Iodine-125 is a radioisotope of iodine which has uses in biological assays and in radiation therapy to treat prostate cancer and brain tumors. Its half-life is around 60 days and it emits gamma-rays with maximum energies of 35 keV, some of which are internally converted to x-rays. Iodine-125 is created by the electron capture decay of Xenon-125, which is a synthetic isotope of Xenon, itself created by neutron capture of the slightly radioactive Xenon-124, which occurs naturally with an abundance of around 0.1%. Because of the synthetic production route of Iodine-125 and its short half-life, the natural abundance is effectively 0%.