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Fundamental particles of an “ATOM”.

Done by :SRUJAN REDDY.

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Introduction

By the year 1932, only three elementary particles namely electrons, proton and photon were known.

The discovery of neutron by Chadwick in 1932 raised their number to four.

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Rutherford: atoms are not elementary particles!

1911Rutherford found a nucleus in the atom by firing alpha particles at gold and observing them bounce back

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Quarks detected within protons

Stanford (SLAC), California, late 1960s Fire electrons at proton: big deflections seen!

2 miles long acceleratorEnd Station Aexperimental area

Freeway 280

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What is fundamental particles of an ATOM? An atom is not a fundamental

particle, because it consists of protons and neutrons in its nucleus and has a cloud of electrons orbiting the nucleus. Protons and neutrons are also not fundamental particles, because they consist of quarks.

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THE WEAK FORCEBeta Decay

n p

Antineutrino

Electron

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BARYONS(Or)HEAVY PARTICLES

Proton and particles heavier than protons from this group.

Protons and neutrons are called nucleons and the rest mass are called hyperons.

If a number ,called the baryon number +1 is assigned to baryons and a number -1 is assigned to antibaryons , then in any closed system interaction or decay , the baryon number doesn’t change.

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Hyperons

Time decay of the order of 10-10 seconds.

Mass value intermediate between neutron 1and deuteron.

Their decay time is very much greater than the time of their formation.

Four types – lambda , sigma, xi , omega.

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Leptons

It contains electrons , protons , neutrino and muon.

all these elementary particles have masses smaller than that of a pion.

ELECTRON First discovered particle. Negative charge and stable particles An electrostatic field exists between

two electons.

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Photon No charge and no rest mass. It has an equivalent mass given by

Einstein's equation E=mc2Neutrino

No charge and rest mass is zero. It travels with the speed of light. 1956- beta ray spectra in

radioactivity.

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Muon

It is negatively charged and has a spin of ½.

It is similar to the electron except that its mass is about 200 times that of an electron.

It was firs discovered during the study of cosmic rays.

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Mesons

They are unstable . They decay into lighter mesons or

leptons. They have either positive , negative

at zero. Masses are between those of leptons

and baryons. The mesons include the pion , kaon

and eta particles.

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Positive pimeson (pion) Mass equal tom 273 times the mass

of the electron. Neutral Pion

No charge Mass is equal to 264 times the mass

of the electron.

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Particles and anti-particles

Same mass and the same spin but opposite charge.

They annihilate each other with the emission of photons.

The existence of an antiparticle for the electron was actually predicted by Dirac, because of a symmetry of the relativistic quantum theory of the electron.

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Electromagnetic force

e- e-

Photon

The repulsive force that two approaching electrons “feel”

Photon is the particle associated to the electromagnetic force“smallest bundle” of force

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Websites used for making the ppt : Chemactive.com Wikipedia Brown presentation Slideshare.com Slideplayer.com www.pa.msu.edu

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Thank you for your valuable time.