1. Modern Physics By
Neil Bronks

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

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

4. Helium
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
Neutron
Proton

5. 4 Forces of Nature (Order of strength)
Strong Nuclear –
Holds nucleus together
- Very Short Range
Electromagnetic –
Positive and negative
4 Forces of Nature (Order of strength)
Weak Nuclear-
Associated with beta
decay
Gravitational
- Only Positive
- Very long range

6. J’ai fais ça !
Radiation
Dodgy
Beard
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

7. Safety
Wear Gloves or Apron of lead
Don’t point at anyone
Don’t eat!!!

8. Nuclear Equations Top and bottom must add up Top is mass number
Bottom is atomic number
Proton H Neutron electron
And Alpha

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

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

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

12. Penetrating Power   
Al foil
Paper
Concrete

15. H/W
LC Ord 2007
Q11

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 Rule
Particles in Fields   
Radioactive
Source
Cloud Chamber

18. Click here for internet demo

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

20. 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

21. 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.

22. Geiger Muller Tube

23. H/W
LC Ord 2004
Q10

24. 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

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

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

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

28. Half-Life – time it takes for half the radioactive particles to decay
Atoms Not Decayed
Time 1 2 3 4

29. Half life demo from internet click here

30. Half Life Calculations
4000 particles time=0
2000 particles time=3s 1 half-life
1000 particles time=6s 2 half-life
500 particles time=9s 3 half-life
250 particles time=12s 4 half-life
125 particles time=15s 5 half-life

31. Calculations – we use the decay constant λ in our calculations.

32. 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

33. Calculations
1) 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 lives
Time = 3 x = days

34. Calculations
2) 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 lives
100%>50%>25%
2 half lives =120 days
1 half life = 60 days

35. Calculations (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

36. Calculations = 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 = -N
N= Moles x 6x1023 = 2 x 6x1023
Activity = 6.62 x 10-7 x 12x1023 =
= 7.3 x1017 Bq

37. Isotopes
Same atomic number different mass number

38. Isotope pp

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

40. Isotopes
Same Atomic number different Mass number

41. 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

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

43. Rutherford Scattering
Do I look like
Freddie?
Rutherford Scattering

44. Rutherford on internet

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

46. Rutherford Scattering – alpha particles fired at gold foil.
Nucleus
A small number of high energy alphas are Deflected
Some reflected completely back - Nucleus totally positive.

47. 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.

48. Cockcroft and Walton Hydrogen discharge tube Alpha  Proton
Accelerated by
An huge electric
Field (700000v)
Alpha strikes the screen
Producing a flash that
Is seen with the microscope
Alpha  Al p h a Al p h a a
Lithium
Target

49. Internet explanation

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

51. E=mc2 Binding Energy The total nucleus weighs less than all its parts
Difference is Mass Defect
Converted to energy to hold the nucleus together
E=mc2

52. 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

53. 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:
mproton = u (u is Atomic mass unit)
mneutron= u
mproton + mneutron = = u
The mass of the deuteron is:
Atomic mass 2H = u
The mass difference =
= u

54. Convert to Kg Multiply by conversion factor 1u = 1.66x10-27 Kg
Mass = m = ( ) x 1.66x10-27
Mass = m = 3.96x10-30 Kg

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

56. Fusion – 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

57. Fission
The 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

58. Also produced 3 fast neutrons that can cause another fission and so a chain reaction
Subtract mass in a.m.u.
Convert to kg
Use E=mc2
Uranium-235

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

62. Moderators (Graphite) slow down the neutrons to the right speed
Control Rods (Boron Steel) absorb neutrons to stop the reaction and prevent meltdown
Heat to heat exchanger prevents Radiation escaping steam to turbine
Fuel rods contain the Uranium-235 (Enriched to ensure chain reaction)

63. H/W
LC Ord 2006
Q 9

64. 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

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

67. Matter combining with anti-matter to form energy in the form of e-m radiation
Annihilation e+ e-
2 photons conserve momentum
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

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

69. Convert to Kg Multiply by convertion factor 1u = 1.66x10-27
Mass = m = ( ) x 1.66x10-27
Mass = m = 3.34x10-27 Kg

70. E=mc2 E= 3.34x10-27 Kg x (3x108 m/s) 2 E = 3.01x10-10 Joules
Use Famous Formula
E=mc2
E= 3.34x10-27 Kg x (3x108 m/s) 2
E = 3.01x10-10 Joules

71. Use Planks Equation E=hf
h= planks constant
3.01x10-10 Joules = (6.6x10-34 js)x(f)
f= 3.01x10-10 Joules / 6.6x10-34 js
= 4.56x1023 Hz
In practice this is low as KE from particles increases this.

74. A matter and anti-matter pair being created by energy from an e-m wave
Pair Production 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 = 2mc2

75. Annihilation and Production+ 0 - p+ p-
New particles are produced from the KE of the colliding protons They must conserve charge
If 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 J
Subtracting we find the KE after collision.

76. H/W
LC Higher (a)

77. Quarks - Inside the Hadrons
6 Anti-Quarks – Opposite Signs UP
+2/3
STRANGE -1/3
TOP
DOWN
-1/3
CHARMED +2/3
BOTTOM -1/3

78. Feels strong nuclear force
Hadrons
Baryons
Mesons
3 quarks
Quark+anti-quark
Proton
Pion
uud ud
Feels strong nuclear force

79. Baryon
Meson

80. Hadrons on internet

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

82. 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
n0 → p+ + e-
Pauli said there must be a new particle called a neutrino

83. 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.

84. Nuclear Formula

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

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

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

88. Magnets force particles in circular path so stay in tube
Circular more compact
High velocity needed to overcome repulsion
Vacuum to avoid collisions increase mean free path
More velocity more KE so more new particles made

89. Detectors

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

92. H/W Roundup (Yeh har) 2007 q11 2004 q10 2003 q11 2005 q12(d) 2006 q 9