Physics Hot Spots

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Physics Hot Spots
2014-04-06 12:31:34
radiation therapy
Registry Review
Registry Review: Physics Hot Spots
Show Answers:

  1. Coherent (Thompson) scattering primarily occurs at energies below ______.
    10 KeV
  2. The probability of Compton scattering ________ as x-ray energy ________.
    the probability of Compton scattering DECREASES as x-ray energy INCREASES.
  3. The ________ is total x-ray absorption so there cannot be more than one event per photon.
    Photoelectric Effect
  4. An x-ray with less than _____ (energy) cannot undergo Pair Production.
    1.022 MeV
  5. The process by which the positron unites with a free electron and the mass of both particles is converted to energy:
    Annihilation Radiation
  6. Cobalt 60 decays by ______ decay to an excited state of _______.
    Cobalt 60 decays by BETA MINUS DECAY (β-) to an excited state of NICKLE (60Ni)
  7. Large, unstable atoms that have a large amount of excess energy tend to undergo radioactive decay by the emission of ___________.
    Alpha particles (α)
  8. When a particle identical to an electron is emitted as a result of nuclear decay:
    Beta minus decay (β- decay)
  9. When a positron is ejected from an atomic nucleus, a nuclear proton decays into a neutron and a positron:
    Beta plus decay (β+ decay)
  10. When an electron strays too close to the nucleus, it can be captured and combined with a proton, reversing the process for β- decay:
    Electron capture
  11. Both _______ and _______ result in the Z of the parent nucleus being decreased by 1 and the N/Z ratio of the atom increases
    Electron capture & Beta plus decay (β+)
  12. This type of radiation is a result of when an electron is taken from its shell, leaving a "hole" in the shell, thus placing the atom in an unstable configuration; then an electron from a higher shell to fall/cascade to a lower shell and losing energy in the form of an x-ray to become stable
    Characteristic radiation
  13. This represents a daughter product of some other kind of decay that is itself in an excited state, but instead of instantly decaying by gamma ray (γ) emission, it remains in this excited state for a given period of time & then decays.
    • Isomeric transition or Gamma decay
    • (γ decay)
  14. Name the interaction in which the incident photon is absorbed but lacks sufficient energy to ionize so the atom re-emits a photon of identical energy but in a different direction:
    Coherent Scattering
  15. Name the interaction in which the incident photon interacts the inner electron shells of an atom and an Auger electron is ejected:
    Photoelectric Scattering
  16. Which interaction produces characteristic radiation:
    Photoelectric Scattering
  17. What is the photon interaction that is most commonly witnessed in the energy ranges used in radiation therapy (1-5 MeV or 25 keV & higher)?
    Compton scattering
  18. Which interaction is most commonly witnessed in diagnostic x-ray and CT scans:
    Photoelectric scattering
  19. Name the interaction in which the incident photon interacts with free (outer) electrons and ejects an electron:
    Compton scattering
  20. Which interaction produces back-scatter?
    Compton scattering
  21. Name the interaction in which the incident photon passes close to the nucleus, is absorbed & instantly the energy is re-emitted as an electron-positron pair (β- , β+):
    Pair production ()
  22. What is the energy of each the electron-positron pair (the result of pair production)
    0.511 MeV each
  23. Name the interaction in which the incident photon strikes the nucleus, is absorbed and then the atom emits both neutrons and gamma rays (γ rays) in an attempt to maintain stability:
  24. Which interaction occurs mainly in high Z materials and at higher energies?
  25. Which interaction can result in triplet production?
    • Pair production
    • 2.044 MeV required
  26. In which photon interaction(s) does the incident photon lose all of its energy?
    • Photoelectric
    • Pair Production
    • Photodisintegration
  27. Which photon interactions ionize the atom?
    • Photoelectric
    • Compton
  28. Which interactions do NOT ionize the atom?
    • Coherent
    • Pair Production
    • Photodisintegration
  29. What is the most important method of x-ray production in therapy machines?
  30. The _________ effect occurs independently of atomic number.
  31. The production of bremsstrahlung x-rays _________ with increasing atomic number.
  32. Penumbra ________ with source size & SSD but is independent of field size.
  33. Percentage depth dose ___________ with field size, energy & SSD but will _________ as the depth increases.
    • Increases
    • Decrease
  34. Photon energy is DIRECTLY proportional to __________.
  35. Photon energy is _________ proportional to photon wavelength.
  36. At a given velocity, the wavelength & __________ are inversely proportional.
    Wavelength & FREQUENCY are inversely proportional
  37. The equation to find maximum number of electrons in outer shells is ______, however, the outermost shell cannot have more than ____ electrons.

    no more than 8
  38. The total number of protons & neutrons is known as the:
    Atomic Mass Number (A)

  39. The total number of protons is known as the:
    Atomic Number (Z)

  40. Atoms that have different numbers of protons & different numbers of neutron but the same total number of nucleons are known as:

    • 32Ce76 and 34Se76
    • (isobAr = same Atomic mass #)
  41. Atoms that have the same atomic number & same atomic mass number but exist at a different energy state due to differences in nucleon arrangement are known as:

    Ir192m and Ir192m

    (isoMer = Metastable)
  42. Atoms that have the same number of protons (Z) but different atomic mass number (A) are known as:

    27Fe59 and 27Fe58

    (isotoPes = same # Protons)
  43. Atoms that have the same number of neutrons but different number of protons are know as:

    11Na22 and 10Ne21

    (isotoNes = same # Neutrons)
  44. The negative side of the x-ray tube;    Contains a filament & a focusing cup:
    the Cathode
  45. The positive side of the x-ray tube;  Contains the target;  Conducts electricity & radiates heat:
    the Anode
  46. Due to the Heel effect, the _______ side of the x-ray tube should be positioned over the thick portion of the body.
    • Cathode
    • cathode over thick

    (side note: the smaller the anode angle, the larger the Heel effect)
  47. Both photoelectric () and compton () are seen in the energy range of 50 keV - _____.
    90 keV