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.
3. ANSWER: A-TRUE, B-TRUE, C-TRUE, D-TRUE
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.
5. ANSWER: A-TRUE, B-TRUE, C-TRUE, D-FALSE, E-TRUE
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.
6. ANSWER: A-TRUE, B-TRUE, C-TRUE, D-FALSE, E-FALSE
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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