title: Application of ion exchange and extraction chromatography to the separation of actinium from proton-irradiated thorium metal for analytical purposes.
abstract: Actinium-225 (t1/2=9.92d) is an α-emitting radionuclide with nuclear properties well-suited for use in targeted alpha therapy (TAT), a powerful treatment method for malignant tumors. Actinium-225 can also be utilized as a generator for (213)Bi (t1/2 45.6 min), which is another valuable candidate for TAT. Actinium-225 can be produced via proton irradiation of thorium metal; however, long-lived (227)Ac (t1/2=21.8a, 99% β(-), 1% α) is co-produced during this process and will impact the quality of the final product. Thus, accurate assays are needed to determine the (225)Ac/(227)Ac ratio, which is dependent on beam energy, irradiation time and target design. Accurate actinium assays, in turn, require efficient separation of actinium isotopes from both the Th matrix and highly radioactive activation by-products, especially radiolanthanides formed from proton-induced fission. In this study, we introduce a novel, selective chromatographic technique for the recovery and purification of actinium isotopes from irradiated Th matrices. A two-step sequence of cation exchange and extraction chromatography was implemented. Radiolanthanides were quantitatively removed from Ac, and no non-Ac radionuclidic impurities were detected in the final Ac fraction. An (225)Ac spike added prior to separation was recovered at ≥ 98%, and Ac decontamination from Th was found to be ≥ 10(6). The purified actinium fraction allowed for highly accurate (227)Ac determination at analytical scales, i.e., at (227)Ac activities of 1-100 kBq (27 nCi to 2.7 μCi).
authors.affiliation: Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545, United States.
authors.forename: V
authors.initials: V
authors.lastname: Radchenko
authors.affiliation: Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545, United States.
authors.forename: J W
authors.initials: JW
authors.lastname: Engle
authors.affiliation: Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545, United States.
authors.forename: J J
authors.initials: JJ
authors.lastname: Wilson
authors.affiliation: Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545, United States.
authors.forename: J R
authors.initials: JR
authors.lastname: Maassen
authors.affiliation: Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545, United States.
authors.forename: F M
authors.initials: FM
authors.lastname: Nortier
authors.affiliation: Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545, United States.
authors.forename: W A
authors.initials: WA
authors.lastname: Taylor
authors.affiliation: Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545, United States.
authors.forename: E R
authors.initials: ER
authors.lastname: Birnbaum
authors.affiliation: Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545, United States.
authors.forename: L A
authors.initials: LA
authors.lastname: Hudston
authors.affiliation: Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545, United States.
authors.forename: K D
authors.initials: KD
authors.lastname: John
authors.affiliation: Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545, United States. Electronic address: mifa@lanl.gov.
authors.forename: M E
authors.initials: ME
authors.lastname: Fassbender
mesh_terms: D000186:Actinium / Q000302:isolation & purification*; D002852:Chromatography, Ion Exchange; D006801:Humans; D059625:Liquid-Liquid Extraction; D011522:Protons; D013910:Thorium / Q000302:isolation & purification* / Q000528:radiation effects
chemical_list: D011522:Protons; D013910:Thorium; D000186:Actinium
keywords: Actinium isotopes; Extraction chromatography; Ion exchange; Lanthanide separation; Thorium chelation; Thorium metal