A radioactive isotope has a decay constant of 3.0×10−4s−1. Initially the sample contains 4.0×106 undecayed nuclei.
(i) Calculate the number of nuclei that remain undecayed after 20 minutes.
(ii) Determine the number of nuclei that have decayed during this 20-minute interval.
(iii) Find the time (in seconds) required for the number of undecayed nuclei to fall to 1 % of the initial number.