Elementary Particles | Interactions Of Charged Particles |

Elementary Particles - Part One

Elementary particles are the most interesting topic of physics.

At the first

Many of them decay rapidly after being created by high energy collisions between other particles.

Interactions Of Charged Particles  

Energy Lose

Heavy charged particles like alpha particle and deuterons lose energy in passing through matter chiefly by electric interactions with electrons of electrons. The electrons are either raised to excited states or, more often, pulled from their parent atom. Electrons which has ejected have sufficient energy to ionize atom along their own path. This is the magic of Elementary Particles.

Energy loss in absorber-

Energy-loss minima

For the particles with speeds less than about 0.6c the relativistic terms involving v/c nearly cancel and can be ignored as gravity gets ignored at quantum mechanics experiments.

Because the 1/v^2 factors varies more rapidly with v than in ln(2mv^2/I).

 Range

The integration should be carried numerically.

                           

Bremsstrahlung

The word "Bremsstrahlung"

Bremsstrahlung is the electromagnetic radiation given off whenever an electric charge is accelerated. Energy loss due to bremsstrahlung is important for electrons because they are more violently accelerated when passing near nuclei in their path.

The energy loss depends on the energy and atomic number of the electrons. 

Cerenkov Radiation

When the charged particle moving with the speed greater than phase velocity of the medium than the radiation emits called Cerenkov radiation.

Although electrons cannot move faster than the speed of light (in free space). Particle can move faster than c/n. n is the index of refraction.

The formula of  Cerenkov Radiation -

Gamma-Ray Absorption

Gamma-rays are the radiation emitted from radioactive decay of nuclei.

There are three ways by which photon interacts with matter-

 

• Compton scattering
• Photoelectric effect 
• Pair production

Compton Scattering

The phenomena in which photon loses part of its energy to an atomic electron, this cause in decreasing in energy and frequency but increasing in wavelength.

Photoelectric Effect

This is the incident in which all the energy of photon gets transfer to its atomic electrons.

Pair Production

Pair production is the phenomenon in which anti-particle forms along with its subatomic particle.

When photon energy is at least 1.02 MeV then pair of electron-positron forms.

Low-Energy Photons

As the importance of photoelectric effect decreases with the increase in energy to be succeed by Compton scattering therefore the photoelectric effect becomes the chief mechanism of energy loss.

The photoelectric effect remains significant with higher energies. So in higher atomic number atoms, the photoelectric effect remains significant but in lighter elements, Compton scattering dominants at photon energies of few tens of KeV.

High-Energy Photon

When the photon energy exceeds the threshold of 1.02 MeV then the pair production becomes more likely.

The greater the atomic number of the absorber the lower the energy with which the pair production takes place the principal mechanism of energy loss by gamma-rays.

Attenuation Coefficient

The intensity 

Radiation Intensity   -             I=I0.e-μx

 

 Methods of Particle Detection-

1. Ionization chamber and Geiger counter
2. Scintillation counter
3. Semiconductor detector
4. Neutro detector
5. Bubble chamber
6. Nuclear emulsion
7. Spark chamber

Leptons

Lepton is the simplest elementary particle. There is no hint of the internal structure and extension in space of leptons.

Electrons and neutrino are the examples of the leptons.

Dirac theory of the electrons : 

You know that electron was the first particle for which the satisfactory theory eas developed.

P.A.M. Dirac obtained a relativistically correct wave equation in 1928. When the observed mass and charge of the electron are inserted in the solutions this equation, the intrinsic angular momentum of the electron is found to be eħ/2m ( one Bhor magneton).

Positrion

Negative and positive electrons are the unexpected result theory of Dirac theory.

In 1932,  positive electrons unambiguously detected in the flux of cosmic radiation at the earth 's.

Positive electrons are called positrions.

Most elementary particles have antiparticles

Electrons are the antiparticle of positrions. Nearly all the elementary particles have antiparticles.

But graviton is the antiparticle of itself.

Antiparticle has the same spin, mass, and life but charge on them is different.

The decay of charged pions

Let me introduce to the muons, muons are the other member of the lepton family.

The symbol of muon is µ.

Muon is produced along with neutrino when pions decays.

Hadrons

Unlike leptons, hydrons are elementary particles subjected to both strong and weak interactions.

They also occupy space but in

Mesons and baryons

Mesons are the hydrons. It has zero spin, its masss lies between  those of muon and proton.

Kaons

Kaon is havier than pion.

Quarks

What will you answer if I ask that what is the fundamental unit of tan atom.

I know some will say electrons, protons, and neutrons.

Congratulations you are wrong.

Its quarks, quarks are the fundamental particles of the atom even of electrons, protons and neutrons

There are 3 types of quarks

1. UP and down
2. Charm and strange
3. Top and bottom

Up and down quarks are represented by u and d respectively.

Charm and strange are represented by c and s respectively.

Top and bottom are represented by t and b respectively.

To be continued.....