Kamland: Investigate the sources of heat emitted from the earth

Scientists at the Berkeley Laboratory, USA, and colleagues used the KamLAND detector to measure the amount of radiation emitted by earth's heat sources.

What makes the continental floors move as well as the sea floor? Melts the outer iron core and creates the Earth's magnetic field? The answer is: melting heat. Geologists have used temperature measurements from more than 20,000 boreholes around the world to estimate that there are about 44 terawatt (44 trillion watts) of continuous heat emission into space, from the heat source in the left land. So where do these heat sources come from?

Radioactive decay of uranium, thorium, and potassium in the earth's crust and crust is a major source of heat, and in 2005 KamLAND research collaboration scientists, based in Japan, For the first time, there is a way to measure direct heat contributions. The secret is to capture what KamLAND discovered: the emission of geo-antineutrinos, when radioactive isotopes decay. (KamLAND also known as geoneutrinos detector, using Antineutrino glowing substance).

A major heat source of about 44 trillion watts of internal flow of Earth is the decay of radioactive isotopes in the mantle and crust crust.Scientists using Japanese KamLAND neutrino detectors have measured the amount of heat generated in this way by trapping geoneutrinos arising during radioactive decay.

" Geoneutrin detector uses Antineutrino (KamLAND) luminaire, has obvious advantages and plays an important role " according to Stuart Freedman, working at Lawrence Berkeley National Laboratory, US Department of Energy (Laboratory Berkeley). Freedman, a member of the Berkeley Department of Nuclear Science and Laboratory and a professor at the Department of Physics, California Berkeley University, USA, leader of the US research team. " KamLAND is specially designed to study antineutrinos. We can detect antineutrinos from noise with very high sensitivity ."

KamLAND scientists have published new data on heat energy emitted by radioactive decay in Nature Geoscience . By improving the sensitivity of detector antineutrinos (KamLAND), and valuable data has been added for many years, the new prediction is not merely " consistent " with the predictions of the geological model. Acceptable logic must have sufficient accuracy to support refining in the models.

One thing is for sure, 97% of radioactive decay will provide at least about half of the Earth's heat. The remaining heat may come from the formation of the planet . or from other unexplored sources.

Tracing neutrinos emanating from deep in the earth:

Antineutrinos are manufactured not only by decay of uranium, thorium and potassium isotopes but also require a range of other factors, including fission products in nuclear power reactors. In fact, the main reaction from the antineutrinos production is that the first neutrino is detected directly (neutrinos and antineutrinos are distinguished from each other by interaction, when they occur simultaneously).

Neutrinos interact with each other by weak forces and gravity, insignificant except on the scale of the universe - they pass through the earth like going through a transparent environment. This makes it difficult to identify neutrinos, but on very rare occasions antineutrinos collide with a proton inside the antineutrinos detector (KamLAND) - a sphere containing about a thousand tons of sparkling mineral oil. , creating an unmistakably doubled amplifier signal.

The first signal comes when the antineutrino converts the proton to a neutron plus a positron (antineircraft), quickly destroyed when colliding with a normal electron, which is the reverse beta decay process. The faint light of light from ionized positrons and the annihilation process is chosen by more than 1,800 photovoltaic nuclei in the antineutrinos detector (KamLAND). Several hundred million parts of a second later, a neutron in the decay process is captured by a proton in a hydrogen-rich liquid and emits a gamma ray, this is the second signal. This " coincidence delay " allows antineutrino interactions to be distinguished from background events such as the penetration of cosmic rays onto the kilometer of rock above the antineutrinos detector (KamLAND).

Freedman said: " As if looking for a mixed spy in a crowd on the street. You can't detect this spy. But if there's a second spy in this crowd, then though identification signs are still quite small, but easier to detect ".

KamLAND (KamLAND) was originally designed to detect antineutrinos from more than 50 Japanese nuclear reactors, some at close range and some at long distances, to study neutrino oscillations. The reactor produces neutrino electrons, but as they move, they vibrate in basic particles: the Muyon neutron and the tau neutron.

Monitoring nuclear reactors means that the KamLAND detectors recorded by antineutrinos are also taken into account in determining geoneutrino particles. This is done by determining the characteristic energy and other factors of the antineutrinos reaction, such as the different rates of production compared to the stable appearance of geoneutrinos. Reaction Antineutrinos is calculated and subtracted from the total. What is left are geoneutrinos.

Heat monitoring:

All internal models of the Earth depend on indirect evidence. The top model of the type is called BSE: assuming that the mantle crust and crust crust contain lithophiles and the core consists of siderophiles (" iron-like " elements). Thus all the heat from radioactive decay comes from the crust and mantle crust of about 8 terawatts from uranium 238 (238U), 8 terawatts from thorium 232 (232Th), and 4 terawatts from potassium 40 (40K).

KamLAND's double coincidence using the antineutrinos method is not sensitive to the low energy portion of the geoneutrino particle signal from 238U and 232Th and is completely insensitive to 40K antineutrinos. The types of radioactive decay are also ignored by the detector, but compared to uranium, thorium, and potassium, the low energy sources have made negligible contributions to the heat generated from the earth.

How radioactive elements are distributed (whether uniform or concentrated in a " sunken layer " at the core boundaries - the crust of the earth), due to the radioactive elements variations in the geology local (in the case of the KamLAND program, there is less than 10% of the expected throughput), antineutrinos from fission products, and how neutrinos vibrate as they pass through the crust and mantle. This alternative theory is also considered, including the idea that speculation has a natural nuclear reactor somewhere deep inside the earth, where fission elements can accumulate and begin. a sustainable fission reaction.

The KamLAND program detected 841 antineutrino events between March 2002 and November 2009, including about 730 events from reactors. The rest, about 111 events, from radioactive decay of uranium and thorium inside the earth. These results are combined with data from the Borexino experiment at Gran Sasso in Italy to calculate the contribution of uranium and thorium to produce the earth's heat. The answer is about 20 terawatts; Based on models, one terawatt is estimated from other isotope decays.

This is more heat source than the most popular model of the BSE model, but still less than the total amount of heat generated from the earth. Freedman, said: " One thing we can say with certainty is that radioactive decay is negligible compared to the earth's thermal energy. Whether the rest is primitive heat or from some other source, it is still a question no one has answered . "

A better model could result when more antineutrinos (KamLAND) are placed in different places around the globe, including in the submerged mountain ranges, where the earth's crust is thin and zoomed in. radiation (not to mention nuclear reactors) at a minimum.

Freedman, said: " This is an inverse problem, where you have a lot of information but there are also many complex input variables. Sort these input data to give the best explanation ."

" A part of Earth's thermal radiation model is shown through the " geoneutrino measurement "of detector antineutrinos (KamLAND), according to Itaru Shimizu of Tohoku University, Sendai, Japan, co-author, published in the journal Nature. Geoscience .

The KamLAND Research Program is supported by the Japanese Ministry of Culture, Education, Sports, Science and Technology and the Science Agency of the US Department of Energy.