 The damage from the more penetrating gamma radiation and 127 keV internal conversion electron radiation from the initial decay of 123Te is moderated by the relatively short half-life of the isotope.123I is the most suitable isotope of iodine for the diagnostic study of thyroid diseases.The half-life of approximately 13.13 hours is ideal for the 24-hour iodine uptake test and 123I has other advantages for diagnostic imaging thyroid tissue and thyroid cancer metastasis.