modern physics by neil bronks atoms c 12 6 mass number mass number - number of protons + neutrons....

Download Modern Physics By Neil Bronks Atoms C 12 6 Mass Number Mass Number - Number of protons + Neutrons. Atomic Number Atomic Number - Number of protons In

If you can't read please download the document

Post on 30-Mar-2015

214 views

Category:

Documents

1 download

Embed Size (px)

TRANSCRIPT

  • Slide 1

Slide 2 Modern Physics By Neil Bronks Slide 3 Atoms C 12 6 Mass Number Mass Number - Number of protons + Neutrons. Atomic Number Atomic Number - Number of protons In a neutral atom the number of electrons and protons are the same. In Carbon it is 6 Slide 4 Hydrogen Electron Proton The simplest atom has one negative electron orbiting one positive proton. The electron is very light compared to the proton. Slide 5 Helium Neutron In this atom we see two neutrons and two protons forming the nucleus. The Neutron has no charge but is the same mass as the proton. Electron Proton Slide 6 4 Forces of Nature Gravity - Only Positive - Very long range Weak Nuclear- Associated with beta decay Strong Nuclear Holds nucleus together - Very Short Range Electromagnetic Positive and negative Slide 7 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 Jai fais a ! Dodgy Beard Slide 8 Safety Wear Gloves or Apron of lead Dont point at anyone Dont eat!!! Slide 9 Alpha Particles Helium Nuclei Positive Charge Heavy so not very penetrating Very Ionizing Very Ionizing 14 7 N + 4 2 He 17 8 O + 1 1 H Slide 10 Beta Particle Fast electron from the nucleus Negative charge Moderately Penetrating Moderately ionizing 14 7 N 14 8 O + 0 -1 Slide 11 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 Slide 12 Penetrating Power Paper Al foil Concrete Slide 13 H/W LC Ord 2007 Q11 Slide 14 Particles in Fields 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 Radioactive Source Cloud Chamber Slide 15 Slide 16 http://www.absorblearning.com/m edia/attachment.action?quick=br& att=838 Slide 17 Ionisation We can prove that radiation creates ions as we bring a source close to a charge electroscope Slide 18 Ionising Power Alpha is heaviest and so does most damage poison with Polonium Beta is only moderately ionising Gamma is only slightly ionising but difficult to stop Slide 19 Solid State Detector PN This a P-N junction in reverse bias. This creates a huge depletion layer. + - A piece of radiation passes through the depletion layer and creates enough carriers to carry one pulse of current. Slide 20 H/W LC Ord 2004 Q10 Slide 21 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 Slide 22 Penetration A Gieger Muller Tube and Counter. Plot the activity against the thickness or the type of barrier Slide 23 Distance A Gieger Muller Tube and Counter. Plot the activity against the distance r. r Slide 24 Half Life A Gieger Muller Tube and Counter. Plot the activity against the time Time it takes for half the atoms to decay Slide 25 Half-Life time it takes for half the radioactive particles to decay Atoms Not Decayed Time 1234 Slide 26 Half Life Calculations 1000 particlestime=6s 2 half-life 500 particles time=9s 3 half-life 250 particlestime=12s 4 half-life 125 particlestime=15s 5 half-life 4000 particlestime=0 2000 particlestime=3s 1 half-life Slide 27 Calculations we use the decay constant in our calculations. =0.693/T =0.693/3s =0.231s -1 Slide 28 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 Slide 29 Isotopes Same atomic number different mass number Slide 30 Uses of Radioactive Isotopes Medicine treatment and imaging Smoke detectors Food Irradiation Carbon-14 Dating Slide 31 Isotopes Same Atomic number different Mass number Slide 32 Carbon-14 Dating At death all animals contain the same ratio of C-14 to C-12 The rate of decay of C-14 is fixed The C-14 left tells us how long ago it died %C-14 time Slide 33 H/W LC Ord 2005 Q12(d) LC Higher 2003 Q11 Slide 34 Rutherford Scattering Do I look like Freddie? Slide 35 Rutherford on internet Slide 36 Rutherford Scattering alpha particles fired at gold foil. very small Most pass unaffected - So the nucleus is very small Slide 37 Rutherford Scattering alpha particles fired at gold foil. Nucleus Deflected A small number of high energy alphas are Deflected totally positive. Some reflected completely back - Nucleus totally positive. Slide 38 Rutherford Scattering alpha particles fired at gold foil. Nucleus Deflected A small number of high energy alphas are Deflected very small More pass unaffected - So the nucleus is very small totally positive. Some reflected completely back - Nucleus totally positive. Slide 39 Cockcroft and Walton Alpha pha Lithium Target Alpha Hydrogen discharge tube Accelerated by An electric field Proton Alpha strikes the screen Producing a flash that Is seen with the microscope Slide 40 Nobel Prize for Physics Proton + Lithium 2xAlpha + Energy Proves Einstein s Law E=mc 2 First Transmutation by artificial Bombardment of an element Ernest Walton Slide 41 Binding Energy The total nucleus weighs less than all its parts Mass Defect Difference is Mass Defect Converted to energy to hold the nucleus together Converted to energy to hold the nucleus together E=mc 2 E=mc 2 Slide 42 As Iron is the most stable as you go towards it you release energy So Carbon-12 is lighter than 12 protons The difference is the binding energy Slide 43 Binding Energy of a Deuteron A deuteron is the nucleus of a deuterium atom, and consists of one proton and one neutron. The masses of the constituents are:deuteriumprotonneutron m proton = 1.007276 u (u is Atomic mass unit ) Atomic mass unit m neutron = 1.008665 u m proton + m neutron = 1.007276 + 1.008665 = 2.015941 u The mass of the deuteron is: Atomic mass 2 H = 2.013553 u The mass difference = 2.015941 - 2.013553 = 0.002388 u Slide 44 Convert to Kg Multiply by conversion factor 1u = 1.66x10 -27 Kg Mass = m = (0.002388) x 1.66x10 -27 Mass = m = 3.96x10 -30 Kg Slide 45 Use Famous Formula E=mc 2 E=mc 2 E= x 2 E= 3.96x10 -30 Kg x (3x10 8 m/s) 2 E = E = 3.56x10 -13 Joules Slide 46 Fusion The sun and the stars Fusion is the joining together of 2 light nuclei to make one nucleus with release of energy. 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. Caused by a super fast collision at high temperature in a magnetic bottle. 21H21H 21H21H Slide 47 Fission The breaking apart of a heavy nucleus to form smaller products with release of energy. The breaking apart of a heavy nucleus to form smaller products with release of energy. Caused artificially by the bombardment of the right speed of neutron. MASS DEFECT In both fusion and fission the products are lighter than the reactants and the MASS DEFECT is turned into Energy E=mc 2 Slide 48 1.Subtract mass in a.m.u. 2.Convert to kg 3.Use E=mc 2 Also produced 3 fast neutrons that can cause another fission and so a chain reaction Uranium-235 Slide 49 Nuclear Equation In the isotope U-238 the neutrons must be slowed down by a moderator - Graphite Slide 50 Fuel rods contain the Uranium-235 (Enriched to ensure chain reaction) Moderators slow down the neutrons to the right speed Control Rods stop the reaction and prevent meltdown Heat to steam to turbine Slide 51 H/W LC Ord 2006 Q 9 Slide 52 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 Slide 53 Slide 54 Annihilation e+e+ e-e- An electron and a positron collide to make energy. All the mass of the electrons gets turned into gamma waves So Energy E=mc 2 To find frequency of wave E = 2h.f Matter turns Into energy Matter combining with anti-matter to form energy in the form of e-m radiation Slide 55 Wave made by Anihilation A proton and a Anti proton. The masses of the constituents are:protonAnti m proton = 1.007276 u (u is Atomic mass unit)Atomic mass unit m proton + m anti = 1.007276 + 1.007276 = 2.014552 u The mass difference = 2.014552 u To use this in a calculation we covert to kg Slide 56 Convert to Kg Multiply by convertion factor 1u = 1.66x10 -27 Mass = m = (2.014552) x 1.66x10 -27 Mass = m = 3.34x10 -27 Kg Slide 57 Use Famous Formula E=mc 2 E=mc 2 E= x 2 E= 3.34x10 -27 Kg x (3x10 8 m/s) 2 E = E = 3.01x10 -10 Joules Slide 58 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 = 4.56x10 23 Hz Slide 59 Slide 60 Pair Production e+e+ e-e- 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 = 2mc 2 A matter and anti-matter pair being created by energy from an e-m wave Slide 61 Annihilation and Production p+p+ p-p- New particles are produced from the KE of the colliding protons They must conserve charge If we carry in 4Gev (1.6x10 -19. 4x10 9 = 4x10 -10 J) As Energy to make 3 Pions is E=mc 2 =(3x 2.4842x10 -28 xcxc) =6.7x10 -11 J Subtracting we find the KE after collision. p+p+ p-p- + 0 - Slide 62 H/W LC Higher 2003 10(a) Slide 63 Quarks - Inside the Hadrons 6 Quarks 6 Anti-Quarks Opposite Signs UP +2/3 STRANGE -1/3 TOP +2/3 DOWN -1/3 CHARMED +2/3 BOTTOM -1/3 Slide 64 Hadrons BaryonsMesons 3 quarksQuark+anti-quark ProtonPion uudud Feels strong nuclear force Slide 65 Baryon Meson Slide 66 Subject to all forces Particle Zoo Hadrons Leptons Fundamental particles Do not feel Strong Nuclear Force Baryons 3 Quarks Proton uud Mesons Quark + Anti-quark Pion ud Slide 67 Ghost Particle Mystery By 1930 most of the parti

View more