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

Abstract

The alpha-emitters 225 Ac and 213 Bi 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 229 Th (t 1/2 = 7880y). 229 Th can be produced by proton irradiation of 232 Th and 230 Th, either directly or through production of isobars that beta-decay into 229 Th. To obtain excitation functions, 232 Th and 230 Th 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 229 Pa and its daughter 225 Ac from both 232 Th and 230 Th. Differential cross-sections for production of 229 Pa and other Pa isotopes have been obtained.

Large scale accelerator production of 225Ac: Effective cross sections for 78–192 MeV protons incident on 232Th targets

“…Producing relevant quantities of 229 Th is challenging due to its extremely long half-life. Despite the ~160 mb cross section for the 232 Th[p,4n] 229 Pa reaction at ~30 MeV, dedicated accelerator production of 229 Th may not be viable due to long irradiation times and high currents required to produce a substantial quantity of 229 Th (Jost et al, 2013). However, substantial 229 Th could be generated if 232 Th were used as a beam stop for several years at any high-current proton accelerator facility.…”

New developments in the experimental data for charged particle production of medical radioisotopes

“…It can also be used as a generator for the production of 211 Pb [30]. Proton induced production of more than 80 isotopes on thorium was measured at high and low proton energies [31,32]. New results on production of 223 Ra, 225 Ac [24] and 227 Th [23,24] were published recently.…”

“…From the results presented in Fig. 4, only the data of Jost [32] for proton irradiation and the data of Simeckova [44] for deuteron irradiation are new (from the last three years), the others are presented for comparison. The figure shows that the newest 62 Zn data for proton irradiation support the previous results and also confirm that the proton induced route is preferable than the deuteron one for its production.…”

“…The most important generator/daughter pair is the 99 Mo/ 99m Tc, which was discussed in detail in a previous section. As an example for this part, the new [32,41,42,43]) and deuteron (Simeckova [44]) irradiation of copper targets results on 62 Zn for 62 Cu generator is shown in Fig. 4.…”

“…4. It contains both proton [32,41,42,43] and deuteron [44] induced routes. From the results presented in Fig.…”