Recent measurements show that about half of the 40 trillion watts of heat radiated continuously by the Earth comes from radioactivity taking place in its mantle and crust, while the remainder is due to the primordial heat that was created at the formation of the Earth and is located mainly in the core.
Historians of science are aware of the importance of the discovery of the radioactivity as an ongoing source of the heating of the Earth. Before the immense amount of heat associated with radioactive decay was discovered around 1903, physicists like Lord Kelvin had calculated the age of the Earth by treating it as an initially hot body that was steadily cooling. They concluded that it could not be older than 100 million years and could be as low as 20 million years. This made it very difficult, if not impossible, for the theory of evolution by natural selection, because it was a slow process that required long time scales. This was seized upon by religious people to argue against the evolution and in favor of the special creation of species by god. (See my series on the age of the Earth for a more detailed discussion of this.)
The discovery of radioactivity had two revolutionary impacts. It created an awareness that radioactivity was an ongoing source of the heating of the Earth that undermined all the earlier calculations of Kelvin and others, and it provided an important new tool for measuring time that opened the gates to new discoveries that rapidly pushed the age of the Earth to more than four billion years, giving plenty of time for evolution to take place.
I realize the link is just a summary article, but it raises questions for me.
1. Antineutrinos are associated with beta decay. Beta particles have a spectrum of energy, they are not monoenergetic. This means the antineutrinos would also have a spectrum of energy. With lots of isotopes emitting varying energies of antineutrinos, how can th authors really know which antineutrinos originated from nuclear power plants and which did not?
2. Is it not also possible that there is a natural fission reactor(s) within the Earth which is a source of the antineutrinos?
The reactor neutrino background came from a nearby nuclear reactor. Two things enabled them to distinguish those neutrinos from geoneutrinos. The reactor neutrino flux varies with the power output of the reactor, enabling them to model it. Secondly, an earthquake nearby in 2007 resulted in a temporary shut down of the reactor.
But reactor antineutrinos could originate from anywhere, not necessarily nearby. And they could have originated from spent fuel or other radioactive wastes, which aren’t associated directly with reactor power.
Sure, but the amount of neutrinos form reactors and other point-like sources that would pass through the detector would decrease rapidly (as 1/r^2) with distance and estimating the amount of background radiation produced by sources and subtracting them out is standard practice.
I agree with the 1/r^2 decrease, but every point source on (or in Earth) is a potential contributor. And power plants and many other facilities are contributing from an initial emission rate of millions of times higher than dilute terrestial isotopes (note that there is a 1.8 Mev threshold with this detector, so much of the terrestial and fission antineutrinos cannot even be detected).
Subtracting out background is standard practice when background is a small signal relative to an anticipated larger signal.
However, in this case, any signal is small. And in this case, reactor events EXCEED terrestial events -- http://geology.com/press-release/earths-internal-heat/:
“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”
According to my link above, there are more than 50 reactors in Japan that this system was intend to detect. The researchers would have had to look at and compensate for operational data from all of them, not just one. And we’re still ignoring other potential sources…nuclear powered subs/ships, is one example which the researchers probably would have no data on.
I still don’t see how they can make the differentiation.