Gamma Does Dose and Risk

Gamma, Dr. Egghead's dog, has just learned some new equations on calculating cancer risk from exposure to radiation. Because his paws are too big to operate a calculator, he needs your help in doing some sample calculations. Gamma has decided to use the linear no-threshold hypothesis in all the calculations.

Population Doses: Remember that a population dose is the sum of doses received by all the individuals in a population. Population dose is sometimes called "collective" dose and is measured in units of person-rem or person-sievert.

1) People in a large town of 100,000 are exposed to a dose of 1 rem each. What is the population dose?

2) People in a bustling city of 1 million are exposed to a dose of 1 rem each. What is the collective dose?

3) a) The collective dose received by the citizens of a town of 10,000 was 100,000 person-rem. What was the average dose per person? b) Is it possible that certain persons in the town would receive more or less than the average dose?

Risk of cancer from doses: Remember that a person-sievert is a signal to the reader that more than one person is involved. If 0.05 sievert were delivered to a population of 100, then the population dose would be 5 person-sieverts.

4) BEIR V cites a risk of 0.08 fatal cancers per person-sievert when the dose is delivered at once.
a) What term is used to describe the number 0.08?
b) How many sieverts would be needed to produce one fatal cancer in a population?
c) If the population is 100,000 and the number of fatal cancers due to man-made radiation is estimated to be twenty, what was the average dose per person?
d) If the population is 100,000 and is exposed to 0.1 Sv per person, what is the estimate of the number of fatal cancers? (The annual dose limit for the general public for non-medical radiation is 0.001 Sv)

5) If the Dose Rate Effectiveness Factor (DREF, see box) for low dose rates is assumed to be 2, and the unadjusted cancer risk is 0.08 fatal cancers/person-Sv, what is the adjusted risk?

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