Discuss the use of radioactive tracers in medicine and industry. Indicate how the thyroid gland requires iodine for the synthesis of thyroxine, and absorbs it actively from the blood. Radioactive iodine can be used to determine the health of the gland. Nuclear fission was introduced by looking at the work of Fermi in 1934. The discovery that bombarding Uranium 235 with neutrons produced 2 fragments and the release of energy was discussed. By 1939 the fragments were shown to be bismuth and krypton, and the energy release had great potential as a weapon. The definition of fission and why the uranium atom splits due to elongation when bombarded with a neutron, was presented along with the reaction formula.