• Section 9 Sources of Radiation to the Human Population Answers and Feedback

  • Section 9 Sources of Radiation to the Human Population (NCRP 160) Answers and Feedback 

    1. ANSWER:  A
    FEEDBACK: At the time of the Three Mile Island accident, it was estimated that the number of cancer deaths due to the release of radioactive materials was about 0.5. The closest and correct option is A. 

    2. ANSWER: A
    FEEDBACK: The excess cancer risk estimated by the UNSCEAR and BEIR V committees was 8%/Sv, based on the data from the Japanese survivors. However, the Japanese survivors experienced an acute exposure. The ICRP uses a dose and dose-rate reduction factor (DDREF) of 2, so that the estimate of cancer risk at low doses and low dose rate, applicable to the radiation protection of a working population, is 4%/Sv. The correct option is A. 

    FEEDBACK: The total number of excess malignancies attributable to radiation at Hiroshima and Nagasaki is about 600. Option A is true. There was an increase in leukemia and many solid tumors, including those of the breast. Option B is true. Exposure in utero led to an increased incidence of reduced head diameter and mental retardation. Option C is true. While there is a trend, there was no statistically significant increase in hereditary (genetic) effects in the first-generation children of persons exposed. Option D is true.

    4. ANSWER: 1-D, 2-C, 3-A, 4-B
    FEEDBACK: The effective dose from average background radiation, including radon, for the United States is about 3 mSv per year. D matches with 1. Once a pregnancy is declared, the NCRP dose limit to the conceptus is 0.5 mSv per month. Until a pregnancy is declared, there are no special dose limits other than those applicable to any radiation worker. C matches with 2. The effective dose received in flying across the North Atlantic in a commercial jetliner is about 0.05 mSv. This is due to the cosmic radiation at the altitude of about 35 ,000 feet. A matches with 3. The genetically significant dose (GSD) is the dose that if given to everyone in the U.S. population would result in the same number of mutations as would the actual variable dose received by part of the population during medical irradiation. The GSD is about 0.25 mSv. B matches with 4. 

    FEEDBACK: Radon tends to accumulate in the basement of a house as it seeps in from rocks and soil. This is particularly true in winter when the house is heated and the pressure inside is a little less than that outside. This draws radon into the house. In the outside air, radon dissipates. Option A is true. The BEIR VI best estimate of lung cancer deaths from radon was 15,400 to 21,800 per year, depending on which model is adopted. This is about 10% of the lung cancer deaths per year, which were about 157,990 in 2003 in the United States. Option B is true. Two of the progeny of radon emit energetic alpha particles, which are thought to be the cause of lung cancer. Option C is true. When radon decays into solid progeny, it does so with a half-life of about 3 days. Option D is false. The parent is indeed radium. Option E is true. 

    FEEDBACK: Radon is a naturally occurring radioactive gas that seeps out of the ground into mines and the basements of homes. Option A is true. Radon constitutes about 55 % of the effective dose to the U.S. population, which is about double that from medical x rays. Option B is true. In the United States, the action level for radon (the maximum concentration in the lived-in area of a house above which modifications to the building are recommended) is 4 pCi/L. This is lower than the action levels in Canada and Europe. Option C is true. The half-life of radon is about 3 days; it is radium that has a half-life of about 1,600 years. Option D is false. Two of the progeny of radon emit energetic alpha particles, which are thought to cause lung cancer. Option E is false.  

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