A method for forming a metal oxide includes a step of adding citrate acid to a salt-containing solution to produce a precursor solution. Characteristically, the salt-containing solution includes a neodymium salt or an americium salt. A chilled solution of hexamethylenetetramine (HMTA) and urea is added to a chilled precursor solution to form a citrate gel. Advantageously, citrate gel can be produced with an R-value of 0.5 to 3, wherein the R-value is a molar ratio of HMTA to Nd. The citrate gel is then heated to form the metal oxide of neodymium or americium.

Reactor target assemblies are provided that can include a housing defining a perimeter of at least one volume and Np or Am spheres within the one volume. Reactor assemblies are provided that can include a reactor vessel and a bundle of target assemblies within the reactor vessel, at least one of the target assemblies comprising a housing defining a volume with Np or Am spheres being within the volume. Irradiation methods are also provided that can include irradiating Np or Am spheres within a nuclear reactor, then removing the irradiated spheres from the reactor and treating the irradiated spheres.