Two samples initially contain the same number of undecayed nuclei. They emit the same type and energy of radiation and are compared at the same distance with identical shielding. P has a much shorter half-life than Q. Which statement correctly compares the initial exposure rates and the time for activity to halve?
P gives a lower initial exposure rate and its activity halves sooner.
P gives a higher initial exposure rate and its activity halves sooner.
P gives a lower initial exposure rate and its activity halves later.
P gives a higher initial exposure rate and its activity halves later.