Examination in Nuclear and Particle Physics

Size: px

Start display at page:

Download "Examination in Nuclear and Particle Physics"

Dominick Gregory
5 years ago
Views:

1 Eamination in Nuclear and Particle Physics Time: Monday 9 October 009, 4:00-9:00 hours. Allowed means: Physics Handbook - Nordling and Österman, β Mathematical Handbook, Charts of the Nuclides and Pocket Calculator, Dictionary. N.B. If there is a difference in the information between the particle data sheet attached to this eam and Physics Handbook, use the information from the data sheet. Instructions: Use the distributed sheets for the answers and write your name on each sheet. Write clearly and readably, define used symbols, motivate equations and state the numerical values with units that are used. Attach this sheet to the answers. The eamination contains problems giving a maimum of 40 points. Good luck! Tord Johansson & Olga Botner. Name: Personal code nr: (Personnummer) Programme: Together with this sheet, I attach answers to the following problems ( Tick! ): ( ) ( ) 3 ( ) 4 ( ) 5 ( ) 6 ( ) 7 ( ) 8 ( ) 9 ( ) 0 ( ) ( ) ( ) I want to have a passed result published on Studentportalen yes ( ) no ( )

2 . Multiple choice questions (N.B.: More than one answer may be correct. All correct answers must be given per question to get the corresponding point). [5 p] Electron capture is an alternative process to To eplain the ordering of levels in a nucleus one needs, in addition to a central potential, 3 The probability for α-decay 4 An oscillatory pattern observed in elastic electron scattering on nuclei reflects 5 The fact that the deuteron does not have any ecited states reflects 6 The fusion of two protons into a deuteron in the Sun goes via 7 A state containing (at least) one strange anti-quark 8 Neutral weak currents 9 Mesons 0 Evidence for quarks is provided by β + -decay. β -decay. γ-decay a spin-spin potential. a tensor potential. a spin-orbit potential. increases with the α kinetic energy. decreases with the α kinetic energy. depends on the transition matri. the quark structure of the nucleons. the sharpness of the nuclear surface. a Gaussian charge distribution. the influence of Coulomb interaction. the potential depth. the spin-spin interaction. the strong interaction. the electromagnetic interaction. the weak interaction. is always an antiparticle. may be a meson. is a hadron. conserve flavour. are mediated by W bosons. act only on leptons. are bosons. are fermions. can be both, fermions and bosons. analysis of the muon decay. deep inelastic lepton-nucleon scattering. two-jets events.

3 . (a) Why is it advantageous to use elastic electron scattering from nuclei, rather than elastic α-particle scattering, in the determination of the nuclear charge density? [p] (b) Describe how the charge distribution is determined from these eperiments. [p] + 3. The first three ecited states in Ca have spin parity,, and, respectively. Interpret these states in terms of the shell model and give their shell population [p] 3. A nuclear ecited state decays by an E transition to the ground state which has spin (I)-parity(π), I π = (3/) +. List the possible spin-parity assignements of the ecited state. [p] 4. The spectrum above shows the number of electrons as a function of the kinetic energy from a radioactive source. (a) Eplain why there is a continuous energy distribution of electrons. (b) Eplain the origin of the superimposed monoenergetic peaks. (c) How would the shape of the continuous energy distribution above be changed if there would be emission of positrons instead? [p] [p] [p]

4 5. A fusion reaction between deuterium (D) and tritium (T) is used in fusion reactors and thermonuclear bombs. (a) Specify the reaction that takes place and calculate its Q-value. [p] (b) Assuming that all eplosive power in a big thermonuclear bomb of 50 MT (mega ton) stems from the D-T fusion. How much D-T gas, by weight, is required to produce this eplosive power? Hint. The eplosive power is defined in units of TNT. g TNT corresponds to 4 kj of liberated energy [p] 6. Naturally occurring Samarium contains the radioactive isotope 47 Sm which decays with α-emission. The activity from g of nat Sm is measured to be 89 s -. (a) Calculate the half-life of 47 Sm from this measurement. [p] (b) Give a qualitative eplanation why α-decay is a much more likely decay for nuclei that also decay by spontaneous fission. [ p] (c) There is a strong correlation between the half-life of an isotope and the kinetic energy of the α-particle. Which? [p] 7. Protons striking a stationary target produce τ leptons through the reaction where X stands for one or more particles. Suggest a possible particle/set of particles X. (Hint: use as few and as light particles as possible) (a) For this X, compute the minimum beam (kinetic) energy required for the reaction to take place. (b) τ s can also be produced in e + e collisions. If the beams have equal energy, what is the minimum beam energy required for τ production? [3p]

5 8. The K + often decays into but the kinematically similar decay has never been observed. (a) What interaction would be responsible for each decay? What forbids the second process? (b) Draw the Feynman diagrams for the allowed process. [ p] 9. Which of the following particle reactions and decays are allowed? If forbidden, indicate why. If allowed, state which interaction and draw the relevant quark line (or Feynman) diagram (a) (b) (c) (d) (e) (f) (g) (h) [4 p] 0. A neutrino beam is produced at an accelerator by letting kaons and pions decay into muons and neutrinos. The neutrinos are observed at a detector behind a 300 m thick shield of earth and steel. The detector consists of 5000 kg of water viewed by photo-multipliers. (a) Eplain why muons (and hadrons from kaon decays) are stopped by the shield but not the neutrinos. Which interactions are responsible? (b) Assume that the neutrino flu at the detector is 0 m - year -. What is the observed reaction rate? (The neutrino-nucleon cross-section is 0-37 cm.) [ p]

. Assume a quark model with 4 quark flavours: u, d, c and s. (a) What is the quark content of all possible mesons that you can construct from these quark flavours?

6 . Assume a quark model with 4 quark flavours: u, d, c and s. (a) What is the quark content of all possible mesons that you can construct from these quark flavours? (b) Group the mesons into families according to (first) the value of charm (C) and (second) the value of strangeness (S). (c) For each family, determine the values of isospin, I and I 3. [3 p]. The muon decay is purely leptonic. (a) Draw the diagram for this decay. (b) From the diagram, the muon lifetime is calculated theoretically to give where m µ is the muon mass and G F is a constant: G F = MeV fm 3. Restore the missing and c in the formula and compute the muon lifetime. [ p]

Nuclear and Particle Physics 3: Particle Physics. Lecture 1: Introduction to Particle Physics February 5th 2007

Nuclear and Particle Physics 3: Particle Physics Lecture 1: Introduction to Particle Physics February 5th 2007 Particle Physics (PP) a.k.a. High-Energy Physics (HEP) 1 Dr Victoria Martin JCMB room 4405