A neutrino can be defined as an elementary subatomic particle with no charge and 1/2 unit spin. They are fermions that react via weak interaction and gravity. Neutrino has rest mass is almost negligible hence considered to be zero. The rest mass of the neutrino is much less in comparison to other elementary particles. Wolfgang Pauli discovered neutrino in 1930, and the name was popularised by the Italian physicist Enrico Fermi. Neutrinos, which in Italian means “the little neutral ones” are electrically neutral particles, and their size is smaller than that of the neutrons. Here’s what you always wanted to know about neutrinos.
Alpha and beta rays were discovered in 1899 by Rutherford. A study of radioactive disintegrations led to the conclusion that alpha rays were ‘monokinetic’ and consumed the entire energy available in the decay. Beta rays on the other hand took a certain part of the energy of the entire decay. This created a contradiction with the conservation of energy law. The missing energy led Neil Bohr to propose that the conservation of energy law was not prevalent in all cases. This was a mortal sin for physicists.
A physicist Wolfgang Pauli postulated the existence of an electrically neutral particle that is emitted with a beta particle in beta decay was a hypothetical third body that took the extra energy which was not taken by the beta particle. Hence, the law of conservation of energy was saved. This hypothesis found support from Enrico Fermi, an Italian physicist. The conference of Solvay in 1933 proposed that an electron-neutrino pair is spontaneously produced by the nucleus during beta decay. Francis Perrin suggested that such a particle would have zero mass and would be lightweight even by comparison with an electron.
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Figure: Neutrinos- The super-fast subatomic particles of the universe
Properties of Neutrino
The properties of the subatomic particle neutrino are as follow:
Neutrinos belong to the family of leptons. This particle family has weak interactive forces.
Neutrinos are of three kinds depending upon the charged lepton they are associated with. These charged leptons are the electron, the muon and the tau. The associated electrons are named electron-neutrino, muon-neutrino, and tau-neutrino.
A neutrino also has an antimatter component known as an antineutrino. Neutrino and antineutrino together comprise a hot area of research in modern physics.
Neutrinos are not affected by electromagnetic forces and hence, do not cause ionization of matter.
Neutrinos react with matter only through extremely weak interactive forces.
They are capable of passing through an enormous number of atoms without causing any reaction and hence they are the most penetrating subatomic particle.
Neutrinos can change a nucleus into another and this process is used in a radiochemical neutrino detector.
Types of Neutrinos
As mentioned earlier, neutrinos are of three types or flavours and each of them has its respective properties. The first discovered neutrino is the electron-neutrino. Electron-neutrino has no electric charge and mass. It was discovered by Wolfgang Pauli to satisfy the energy loss in the process of radioactive beta decay. This particle is emitted along with a positron in positive beta decay. For negative beta decay, an electron with its antimatter particle that is an antineutrino is emitted.
Post the discovery of the second charge lepton, the muon, eventual identification of the second type of neutrino, the muon-neutrino started. On the basis of the results of a particle-accelerator experiment, high energy muon-neutrinos were discovered in 1962. They were produced from the decay of pi-meson. Though usually unreactive like other neutrinos, sometimes muon-neutrino reacts with protons and neutrons to produce muons.
In 2000, physicists experimentally showed the first evidence of the existence of the tau-neutrino. It was after the discovery of the tau leptons.
There are many active research areas involving neutrinos. Neutrino properties, testing predictions of their behaviour, and masses and rates of CP violation which is still unpredicted from the current theories. These subatomic particles are indispensable for the validation of the law of conservation of energy. They are related to radioactivity and play a very important role in nuclear physics. Knowledge of neutrinos and their properties enable physicists to understand the dynamics of several nuclear reactions.
Did You Know?
Extra-terrestrial sources of neutrinos are a subject of infancy. The only extra-terrestrial sources as reported till 2018 are the sun and the supernova 1987A in the Large Magellanic Cloud. Neutrino astronomy is a branch of astronomy in which astronomical objects are observed with the help of neutrino detectors in a special observatory. Radioactive decay and nuclear reactions take place in the sun which is similar to the ones taking place in nuclear reactors or when atoms are hit by cosmic rays. This enables us to study processes that are taking place in space. The processes which are inaccessible to the optical telescopes can be observed by neutrinos due to their extremely weak interactions.