PHY320 Class Test Topic 1 Elemental Abundances All questions are worth 1 mark unless otherwise stated

Transcription

1 Topic 1 Elemental Abundances 1. What is the origin of the Earth s atmosphere? 2. Name the 2 distinct topographical regions on the Moon. 3. In the model of chemical affinities which class of elements forms much of the Earth s mantle? 4. What evidence is there to support the idea that the Moon was once in a molten state? 5. What type of meteorite is most abundantly found on Earth? 6. What is a chondrule? 7. In the study of the Earth s structure using seismic information which of the 2 types of body wave is able to pass through all materials? 8. It is widely believed that the Russian dissident Alexander Litvinenko was poisoned using Polonium-210, an alpha emitter. It is estimated that he ingested 10µgrams of the substance in a London sushi bar on 1 st November Given that the half-life of Polonium-210 is 138 days estimate how much of the 10 µgrams of Polonium-210 was present in his body at the time of his death on 23 rd November (3 marks) Topic 2 Spectral Lines k = 1.38 x J K -1 = 8.62 x 10-5 ev K -1 m H = x kg = MeV/c 2 9. Why are spectral lines in the UV region not detected by an observer on Earth? 10. Which theory is responsible for the existence of natural broadening?

2 11. Why are Lithium and Beryllium more common on Earth than in the Sun? 12. Of the two star populations I and II which has the highest heavy element content? 13. Using the graph in the lecture notes estimate the peak emission wavelength (in Å or nm) of a star with the surface temperature of 7000K. 14. The Wien Law gives the wavelength at which the intensity radiated by a black body at a particular temperature is a maximum. It can be written as: λ max T = x 10-3 m K Use this relationship to estimate the temperatures equivalent to the colours violet (420 nm), green (530 nm), and red (650 nm) (2 marks) 15. Calculate the FWHM of the thermal Doppler broadening of the hydrogen-alpha spectral line (wavelength=6563å) due to the Maxwellian velocity distribution of the hydrogen if its temperature is 6000K. (3 marks) Topic 3 Primordial Nucleosynthesis Boltzmann s constant, k B = 1.38 x J.K -1 = 8.62 x 10-5 ev.k -1 Mass of a proton, m p = x kg = MeV.c -2 Mass of a neutron, m n = x kg = MeV.c -2 1 parsec (pc) = 3.08 x m 16. Give 2 pieces of observational evidence for the Big Bang. 17. What is the mean photon energy at a temperature of K? 18. List 4 elements that were formed during primordial nucleosynthesis. 19. What is the recessional velocity of a galaxy with redshift z=0.183? 20. What is the current temperature of the Cosmic Microwave Background? 21. Using the upper limit of the Hubble constant from the lecture notes calculate the age of the Universe in years. 22. Place the following 6 events in the order that they occur after the Big Bang (4 marks)

3 a. Formation of hadrons (baryons and mesons) b. Formation of galaxies c. Neutrinos decouple from matter d. Photons decouple, origin of CMB e. All fundamental forces are unified f. Primordial nucleosynthesis starts Topic 4 Thermonuclear Fusion 23. What is the source of thermal energy that enables nuclei to undergo fusion in stars? 24. What process hinders nuclear fusion? 25. Which reaction dominates the timescale in the pp chain? 26. What is meant by photo-disintegration? 27. Why does the synthesis of elements in thermonuclear fusion stop at Iron? 28. Why is there high nitrogen abundance during the CNO cycle? 29. What is the final evolutionary stage of a star of mass less than 1.4 solar masses? 30. From the details of the ppi chain in the lecture notes calculate the net release of energy per proton in the formation of one 4 He nucleus. Include the energy from the annihilation of the positrons. (show your working, 3 marks) Topic 5 Neutron Capture 31. From the portion of the chart of nuclides overleaf, or otherwise, write X down 3 isotopes in the form ZA N 32. Where does the local approximation equality break down? 33. What are typical fluxes for the r- and s- process to occur?

4 34. Write out the following nuclear reactions and their effects on a nucleus with Z protons and A nucleons. (4 marks) For example: (n, γ) is equivalent to: (A,Z) + n (A+1,Z) + γ (a) (p,γ) (b) (α,γ) (c) inverse beta-decay (d) (d,p) (d=deuteron) 35. What mechanism terminates the r-process in the mass region 230 < A < 270? 36. What is the line of beta stability? 37. Why do s-process neutrons tend to have a Maxwell-Boltzmann type distribution? 38. Draw the path of the s-process on the part of the chart of nuclides, starting at 56 Fe and ending at 64 Cu (Shaded boxes with a percentage value, (e.g %) are isotopes that are stable against β decay, other boxes with half-lives (e.g d) are isotopes that do beta decay). (2 marks) Topic 6 - Supernovae

5 n = amu 4 He = amu 12 C = amu 16 O = amu 1 amu = MeV/c 2 = 1.66x10-27 kg 39. What is the key feature that distinguishes SN of types I and II? 40. The following reaction takes place in a Red Giant, calculate its Q-value. 12 C + 4 He 16 O + n 41. Is the above reaction exothermic or endothermic? 42. Write down the reaction for the photodissociation of Iron in the core of a star prior to a type II supernova. 43. Under what circumstances might a hydrogen/helium flash (nova) occur? 44. How have type Ia SN been used recently in cosmology? 45. What objects are formed from the core remnant of a type II SN? 46. Explain the lack of H emission and absorption lines in type I SN. 47. What reaction governs the late light curve in most SN? What is the critical timescale here? (2 marks) 48. What is the key method of transportation of energy out of a SN explosion? What experimental evidence do we have to support this? (2 marks) Topic 7 Cosmic Rays 49. What is a primary cosmic ray? 50. Write down the decay of an anti-muon (positively charged muon) into a positron and neutrinos. 51. Name 2 possible sources of the highest energy cosmic rays.

6 52. What is fluorescence? 53. Why is it difficult to pinpoint the sources of cosmic rays? 54. Do recent results from AUGER confirm or reject the GZK hypothesis? 55. An electron travels with velocity 2.5x10 8 m.s -1 through a medium of refractive index 1.3. Using the relationship in your notes, what is the angle between the electron and the resulting Cerenkov photons? (show your working, 3 marks). 56. A detector records 2500 cosmic rays per hour at 1 GeV, how many would it detect per hour at 20 GeV assuming the detector is 100% efficient at both energies (assume an E -2.6 energy dependence of the cosmic ray spectrum)? (2 marks) 57. What is the principal decay product of cosmic rays as seen at ground level? Topic 8 Galactic Chemical Evolution 58. The return fraction R represents the fraction of a star that is returned to the ISM. What are the 2 main ways in which this happens? (2 marks 59. What is meant by metallicity? 60. Why are so-called dredge-up events important? 61. What is a primary element? 62. In the so-called Simple GCE model it is assumed that the system is isolated what does this mean? 63. What is the problem in assuming that the initial conditions of a system is a gas containing primordial nucleosynthesis abundances?