Low LET Gamma and High LET Alpha Degradation Studies of the Actinide Lanthanide Separation Process

An organic solution comprising the Actinide Lanthanide Separation Process (ALSEP) extracting solvent consisting of 0.5 M 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (HEH[EHP]) and 0.05 M N,N,N’,N’-tetra(2-ethylhexyl)diglycolamide (T2EHDGA) in n-dodecane were subjected to low LET gamma and high LET alpha irradiation before and after equilibration with 3 M HNO₃. Degradation dose constants revealed greater ligand degradation due to gamma irradiation than alpha irradiation for both ligands and equilibration with nitric acid did not have a significant impact on degradation kinetics for either irradiation source. Identified degradation products were similar for both gamma and alpha irradiation and occurred mostly through the rupture of the N-C_carbonyl and C-O_ether bonds for T2EHDGA and the C-O_ether bond in HEH[EHP], and acid contact appears to alter the degradation pathway by favoring the formation of higher molecular weight recombination products. Mixed T2EHDGA-HEH[EHP]-NO₃ complexes were formed with Nd(III) after extraction from 3 M HNO₃, and low LET gamma irradiation of the Nd(III) loaded organic solution produced similar degradation products as the organic solution absent of Nd(III). Additionally, likely due to the greater radiolytic susceptibility of T2EHDGA than HEH[EHP], a HEH[EHP]-Nd(III) complex appears to form with increasing absorbed dose.