Thulium-170
Thulium-170 is a radioactive isotope of thulium proposed for use in radiotherapy and in radioisotope thermoelectric generators.
Properties
Thulium-170 has a half-life of 128.6 days, decaying by β− to 170Yb about 99.87% of the time, and by electron capture to 170Er about 0.13% of the time. About 18.1% of β− decays populate an excited state of 170Yb at and this produces the main gamma ray emission from 170Tm; lower-energy photons are also produced through X-ray fluorescence at 7.42, 51.354, 52.389, 59.159, 59.383, and 60.962 keV.
The ground state of thulium-170 has a spin of 1−. The charge radius is, the magnetic moment is, and the electric quadrupole moment is.
Proposed applications
As a rare-earth element, thulium-170 can be used as the pure metal or thulium hydride, but the most common form is as thulium oxide due to the refractory properties of that compound. The isotope can be prepared in a reactor by neutron irradiation of natural thulium, which has a high neutron capture cross section of.
Medicine
In 1953, the Atomic [Energy Research Establishment] introduced thulium-170 as a candidate for radiography in medical and steelmaking contexts, but this was deemed unsuitable due to the predominant high-energy bremsstrahlung radiation, poor results on thin specimens, and long exposure times. 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.
Radiothermal generator
has been proposed as a radiothermal source due to it being safer, cheaper, and more environmentally friendly than commonly used materials that contain isotopes such as plutonium-238. The heat output from a 170Tm source is initially much greater than from a 238Pu source relative to mass, but it declines rapidly due to its shorter half-life.