FIG. 9 shows the probability of producing protons at different iron thicknesses as a function of neutron energy. The probability is maximum at 0.25 mm thickness for the 20 MeV neutron energy and decreases as the neutron energy decrease. The iron and manganese have similar proton production probabilities, both are equal but less than the nickel case.

Combining the results for nickel, manganese, and iron, it can be concluded that the neutron source must possess an energy greater than 10 MeV to produce Ac-225 in addition to a high probability of producing protons. Since Cf-252 emits a spectrum of energies, additional simulations were run to find the optimum nickel thickness between 0.01 and 0.06 mm. The 0.01 mm thickness produced 3.3 MeV average proton energy and the 0.05 mm thickness produced 2.7 MeV average energy with about 90% more protons than the 0.01 mm thickness. Thus, the 0.05 mm of nickel was chosen to be paired with Cf252.

On the other hand, all RaCl₂ thicknesses produced a similar amount of Ac-225, and so a 1 cm thickness was used. The simulation results showed that in order to produce a single Ac-225 atom, a Cf-252 source with an estimated activity of 7.15E12 Bq is needed. A further set of simulations was run replacing the Cf-252 with a typical neutron generator with a 14 MeV energy. The activity needed to produce a single Ac-225 atom with the neutron generator is 2.21E9 Bq. The Cf-252 and the neutron generator both produced isotopes/fragments in addition to the Ac-225. Some of the isotopes are radioactive and some are not, so the chemical separation stage is important to produce pure an Ac-225 solution that does not contain other radioactive materials to ensure the dose delivered to the patient is optimized.