Classification of elementary particles.

On the basis of spin property, elementary particles are classified into two types namely;

Bosons

Fermions

Bosons

Bosons are the particles having integral spin and follows Bose Einstein Statistics. Bosons are further classified into two types namely massless bosons and mesons.

Massless bosons

Massless bosons include photons and gravitons.

Photons

Photons are quantum of electromagnetic radiation. They are massless and chargeless particle and have spin 1.

Gravitons

Gravitons are supposed to be responsible for the gravitational field. No gravitons are detected experimentally so far. Gravitons are massless, chargeless particles having spin 2.

Both photons and gravitons are consider to be antiparticles of themselves.

Mesons

Mesons are strongly interacting zero spin particle. Mesons owe their existence to cosmic rays. The members of this group are π mesons, η mesons and k mesons.

π mesons

π mesons are also called pions. π mesons are of three types π⁺, π⁻ and π⁰ mesons. The antiparticle of π⁰ is itself. π⁻ is the antiparticle of π⁺.

k mesons

k mesons are also called kaons. K mesons are of four types.

Types of k mesons.

η mesons

η mesons are neutral particle. η⁰ is the antiparticle of itself.

Fermions

Fermions are the particles having half integral spin and follows Fermi Dirac Statistics. Fermions are further classified into two types namely leptons and baryons.

Leptons

Leptons are light particle having spin 1/2. The member of this group are electrons and positrons, positive and negative muons and neutrino and antineutrino.

Electrons and positrons

Electrons are negatively charged, stable atomic particles. The positrons are similar to electrons in all respect except that it is positively charge. Positrons are antiparticle of electrons.

Muons

The positive and negative 𝜇 particles ( 𝜇⁺, 𝜇⁻) are called muons. Muon is an unstable particle and soon decays.

Neutrino and antineutrino

These particles have negligible rest mass and zero charge.

Baryons

Baryons are the particles having rest mass equal to or greater than that of nucleons. Baryons are fermions with half integral spin i.e 1/2, 3/2 etc. Baryons include nucleons and hyperons. Baryons and mesons are together called hadrons.

Nucleons

Nucleons include protons, neutrons and their antiparticle antiprotons and antineutrons. Both protons and neutrons have spin 1/2.

Hyperons

These are the particles having rest mass greater than that of nucleons. Hyperons include lambda particle Λ⁰, sigma particle (Σ), cascade particle (𝜩) and omega particle (𝛀). All these particles have spin 1/2 except 𝛀 particle which have spin 3/2.

Classification of elementary particles.

Comments

Mass defect, packing fraction and binding energy.

Mass defect, packing fraction and binding energy: It was assumed that mass of the nucleus is equal to the mass of its constituents (i.e protons and neutrons). But experimentally it was found that the actual mass of the nucleus is less than the theoretical mass. Thus, the difference between the theoretical mass and experimental mass is called mass defect i.e ∆m={[Zmₚ + (A-Z)mₙ] - M} Where mₚ= mass of proton mₙ= mass of neutron M= actual mass of nucleus Z= atomic number A= mass number The ratio of mass defect and mass number (A) is called packing fraction (f) f = ∆m/A Thus packing fraction is the mass defect available per nucleon. The packing fraction explains the stability of the nucleus. The packing fraction may be positive, negative or zero. The positive value of packing fraction indicates that the nuclei is unstable while the negative value of packing fraction indicates that a fraction of nucleus mass has been converted into e

Different kinds of beta decay.

Different kinds of beta decay 1) Negative beta decay process: When there is excess number of neutrons in the nucleus, the neutron is converted into proton with the emission of electron and antineutrino particle and this process is called negative beta decay process. Negative beta decay. 2) Positive beta decay process: When there is excess number of protons in the nucleus, the proton is converted into neutron with the emission of positron and neutrino particle and this process is called positive beta decay process. Positive beta decay. 3) Electron Capture: When there is excess number of protons in the nucleus, sometimes the nucleus will absorbed the nearby electrons in the nearest electron orbital emitting neutron and a neutrino and this process is called electron capture. Electron capture. 4) Inverse beta decay: Inverse beta decay. Thus such kind of reaction in which neutrinos are absorbed to create some sort of beta decay is called inverse beta decay. Inverse beta decay confirm the e

LS coupling and jj coupling.

Total angular momentum: The total angular momentum of an electron is the sum of the orbital angular momentum and spin angular momentum of the electron i.e Coupling Scheme Since an atom consist of large number of electrons having different orbital and spin momenta, Coupling scheme is necessary to obtain the resultant orbit and spin momenta of atom as a whole. There are two types of coupling scheme namely 1) LS Coupling 2) JJ Coupling. 1)LS Coupling: In this coupling the 'l' vectors of all electrons combine to form resultant 'L' vector and all the 's' vectors of these electrons combine to form resultant 'S' vector. Then the 'L' vector and 'S' vector undergoes vector addition to give resultant 'J' vector which represents the total angular momentum of an atom. Symbolically LS coupling is represented as This type of coupling is governed by the following principles: 1) All the three vectors (L,S and J vectors) are quantized. 2)L is an

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