Early in his career, he was a pioneer in nuclear medicine and discovered isotopes of elements with important applications in the diagnosis and treatment of diseases, including iodine-131, which is used in the treatment of thyroid disease.
Tidligt i sin karriere var han en pioner inden for nuklearmedicin og opdagede isotoper af grundstoffer med vigtige anvendelser inden for diagnosticering og behandling af sygdomme, særligt iod-131, som bruges i behandling af sygdomme i skjoldbruskkirtlen.