Properties:
Thorium-228 (once called radiothorium due to its occurrence in the disintegration chain of Thorium-232) is an alpha emitter with a half-life of 1.91 years that decays into 224Ra (half- life 3.66 d; α, 100% at 5,520 keV).
Toxicity: Unbound 228Th accumulates in bones
Manufacturing:
228Th is obtained by separation from natural thorium ore. 228Th is a decay product of 232Th and the Orano group has developed some specific patented technologies enabling to extract larger amounts of 228Th from 232Th.
Another possible route of preparation of 228Th is based on the irradiation of 226Ra by thermal neutrons. One gram of 226Ra allows obtaining theoretically about 37 Ci of 228Th.
Source and availability:
Small amounts for research purpose are available from the companies providing also other thorium isotopes or actinium.
In December 2019, EZAG signed a multi-year supply agreement with Alpha Tau Medical (Tel Aviv, Israel) for the supply of Thorium-228. The radioisotope is used for the production of Alpha DaRT, a new innovative brachytherapy treatment for a variety of solid tumors.
Derivatives:
228Th is the precursor of 224Ra which is needed for the production of RadSpherin. Thorium-228 is also the precursor in the 228Th/224Ra generator developed by OncoInvent.
Price:
Unknown at this stage. Small amounts are available from the company EZAG.
Comments:
228Th has no direct application in nuclear medicine. EZAG does have stocks of some 228Th but also of not highly pure 226Ra. This could be the starting material for the production of 228Th.