neutrinos

Neutrinos are almost zero mass particles, which originate from the decay of neutrons.

Neutrinos have been an enigma since the mid-20th century

One of the great mysteries of science has been this very elusive little subatomic particle: the neutrino.

The cover image shows a 50 million liter water tank. The image was published in the newspaper “La Razón”, by Alberto Aparici on September 20, 2020.

Those of us who live outside the academic world do not perceive the gigantic advances that thousands of large laboratories and tens of thousands of scientists are making in transcendental research.

Neutrinos Raymond
Raymon Davis. Crédito: web rinconeducativo.org/es/

Raymond Davis (1914 – 2006), American physicist who stood out for his pioneering contributions in astrophysics, particularly in the detection of neutrinos from the Sun and outer space.

In 1967, Raymond Davis got BrookHaven National Laboratory to install a neutrino detector inside an old South Dakota gold mine.

The detector was a large deposit of 400,000 liters of perchlorethylene, located 1,500 meters deep.

The detector was installed at this great depth so that cosmic rays from space could not reach the reservoir. Only the elusive neutrinos would make it through that one-mile-long rock face of massive rock.

Raymond Davis and his collaborators were able to detect neutrinos, using the peculiarity that neutrinos colliding with chlorine atoms produced atoms of a reactive isotope of argon.

neutrinos
The gigantic Japanese superdetector. Credit: web nature.com/articles

Inspired by these interesting findings, the Japanese physicist Masatoshi Koshiba, in 1980, obtained the support of the University of Tokyo to design an experiment specifically designed to detect solar neutrinos and also neutrinos from supernovae, anywhere in our galaxy.

The work culminated in 1995, with the construction of the detector called Super-Kamiokade, located in the depths of a mine located on the east coast of Japan.

The detector consists of a large tank full of water (50,000 tons of extra-pure water). In this experiment, called Tokai to Kamioka (T2K), 508 scientists from 12 countries participate, including Spain.

In 1998, scientists in this laboratory announced the first evidence that neutrinos have mass, although the value is very small.

In 2002, Raymond Davis and Masatoshi Koshiva were awarded the Nobel Prize in Physics for their work in detecting the elusive neutrinos.

neutrinos Masatoshi
Masatoshi Koshiva (1926-2020). Credit: es.wikipedia.org

In the bowels of the Somport tunnel, 8,608 meters long and that separates Spain from France, in Canfranc (Aragon), almost a kilometer deep is a laboratory where the Spanish physicist Juan José Gómez and the team have been working since 1985.

There they carry out an experiment destined to test the theories that they elaborate in the “Institute of Corpuscular Physics of the University of Valencia”.

The unknown they are trying to solve is whether the neutrino is its own antiparticle. That is, if it can be matter and antimatter at the same time.

This would be absolutely momentous in physics. Proving this hypothesis is a slow, expensive and very complex process. Whoever succeeds will surely win a Nobel Prize.

neutrinos Pauli
Wolfgang Pauli (1900-1958). Credit: web rinconeducativo.org/es/

Austrian physicist Wolfgang Ernst Pauli is one of the founders of quantum mechanics.

In 1930, when studying the decay of radioactive nuclei, Wolfgang Pauli discovered that there was an apparent loss of energy and momentum in the β decay of neutrons.

This phenomenon made him think about the possibility that hitherto unknown particles existed.

As Wolfgang Pauli had deduced, these hidden particles had to be devoid of mass, they should not have any electrical charge and they would not have to be affected by the strong nuclear force.

These three theoretical characteristics meant that, with the means available in those years, it was not possible to detect them in the laboratory.

The idea of ​​what he later called a neutrino was put on hold for 25 years, until 1956, when neutrinos were first detected.

Neutron
Neutron with 3 quarks. Credit: web es.wikiquote.org/wiki/

Neutrons are not stable and their probable existence is only 15 minutes. When the neutron decays, it produces a proton and an electron.

Furthermore, the decayed neutron produces a third particle very difficult to detect with the means available in the middle of the 20th century: the neutrino.

neutrinos
A neutron decays into a proton, an electron, and an antineutrino. Credit: es.wikipedia.org/wiki/

The image shows that a neutron (n) becomes a proton (p), an electron (e) and an antineutrino (Greek letter nu)

There is another similar type of decay, in which a neutron (n) becomes a proton (p), an electron (e) and a neutrino (nu)

So far, only three classes of stable particles are known in the universe: electrons, protons, and neutrinos.

All other particles have a very short-lived existence and disintegrate after a few thousandths of a second.

This circumstance gives a lot to think about, if you think about it when we look at our body, which is made up entirely of electrons, protons, and neutrons.

Reines
Frederick Reines, Nobel Prize in Physics 1995. Credit: es.wikipedia.org/wiki/

The name of the American physicist Frederick Reines (1918 – 1998) is closely associated with the discovery of the neutrino and with the subsequent investigation of its fundamental properties.

In 1956, Frederick Reines and his colleague Clyde Cowman experimentally demonstrated the existence of neutrinos.

To do this, they bombarded pure water with a beam of 1018 neutrons per second.

By observing the emission of photons that originated this bombardment, they reliably determined the existence of these elusive particles.

In 1995, Reines was awarded the Nobel Prize in Physics, for the discovery of the neutrino and the antineutrino that he made together with Clyde Cowman.

From then on, astronomical and cosmological studies provided a surprising amount of information about neutrinos.

The neutrino was initially thought to be a massless particle and therefore to travel at the speed of light, just like photons.

Astronomical observations were the first to show physicists that neutrinos have mass. The connection between laboratory experiments, astrophysics and cosmology allows researchers to advance the knowledge of our Universe.

The latest studies have confirmed that neutrinos have mass, although it is very little, very little. Although the exact mass of a neutrino is not known, it is estimated to be approximately 500,000 times smaller than the mass of the electron.

Neutrinos are not affected by the electromagnetic force or the strong nuclear force; but they are affected by the weak nuclear force and by the force of gravity

It is curious to know that from the fact that three classes of neutrinos are detected on Earth (electron neutrino, muon neutrino and tauon neutrino) it is possible to deduce the amount of helium that was generated at the time of the Big Bang.

neutrinos Sun
The Sun is a source of neutrinos. Credit: NASA / SDO / AIA, website “nbcnews.com”

The Sun is the most important source of the neutrinos that reach Earth.

The beta decay processes of the reactions that take place in the solar nucleus, generate enormous amounts of neutrinos.

As these do not interact easily with matter, they escape freely from the solar nucleus, reach the Earth and pass through it with little difficulty.

In fact, a human being is pierced, every second, by billions of these tiny particles, without knowing it. It has been very difficult to devise any system that could detect them.

The neutrinos generated in type II supernovae cause the expulsion of a good part of the star’s mass into the interstellar medium.

Los neutrinos
El español Carlos Pobes en la Antártida. Crédito: web elmundo.es/elmundo/2012/02/15/ciencia/1329323292.html

In 2012, a group of 50 people, including the Spaniard Carlos Pobes, from the University of Zaragoza, began an 8-month job at the American Amundsen-Scott scientific base in Antarctica.

Taking advantage of the 3 km thick Antarctic ice, they tried to capture neutrinos from all corners of space. The experiment involved 39 research institutes from 11 countries.