At Chernobyl, one of the harmful radioactive isotopes was ¹³¹I, a beta emitter with a halflife of 8 days. Suppose some of this isotope is deposited on a field. What can we say about this field 40 days later? A) Its radioactivity level has decreased to 1/32 of its original level. B) Its radioactivity level has decreased to 1/64-- one sixty- forth-- of its original level. C) Its radioactivity has decreased to harmless levels. D) Its radioactivity level has decreased to 1/16 of its original level. E) It is just as radioactive as it was to begin with.

Question

Quizplus · Accepted Answer

The half-life of I-131 is 8 days. After 40 days, which is 5 half-lives (40/8), the radioactivity level decreases to (1/2)^5 = 1/32 of its original level.

At Chernobyl, One of the Harmful Radioactive Isotopes Was 131I

At Chernobyl, One of the Harmful Radioactive Isotopes Was ¹³¹I