| Thulium-170 | |
| Symbol: | Tm |
| Mass Number: | 170 |
| Num Protons: | 69 |
| Num Neutrons: | 101 |
| Abundance: | Synthetic |
| Spin: | 1− |
| Decay Product: | Ytterbium-170 |
| Decay Mass: | 170 |
| Decay Symbol: | Yb |
| Decay Product2: | Erbium-170 |
| Decay Mass2: | 170 |
| Decay Symbol2: | Er |
| Decay Mode1: | β− |
| Decay Energy1: | 0.8838, 0.9686 |
| Decay Mode2: | EC |
| Decay Energy2: | 0.2341, 0.3122 |
Thulium-170 (170Tm or Tm-170) is a radioactive isotope of thulium proposed for use in radiotherapy and in radioisotope thermoelectric generators.
Thulium-170 has a binding energy of per nucleon and a half-life of . It decays by β− decay to 170Yb about 99.869% of the time, and by electron capture to 170Er about 0.131% of the time. About 18.1% of β− decays populate a narrow excited state of 170Yb at, 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.
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 .[1]
As a rare-earth element, thulium-170 can be used as the pure metal or thulium hydride, but most commonly thulium oxide due to the refractory properties of that compound. The isotope can be prepared in a medium-strength reactor by neutron irradiation of natural thulium, which has a high neutron capture cross section of .
In 1953, the Atomic Energy Research Establishment introduced thulium-170 as a candidate for radiography in medical and steelmaking contexts,[2] 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.
As the oxide, 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.[3] 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.