Phys 328 Nuclear Physics and Particles Introduction Murat

Transcription

1 Phys 328 Nuclear Physics and Particles Introduction 1

2 Syllabus COURSE OUTLINE PHYS328 NUCLEAR PHYSICS AND PARTICLES Instructor: Prof. Dr. A. Murat Güler Room: 333, Class Schedule: Monday 9:00-11:30 in P350 Wednesday 9:40-10:30 in P350 Text Book B.R. Martin, Nuclear and Particle Physics 2

3 Syllabus Topics: Introduction Basic Concepts Nuclear Phenomenology Particle Phenomenology Experimental Methods Applications of Nuclear Physics 3

4 History Grading Midterm : 25 % Final : 40% Project work: 30 % Attandance : 5% Dates: Midterm Examination First week of May. 4

5 Basic Concepts -Provides historical introduction to the field of nuclear and particle physics. -A number of concepts and tools are introduced concerning the nuclear and particle physics. -Give the basic principles and interpretations in nuclear and particle physics 5

6 History 19th Century : atoms are indivisible 6

7 History Radioactivity In 1896: Henry Becquerel dicovers radioactivity (β-radiation from uranium salts) When the salts were placed near to a photographic plate covered with opaque paper, the plate was discovered to be fogged. The phenomenon was found to be common to all the uranium salts studied and was concluded to be a property of the uranium atom. Henri Becquerel The Nobel Prize in Physics

8 History Rutherford and Pierre & Marie Curie establish existence of α and β rays and nature of radiactivity Through a long series of experiments he realized that there were two kinds of radiation emitted from Uranium. Rutherford called them alpha and beta. In a few years it was concluded that beta rays were cathode rays, that is, electrons. The precise nature of alpha particles remained a mystery although both Rutherford and the Curies suspected they were particles, atoms electrically charged and projected at high speed. They also knew they could be stopped by extremely thin shields (e.g. paper) and were deflected to only a small extent in a magnetic field. 8

9 History In 1896 Roentgen discovered X-rays X-rays were first discovered accidentally by Wilhelm Conrad Röntgen. X-rays are waves of electromagnetic energy that have a shorter wavelength than normal light He discovered that these new invisible rays could pass through most objects that casted shadows including human tissue but not human bones and metals. Within a year of the discovery many scientists replicated the experiment Röntgen performed and began using it in clinical settings In 1901 Röntgen won the first Nobel Prize in Physics 9

10 X-ray production 10

11 History Television Computer Monitor Cathode ray tubes pass electricity through a gas that is contained at a very low pressure. 11

12 History In 1898 Pierre and Marie Curie α-radiation m 1 M m 2 12

13 History 1900 Villard γ-radiation Villard investigated the radiation from radium salts that escaped from a narrow aperture in a shielded container onto a photographic plate, through a thin layer of lead that was known to stop alpha rays. He was able to show that the remaining radiation consisted of a second and third type of rays. One of those was deflected by a magnetic field (as were the familiar "canal rays") and could be identified with Rutherford's beta rays. The last type was a very penetrating kind of radiation which had not been identified before... 13

14 History 1897: Thomson discovers the electron cathode rays, and measured mass and charge Plum pudding model of atom Poor agreement with experiment JJ Thomson Nobel Prize in Physics,

15 History 1911: Rutherford experiments > positive nucleus orbited by electrons (planetary model) Ernest Rutherford (Nobel Prize in Chemistry, 1908) 15

16 History Most of the particles passed right through A few particles were deflected VERY FEW were greatly deflected Conclusions: a) The nucleus is small b) The nucleus is dense c) The nucleus is positively charged 16

17 History Based on his experimental evidence: The atom is mostly empty space All the positive charge, and almost all the mass is concentrated in a small area in the center. He called this a nucleus The nucleus is composed of protons and neutrons (they make the nucleus!) The electrons distributed around the nucleus, and occupy most of the volume His model was called a nuclear model 17

18 History 1913: Bohr model of atom: first window into quantum physics Atom was like a miniature planetry system with electrons circulating about the nucleus (like planets circulating about Sun). But accelerated charge radiates electromagnetic energy. As it radiates this energy its total energy would decrease and electron spirals in toward the nucleus and atom would collapse. Prize motivation: "for his services in the investigation of the structure of atoms and of the radiation emanating from them" Nobel prize in Physics in

19 History Bohr proposed that there are certain special states called stationary states. İn which angular momentum of electron may have magnitude h, 2h,...(quantization of angular momentum). Only orbits of certain radii and thus only certain only quantized energies are allowed. Allowed radii is n= 1,2,3... a 0 is Bohr radius Quantized radiation is emitted /absorbed if an electron changes its orbit. 19

20 Where does this go wrong? The Bohr model s successes are limited: Doesn t work for multi-electron atoms. The electron racetrack picture is incorrect. That said, the Bohr model was a pioneering, quantized picture of atomic energy levels. 20

21 Discovery of Neutron Discovery of the neutron, by J. Chadwick in 1932 Be 1) Neutral Gamma? No! protons too energetic 2) m n ~ m p Interpretation: non - ionizing radiation 4 2 He 9 4 Be 1 0 n 12 6 C James Chadwick Nobel Prize in 1935 Outside the nucleus, free neutrons are unstable and have a half life of ±1.0s. 21

22 Discovery of Isotopes Frederick Soddy ( ) proposed the idea of isotopes in 1912 Isotopes are atoms of the same element having different masses, due to varying numbers of neutrons. We can also put the mass number after the name of the element: carbon-12 carbon-14 uranium-235 Soddy won the Nobel Prize in Chemistry in 1921 "for his contributions to our knowledge of the chemistry of radioactive substances, and his investigations into the origin and nature of isotopes". 22

23 Isotopes Atomic mass is the average of all the naturally occurring isotopes of that element Isotope Carbon- 12 Carbon- 13 Carbon- 14 Symbol Composition of the nucleus 12 C 6 protons 6 neutrons 13 C 6 protons 7 neutrons 14 C 6 protons 8 neutrons Carbon = % in nature 98.89% 1.11% <0.01% 23

24 Elementary particles 1930s The known 'Elementary Particles' were : electron proton neutron (inside the nucleus) 'neutrino' (now anti-neutrino) in beta decay photon (γ) the quantum of the electromagnetic field 24

25 Elementary particles Heisenberg et al applied QM to nucleons bound together byshort range strong nuclear force 1930 s: Nucleus is composite consisting of nucleons: protons and neutrons 1960 s: Nucleons are bound states of quarks which have fractional electric charge Gell Mann (NP 1969) 1930: Neutrino postulated by Pauli to save energy conservation in β decay 1956: Reines and Cowan discover neutrino (Reines NP 1995) 25

26 Elementary particles Questions that are asked since 2000 years What are the building blocks of matter? What forces act on matter? 400 v.chr Demokritos atom Newton forces Maxwell electromagnetism Einstein a lot 26

27 Standard Model Elementary particle: mass, charge, spin Fundamental forces: Electromagnetic Weak Strong Gravity Fundamental particles Fermions and bosons. There are also antiparticles. Proton (uud) and neutron (udd) are not elementary particles. 27

28 Relativity and Antiparticles We know that E=mc 2 and λ=h/p High energies are required to make new particles Proton radius is ~10 15 m, >10 3 m e energy required So relativistic effects are important Quantum Theory + Special Relativity: each particle must have an antiparticle with opposite quantum numbers: electric charge, spin, lepton charge, etc. Described by Dirac equation: Particle+antiparticle annihilation (γ s or other) Symmetry between particles and antiparticles Dirac made theoretical prediction of anti particles 1933 Anderson discovered positron (NP 1936) 1959 Segre & Chamberlain NP for discovery of anti proton 28

29 Space Time Symmetries and Conservation Laws Emmy Noether s theorem Space, time translation & orientation symmetries are all continuous symmetries Translational invariance p Rotational invariance L Time invariance E Additional symmetries of interest for nuclear and particle physics are: parity charge conjugation time reversal 29

30 Discrete Symmetries Parity, P Parity reflects a system through the origin. Converts right-handed coordinate systems to left-handed ones. Vectors change sign but axial vectors remain unchanged x -x, p -p, but L = x p L Charge Conjugation, C Charge conjugation turns a particle into its anti-particle e + e -, K - K + Time Reversal, T Changes, for example, the direction of motion of particles t -t 30

31 Parity Parity Refers to spatial reflection r r P eigenvalue is called intrinsic parity, or simply parity. Strong and EM interactions conserve parity. Weak interaction violates parity. Leptons and quarks have parity +1 Antileptons and antiquarks have parity 1 Additional contribution to parity from orbital angular momentum 31

32 Charge Conjugation Charge Conjugation Changes particles into antiparticles a electrically neutral particles, b electrically charged particles C a phase factor Weak interaction violates parity EM and strong preserve parity 32

33 Time Reversal t t = t If conserved T is not Hermitian, so it is not observable when conserved. However, rates of time reversed processes must be the same(if no weak interaction is present violates parity). There is a general CPT theorem any relativistic field theory is invariant under the combined CPT. 33

34 Particle Reactions Scattering Reactions 34

35 Decays 35

36 Feynman Diagrams 36

37 Feynman Rules 37

38 Feynman Rules How to calculate amplitude M? The drawing is a mathematical object! p 1 1/(q M= 2 -m 2 ) g g p 2 p 3 38

39 Weak Interactions 39

40 Strong Interactions 40

41 Four Vectors 41

42 Four Vectors 42

43 Particle Exchange 43

44 Klein-Gordon Equation 44

45 Yukowa Potential 45

46 Units 46

47 Units 47