Thulium-170 (170Tm or Tm-170) is a radioactive isotope of thulium proposed for use in radiotherapy and in radioisotope thermoelectric generators.
[1] About 18.1% of β− decays populate a narrow excited state of 170Yb at 84.25474(8) keV (t1/2 = 1.61 ± 0.02 ns), and this is the main X-ray emission from 170Tm; lower bands are also produced through X-ray fluorescence at 7.42, 51.354, 52.389, 59.159, 59.383, and 60.962 keV.
[3][6] In 1953, the Atomic Energy Research Establishment introduced thulium-170 as a candidate for radiography in medical and steelmaking contexts,[7] but this was deemed unsuitable due to the predominant high-energy bremsstrahlung radiation, poor results on thin specimens, and long exposure times.
[8] However, 170Tm has been proposed for radiotherapy because the isotope is simple to prepare into a biocompatible form, and the low-energy radiation can selectively irradiate diseased tissue without causing collateral damage.
[3][9] As the oxide (Tm2O3), thulium-170 has been proposed as a radiothermal source due to it being safer, cheaper, and more environmentally friendly than commonly used isotopes such as plutonium-238.