Speaker
Description
At RIBF, heavy radioactive isotopes are produced via projectile fragmentation reactions using a $^{238}\mathrm{U}$ beam, including the medical alpha emitter $^{225}\mathrm{Ac}$. In this study, a 345-MeV/u $^{238}\mathrm{U}$ beam was irradiated on a Be target to produce a $^{225}\mathrm{Ac}$ beam, and its production cross-section was measured. The fragments were separated using the RI beam separator BigRIPS, and particle identification was performed by measuring $A/Q$ and $Z$. To determine the cross-section, both the number of identified $^{225}\mathrm{Ac}$ events and the transmission through BigRIPS were required.
For heavy isotopes, frequent charge‑state changes in beamline materials make particle identification complicated. To transport specific charge states, the slit at the first momentum‑dispersive focal plane F1 was narrowed to select specific charge states, which limited the measurable momentum range. Therefore, two approaches were used: (1) scanning the F1 slit position to measure the full momentum distribution, and (2) calculating the transmission.
(1) For isotopes whose full momentum distributions at F1 could be scanned by combining data from multiple settings of the slit position, the production cross-sections were determined. (2) For the remaining isotopes, a Monte Carlo simulation incorporating charge‑state changes occurring in materials is being developed and evaluated to calculate the transmission. We will present the results of the production cross‑section measurements.