Electron energy‐loss spectroscopy (EELS) of iodine in thyroxine: parameters of radiation‐induced loss of iodine

The loss of iodine during irradiation with electrons was measured in order to determine whether it can be detected by electron spectroscopic imaging (ESI). Since iodine can be bound to organic molecules, it could be a candidate for tracer studies by ESI in biomedical research. A solution of thyroxine spread over a carbon film was used as a test specimen. Thyroxine contains four iodine atoms covalently bound to aromatic rings. For ESI, higher doses have to be used than in conventional electron microscopy. The iodine content was therefore measured after irradiation with doses of up to 3 × 107 el nm−2. The measurements were carried out for different specimen thicknesses, temperatures and dose rates, and it was found that iodine can be detected with ESI if moderate dose rates are used at a temperature of −160 °C.