Measurement of cross sections for the 232Th(P,4n)229Pa reaction at low proton energies

The alpha-emitters 225Ac and 213Bi are of great interest for alpha-radioimmunotherapy which uses radioisotopes attached to cancer-seeking antibodies to efficiently treat various types of cancers. Both radioisotopes are daughters of the long-lived 229Th(t1/2 = 7880y). 229Th can be produced by proton irradiation of 232Th and 230Th, either directly or through production of isobars that beta-decay into 229Th. To obtain excitation functions, 232Th and 230Th have been irradiated at the On-Line Test Facility at the Holifield Radioactive Ion Beam Facility at ORNL. Benchmark tests conducted with Cu and Ni foils show very good agreement with literature results. The experiments with thorium targets were focused on the production of 229Pa and its daughter 225Ac from both 232Th and 230Th. Differential cross-sections for production of 229Pa and other Pa isotopes have been obtained.