One of the problems of in-air testing of nuclear weapons (or, even worse, the us
ID: 2203100 • Letter: O
Question
One of the problems of in-air testing of nuclear weapons (or, even worse, the use of such weapons!) is the danger of radioactive fallout. One of the most problematic nuclides in such fallout is strontium-90(^90 sr), which breaks down by beta- decay with a half-life of 28 years. It is chemically similar to calcium and therefore can be incorporated into bones and teeth, where, due to its rather long half-life, it remains for years as an internal source of radiation.
1)What percent of the original level of^90 sris left after 56 years?
2)How long would you have to wait for the original level to be reduced to 4.88
Explanation / Answer
28=ln2 / k =>k=0.024 years ^-1 ln(A)= -k*t+ ln(A0) =>ln (A/A0)= -k*t 1)>ln (A/A0)=-1.344 =>A=0.26 A0 so 26% is left after 56 years 2)ln(4*10^-4*A0/A0) = -k*t =>t=326 years
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