Cold fusion: derided old hope regains its place as energetic promise

After decades of disrepute, this year there was renewed hope of producing large amounts of energy from small portions of matter and little energy investment. If for decades, experiments around the world have failed to demonstrate the effectiveness of nuclear fusion for power generation, a publication made by a researcher and collaborators at the Massachusetts Institute of Technology (MIT) in February seems to be turning that tide. . Scholars have proposed mechanisms that increase nuclear fusion rates over what has been achieved so far, which led the US Department of Energy to change its stance and start offering funding for research into low-energy nuclear reactions. The European Union Research Council also provides funding.

The so-called cold fusion is an alternative to the fission of heavy elements, such as uranium, in nuclear power plants. While fission is the spontaneous separation of the particles that form the large nucleus of an atom, fusion is the induced joining of small nuclei. Both processes release energy, but fusion has greater potential. With the energy crisis triggered by the war in Ukraine, in addition to skepticism about the effectiveness of so-called clean energies, interest in nuclear energy, both the traditional fission-based and the promising, but more uncertain, fusion-based, draws the attention of governments. . Canada, for example, announced last Tuesday (30) that it will invest US$2016 million (R$3.8 billion) in small modular fission reactors.

The abundant energy we receive from the Sun, our local star, is produced by a fusion process of hydrogen atom nuclei, which results in helium atoms. Other heavier elements, including carbon, which makes life possible, and oxygen, which shaped life on Earth and protects us in the atmosphere in the form of ozone, are similarly produced in larger stars. Therefore, astronomer Carl Sagan, in his popular works, said that we are made of the substance of stars.

As nuclei of atoms have the same positive electrical charge, they naturally repel each other, like equal poles. of a magnet. Therefore, very high temperatures and pressure are needed for nuclear fusion, and a lot of energy is released when it happens. It would seem, therefore, that only in the more than scorching temperatures of the Sun could this process be carried out. In fact, scientists can reproduce these high temperatures, but the energy expenditure to obtain them is very high, not compensated by the amount of energy released in the hot fusions carried out in the laboratories.

For decades, hopes of performing “cold” fusion—which is relative “cold,” not something literally near or below 0°C—turned out to be rushed or even potentially fraudulent. One of those accused of fraud was Italian businessman Andrea Rossi, who did not accept an offer of one million dollars to prove that his device worked. With a series of new experiments since 2010, hopelessness is losing ground.

How is it possible to imitate the Sun in the laboratory?

As we learned in school, the nuclei of atoms are surrounded by clouds of electrons, negatively charged particles smaller and lighter than the protons in the nucleus. The clouds of electrons from different atoms repel each other because they are both negatively charged. To bring one nucleus closer to another, as a first step in fusion, physicists use techniques such as replacing electrons with muons, which are heavier versions of electrons and therefore orbit the nucleus more closely. The process is called muon-catalyzed fusion, and it was proposed in the years 1940, with tests in the years 1950. As particle accelerators are needed for the process, the energy cost is higher than production.

Another fusion method is to launch deuterium nuclei, which is a heavier version of hydrogen, onto plates of a metal such as titanium. Deuterium, in addition to a proton, has a neutron (uncharged particle) in the nucleus. When released, deuterium builds up to a certain critical mass after which it begins to fuse nuclei, releasing neutrons. The technology already exists and is used in devices with small metal plates of a few millimeters. Its purpose, in fact, is not to release energy, but to produce neutrons, which have applications such as making materials stronger or cleaning an area with radioactive material. Only about one in a million deuterium nuclei fuse in this procedure. The method is called “solid state fusion”.

From this method evolved the proposal of two electrochemists in 1940, Martin Fleischmann and Stanley Pons With money from their own pocket, they created an apparatus in which they applied an electric current to water made of deuterium containing a plate of palladium metal. The apparatus would have released excess heat, in addition to particles that are signs of nuclear reaction, which they interpreted as a sign of cold fusion. Many scientists have tried to reproduce the results, without success — the last attempt was in 2019, funded by Google and published in the journal Nature. The US Department of Energy investigated the matter at 1989 and at 2004, concluding that the apparatus was unconvincing. as a source of energy, denying funding for the project.

After the failure of Fleischmann and Pons, scientists were more wary of trying to make cold fusion work again. The philosopher Huw Price, asking if cold fusion is really impossible or if physicists simply want to avoid falling into disrepute by failing in the area, christened the phenomenon the “reputation trap”.

To avoid the trap, one strategy is to change vocabulary. That’s what happened with research in an area that those involved prefer to call Low-Energy Nuclear Reactions (LENR). Doing something broadly similar to the Fleischmann and Pons apparatus, in 2010 Peter Hagelstein, from MIT, published, together with his collaborators, an article in which he described that the use of a laser at certain frequencies increased energy production by fusion. But the result also failed to replicate.

Another LENR scientist who tried to make a modified version of the apparatus work was Edmund Storms, in 2010. After further replication failures, he proposed that replicating the experiments is difficult because of “nano-cracks” in the palladium. The proposal is unorthodox, but it is true that aspects of the experiment are difficult to measure, especially the heat released.

The tide of hopelessness really began to change in February of this year, when Florian Metzler, a researcher from MIT, proposed together with collaborators mechanisms that increase nuclear fusion rates in the solid state method. The mechanisms, which are based on phenomena such as nuclei “resonance” and palladium properties, would increase production by 30 orders of magnitude. Metzler and colleagues argue that deuterium fusion needs to increase by 50 orders of magnitude to become viable as a technology. Because of publications like this, the US Department of Energy has changed its stance and now offers funding for research into low-energy nuclear reactions. The European Union Research Council also provides funding.

For German theoretical physicist Sabine Hossenfelder, physicists who think that cold fusion is impossible are overestimating current knowledge of nuclear physics and chemistry. What fundamental particles exist in the universe is still a matter of empirical study in particle accelerators, and it is possible that the most accepted theory, the Standard Model of particles, is wrong in the details and does not give us sufficient ability to predict what happens when nuclei merge. She remains skeptical about the possibility of making cold fusion viable, as it is not clear that the energy output in the experiments exceeds the energy invested, but says that “something strange is happening in these experiments and deserves further study”.

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