2002 and November of 2009, of which about 730 were reactor events or other
background. The rest, about 111, were from radioactive decays of uranium and
thorium in the Earth.
These results were combined with data from the Borexino experiment at Gran Sasso in
Italy
This is more heat energy than the most popular BSE model suggests, but
still far less than Earth's total. Says Freedman, "One thing we can say
with near certainty is that radioactive decay alone is not enough to account
for Earth's heat energy. Whether the rest is primordial heat or comes from some
other source is an unanswered question."
Better models are likely to result when many more geoneutrino detectors
are located in different places around the globe, including midocean islands
where the crust is thin and local concentrations of radioactivity (not to
mention nuclear reactors) are at a minimum.
Says Freedman, "This is what's called an inverse problem, where
you have a lot of information but also a lot of complicated inputs and
variables. Sorting those out to arrive at the best explanation among many
requires multiple sources of data."
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