Modern Physics

 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...

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...

 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 f...

 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 t...

 Beta decay; Beta decay is a spontaneous radioactive decay process in which either a neutron gets converted into proton or a proton gets converted into neutron with the emission of electron or positron respectively. Whenever proton or neutron are in higher energy level because they are in excess they get converted into another kind of particle and thus decreasing the energy of the system and increasing its stability. In ¹²B there are seven neutrons and five protons while in ¹²C there are six neutrons and six protons, since both protons and neutrons are fermions and no more than two same kind of fermions can occupy the given energy level. Thus the figure below shows the nuclear energy diagram of ¹²C and ¹²B. Since in ¹²B nucleus, there are two neutrons present in excess, if a neutron gets converted in proton, then this new proton occupies an energy level lesser in energy than that of neutron and thus giving a stable ¹²C nucleus. Pauli theory of beta decay; An interesting historical ...

Radioactivity In 1996, Becquerel discovered natural radioactivity. The emission of radiation from number of elements due to disintegration of nuclei is called radioactivity. The elements which shows this phenomena are called radioactive elements. Rutherford discovered that two types of radiations are emitted alpha ray and beta ray. Later Vollard discovered that third type of radiation is also emitted which he named gamma ray. Atoms do radioactive decay because they are unstable. It is the number of protons and neutrons in the nucleus that determines whether the atom is stable or not. So, when they do radioactive decay they want to change that number of protons and neutrons. Alpha Decay Alpha Decay is a spontaneous decay process in which a large size nucleus spontaneously undergoes a decay process which lead to the emission of 𝛂 particle (i.e Helium nuclei). Alpha Decay. Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together i...

 Liquid drop Model; Bohr proposed this model because of some basic similarities between nucleus and a liquid drop. There is analogy of cohesive forces between the molecules in the liquid with the short range attractive force between the nucleons in the nucleus. The assumption of liquid drop Model are given below: 1) The nucleus was assumed to be an incompressible sphere just like a liquid drop. The nuclear density is independent of nuclear volume as that of a liquid drop. Unlike the liquid drop, the nuclear density is also independent of nuclear matter. 2) The nuclear forces between the nucleons is independent of charges. It is a short range force and is attractive in nature. 3) The spherical shape of liquid surface is due to symmetrical surface tension forces which acts towards the centre of the drop, the nuclear forces are similar in this case. Inside the nucleus, the nucleons are attracted from all sides equally but on the surface the nucleons are attracted downward as there is ...