Strontium 90, a radioactive isotope of strontium, is present in the fallout resulting from nuclear explosions. It is especially hazardous to animal life, including humans, because, upon ingestion of contaminated food, it is absorbed into the bone structure. Its half-life is 27 years. If the amount of strontium 90 in a certain area is found to be eight times the "safe" level, find how much time must elapse before an "acceptable level" is reached.
A) 81 year(s) must elapse before an "acceptable level" is reached.
B) 78 year(s) must elapse before an "acceptable level" is reached.
C) 66 year(s) must elapse before an "acceptable level" is reached.
D) 57.3 year(s) must elapse before an "acceptable level" is reached.

Question

Strontium 90, a radioactive isotope of strontium, is present in the fallout resulting from nuclear explosions. It is especially hazardous to animal life, including humans, because, upon ingestion of contaminated food, it is absorbed into the bone structure. Its half-life is 27 years. If the amount of strontium 90 in a certain area is found to be eight times the "safe" level, find how much time must elapse before an "acceptable level" is reached. ​
A) 81 year(s) must elapse before an "acceptable level" is reached.
B) 78 year(s) must elapse before an "acceptable level" is reached.
C) 66 year(s) must elapse before an "acceptable level" is reached.
D) 57.3 year(s) must elapse before an "acceptable level" is reached.

Quizplus · Accepted Answer

To reduce the strontium 90 level to 1/8th (which is the "safe" level from being 8 times the safe level), it would take three half-lives (since 2^3 = 8). Given the half-life is 27 years, it would take 3 * 27 = 81 years to reach the safe level.

Strontium 90, a Radioactive Isotope of Strontium, Is Present in the Fallout