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 a neutral atom the number of electrons and protons are the same. In Carbon it is……… 6

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

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 J’ai fais ça ! Dodgy Beard

Alpha Particles  Helium Nuclei Positive Charge Heavy so not very penetrating Very Ionizing Very Ionizing 14 7 N He  17 8 O H

Beta Particle ß Fast electron from the nucleus Negative charge Moderately Penetrating Moderately ionizing 14 7 N  14 8 O ß

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

Penetrating Power  Paper Al foil Concrete

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

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.

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

Half-Life Atoms Not Decayed Time 1234

Calculations =0.693/T ½ =0.693/3s =0.231s -1

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

Isotopes Same atomic number different mass number

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.

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 4000kv 0kv

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

Use Famous Formula E=mc 2 E=mc 2 E= x 2 E= 3.96x Kg x (3x10 8 m/s) 2 E = E = 3.56x Joules

Fusion 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

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 Fission-The breaking apart of a heavy nucleus to form smaller products with release of energy.

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 Hot water to turbine

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

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

Use Planks Equation E=hf h= planks constant f= frequency 3.01x Joules = (6.6x js)x(f) f= 3.01x Joules / 6.6x js = 4.56x10 23 Hz

Pair Creation 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

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 (1.6x x10 9 = 4x J) As Energy to make 3 Pions is E=mc 2 =(3x x xcxc) =6.7x J Subtracting we find the KE after collision. p+p+ p-p- +0-+0-

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

Baryon Meson

Beta decay In β− decay, the weak force converts a neutron into a proton while emitting an electron and an antineutrino n 0 → p + + e - + ν e 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.

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