| General | |
|---|---|
| Symbol | 170Tm |
| Names | Thulium-170, 170Tm, Tm-170 |
| Protons (Z) | 69 |
| Neutrons (N) | 101 |
| Nuclide data | |
| Natural abundance | Synthetic |
| Half-life (t1/2) | 128.6±0.3 d[1] |
| Isotope mass | 169.935807093(785)[1] Da |
| Spin | 1+[1] |
| Binding energy | 1377937.45±0.73[1] keV |
| Decay products | 170Yb 170Er |
| Decay modes | |
| Decay mode | Decay energy (MeV) |
| β− | 0.8838, 0.9686[2] |
| EC | 0.2341, 0.3122[2] |
| Isotopes of thulium Complete table of nuclides | |
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 8105.5144(43) keV per nucleon and a half-life of 128.6±0.3 d. 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.[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.[2][3]
The ground state of thulium-170 has a spin of 1+. The charge radius is 5.2303(36) fm, the magnetic moment is 0.2458(17) μN, and the electric quadrupole moment is 0.72(5) e⋅b.[4]
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.[5][6] 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 103 barns.[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.[10][11] 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.[6]