PHY138Y Nuclear and Radiation

Transcription

1 PHY138Y Nuclear and Radiation Professor Tony Key MP401 Question Would you prefer to have music playing in the 6-7 minutes before class while Larry and I set up? A. YES B. NO C. DON T CARE EITHER WAY Extra Problems, etc. All that you need for this section is contained in the Supplementary Notes. Read Knight for extra understanding where relevant. Extra problems check out the Suggested Extra Problems, relevant ones in Knight, old problem sets, old tests, old exams. Also see Worked Examples. This Week Readings Supplementary Notes II : SNII X- rays Production Characteristics and Use Today Quick review and wrap-up of SNI X-rays production, interaction Who first measured the charge of the electron? A. Coulomb B. Thomson C. Millikan D. Rutherford E. Boltzmann 1

2 Protons and neutrons together are referred to as: A. Nuclei. B. Neutrinos. C. Nucleons. D. Mesons. E. Leptons. Review Mass unit, MeV/c 2, Binding Energy Nuclear Binding Energy The Binding Energy is the energy required to break the nucleus into its component parts Atomic Binding Energy The Binding Energy is the energy required to break the atom into its component parts ENERGY NUCLEUS INDIVIDUAL PROTONS AND NEUTRONS + + B + m nucleus = Z m p + N m n So... B = ( Z m p + N m n ) - m nucleus ENERGY + ATOM INDIVIDUAL ELECTRONS AND NUCLEUS B + m atom = Z m e + m nucleus nuclear mass The binding energy of the electrons in the atom B.E. of electrons ~ 10-6 x B.E. of nucleons So... can be ignored in all problems in this section Review Mass unit, MeV/c 2, Binding Energy Worked Example: Binding Energy of 12 C nucleus see journal notes from last week! 1. Use formula (easy) 2. Remember to convert atomic mass to nuclear mass (subtract masses of electrons) 3. Use mass to energy conversion u to MeV/c 2 2

3 X-Rays 12 C nucleus α particle 4 2 He X-rays production: bremsstrahlung line spectra Interaction of X-rays with matter Photoelectric effect Compton Effect Pair Production Units of Measurement Attenuation of Radiation Wilhelm Roentgen The First X-ray First Nobel Prize 1901 WARNING! The next slide is intended for adults. It is a scene of horror and nudity (and possibly adult language) Viewer discretion is strongly advised. 3

4 Shoe Fitting The Electromagnetic spectrum Production of X-rays What is the energy of an electron which is accelerated across a potential difference of 50,000 volts? A. 20 kev B. 40 kev C. 50 kev D. 100 kev E. 5 kev 4

5 What is the energy of an electron which is accelerated across a potential difference of 50,000 volts? A. 20 kev B. 40 kev C. 50 kev D. 100 kev E. 5 kev Worked Problem An X-ray tube has a HV of 20 kv. What is the low wavelength cutoff for this tube, in pm? 62 pm High Energy X-ray Machine 5

6 Interaction of Photons with Matter The Photo-electric Effect (Pac man) The Compton Effect Pair Production increasing energy electron out AN ATOM photon in PHOTOELECTRIC EFFECT electron AN ATOM photon in photon out positron AN ATOM high energy photon in electron COMPTON EFFECT PAIR PRODUCTION Review Who is this man? A. He explained the Compton Effect B. He explained the photoelectric effect C. He explained Pair Production D. Don t Know E. Don t Care Review Who is this man? A. He explained the Compton Effect B. He explained the photoelectric effect C. He explained Pair Production D. Don t Know E. Don t Care 6

7 The Compton Effect Pair Production. Dirac s equation for the electron generated positive particles. Later identified as the anti-particle of the electron. Observed by Anderson in 1932 Arthur Holly Compton Dirac Anderson P A I R P R O D U C T I O N P A I R P R O D U C T I O N 7

8 Probability. of Interaction Summary of Interaction Probability of X-rays ~100 kev ~ MeV PhotoElectric Compton Effect Pair Production TOTAL X- Ray Energy (MeV) The voltage of an X-ray tube is increased, with the current being kept constant. Which of the following quantities of the emitted X-rays, if any, are increased as a result? 1. the bremsstrahlung wavelength 2. the bremsstrahlung frequency 3. the fluence rate (no. of photons m -2 s -1 ) 4. the line spectra wavelengths 5. the line spectra frequencies The current of an X-ray tube is increased, with the voltage being kept constant. Which of the following quantities of the emitted X-rays, if any, are increased as a result? 1. the bremsstrahlung wavelength 2. the bremsstrahlung frequency 3. the fluence rate (no. of photons m -2 s -1 ) 4. the line spectra wavelengths 5. the line spectra frequencies Worked Problem An X-ray photon of energy 120 kev undergoes a Compton scattering, emerging with an energy of 50 kev. The electron that is also produced in the Compton scattering then produces a bremsstrahlung photon, and continues with an energy of 30 kev. What is the energy of the bremsstrahlung photon? 8