Showing posts with label meson. Show all posts
Showing posts with label meson. Show all posts

PHYSICS DICTIONARY

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Mechanical Wave
It is a disturbance which transmits from one part to the other part of the medium with a constant speed by periodic oscillations of the medium particles.


Mechanics

Branch of physics which deals with behavior of environmental objects under force.

(or)

Branch of physics which deals with energy & forces acting on materialistic bodies in motion is called mechanics.


Median

The median, as implied by its name, is the middle value in a distribution of values. To calculate the median, simply sort all of the values from lowest to highest and then identify the middle value.


Medical Physics

Branch of physics which uses physics principles in practice of medicine. It is most often used to describe physics applications related to use of radiation in medicine.

Medical physics is a branch of physics dealing with the application of physics to medicine, most generally in three areas:  Diagnostic imaging physics, Nuclear medicine physics and Radiotherapy physics. While nuclear medicine concentrates mainly on application of unsealed radio nuclides for diagnosis and treatment of disease, the use of x rays forms an important component of diagnostic radiology as well as radio therapy.


Mega

Prefix in metric system denoting a factor of million i.e. 106 of basic unit.         


Meissner Effect

The property of exhibiting perfect diamagnetism by super conductor is called Meissner effect.


Melanin

It is pigment on human skin which absorbs UV rays.


Melody

When two or more notes are sounded one after the other, the combined note producing pleasing effect on the ear, is called melody.


Melting

Physical process which results in phase transition and a substance from solid to liquid under influence of temperature.


Melting Point

Temperature at which solid changes its state from solid to liquid at atmospheric pressure.

 

Membrane

 A semi permeable thin layer of material capable of separating


MEMS

 A large number of miniature mechanical devices that are integrated with electrical elements on a silicon substrate. Mechanical components act as micro sensors and micro actuators and are in form of beams, gears, motors and membranes. In response to micro sensor stimuli, the electrical elements render decisions that direct responses to the micro actuator devices.


Meniscus

The curved upper surface of a non turbulent liquid in a container fixed close to the surface of container, caused by surface tension. It can be either convex or concave.


Meson

Modern definition of Meson is that it is a particle that is believed to be fundamental, not composite capable of participating in strong interactions. It is a Boson


Meta Stable State

Atomic or nuclear energy level, which has life time of order 10-3 sec or more.


Metallic Bond

In this type of bonding, the valence electrons which hold atoms together are not bound to individual atoms or pairs of atoms but moves freely throughout the whole metal.


Meteor

It is a small body of matter from other space that enters the earth’s atmosphere appearing as streak of light.


Meteorology

 It is science of weather. It is interdisciplinary science because atmosphere, land and ocean constitute integrated system. The 3 basic aspects of meteorology are observation, understanding and prediction of weather.


Mho

Unit for electrical conductance; the name suggested by Thomson.

Refer Siemens also.


Michelson’s Interferometer
The Michelson interferometer produces interference fringes by splitting a beam of monochromatic light so that one beam strikes a fixed mirror and the other a movable mirror. When the reflected beams are brought back together then interference pattern results. Precise distance measurements can be made with the Michelson interferometer by moving the mirror and counting the interference fringes which move by a reference point. 

Discovery of Meson

Yukawa predicted that it is due to the exchange of a massive particle between the nucleons leading to a short range force.

A result of much calculation is that the Range of a force is of same order of magnitude as compton wave length of exchanged particle. By analogy the nuclear force has a Range of about 1.4 x 10⁻¹³ cm.

A particle for which ℏ/mc = 1.4 x 10⁻¹³ cm will have its rest mass energy equal to 150 MeV or about 275 times the mass of electron.

The name Mesotron was given to this exchanged particle whose mass is intermediate between that   of electron and Proton. The modern name is Meson.

In 1937, a particle believed to be of the type was discovered by "S H Neddermeyer" and "C D Anderson" and independently by "J C Street" and "E C Stevenson" in cloud chamber studies of cosmic rays.

Estimates of the mass of this Meson were made from measurements of curvature of its track in a magnetic field which yielded values for mass of Meson in neighbourhood of 200 electron masses. Both positive and negative particles were observed.

WB Fretter (1946) made some very careful measurements of masses of mu particles, using two cloud chambers, one above the other. They were expanded simultaneously when ever a penetrating particle passed through them. This was accomplished by placing the Geiger Counters above each chamber, the two sets of actuating the expansion mechanism whenever an ionizing particle passed through  them as shown in below Fig.





The upper cloud chamber was placed in a magnetic induction of 5300 Gauss so that momentum of particle could be measured. The lower cloud chamber had a set of lead plates 0.5 inch thick and placed 1.5 inch apart so that Range in lead of particles could be measured. Out of 2100 tracks observed, 26 were suitable for measurement, their mass determination is yielded a value of 202Me.

The present accepted value is 207mₑ.

Later Occhialini and Powell and D M Perkins using a special nuclear emulsion photographic plates exposed at high altitudes, observed that some of Mesons stopped in photographic emulsions and produced so called stars - that is, nuclear disintegration with the emission of slow protons or alpha particles.

The photographs showed the curved track of heavy Meson which is named '𝚷' Meson; when captured by a nucleus in the emulsion, the resulting nuclear disintegration produces a star in which 3 charged particles are emitted.

The kinetic energy of muon emitted in the decay of a Pi Meson is always same and is equal to about 4 MeV.

𝚷⁺  ------------>  𝛍⁺ + 𝝂
𝚷⁻  ------------>  𝛍⁻ + 𝝂'    ;   ð‚' is anti neutrino     







Properties of Pions

  • Pions are Mesons
  • There are 3 kinds of Pions: π⁺, π⁻, π⁰
  • Either charged Pion possess a mass of 139.6 MeV and neutral Pion is 135.0 MeV.
  • Pions have spin zero.
  • P+P → π⁺ + n + P
  • P+P → π⁰ + P + P
  • P+n → π⁻ + P + P

  • Charged Pions decay into Muons (Weak Process in Decay):

π⁺ → 𝜇⁺ + 𝜈
π⁻ → 𝜇⁻ + 𝜈

  • The mean life is 2.6 x 10⁻⁸ Sec. 

  • The neutral Pion decays in different way; process is 

π⁰ → 𝛾 + 𝛾 ; This decay is Electromagnetic in nature.

The presence of photons in final state leads us to expect the process is electromagnetic in nature.

The Photons from the decay always seem to come from the spot at which π⁰was produced in some bombardment process. The measurement of life time of such a short lived object is not easy but emulsion techniques provide enough spatial resolution so that in case of rare decay modes

 Ï€⁰ → 𝛾 + 𝛾
π⁰ → 𝛾 + 𝛾 

it is barely possible to measure separation of electrons from place at which  π⁰ was produced.

  •  The mean life of  π⁰ is about 0.89 x 10⁻¹⁶ Sec.