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    • Section 11 Radiation Protection Answers and Feedback

    • Section 11 Radiation Protection Answers and Feedback 

      1. ANSWER: A
      FEEDBACK: Carcinogenesis by radiation is considered to be a stochastic process (i.e., it is an all-or-nothing event). The severity of the response is not dose dependent, although the probability of it occurring is. There is no threshold (i.e., there is no dose below which there is no risk). The BEIR V and UNSCEAR committees found that for solid tumors in the Japanese survivors, the excess cancer incidence was a linear function of dose, with no threshold. The leukemia data were best fitted with a linear-quadratic function of dose. The correct option is A. 

      2. ANSWER: C
      FEEDBACK: The maximum permissible doses recommended by the NCRP are effective
      doses. Also, the dose outside the lead apron does not reflect the dose under the lead apron. The dose under the lead apron is usually lower by about a factor of 20. The dose to the conceptus is more than a factor of two less than this because of protection from the mother’s overlying tissues. Therefore, the actual dose to the conceptus is less than about 0.1 mSv for the 90-day period. This is less than 0.05 mSv to the conceptus per month, which is much lower than the 0.5-mSv monthly limit recommended by the NCRP. Option C is correct. Option A is false for two reasons: (a) The dose to the conceptus is not at a level of true concern, and (b) the Nuclear Regulatory Commission (NRC) regulates exposures only to radionuclear by-product material. The NRC would be an improper agency to notify for exposures to x-rays. The individual can continue to work in fluoroscopy as long as she maintains proper radiation management practices. Option B is false. Since the radiation levels are well below any of concern, option D would be unnecessary.

      3. ANSWER: B
      FEEDBACKAccording to the NCRP 160, medical sources now contribute nearly half of the collective dose of radiation to the population. The chart in option A reflects the source of most radiation to the US population in the early 1980’s. The correct option is B. 

      4. ANSWER: C
      FEEDBACK: Radon is the largest single contributor to the “effective” dose. The effective dose is the product of the absorbed dose, the radiation weighting factor (Wr), and the tissue weighting factor (Wt). The radiation weighting factor for the alpha particles emitted by radon progeny is 20, while the tissue weighting factor for the lung, the only tissue irradiated by radon progeny, is 0.1. The correct option is C. 

      5. ANSWER: D
      FEEDBACK: Medical (including dental) radiation represents about half of the effective dose to the U.S. population and is therefore by far the largest source of exposure from human activity. Natural background radiation is slightly greater. The correct option is D. 

      6. ANSWER: C
      FEEDBACK: Of the options given, fluoroscopy of the trunk of the body involves by far the largest dose to the operator. The correct option is C. 

      7. ANSWER: C
      FEEDBACK: Until a worker declares a pregnancy, no special protection limits apply apart from those generally applicable to a radiation worker. Once a pregnancy is declared, the recommended limit is 0.5 mSv per month. If this is adhered to, the dose for the duration of the pregnancy would be similar to that allowed for an occasional exposure of a member of the general public. The mother may be a radiation worker, but the conceptus is not. The correct option is C. 

      8. ANSWER: D
      FEEDBACK: Hands and legs are of concern for deterministic effects, which do not include cancer induction. Option A is false. The risk of cancer from low-dose-rate exposures is about 4%/Sv. Option B is true. Hands are allowed a larger maximum dose (500 mSv) than the eyes (15150 mSv) because the eyes are much more sensitive to radiation. Option C is false. Because of repair of damage, a low-dose-rate exposure is less effective than a high-dose-rate exposure. Option D is correct.

      9. ANSWER: 1-C, 2-B, 3-D, 4-A
      FEEDBACK: The maximum permissible effective dose for individuals occupationally exposed is 50 mSv per year. C matches with 1. The public is allowed an exposure that is one-tenth of the occupational cumulative dose limit of 10 mSv per year. B matches with 2. After a pregnancy is declared, the maximum permissible dose per month to the conceptus is 0.5 mSv, so that during the duration of the pregnancy the dose is similar to that allowed a member of the general public as an occasional exposure (one-tenth of the annual occupational effective dose limit). A matches with 3. The limit for the eye of an occupationally exposed individual is 15150 mSv, which is designed to prevent a deterministic effect. D matches with 4. 

      10. ANSWER: D
      FEEDBACK: The maximum permissible dose for the hands is 500 mSv because the main concern for the hands is not skin cancer but deterministic effects. Maximum permissible dose is based on low-dose-rate exposures, and nuclear power plant employees have not contributed to the database for hand exposure. The correct option is D. 

      FEEDBACK: The minimum age for occupationally exposed workers is 18 years. Option A is true. It is assumed that medical radiation confers some benefit, so it is not included in the dose allowed to a person occupationally exposed. Option B is false. ALARA is intended to minimize occupational exposure. Option C is false. The purpose of radiation protection for those occupationally exposed is to prevent deterministic effects and limit stochastic effects to levels that are acceptable against a background of other risks in society. Option D is true. 

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