Particle Physics and Fundamental Particles

GCE A Level Physics

1. The Atom and its Nucleus .

2. Atomic Structure John Dalton revived the idea first put forward by Demokritos that said matter was made up of tiny indivisible spheres called atoms 1897 J. J. Thomson discovered that all matter contains tiny negatively‑ charged particles. He showed that these particles are smaller than an atom. He had found the first subatomic particle ‑ the electron.

3. Scientists then set out to find the structure of the atom. Thomson thought that the atom was a positive sphere of matter and the negative electrons were embedded in it as shown here This `model' was called the `plum‑pudding' model of the atom.

4. Ernst Rutherford decided to probe the atom using fast moving alpha ( α ) particles. He got his students Geiger and Marsden to fire the positively‑ charged α ‑particles at very thin gold foil and observe how they were scattered.

5. The famous Geiger-Marsden Alpha scattering experiment In 1909, Geiger and Marsden were studying how alpha particles are scattered by a thin gold foil. (Video) Alpha source Thin gold foil

6. Most α ‑particles are hardly deflected because they are far away from the nucleus and the field is too weak to repel them much. The electrons do not deflect the α ‑particles because the effect of their negative charge is spread thinly throughout the atom.

7. In 1911 Rutherford concluded that: All of an atom's positive charge and most of its mass is concentrated in a tiny core . Rutherford called this the nucleus. The electrons surround the nucleus, but they are at relatively large distances from it. The atom is mainly empty space!

8. Rutherford did the calculations! That’s 100 000 times smaller than the size of an atom ( about 10 -1 metres ) .

9. The atom orbiting electrons Nucleus (protons and neutrons)

10. The Nuclear Model of the atom

11. Nuclide notation Li 3 7 Proton number (Z) = number of protons Nucleon number (A) = number of protons + neutrons Neutron number (N) = A - Z

12. Isotopes Li 3 7 It is possible for the nuclei of the same element to have different numbers of neutrons in the nucleus (but it must have the same number of protons) Li 3 6

13. Isotopes of Hydrogen H 1 1 The three isotopes of Hydrogen even have their own names! H 1 2 H 1 3 Hi! I’m hydrogen They call me deuterium Hola! Mi nombre es tritium y yo soy de Madrid!

14. Nuclide One type of nucleus with a particular nucleon number and a particular proton number

15. Rodio - activity

16. Neutrinos Neutrinos are bizarre particles. They have very little mass (much less than an electron) and no electric charge, which makes them very difficult to detect. In β+ decay , a proton decays to become a neutron and an electron neutrino (symbol ν) is released:  

17. Antineutrinos β-particles are emitted with a range of speeds – some travelled more slowly than others, It was deduced that some other particle must be carrying off some of the energy and momentum released in the decay.

18. Antineutrinos This particle is now known as the electron antineutrino, with symbol In a nuetron changes into a proton  

19. Summary of properties of radioactive emissions

20. Some values you should know Radius of proton and radius of a proton 10 -15 m radius of a nucleus 10 -15 m- 10 -14 m radius of atom 10 -10 m

21. The electronvolt (eV) When an electron (with a charge of magnitude 1.60 .10 –19 C) travels through a potential difference, energy is transferred. The energy change W is given by: W = QV = 1.60 . 10 –19 . 1 = 1.60 . 10 –19 J So we define the electronvolt as follows: the energy transferred when an electron travels through a potential difference of one volt. Therefore: 1 eV = 1.60 . 10 –19 J

22. NB: Density of the nucleus is much larger than density of the atom:

23. (c) A uranium.238 nucleus has a radius of 8.9 × 10 –15 m. Calculate, for a uranium.238 nucleus, ( i ) its mass,   mass = ................... kg [2] (ii) its mean density . density = ..............kg m –3 [2]

24. What is conserved in a nuclear decay nucleon number A is conserved. proton number Z is conserved mass–energy is conserved. E= mc 2

25. Fundamental Particles

26. Fundamental Particles

27. What are Leptons and Quarks? All matter is comprised of Leptons and Quarks. They are sub-atomic particles. They are fundamental particles incapable of being subdivided into smaller particles. There are 6 Leptons and 6 Quarks. The nucleus is made up of quarks which manifest themselves as protons and neutrons. Each elementary particle has a corresponding antiparticle.

28. Matter vs. Anti-Matter For every particle, there is an anti-particle. Anti-particles have the same mass as the particle. Anti-particles have the same but opposite charge. Anti-particles have the opposite spin. Particle Anti-particle Name up quark Anti-up quark Symbol u ū mass 7.11x10 -30 kg 7.11x10 -30 kg Charge + ⅔ - ⅔

29. Neutrinos Neutrinos are three of the six leptons They have no electrical or strong charge Neutrinos are very stable and are all around Most neutrinos never interact with any matter on Earth

30. Quarks

31. Hadrons Consist of particles that interact through the strong force. Hadrons are composed of other, smaller particles Hadrons are in two categories Baryons & Mesons

32. Baryons Baryons are composed of three quarks All but two baryons are very unstable, they are: The proton and neutron!! Most baryons are excited states of protons and neutrons

33. Protons Protons are made of three quarks, two up quarks and a down quark Protons uud  

34. Neutrons Neutrons are also made up of three quarks, one up quark and two down quarks Neutron udd  

35. Generations of Matter

36. The Four Fundamental Forces These forces include interactions that are attractive or repulsive, decay and annihilation. Strong Weak interaction Electromagnetic Gravity

37. The Strong Force The strongest of the 4 forces Is only effective at distances less than 10 -15 meters (about the size of the nucleus) Holds quarks together This force is carried by gluons

38. The Weak interaction Force A very short-ranged nuclear interaction that is involved in beta decay This force is carried by the W + , W - , and the Z o boson particles.

39. The Electromagnetic Force Causes opposite charges to attract and like charges to repel Carried by a particle called a photon

40. Gravity Has a negligible effect on elementary particles A long-range force Carried by the graviton This is by far the weakest of the 4 fundamental forces