The count rate of a radioactive source decreases from 1600 counts per minute to 400 counts per minute in 12 hours. What is the half-life of the source?

When can a theory be modified if a new type of technology allows for new observations that raise new questions? a-immediately, while the questions about the theory are being asked b-after new hypotheses related to the theory are tested in experiments c-only after the new observations disprove all parts of the theory d-while scientists begin to think about how the theory could improve