Thorium-229 quantified in historical Thorium-228 capsules

Thorium-229 is a valuable, but scarce, radionuclide for nuclear clock applications or targeted alpha therapy. While it is mostly produced by the decay of 233U, 229Th can also be produced by neutron irradiation of 226Ra. At SCK
- CEN, capsules containing mainly 228Th (by-product of 226Ra irradiation) were characterized to quantify the present amounts of 229Th, 228Th, 227Ac, 226Ra with high resolution gamma spectroscopy, after a decay period of 40 years in which 228Th has decayed. High purity 229Th was quantified, and after recovery using radiochemical separation processes, it can be used to support ongoing research.