Modern Physics

Quarks Gellmann and independently George Nishijina propose that all baryons consist of three fundamental particles. Gellmann named these particles 'quarks' from the phrase 'three quarks for Muster Mark' appear in the novel Finnegann's Wake. The three fundamental quarks are up, down and strange. The up and down quarks have strangeness number zero and the strange quark have strangeness number -1. Since each baryon (B = 1) consist of three quarks, thus each quark has baryon number B = 1/3. Each antibaryon (B = -1) consist of three antiquarks, thus each antiquark have B = -1/3.  A meson (B = 0) is supposed to consist of a quark and an antiquark. Quarks and antiquarks have spin equal to 1/2. Each quark have fractional charge. No particle in nature have fractional charge, so quark hypothesis was hard to accept at the beginning. The existence of quark was proved by the simple experiment which involved scattering of high energy electrons by protons.  Flavour of quarks There

Quantum numbers; In case of elementary particles, while considering reactions, we must consider various parameters. One of the major parameter is quantum numbers.  Baryon and lepton numbers A set of quantum numbers is used to characterise baryons and three families of leptons. Baryon and lepton numbers.   The significance of these numbers is that in any kind of reaction the total baryon numbers (B) and lepton numbers are conserved. Baryon and lepton quantum numbers are conserved. Strangeness number (S) Gellmann and Nishijina introduced a new quantum number called strangeness quantum number. Strangeness number is assigned to strange particles, which are named due to their strange behaviour i.e they are produced via strong interaction or electromagnetic interaction, but they decay via weak interaction. Another fact about these particles is that they are always produced in pairs. The assignment of strangeness number to particle is shown in Table below. Strangeness number of hadrons. The a

 Fundamental interactions There are four types of interaction between the elementary particles. These are 1) Gravitation interaction The relative magnitude of gravitational interaction is 10⁻³⁹ and thus is the weakest interaction. The range of gravitation interaction is infinite. The particles exchange during gravitation interaction are gravitons. Every particle having mass is affected by gravitational interaction. It has characteristic time 10⁻¹⁶s and it has spin 2. Example of gravitational interaction is astronomical forces. 2) Electromagnetic interaction The relative magnitude of electromagnetic interaction is 10⁻³. It is a long range interaction (infinite). The particles exchange during electromagnetic interactions are photons. The particles affected by electromagnetic interactions are charged particles. It has characteristic time 10⁻²⁰s and it has spin 1. Example of electromagnetic interaction is atomic forces. 3) Strong interaction The relative magnitude of strong interaction is

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

 Gamma decay A nucleus can exist in states whose energies are higher than that of its ground state, as an atom can. An excited nucleus is denoted by an asterisk on its usual symbol. The excited nucleus return to its ground state by emitting photon whose energy corresponds to the energy difference between initial and final states in the transition involved. The photons emitted by the nucleus have energy in the range of several MeV and is traditionally called gamma decay. Unlike, alpha decay and beta decay, the parent nucleus does not undergo any physical change in the process, daughter and parent nuclei are the same. Most of the time, gamma decay occurs after the radioactive nuclei have undergone an alpha or a beta decay. The alpha and beta decays leave the daughter nuclei in an excited state. From the excited state, the daughter nuclei can get back to the ground state by emitting one or more high energy gamma rays.  The relationship between decay and energy level is shown in figure bel

 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