Head of Neutrino Observatory Borexino (BOREX, Boron Solar Neutrino Experiment in Italy) Gran Sasso National Laboratory In Italy, they announced in the magazine this week natural The first discovery of the so-called solar neutrinos CNO cycle (Carbon-nitrogen-oxygen).
To commemorate its discoverer, this cycle is also known as the Bethe-Weizsack cycle. It is one of two nuclear fusion reactions. The star converts hydrogen into helium through this reaction, the other Proton-proton chain. In fact, they glow due to these nuclear fusions.
The CNO cycle is one of the dominant stars and is more massive than our sun. Therefore, the observation results now proposed are experimental evidence of the CNO cycle. The main hydrogen fusion reaction in the universe. Therefore, the significance of the new measurement for understanding the functional mechanism of stars is huge.
He said: “This is a historic result. It completes a chapter in physics that began in the 1930s.” David Bravo Berguño,researcher Autonomous University of Madrid (UAM) And a member of the international cooperation organization Borexino.
The existence of the carbon-nitrogen-oxygen cycle was first proposed in 1938, when scientists Hans Bethe and Karl von Weizsacker It is proposed (independently) that hydrogen fusion in stars can also be carried out in a series of periodic nuclear reactions through the heavy nuclei of these three elements to supplement the proton-proton chain sequence.
Although indirect proofs have been obtained from astronomical and astronomical observations, direct experimental confirmation of this hypothetical stellar generator system has been sought for decades.
The focus of this strategy is Neutrino, The particles produced in large numbers in these reactions. Specifically, in solar neutrinos, only high-sensitivity detectors that can eliminate background noise sources (minor traces of natural and cosmic radioactive pollution) can be observed.
Unique onion design detector
In order to obtain the necessary sensitivity, Borexino began to adopt the “onion” design in 1990, which is characterized by an increase in radioactive purity towards its center and such a low background level (incomparable in any other experiment) that it becomes a detection The only one in the device. world.
The detector contains a sphere with 2212 photomultiplier tubes mounted on the wall to collect the light signals emitted by the neutrinos in the liquid scintillator.
The depth of the laboratory of the Gran Sasso Underground Laboratory can protect it from cosmic rays, except for the neutrinos themselves, which pass through the earth almost without attenuation.
In previous work, the collaboration with Borexino has studied in detail the main mechanism of energy generation under the sun: the proton-proton chain, which can individually detect all the neutrino fluxes it generates.
Now, the neutrinos produced in the measurement cycle CNO, 1% in the sun In general, this is when the detector obtains the first experimental evidence of the existence of this additional energy generation mechanism.
He declared: “We finally have a groundbreaking and groundbreaking confirmation that stars are much heavier than our sun. This is the result of 30 years of joint efforts.” Gianpaolo Bellini, One of the founders of the experiment.
Measuring neutrinos in the CNO cycle is a complex task that requires a lot of technology and computer technology. One of the cooperating speakers, Marco PallaviciniHe pointed out that the experiment “makes the development of liquid scintillator technology beyond any limit so far, making the core of Borexino the lowest radioactive substance in the world.”
He concluded: “Despite the success in the past and the existence of ultrapure detectors, we must still work hard to further improve the suppression and understanding of the low residual background in order to finally determine the neutrinos in the CNO cycle.” Gioacchino Ranucci, Is the current spokesperson of Borexino.
Borexino cooperation. “Experimental evidence for the production of neutrinos in the sun’s CNO fusion cycle.” natural, 2020 year