A researcher studying a short-lived radioisotope X records its activity as 6.4×105 Bq at 10:00 a.m. and 1.0×105 Bq at 1:00 p.m. on the same day. Assume Avogadro constant NA=6.022×1023mol−1 and atomic mass of X = 40 g mol−1.
(i) Calculate the decay constant of the radioisotope X.
(ii) Hence find the half-life of X in minutes.
(iii) If the sample contained 2.0 mg of X at 10:00 a.m., determine the mass that will remain at 5:00 p.m. on the same day.