Showing posts with label helicity. Show all posts
Showing posts with label helicity. Show all posts

PHYSICS DICTIONARY

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Hadrons

Kaons, Pions together with Baryons are placed in group of strongly interacting particles called Hadrons.


Half Life

Term used in nuclear physics. It represents the time it takes for a radioactive isotope for decaying its activity to half of its present value.


Half Wave Plate

Plate of uniaxial double refracting crystals such as quartz and calcite with optic axis parallel to their refracting surface, the thickness of which is such that it produces a path difference of λ/2 or a phase difference Π in between ordinary and extra ordinary waves.


Half-Wave Rectifier

Device which conducts current only during the positive half cycles of input ac supply. The negative half cycles of ac supply are suppressed i.e. during negative half cycles, no current is conducted and hence no voltage appears across load. Therefore, current always flows in one direction (DC) through load after every half cycle. 


Hall Effect

When a piece of semiconductor carrying a current is placed in a transverse magnetic field, an electric field is produced inside the conductor in a direction normal to both current and magnetic field.


Hall Mobility

Mobility of charge carriers under Hall Effect defined as product of hall coefficient and conductivity.


Hall Probe

Hall probe is a magnetic field sensor that passes electric current when the sensor is perpendicular to magnetic field. The stranger the magnetic field the more the current is converted to voltage. They are used for proximity switching, positioning etc.


Hamilton’s Principle

If a particle moves from one point to other in time interval t1 t t2, then the actual path it follows is the one for which action assume stationary value.


Hamiltonian Principle

The path actually traversed by a conservative, holonomic dynamical system from time t1 to t2 is one over which the integral of the lagrangian between limits t1 and t2 is stationary i.e., the time integral of lagrangian is extremum.


Hard Radiation

The term attributed to high energetic X-rays or gamma rays having high penetration power into almost all materials. 


Hardness

Mechanical property which is a measure of materials resistance to localized plastic deformation.


Harmonic Motion

 See simple harmonic motion.


Health Physics

It is branch of physics which deals with radiation protection of occupational workers in nuclear reactors and other radiation material handling centers.

 

Heat Capacity

The quantity of heat required to raise the temperature of the whole body there 1oC or 1oK is called heat capacity of body.


Heat Engine Law

Conversion of total heat energy into work is impossible.


Heat Engine

It is cyclic process in which heat is continuously converted into mechanical work. It has 3 main parts: source, sink and working substance. i) Source of heat at constant temperature to drive heat; ii) Sink at constant temperature, heat can be supplied without change in temperature. iii) Working substance: absorbs heat from source, converts part of the heat into mechanical work & rejects remaining heat to sink.


Heat

It is a form of energy (kinetic energy of molecules constituting the body) which produces sensation of warmth.

                                      (or)

It is energy that is transferred between a system and its environment because of a temperature difference that exists between them.


Heavy Water

Also referred as Deuterium oxide, is a type of water in which Deuterium (an isotope of Hydrogen) substitutes Hydrogen i.e. D2O. It has importance for having properties like Neutron moderation, high boiling point etc.


Heisenberg Forces

Type of nuclear force in which there is exchange of both spin and position coordinates.


Heisenberg’s Uncertainty Principle

Based on wave nature of matter, Heisenberg proposed a principle according to which, macroscopically it is possible to exactly measure position of moving particle and momentum associated with it but microscopically it is not possible. According to this principle, product of uncertainties in the measurement of position and momentum is of order of h/2π; where ‘h’ is Planck’s constant.


Helicity

Lee and yang suggested that the violation of parity in beta decay was direct consequence of longitudinal polarization of emitted electrons and Neutrons. The state and degree of longitudinal polarization of particles is represented by the term Helicity.


Heliocentric Theory

The theory proposed by Nicolas Copernicus, a polish astronomer. Heliocentric system first appeared in his book “De revolutionibus orbium coelestium”, “on the revolutions of heavenly bodies” which appeared in 1543. “Helios” in Greek means “sun”. Heliocentric means that the sun is at the center. As per this theory, sun remains at center and all the planets revolve round it. The moon is only celestial sphere in the system that revolves round the earth and together around sun. 

Paulis Hypothesis of Beta Decay

Pauli introduced concept of third particle, a neutral particle which gets emitted in β⁻decay. This particle has the generic name of Neutrino.

The total energy is shared by 3 particles

The recoil nucleus
The Electron
The Neutrino

Because of its comparatively great mass, the recoil energy of Nucleus is very small and nearly all Kinetic Energy is shared between the Beta particle and the Neutrino.

In addition to laws of conservation of charge and energy, we must also apply the laws of conservation Linear and angular momentum to every nuclear process. Taking our reference system as the parent nucleus at rest, the vector sum of Linear Momenta of the recoil nucleus, the beta particle and neutrino must be zero.

To conserve angular momentum in β⁻decay, we note that parent and daughter nuclei are isobars; i.e. they have equal number of nucleons. Hence, the total change in nuclear angular momenta will be either zero or an integral multiple of ℏ.

The beta particle has an intrinsic spin angular momenta of 1/2ℏ.The vector sum of angular momenta of Neutrino and beta particle will be either zero or one in units of ℏ.

The present accepted theory, which is supported by experimental evidence shows that there are two types of neutrino or two components of Neutrino. It has been found that the axis of spin of neutrino is parallel to its direction of motion; one type spins according to the left hand rule with respect to its direction of motion as its axis, the other component spins according to right hand rule.

The first type is usually called neutrino represented by symbol 𝜈, the second type is called antineutrino.
 
The spin vector of neutrino points opposite to direction of its motion.

The spin vector of anti neutrino points in the direction of its motion.

Another way of saying this is that the helicity of neutrino is negative and that of anti neutrino is positive or one has right handed helicity and other has left handed helicity.