How can neutrinos cause a chain reaction

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Neutrinos are released during nuclear fusion reactions in the Sun's core. This process fuses four protons to form a helium nucleus, which releases two neutrinos — the lightest known elementary particles of matter — as well as other subatomic particles and copious amounts of energy. But it is thought to be the dominant energy source in larger stars. The results mark the first direct detection of neutrinos from this process. Solar neutrinos reveal how the Sun shines.

The findings, which have not yet been peer reviewed, were reported on 23 June by the Borexino underground experiment in central Italy, at the virtual Neutrino conference. The findings are a final milestone for Borexino, which is still taking data but might now shut down within a year.

The detector consists of a giant nylon balloon filled with tonnes of liquid hydrocarbons, that is immersed in water. These reactions spawn neutrinos, too, and the more carbon, nitrogen and oxygen the Sun has, the more of these neutrinos there should be. But CNO neutrinos are so rare that no-one has yet detected them. Will Borexino succeed? The scientists have published their work in Nature. Ken Croswell is an astronomer in the US and the author of eight books on astronomy.

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Sign in to Unlock all the content on the site Manage which e-mail newsletters you want to receive Read about the big breakthroughs and innovations across 13 scientific topics Explore the key issues and trends within the global scientific community. This releases neutrinos and energy that will eventually reach Earth as light and heat. All of the neutrinos produced in the sun are electron neutrinos. An interesting thing happened when scientists started looking for those electron neutrinos in the s.

Only about one third to one half of the predicted number of neutrinos actually showed up in detectors. This became known as the solar neutrino problem, and it took nearly four decades to solve it. It started with the Homestake experiment led by Ray Davis Jr. The experiment used , gallons of dry cleaning fluid perchloroethylene to search for neutrinos. It was housed a mile underground in the caverns of the Homestake Gold Mine in South Dakota, which was then an active mine and is now used for science experiments, including further neutrino research in the Deep Underground Neutrino Experiment.

But only one third of the neutrinos seemed to arrive. Some scientists, including Bruno Pontecorvo, proposed that the neutrino model was the error, but many were skeptical. In , the Kamiokande experiment in Japan added to the confusion. The process of nuclear fusion is essentially the reverse of this procedure. Penetrating the Coulomb barrier still does not necessarily lead to fusion. For example, the reaction of two protons is quite unlikely because there is no stable Helium nucleus containing just two protons.

Instead, the least massive, stable configuration is deuteron, containing a proton and a neutron. In order to produce this, one of the protons must decay into a neutron and a positron while it is within the Coulumb barrier.

This is a very unlikely process. For this reason, burning of elements above Hydrogen takes progressively higher temperatures in order to proceed. Since the mass of the star sets a limit to the maximum temperature it is capable of sustaining in its core, low mass stars are only able to burn through the lower atomic mass elements, while high mass stars are able to reach all the way to Fe, beyond which the mass defect becomes negative and burning requires energy input rather than producing energy.

There are two major reaction paths which are suppliers of energy in the Sun.