Lab researchers examine accelerator-production process at LANSCE for a medical therapy isotope

DOE’s Office of Science provides funding

Mar. 2, 2010—The Isotope Program of Los Alamos National Laboratory is receiving American Recovery and Reinvestment Act stimulus funding from DOE’s Office of Science to develop a proof of concept accelerator production process for Actinium-225 (²²⁵Ac), using proton beams available at LANL’s LANSCE complex (in the Isotope Production Facility) and the Lab’s Weapons Neutron Research facility.

Actinium-225 has extraordinary potential for the treatment of metastatic cancer, because it decays through four daughter isotopes, each yielding an alpha particle useful for local destruction of tumor sites. The alpha particles could destroy cancer cells while causing little damage to surrounding healthy tissue. However, if brought into use, the demand for this isotope would greatly exceed the current national supply, which is from a single 150 mCi thorium-229 source harvested from uranium-233 by Oak Ridge National Laboratory many years ago. The National Institutes of Health and the Nuclear Science Advisory Committee have identified ²²⁵Ac as a critical isotope that requires additional production to address potential use in cancer therapy. Thus, DOE’s funding support to the LANL Isotope Program.

Actinium-225 can be produced through proton-induced nuclear reactions on thorium-232 (²³²Th), but other nuclear reactions can occur to create unwanted isotopes. Therefore, detailed information of the proton energy-dependent cross-sections of all relevant nuclear reactions is needed to develop an accelerator based process to maximize the production of ²²⁵Ac and minimize the production of detrimental long-lived impurity isotopes.

Scientists from LANL's Chemistry and LANSCE divisions completed the first phase of measuring the nuclear cross sections for the accelerator production of ²²⁵Ac. The researchers irradiated ²³²Th foils with 800 MeV protons at LANSCE in the Weapons Neutron Research facility, and then transported the foils to TA-48 for gamma counting and alpha assay. They dissolved one of the thorium foils and separated the fractions by ion exchange for the alpha assay. The foils and separated fractions have been subjected to gamma and alpha assay to investigate the decay of the actinide isotopes of interest as well as all of the co-produced fission products. It is clear that ²²⁵Ac is present among the nuclear reaction products. Similar irradiations using the 100 MeV beam at IPF and a specially generated 200 MeV beam at WNR are planned for later this year. Complete data analysis will provide the first set of energy-dependent, cross-section measurements for this important set of nuclear reactions.

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Frank Valdez of C-IIAC uses the remote manipulators at the Isotope Production Facility (LANSCE).