Weak interaction is one of the four fundamental forces governing all matter in the universe. The remaining three are gravity, electromagnetism, and strong interaction. While other forces hold things together, weak strength plays a large role in destroying them.
Weak interaction is stronger than gravity, but it is effective only at very small distances. Strength acts at the subatomic level and plays a crucial role in providing energy to stars and creating elements. She is also responsible for much of the natural radiation in the universe.
Fermi Theory
The Italian physicist Enrico Fermi in 1933 developed a theory to explain beta decay - the process of converting a neutron into a proton and displacing an electron, which is often called a beta particle in this context. He defined a new type of force, the so-called weak interaction, which was responsible for decay, the fundamental process of the conversion of a neutron into a proton, a neutrino and an electron, which was later defined as an antineutrino.
Fermi initially assumed that there was zero distance and traction. Two particles had to touch in order for the force to work. Since then, it turned out that weak interaction is actually an attractive force, which manifests itself at an extremely short distance, equal to 0.1% of the proton diameter.
Electroweak force
In radioactive decays, a weak force is approximately 100,000 times less than electromagnetic. However, it is now known that it is internally equal to electromagnetic, and these two clearly distinct phenomena are believed to be manifestations of a single electroweak force. This is confirmed by the fact that they are combined at energies of more than 100 GeV.
It is sometimes said that a weak interaction is manifested in the decay of molecules. However, intermolecular forces are electrostatic in nature. They were discovered by van der Waals and bear his name.
Standard model
Weak interaction in physics is part of the standard model - the theory of elementary particles, which describes the fundamental structure of matter using a set of elegant equations. According to this model, elementary particles, that is, that which cannot be divided into smaller parts, are the building blocks of the Universe.
One such particle is a quark. Scientists do not assume the existence of anything less, but they are still looking. There are 6 types or varieties of quarks. Place them in increasing mass:
- upper;
- lower;
- strange;
- charmed;
- charming;
- true.
In various combinations, they form many different types of subatomic particles. So, for example, protons and neutrons - large particles of an atomic nucleus - consist of three quarks each. The two upper and lower constitute a proton. The upper and two lower ones form a neutron. A change in the sort of quark can change a proton into a neutron, thereby transforming one element into another.
Another type of elementary particle is a boson. These particles are carriers of interaction, which consist of energy beams. Photons are one type of boson, gluons are another. Each of these four forces is the result of an exchange of interaction carriers. Strong interaction is carried out by gluon, and electromagnetic interaction - by a photon. Graviton is theoretically a carrier of gravity, but it was not found.
W and Z bosons
Weak interaction is carried by W- and Z-bosons. These particles were predicted by Nobel laureates Steven Weinberg, Sheldon Salam and Abdus Gleshaw in the 60s of the last century, and found them in 1983 at the European Organization for Nuclear Research CERN.
W-bosons are electrically charged and are denoted by the symbols W + (positively charged) and W - (negatively charged). The W boson changes the composition of particles. By emitting an electrically charged W boson, a weak force changes the sort of quark, turning a proton into a neutron or vice versa. This is what causes nuclear fusion and makes the stars burn.
This reaction creates heavier elements that are ultimately thrown into space by supernova explosions to become building materials for planets, plants, people and everything else on Earth.
Neutral current
The Z boson is neutral and carries a weak neutral current. Its interaction with particles is difficult to detect. An experimental search for W- and Z-bosons in the 1960s led scientists to a theory that combines electromagnetic and weak forces into a single "electroweak". However, the theory required carrier particles to be weightless, and scientists knew that theoretically the W boson should be heavy in order to explain its short range. Theorists attributed the mass W to the invisible mechanism, called the Higgs mechanism, which provides for the existence of the Higgs boson.
In 2012, CERN reported that scientists using the world's largest accelerator - the Large Hadron Collider - observed a new particle, "corresponding to the Higgs boson."
Beta decay
Weak interaction appears during β-decay, a process in which a proton turns into a neutron and vice versa. It occurs when in a nucleus with too many neutrons or protons one of them is converted to another.
Beta decay can occur in one of two ways:
- In negative beta decay, sometimes written as β - decay, the neutron splits into a proton, antineutrino, and electron.
- Weak interaction is manifested during the decay of atomic nuclei, sometimes written as β + decay, when the proton splits into a neutron, neutrino and positron.
One of the elements can turn into another when one of its neutrons spontaneously turns into a proton through minus beta decay, or when one of its protons spontaneously turns into a neutron through β + decay.
Double beta decay occurs when 2 protons in the nucleus are simultaneously transformed into 2 neutrons or vice versa, as a result of which 2 electron antineutrinos and 2 beta particles are emitted. In a hypothetical neutrinoless double beta decay, neutrinos do not form.
Electronic capture
A proton can turn into a neutron through a process called electron capture or K-capture. When there is an excess number of protons in the nucleus with respect to the number of neutrons, the electron, as a rule, from the inner electron shell seems to fall into the nucleus. The orbital electron is captured by the mother nucleus, the products of which are the daughter nucleus and neutrino. The atomic number of the resulting daughter nucleus decreases by 1, but the total number of protons and neutrons remains the same.
Thermonuclear reaction
Weak interaction takes part in nuclear fusion - a reaction that supplies energy to the sun and thermonuclear (hydrogen) bombs.
The first step in the fusion of hydrogen is the collision of two protons with sufficient strength to overcome the mutual repulsion experienced by them due to their electromagnetic interaction.
If both particles are placed close to each other, strong interaction can bind them. This creates an unstable form of helium ( 2 He), which has a nucleus with two protons, in contrast to the stable form ( 4 He), which has two neutrons and two protons.
At the next stage, weak interaction comes into play. Due to an overabundance of protons, one of them undergoes beta decay. After this, other reactions, including the intermediate formation and fusion of 3 He, ultimately form a stable 4 He.