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Modern Physics

Modern Physics. By Neil Bronks. Mass Number - Number of protons + Neutrons. Atomic Number - Number of protons. Atoms. C. 12. 6. In a neutral atom the number of electrons and protons are the same. In Carbon it is………. 6. Gravitational - Only Positive - Very long range.

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Modern Physics

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  1. Modern Physics By Neil Bronks

  2. Mass Number - Number of protons + Neutrons. Atomic Number - Number of protons Atoms C 12 6 In a neutral atom the number of electrons and protons are the same. In Carbon it is……… 6

  3. Gravitational - Only Positive - Very long range 4 Forces of Nature Electromagnetic – Positive and negative Weak Nuclear- Associated with beta decay • Strong Nuclear – Holds nucleus together - Very Short Range

  4. Dodgy Beard J’ai fais ça ! Radiation • Decay of nucleus by the emission of a particle or a ray. • Discovered by Henri Becquerel • Units 1 Bq is one decay per second • Natural happens without outside bombardment • Artificial happens due to bombardment

  5. Alpha Particles  • Helium Nuclei • Positive Charge • Heavy so not very penetrating • Very Ionizing 147N +42He178O + 11H

  6. Beta Particle ß • Fast electron from the nucleus • Negative charge • Moderately Penetrating • Moderately ionizing 147N 148O + 0-1 ß

  7. Gamma Ray • High energy e-m wave (A Photon) • No charge - not deflected by field • Very penetrating – Need lead to stop most of them • Not very ionizing • Release energy after reaction

  8.   Penetrating Power Al foil Paper Concrete

  9. Charged particles move in a circular path as the force is always at right angles to the direction of motion- Fleming's Left Hand Rule Particles in Fields   

  10. Solid State Detector This a P-N junction in reverse bias. This creates a huge depletion layer. - + P N A piece of radiation passes through the depletion layer and creates enough carriers to carry one pulse of current.

  11. Experiments • All experiments the same stick a DETECTOR in front of a source and count the decays. • Move it away for distance and plot • Time for half life and plot • Put things in front for penetration

  12. Half-Life Atoms Not Decayed Time 1 2 3 4

  13. Calculations =0.693/T½ =0.693/3s =0.231s-1

  14. Activity Calculations Rate of Decay =  x number you started with dN/dt = - x N Start with 4000 particles and =0.231 Activity = 4000 x 0.231=924 Bq

  15. Isotopes • Same atomic number different mass number

  16. Rutherford Scattering – alpha particles fired at gold foil. Nucleus A small number of high energy alphas are Deflected More pass unaffected - So the nucleus is very small Some reflected completely back - Nucleus totally positive.

  17. Proton Accelerated by An electric field Alpha strikes the screen Producing a flash that Is seen with the microscope Alpha  Alpha  Lithium Target Cockcroft and Walton Hydrogen discharge tube 4000kv 0kv Al p h a Al p h a a

  18. Nobel Prize for Physics • Proton + Lithium  2xAlpha + Energy • Proves Einstein’s Law E=mc2 • First Transmutation by artificial Bombardment of an element Ernest Walton

  19. Use Famous Formula • E=mc2 • E= 3.96x10-30 Kg x (3x108 m/s)2 • E =3.56x10-13 Joules

  20. 21H 21H Fusion • Fusion is the joining together of 2 light nuclei to make one nucleus with release of energy. • Caused by a super fast collision at high temperature in a magnetic bottle.

  21. Fission-The breaking apart of a heavy nucleus to form smaller products with release of energy. • Subtract mass in a.m.u. • Convert to kg • Use E=mc2 Uranium-235 Also produced 3 fast neutrons that can cause another fission and so a chain reaction

  22. Moderators slow down the neutrons to the right speed Control Rods stop the reaction and prevent meltdown Hot water to turbine Fuel rods contain the Uranium-235 (Enriched to ensure chain reaction)

  23. Nuclear Equation In the isotope U-238 the neutrons must be slowed down by a moderator – Graphite Only need one neutron for stable Chain Reaction(Self sustaining) more than one =Meltdown (China Syndrome)

  24. Leptons Fundamental particles 1/1846 of an a.m.u. Does not feel the strong nuclear force Matter – Electron , Muon, Tau, …… Anti-matter – Positron, Anti-Tau Anti-matter first suggested by Paul Dirac

  25. e1+ e1- Matter combining with anti-matter to form energy in the form of e-m radiation Annihilation 0 0 e+1 + e-1 2hf (2g) 0 0 2 photons conserve momentum ?

  26. e1+ e1- Matter combining with anti-matter to form energy in the form of e-m radiation Annihilation 0 2 photons conserve momentum 0 An electron and a positron collide to make energy. All the mass of the electrons gets turned into gamma waves So Energy E=mc2 To find frequency of wave E = 2h.f Matter turns Into energy

  27. Use Planks Equation • E=hf • h= planks constant • f= frequency • 3.01x10-10 Joules = (6.6x10-34 js)x(f) • f= 3.01x10-10 Joules / 6.6x10-34 js = 4.56x1023 Hz

  28. A matter and anti-matter pair being created by energy from an e-m wave e+ e- Pair Creation An electron and a positron are created from a gamma ray. (We can also get a proton and an anti-proton) We do the calculation in reverse To find energy of wave E = h.f As we get 2 electrons E = 2mc2

  29. p+ p+ p- p- Annihilation and Production + 0 - New particles are produced from the KE of the colliding protons They must conserve charge If we carry in 4Gev (1.6x10-19 . 4x109= 4x10-10 J) As Energy to make 3 Pions is E=mc2 =(3x 2.4842x10-28xcxc) =6.7x10-11 J Subtracting we find the KE after collision.

  30. Quarks - Inside the Hadrons • 6 Quarks • 6 Anti-Quarks – Opposite Signs

  31. Baryon Meson

  32. Beta decay • In β− decay, the weak force converts a neutron into a proton while emitting an electron and an antineutrino • n0 → p+ + e- + νe • This explains loss in energy and momentum. Pauli proposed it’s existence in 1930 but was not discovered until 1956 as it is so weakly interacting with other particles.

  33. Subject to all forces Particle Zoo Leptons Hadrons Baryons Mesons Fundamental particles 3 Quarks Quark + Anti-quark Do not feel Strong Nuclear Force Proton uud Pion ud

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