What does the half-life of a radioisotope correspond to?

I think half-life of a radioisotope corresponds to the time taken by on-half of the atoms of a radioactive substance to disintegrate or decay. Half life measures the rate at which a radioactive isotope decays. Radioisotopes have various half lives which may range from a few microseconds to  billion of years. For example the half life of potassium-40 is 1.3 billion years.

The half-life of a radioisotope corresponds to the length of time required for half of a sample of radioactive material to decay

Read the sentences below in 1962, i tried to enroll as the first black student at the university of mississippi. the governor of mississippi blocked my entrance which best describes the verbs used in the sentences? o they are past tense verbs, which are often used in narrative essays o they are past tense verbs, which are not often used in narrative essays. o they are future tense verbs, which are often used in narrative essays o they are future tense verbs, which are not often used in narrative essays.