Chemistry Labs

International Chemistry Olympiad · 1993

Problems

  1. Problem 1131I^{131}\ce{I} is a radioactive isotope of iodine (a β−\beta^{-} emitter) used in nuclear medicine for scintigraphy of thyroid disorders. Its decay rate constant is k=9.93×10−7 s−1k = 9.93\times10^{-7}\ \mathrm{s^{-1}}. (1.1) Write the decay reaction of 131I^{131}\ce{I}. (1.2) Calculate the half-life of 131I^{131}\ce{I} in days. (1.3) Calculate the time (in days) needed for a sample of 131I^{131}\ce{I} to fall to 30 % of its initial activity. (1.4) A Geiger counter detects activities of order 10−4 μ10^{-4}\ \muCi; calculate the minimum mass (in grams) of 131I^{131}\ce{I} detectable by this counter. (1 curie is the amount of a radioisotope producing 3.7×10103.7\times10^{10} disintegrations per second.)Solutions: 1