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

Hydrogen Electron Proton The simplest atom has one negative electron orbiting one positive proton. The electron is very light compared to the proton.

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

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

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 ça ! Dodgy Beard

Safety Wear Gloves or Apron of lead Dont point at anyone Dont eat!!!

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

H/W LC Ord 2007 Q11

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

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Ionisation We can prove that radiation creates ions as we bring a source close to a charge electroscope

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

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.

H/W LC Ord 2004 Q10

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

Penetration A Gieger Muller Tube and Counter. Plot the activity against the thickness or the type of barrier

Distance A Gieger Muller Tube and Counter. Plot the activity against the distance r. r

Half Life A Gieger Muller Tube and Counter. Plot the activity against the time Time it takes for half the atoms to decay

Half-Life – time it takes for half the radioactive particles to decay Atoms Not Decayed Time 1234

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= particlestime=3s 1 half-life

Calculations – we use the decay constant λ in our 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

Uses of Radioactive Isotopes Medicine – treatment and imaging Smoke detectors Food Irradiation Carbon-14 Dating

Isotopes Same Atomic number different Mass number

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

H/W LC Ord 2005 Q12(d) LC Higher 2003 Q11

Rutherford Scattering Do I look like Freddie?

Rutherford on internet

Rutherford Scattering – alpha particles fired at gold foil. very small Most pass unaffected - So the nucleus is very small

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.

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

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

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

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

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 = u (u is Atomic mass unit ) Atomic mass unit m neutron = u m proton + m neutron = = u The mass of the deuteron is: Atomic mass 2 H = u The mass difference = = u

Convert to Kg Multiply by conversion factor 1u = 1.66x Kg Mass = m = ( ) x 1.66x Mass = m = 3.96x Kg

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 – 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

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

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

Nuclear Equation In the isotope U-238 the neutrons must be slowed down by a moderator - Graphite

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

H/W LC Ord 2006 Q 9

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

Wave made by Anihilation A proton and a Anti proton. The masses of the constituents are:protonAnti m proton = u (u is Atomic mass unit)Atomic mass unit m proton + m anti = = u The mass difference = u To use this in a calculation we covert to kg

Convert to Kg Multiply by convertion factor 1u = 1.66x Mass = m = ( ) x 1.66x Mass = m = 3.34x Kg

Use Famous Formula E=mc 2 E=mc 2 E= x 2 E= 3.34x Kg x (3x10 8 m/s) 2 E = E = 3.01x Joules

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 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

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

H/W LC Higher (a)

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

Hadrons BaryonsMesons 3 quarksQuark+anti-quark ProtonPion uudud Feels strong nuclear force

Baryon Meson

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

Ghost Particle Mystery By 1930 most of the particle physics world was understood However the decay of the neutron to a proton producing a beta particle did not obey Einstein's Law n 0 p + + e - Pauli said there must be a new particle called a neutrino

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 its existence in 1930 but was not discovered until 1956 as it is so weakly interacting with other particles.

Nuclear Formula

Particle Accelerators-Linear Very high Voltage electric fields Electro-magnetic attraction pulls particles down.

Circular Accelerators Particles spiral in fields (Flemings Left hand rule) Cyclotron- We put the field at right angles e more power with oscillating field

CERN Particles can travel in opposite directions and double the collision energy

Detectors

H/W LC Ord 2002 Q11 LC Higher (a)