Liquid drop Model.

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 no nucleons above the surface. Therefore under such condition one can conclude that these forces are analogous to surface tension.

4) The binding energy per nucleon is constant just like the latent heat of vapourisation is a constant quantity for a liquid.

5) The nucleons in the nucleus move about the spherical enclosure called the nuclear potential barrier just like the molecules of liquid move about in the spherical drop of liquid.

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 fract...

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 t...

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 ...

Modern Physics

Search This Blog