2C Atoms Mass Number - Number of protons + Neutrons. 126Atomic Number - Number of protonsIn a neutral atom the number of electrons and protons are the same. In Carbon it is………6
3HydrogenThe simplest atom has one negative electron orbiting one positive proton.The electron is very light compared to the proton.ElectronProton
4HeliumIn 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.ElectronNeutronProton
54 Forces of Nature (Order of strength) Strong Nuclear –Holds nucleus together- Very Short RangeElectromagnetic –Positive and negative4 Forces of Nature (Order of strength)Weak Nuclear-Associated with betadecayGravitational- Only Positive- Very long range
6J’ai fais ça !RadiationDodgyBeardDecay of nucleus by the emission of a particle or a ray.Discovered by Henri BecquerelUnits 1 Bq is one decay per secondNatural happens without outside bombardmentArtificial happens due to bombardment
7SafetyWear Gloves or Apron of leadDon’t point at anyoneDon’t eat!!!
8Nuclear Equations Top and bottom must add up Top is mass number Bottom is atomic numberProton H Neutron electronAnd Alpha
9Alpha Particles 147N +42He 178O + 11H Helium Nuclei Positive Charge Heavy so not very penetratingVery Ionizing147N +42He 178O + 11H
10Beta Particle ß 147N 148O + 0-1 ß Fast electron from the nucleus Negative chargeModerately PenetratingModerately ionizing147N 148O ß
11Gamma Ray High energy e-m wave (A Photon) No charge - not deflected by fieldVery penetrating – Need lead to stop most of themNot very ionizingRelease energy after reaction
16 Particles in Fields Cloud Chamber Charged particles move in a circular path as the force is always at right angles to the direction of motion-Fleming's Left Hand RuleParticles in FieldsRadioactiveSourceCloud Chamber
19IonisationWe can prove that radiation creates ions as we bring a source close to a charge electroscope
20Ionising PowerAlpha is heaviest and so does most damage – poison with PoloniumBeta is only moderately ionisingGamma is only slightly ionising but difficult to stop
21Solid State Detector - This a P-N junction in reverse bias. This creates a huge depletion layer.-+PNA piece of radiation passes through the depletion layer and creates enough carriers to carry one pulse of current.
31Calculations – we use the decay constant λ in our calculations.
32Activity Calculations Rate of Decay = x number you started withdN/dt = - x NStart with 4000 particles and =0.231Activity = 4000 x 0.231=924 Bq
33Calculations1) You start with 100 grams of sulfur-35, which has a half life of days. How much time will it take until only 12.5 grams remain?How many half lives?100>50>25> so 3 half livesTime = 3 x = days
34Calculations2) You measure the radioactivity of a substance, then when measuring it 120 days later, you find that it only has 25 % of the radioactivity it had when you first measured it. What is the half life of that substance?How many half lives100%>50%>25%2 half lives =120 days1 half life = 60 days
35Calculations (a) Using the formula =0.693/T½ 3) Your professor gives you 64g of phosphorus-32 (half life = days).(a) What is its decay constant ?(b) What is its activity (Rate of Decay)?(a) Using the formula =0.693/T½=0.693/(14.263x24x60x60)= 6.62 x 10-7 s-1
36Calculations = 6.62 x 10-7 s-1 (b) Using Activity =dN/dt = -N 3) Your professor gives you 64g of phosphorus-32 (half life = days).(a) What is its decay constant ?(b) What is its activity (Rate of Decay)?= 6.62 x 10-7 s-1(b) Using Activity =dN/dt = -NN= Moles x 6x1023 = 2 x 6x1023Activity = 6.62 x 10-7 x 12x1023 == 7.3 x1017 Bq
37IsotopesSame atomic number different mass number
45Rutherford Scattering – alpha particles fired at gold foil. Most pass unaffected - So the nucleus is very small
46Rutherford Scattering – alpha particles fired at gold foil. NucleusA small number of high energy alphas are DeflectedSome reflected completely back - Nucleus totally positive.
47Rutherford Scattering – alpha particles fired at gold foil. NucleusA small number of high energy alphas are DeflectedMore pass unaffected - So the nucleus is very smallSome reflected completely back - Nucleus totally positive.
48Cockcroft and Walton Hydrogen discharge tube Alpha Proton Accelerated byAn huge electricField (700000v)Alpha strikes the screenProducing a flash thatIs seen with the microscopeAlpha AlphaAlphaaLithiumTarget
50Nobel Prize for Physics Proton + Lithium 2xAlpha + EnergyProves Einstein’s Law E=mc2First Transmutation by artificial Bombardment of an elementErnest Walton
51E=mc2 Binding Energy The total nucleus weighs less than all its parts Difference is Mass DefectConverted to energy to hold the nucleus togetherE=mc2
52As Iron is the most stable as you go towards it you release energy So Carbon-12 is lighter than 12 protonsThe difference is the binding energy
53Binding 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:mproton = u (u is Atomic mass unit)mneutron= umproton + mneutron = = uThe mass of the deuteron is:Atomic mass 2H = uThe mass difference == u
54Convert to Kg Multiply by conversion factor 1u = 1.66x10-27 Kg Mass = m = ( ) x 1.66x10-27Mass = m = 3.96x10-30 Kg
55E=mc2 E= 3.96x10-30 Kg x (3x108 m/s) 2 E = 3.56x10-13 Joules Use Famous FormulaE=mc2E= 3.96x10-30 Kg x (3x108 m/s) 2E = 3.56x10-13 Joules
56Fusion – The sun and the stars 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.21H
57FissionThe breaking apart of a heavy nucleus to form smaller nucleus with release of energy.Caused artificially by the bombardment of the right speed of neutron.In both fusion and fission the products are lighter than the reactants and the MASS DEFECT is turned into Energy E=mc2
58Also produced 3 fast neutrons that can cause another fission and so a chain reaction Subtract mass in a.m.u.Convert to kgUse E=mc2Uranium-235
61Nuclear EquationIn the isotope U-238 the neutrons must be slowed down by a moderator - Graphite
62Moderators (Graphite) slow down the neutrons to the right speed Control Rods (Boron Steel) absorb neutrons to stop the reaction and prevent meltdownHeat to heat exchanger prevents Radiation escaping steam to turbineFuel rods contain the Uranium-235 (Enriched to ensure chain reaction)
66Annihilation e+ e- e+ + e- 2hf (2g) 2 photons conserve momentum ? Matter combining with anti-matter to form energy in the form of e-m radiationAnnihilatione+e-e+ + e hf (2g)2 photons conserve momentum ?
67Matter combining with anti-matter to form energy in the form of e-m radiation Annihilatione+e-2 photons conserve momentumAn electron and a positron collide to make energy.All the mass of the electrons gets turned into gamma wavesSo Energy E=mc2To find frequency of wave E = 2h.fMatter turnsInto energy
68Wave made by Anihilation A proton and a Anti proton. The masses of the constituents are:mproton = u (u is Atomic mass unit)mproton + manti = =uThe mass difference = uTo use this in a calculation we covert to kg
69Convert to Kg Multiply by convertion factor 1u = 1.66x10-27 Mass = m = ( ) x 1.66x10-27Mass = m = 3.34x10-27 Kg
70E=mc2 E= 3.34x10-27 Kg x (3x108 m/s) 2 E = 3.01x10-10 Joules Use Famous FormulaE=mc2E= 3.34x10-27 Kg x (3x108 m/s) 2E = 3.01x10-10 Joules
71Use Planks Equation E=hf h= planks constant3.01x10-10 Joules = (6.6x10-34 js)x(f)f= 3.01x10-10 Joules / 6.6x10-34 js= 4.56x1023 HzIn practice this is low as KE from particles increases this.
74A matter and anti-matter pair being created by energy from an e-m wave Pair Productione+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 reverseTo find energy of wave E = h.fAs we get 2 electrons E = 2mc2
75Annihilation and Production +0-p+p-New particles are produced from the KE of the colliding protons They must conserve chargeIf we carry in 4Gev (1.6x x109= 6x10-10 J)As Energy to make 3 Pions is E=mc2 =(3x x10-28xcxc)=6.7x10-11 JSubtracting we find the KE after collision.
81Particle Zoo Subject to all forces Leptons Hadrons Baryons Mesons Fundamentalparticles3 QuarksQuark +Anti-quarkDo not feelStrong NuclearForceProtonuudPionud
82Ghost Particle Mystery By 1930 most of the particle physics world was understoodHowever the decay of the neutron to a proton producing a beta particle did not obey Einstein's Lawn0 → p+ + e-Pauli said there must be a new particle called a neutrino
83Beta decayIn β− decay, the weak force converts a neutron into a proton while emitting an electron and an antineutrinon0 → p+ + e- + νeThis 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.
85Particle Accelerators-Linear Very high Voltage electric fieldsElectro-magnetic attraction pulls particles down.
86Circular Accelerators Particles spiral in fields (Flemings Left hand rule)Cyclotron- We put the field at right angles e more power with oscillating field
87CERNParticles can travel in opposite directions and double the collision energy
88Magnets force particles in circular path so stay in tube Circular more compactHigh velocity needed to overcome repulsionVacuum to avoid collisions increase mean free pathMore velocity more KE so more new particles made