Final answer:
The half-life of cobalt-60 is 5.27 years as stated in the reference material, not calculated from the provided data, which fits the observed decay of the sample over 8 years.
Step-by-step explanation:
The half-life of a radioactive isotope is the time taken for half of its atoms to decay. From the question and reference material, it is provided that for cobalt-60, the half-life is 5.27 years.
After one half-life, 50% of the original sample remains; after two half-lives, 25% remains, and so on.
Given that after 8 years, 0.351 g of an initial 1.000 g sample of cobalt-60 remains, this aligns with a little more than one half-life but less than two half-lives.
Without performing any detailed calculations, we can compare this to the provided information that exactly one half-life is 5.27 years for cobalt-60, therefore the remaining amount of 0.351 g after 8 years suggests that the correct half-life provided in the references is consistent with the sample's decay.