Rutherford scattering & scattering cross section

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Transcript of Rutherford scattering & scattering cross section

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Rutherford Scattering & Scattering Cross-section CLASSICAL MECHANICS

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Classical Mechanics

Submitted to : Ma’am Huma Malik Submitted by : Group-5 B.S Physics (5th Semester) Section (A) GCWU Sialkot

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Group Members: Bisma Shakir 14020210-018 Maria Kousar 14020210-005 Ishrat Fardoos 14020210-012 Warda Jabbar 14020210-048 Fauzia Tehleel 14020210-033

Classical Mechanics

Faiqa Barkat 14020210-027 Nimra Asmat 14020210-021 Maham Idress 14020210-010 Rida Bukhari 14020210-028

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Layout Of Presentation:Rutherford Scattering ExperimentTheory of α–Particle ScatteringScattering via the Coulomb forceGeiger-Marsden ExperimentThe impact parameter/scattering angle relationship 1- Linear Momentum 2- Angular momentumThe Cross-SectionHow Rutherford’s Atomic Model is Different From Thomson Atomic Model???Drawbacks of Rutherford ModelBibliography

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Rutherford’s Scattering Experiment: Rutherford in 1911 , performed some scattering experiments in which he bombarded thin foil of gold with a beam of fast moving alpha particles. The thin gold foil had a circular fluoriscent zinc sulphide screen arround it. Whenever , alpha particles struck the screen , a tiny flash wasproduced at that point. From these experiments , he made the following observations :1. Most of the alpha particles passed through the foil without undergoing any deflection.2. A few alpha particles underwent deflection through small angles.3. Very few mere deflected back i.e., through an angle of nearly 180 .⁰

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Alpha parti-cles hit atoms with massive nucleus cores.

Continue…

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Theory of α–Particle Scattering: Assuming α-particles and nucleus are point charges. Impact Parameter “b” is the minimum distance to which α-particle would approach the nucleus if there is no force between them. b = 0 for head collision. Distance of closest approach “D” is the minimum distance to which particle approaches nucleus head on. Scattering angle “θ” is the angle between the asymptotic direction of approach of α-particle and the asymptotic direction in which it recedes. Trajectories are hyperbolic.

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Continue…

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Scattering via the Coulomb force:Charged-particle induced reactions:

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Continue…Trajectories in Rutherford Scattering:

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Continue…Trajectories in Rutherford Scattering:

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Geiger-Marsden Experiment:

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Geiger-Marsden Experiment:The ironic ways of nature:

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Geiger-Marsden Experiment:

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The impact parameter/scattering angle relationship:

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The impact parameter/scattering angle relationship:

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The impact parameter/scattering angle relationship:

Momentum change in Rutherford scattering:

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The impact parameter/scattering angle relationship:

The momentum change:

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The impact parameter/scattering angle relationship:

Trajectories in Rutherford Scattering:

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The impact parameter/scattering angle relationship:

The momentum change:

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The impact parameter/scattering angle relationship:

The angular momentum:

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The impact parameter/scattering angle relationship:

The angular momentum:

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The impact parameter/scattering angle relationship:

Conservation of angular momentum:

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The impact parameter/scattering angle relationship:

Integration limits:

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The impact parameter/scattering angle relationship:

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The impact parameter/scattering angle relationship:

The distance of the closest approach:

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The Cross-Section:The cross section in Rutherford Scattering :

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The Cross-Section:

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The Cross-Section:Cross-section in Rutherford Scattering:

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How Rutherford’s Atomic Model is Different From Thomson Atomic Model????

Rutherford proposed a model in which electrons revolve around the nucleus in well-defined orbits. There is a positively charged centre in an atom called the Nucleus. He also proposed that the size of the nucleus is very small as compared to size of the atom and nearly all the mass of an atom is centered in thenucleus.

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How Rutherford’s Atomic Model is Different From Thomson Atomic Model????

Thomson proposed the model of an atom to be similar to a christmas pudding. The electrons are in positively charged sphere like christmas pudding and the mass of the atom was supposed to be uniformly disturbed.

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Drawbacks of Rutherford Model:The Rutherford’s atomic model explains the structure of an atom in a very simple way. But , it suffers from the following drawbacks: Rutherford stated that electrons orbits the nucleus.Thus, if the electrons were orbiting the nucleus then they must be accelerating due to the centripetal force acting on it. This proved to be a flaw, due to Maxwell theory that electrons accelerating produces EMR which in turns would mean the electrons would loose energy and crash into the nucleus leading to a unstable atom. Which is not the case. The Rutherford’s model of atom does not say anything about the arrangement of electrons in an atom.

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