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Alexandria University Medical Research Institute Student name: ………………………...... ……………… Department of Radiation Sciences Semester: Spring Ph.D. in Radiobiology Degree Academic year: 2019/2020 Course title: Assessment of occupational radiation doses Time allowed: 1 hr Course code: 1711807 Date: 20 / 7 / 2020 Final Exam Total marks: 75 marks

Question 1: Choose the correct answer (45 marks, 1.5 each, 30 mins)

1. Recommendations regarding dosimetric quantities and units in radiation protection dosimetry are set forth by ……………………………… a. ICRU c. ICRP b. IRPA d. IAEA

2. Ambient and directional dose equivalent link the external radiation field to the ……………………………… a. effective dose c. exposure dose b. radiation weighing factor d. effective dose equivalent

3. The sensitivity is defined as the inverse of the ……………………………… a. Calibration factor c. conversion coefficient b. calibration coefficient d. air kerma in air

4. An example of direct reading dosimeters is ……………………………… a. optically stimulated luminescence detector b. film badge c. Thermo luminescent dosimeter d. electronic personal dosimeter

5. Optically stimulated luminescent dosimeters contain a thin layer of a. phosphate glass c. aluminium oxide b. CaF2:Mn d. LiF:Ti,Mg

6. Personal dosimeters should be calibrated in terms of ……………………………… for individual monitoring of external exposure a. operational quantities c. personal dose equivalent b. directional dose equivalent d. None of the above

7. For individual monitoring, the ……………………………… is used a. directional dose equivalent c. ambient dose equivalent b. personal dose equivalent d. tissue equivalent

8. The relevant depth in the ICRU sphere for strongly penetrating radiation is ……………………………… mm. a. d = 0.07 mm. c. d = 10 mm. b. d = 3 mm. d. none of the above.

9. For weakly penetrating radiation the personal dose equivalent Hp (3) is for the ………………….…… a. soft tissue. c. skin. b. lens of the eye. d. none of the above.

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10. Radiation weighing factor for electrons equals ……………………………… a. 5 c. 1 b. 5-20 d. 20

11. Proportional detectors belong to the class of ……………………………… a. gas filled detectors c. solid state detectors b. radiophotoluminescent detectors d. semiconductor detectors

12. ……………………………… are the major carriers for n-type semiconductors. a. Electrons c. Atoms b. Holes d. Molecules

13. Present radiation safety standards for occupational exposure to whole body radiation limits an individual’s dose equivalent to ….……………………………. a. 100 mrem/week c. 2000 mrem/year b. 166 mrem/month d. 5000 mrem/year

14. Which of the following diseases can be regarded as a stochastic effect due to ionizing radiation? a. reduction in the number of WBC c. temporary sterility b. leukemia d. permanent sterility

15. Direct Reading Dosimeter operate by measuring the ...... produced by radiation. a. current c. ionizations b. pulse d. electrons

16. The most important advantage of film dosimeter is …………………………. a. It is inexpensive c. It can be read in-site b. It gives real-time dose measurement d. It can measure neutron dose

17. The most important advantage of the semiconductor detectors, compared to other types of radiation counters, is their superior ……………….. a. efficiency c. energy resolution b. dead time d. signal multiplication

18. Thermal Neutrons are more likely to interact with tissue through …………………. a. Radiative neutron capture c. Inelastic scattering b. Transmutation d. Elastic scattering

19. The opposite figure represents ………………………………….. a. Semiconductor detector b. Two-diode detector c. Multi-diode detector d. MOSFET detector

20. When exposed to neutrons, most physical effects in detectors show a lower efﬁciency at higher ionization densities owing to ………………………. a. effect of recombination b. greater radiobiological effectiveness c. the protons produced through capture by nitrogen d. the recoil protons from elastic scattering with hydrogen

Page 2 of 5 21. It has been estimated that about ………………….. of biological damage caused by low LET radiation is due to indirect action. a. 25% c. 66% b. 50% d. 75%

22. In OSL, ...... is used to release the trapped energy in the form of luminescence. a. heat b. laser c. optical fiber d. blackening of the film

23. In a semiconductor junction, all interactions with radiation occurs in ...... a. P-type semiconductor c. Reverse bias b. N-type semiconductor d. Depletion region

24. The gas-filled detector that operates in region II is a. Ionization chamber c. Proportional counter b. GM-counter d. Gaseous scintillators

25. A MOSFET devices will respond to energy deposition from all types of charged particle, but with different efﬁciencies owing to...... a. increased recombination c. accumulating positive space-charge b. decreased recombination d. altering the electrical characteristics

26. ……………….. uses several detectors to extend the detectable range and have greatly enhanced sensitivity. a. Two-diode device c. Diode Array Detectors b. Multi-diode device d. MOSFET detector

27. When radiation is absorbed, ...... is a measure of kinetic energy released per unit mass of absorber. a. absorbed dose c. KERMA b. dose rate d. Effective dose

28. Fast Neutrons are more likely to interact with tissue through …………………. a. Radiative neutron capture c. Inelastic scattering b. Transmutation d. Elastic scattering

29. The opposite figure represents ………………………………….. a. Semiconductor junction b. Semiconductor detector c. MOSFET detector d. Reverse bias

30. The major source of difﬁculty, for the measurement of neutron dose is that it involves a ……………….. a. radiobiological effectiveness c. recombination or saturation effect b. ionizing radiation d. weighting factor

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Question no. 2: True or false (20 marks, 1.0 each, 20 mins)

31. Neutron area survey meters operate in the proportional region so that the photon background can be easily discriminated against. ( )

32. Individual monitoring is the measurement of the radiation doses received by individuals working with radiation. ( )

33. Holes are the major carriers for n-type semiconductors and electrons are the major carriers for p-type semiconductors. ( )

34. In badge films, cumulative doses of different radiations are evaluated by measuring the film optical luminescence . ( )

35. Commercially available RPL dosimeters cover the dose range of 30 mSv to 10 Sv . ( )

36. RPL dosimeters are very useful in emergency situations for immediate readout of the equivalent doses received. ( )

37. In insulators, the highest allowed band, called the valence band, is completely occupied. ( )

38. Optically stimulated luminescent dosimeters are less sensitive than thermoluminescence badges with a lower detection limit of 10–30 mSv. ( )

39. Personal monitors must have a wide dose range to cover both radiation protection and background monitoring. ( )

40. Film dosimeters can identify and estimate doses of X rays, ɣ rays, β particles and thermal neutrons. ( )

41. Exposure to ionizing radiation ultimately cause cancer. ( )

42. Uncertainty in a measurement in the workplace may significantly increase because the energy spectrum and orientation of the radiation field are generally not well known. ( )

43. Radiation dosimetry is defined as the measurement of the absorbed dose, or other relevant quantities, which is produced due to the interaction of the ionizing radiation with a material. ( )

44. Ionizing radiation exerts its indirect effects on biological targets through via radiolysis of cellular water, forming hydroxyl ions. ( )

45. Personal monitors must have as wide a dose range as possible so that they can cover both radiation protection and accidental situations. ( )

46. In a Multi-diode Device, there are four surface barrier detectors, three covered with different thickness of 10B, with cadmium shields to absorb incident albedo neutrons and with or without a boron shield on the body side to absorb thermal neutrons. ( ) Page 4 of 5

47. The response of a TLD is dependent upon the dose rate. ( )

48. External dosimetry is a measure of the KERMA produced from radiation sources, which are outside of the body of the exposed worker. ( )

49. Neutron weighting factor is variable depending only on the energy of the neutron. ( )

50. Cells that normally proliferate more rapidly are more sensitive to ionizing radiation. ( )

Question no. 3: Match the two columns (10 marks, 1.0 each, 10 mins) I. Film badge 51 a consists of a small (~1 mm3) chip of carbon doped aluminium oxide. Thermoluminescent Dosimeter 52 b Cannot be reused Optically Stimulated 53 c is a highly insulating silicon dioxide ﬁlm, Luminescence System on irradiation accumulates positive charge which alters the electrical characteristics of the transistors. Direct Reading Dosimeter 54 d Heating the crystal causes the crystal lattice to vibrate, releasing the trapped electrons in the process. MOSFET Dosimeter 55 e contains a small ionization chamber with a volume of approximately two milliliters.

II. Solid State Dosimeter 56 a can be used to detect the charged particles from capture reactions on boron, lithium or nitrogen to cover the albedo region; and protons from elastic scattering on hydrogen for the fast region. Two-diode device 57 b uses several detectors to extend the detectable range to higher neutron energies. Multi-diode device 58 c is a semiconductor detector operating as a microdosimetric counter. An adequate estimation of tissue dose equivalent may be obtained. However, the neutron sensitivity is low. Array Detector 59 d The selection of suitably thin radiator and gate, combined with a detector for subtraction of the photon response, should give a dosimeter of acceptable fast neutron energy dependence. MOSFET Dosimeter 60 e are a group of position sensitive detectors, coupled to a triple dispersive unit.

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