Units (Radioactivity)

A class is designing an experiment to compare the ranges of different types of ionising radiation in air. They list the following possible measurements for their experiment: - The distance from the radioactive source to the detector - The thickness of aluminium sheets placed between the source and detector - The number of decays per unit time measured at the detector For each measurement above, identify and justify the most appropriate unit to use according to the syllabus requirements.

In an investigation of half-life, you are told to record the 'interval' for each measurement of activity and to keep the apparatus at the same separation throughout. Name the correct units you would use to record (i) the time interval between measurements and (ii) the separation between the radioactive source and detector. Briefly justify your answers.