Thulium-170
Isotope of thulium
From Wikipedia, the free encyclopedia
Thulium-170 (170Tm or Tm-170) is a radioactive isotope of thulium proposed for use in radiotherapy and in radioisotope thermoelectric generators.
| General | |
|---|---|
| Symbol | 170Tm |
| Names | Thulium-170 |
| Protons (Z) | 69 |
| Neutrons (N) | 101 |
| Nuclide data | |
| Natural abundance | Synthetic |
| Half-life (t1/2) | 128.6±0.3 d[1] |
| Isotope mass | 169.93580709(79)[2] Da |
| Spin | 1−[1] |
| Nuclear binding energy | 1377937.45±0.73[1] keV |
| Decay products | 170Yb 170Er |
| Decay modes | |
| Decay mode | Decay energy (MeV) |
| β− | 0.968[3] |
| EC | 0.312[3] |
| Isotopes of thulium Complete table of nuclides | |
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.[1] About 18.1% of β− decays populate an excited state of 170Yb at 84.25474(8) keV 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.[3][4]
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.[5]
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 (Tm2O3) due to the refractory properties of that compound.[6][7] The isotope can be prepared in a reactor by neutron irradiation of natural thulium, which has a high neutron capture cross section of 103 barns.[4][7]
Medicine
In 1953, the Atomic Energy Research Establishment introduced thulium-170 as a candidate for radiography in medical and steelmaking contexts,[8] but this was deemed unsuitable due to the predominant high-energy bremsstrahlung radiation, poor results on thin specimens, and long exposure times.[9] 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.[4][10]
Radiothermal generator
170Tm2O3 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.[11][12] 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.[7]