Question

If an isotope's half-life is 100 years:

Select one:


a. That isotope will no longer exist in 50 years

b. In 100 years only half of the atoms in a sample of that isotope will remain

c. That isotope will no longer exist in 200 years

d. In 50 years only half of the atoms in a sample of that isotope will remain

e. In 200 years only half of the atoms in a sample of that isotope will remain

Answer 1

The half-life of an isotope refers to the time required for half of the sample to undergo decay. For an isotope with a half-life of 100 years, only half of the original sample will remain after 100 years. The radioactive material is not gone, but transformed into its decay products. The correct answer is b.

Step-by-step explanation:

An isotope's half-life is 100 years:

In 100 years only half of the atoms in a sample of that isotope will remain. The definition of a half-life in the context of radioactive decay is the time it takes for half of the radioactive nuclei in a sample to undergo decay, not the time it takes for the entire sample to disappear. A half-life of 100 years means that if you start with a given mass of an isotope, after 100 years, you will have half the original mass left. After another 100 years (200 years in total), you would have half of that half, which is one-quarter of the original amount.

Starting with 1 gram of a radioactive isotope with a 100-year half-life, after 100 years, you would have 0.5 grams; after 200 years, 0.25 grams; after 300 years, 0.125 grams, and so on. The isotope itself does not entirely disappear; rather, the radioactive atoms (or 'parent' atoms) are transformed into decay products (or 'daughter' elements).