Showing posts with label Fermi. Show all posts
Showing posts with label Fermi. Show all posts


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Fermi Level

It determines probability of occupancy of allowed energy states.


It is unit of wave length used in nuclear physics which is named after Italian physicist Enrico Fermi. One Fermi is equal to one Femto meter i.e. 10-15 meter.


Elementary particles which obey Fermi Dirac statistics having spin ½. They fall in two main classes according to whether they are lighter than mesons or heavier. The two classes are Leptons or Baryons respectively.


Ceramic oxide materials composed of both divalent and trivalent cations.


In some materials (e.g., Fe, Ni, Co) the non – zero atomic magnetic dipoles interact with one another and spontaneously produce magnetization over small domains of sizes of few microns. The different domains may have random orientations resulting in zero bulk magnetic moment. Macroscopic magnetization arises when the domains are made to align themselves in a common direction. In ferromagnetic materials for each value of magnetization, there is no unique value of the field B; it depends on the history by which the magnetization is reached. This is the phenomenon of hysteresis.


Phenomenon exhibited by a group of dielectric materials which exhibit spontaneous polarization i.e. polarization in absence of an electric field. They are dielectric analogue of ferromagnetic materials. In ferroelectric materials, permanent electric dipoles exist.   

Ferrous Alloy

A metal alloy for which iron is the prime constituent.

Fick’s first Law

The diffusion flux is proportional to concentration gradient.

J=-D(dc/dx); the law holds good for steady state diffusion situations. The negative sign indicates that ‘J’ is positive when movement is down the gradient. ‘D’ is diffusivity or diffusion coefficient.

Fick’s Second Law

The time rate of change of concentration is proportional to second derivative of concentration. This law is employed in non-steady state diffusion situations.

Fictious Force (Pseudo force)

It is force which does not act on object but appears due to acceleration of non inertial frame of reference.


A property of a point in space describing the forces that would be exerted on particle, if it was there.


Any physical quantity which takes different values at different points in space and time.

Fine Structure Constant

The amount of splitting of main spectral lines of atom is characterized by dimensionless constant called fine structure constant. The value is nearly equal to 1/137.

Fine Structure

The splitting of main spectral lines of an atom in to two or more components each representing slightly different wavelength is called as fine structure. It is actually produced when an atom emits light in making the transition from one energy state to another. The fine structure of main lines arise from the interaction of orbital motion of an electron with the quantum mechanical spin of that electron.


Nuclei that can undergo fission when neutron impinges on them are called fissile nuclei.

Fission Chamber

Fission chambers use neutron-induced fission to detect neutrons. The chamber is usually similar in construction to that of an ionization chamber except that the coating material is highly enriched U-235. The neutrons interact with the

U-235, causing fission. One of the two fission fragments enters the chamber while the other fission fragment embeds itself in the chamber wall.

Flint Glass

An optical glass developed by George Ravenscroft in 1675. Flint glass is any highly refractive Lead containing glass used to make lenses & prisms. It has got high dispersion (low abbe number).


The flux integrated over a period of time is called as integrated flux or fluence. Mathematically, it is given by Φ=dN/da; where, dN represents the number of particles passing through the area ‘da’. Since this relation does not explicitly contain time, it can also be interpreted to represent the number of particles incident on a surface area ‘da’ at any instant.

Fluid Pressure

It is normal force per unit area of surface. Surface may be a body immersed in fluid or any imaginary surface with in fluid.


Substances capable of flowing are fluids. They don’t have any fixed shape of their own. They take shape of containing vessel.


There are 3 models of beta radioactivity

i) Negatron (β-) Emission

ii) Orbital Electron Capture

iii) Positron (β+) Emission


Beta ray spectra is of two types:

i) Continuous Spectrum

ii) Sharp Line Spectrum

The continuous spectrum is due to Negatrons and Positrons.

There is a possibility of the daughter nucleus being created in an excited state, which may decay by gamma emission.

Rutherford suggested that part of gamma radiation is absorbed by outer electrons of same atom and as a result the secondary beta ray electrons are ejected.  The process is called “Internal Conversion”.

The sharp Line Spectrum is due to secondary beta rays emitted due to internal conversion.

The process of Beta disintegration differs from alpha disintegration in following two respects:

i) The alpha particles are already present in the initial nucleus while beta particles are not present in the initial nucleus. Beta particles are created at the time of emission.

ii) The energy spectrum of alpha particles is discrete while energy spectrum of beta particles is continuous.

iii) Beta decay is a three body problem while alpha decay is a two body problem.

In the Neutrino, the spin and angular momentum vector are oppositely directed and in anti neutrino these vectors are aligned together.

Since a matter-antimatter pair is formed whenever energy is converted into mass, in a conversion of a nuclear Neutron to a Proton, the negative electron (matter) should accompany anti neutrino (anti matter). Similarly Neutrino is emitted with positron emission and orbital electron capture.


In 1934, Fermi made a successful theory of beta decay. The theory is based on following assumptions:
1) The light particles, the electron and neutrino ar created by transformation of a neutron into a proton in a nucleus or vice versa.

Note:- Neutron or Proton that are transformed to beta particles are not free particles but are bound to Nucleus by Nuclear Forces.

2) The energy remains conserved in decay process, the available energy being shared among the electron and the neutrino.

3) The beta decay process is analogous to the emission of electromagnetic radiation by an atom, with electron-neutrino field acting in place of Electromagnetic field.

4) “Electron-Neutrino” field is weak in contrast to short range strong interactions which exist between Nucleons bound in the nucleus.

5) Time   Dependent Perturbation theory is a very good approximation because of smallness of coupling constants.

6) As Nucleons move with velocities of only nearly c/10 in nuclei calculations can be made with non relativistic nuclear wave functions.