## 4 Conclusions  
The availability of MC codes makes it convenient to study shielding issues of nuclear facilities before construction, especially concerning complex 3D geometry such as mazes and penetrations [25]. The construction of geometric and physical models plays a decisive role in the accuracy of the simulation results. In addition, appropriate variance reduction techniques and strategies can improve the work efficiency and statistics of the results. In this work, the MC platform FLUKA was utilized to assess the RP problems of the target terminal for medical isotope production based on a superconducting proton linac and launch optimizations. A combination of different shielding materials was used, weighing economics and shielding effect; the top shielding thickness is 1.1 m thinner than using a homogenous material. In the case of a 12 kW proton beam impinging on the \({}^{100}\)Mo target, the prompt ambient dose equivalent rates outside the target terminal meet the institute's RP policy. The dose rates inside the terminal drop below 100 \(\mu\)Sv/h at 64 h past EOB; the target chamber made of SS316L is the main source term at this time. The expected service lives of the main electrical actuators in this target system can be effectively extended by 2.7 times with partial shielding. The calculation results can be used for environmental impact assessment. If the construction plan changes later, the simulation strategy weighing the accuracy of simulation results and the project's progress, together with the 3D visualization method of radiation fields utilized in this work, can still serve in further research and design. Methodology, Z.L. ; Software, Y.L. ; Formal analysis, D.C.; Investigation, J.R. and K.Y. ; Resources, H.J. and C.Y. ; Writing--original draft, D.C.; Writing--review & editing, R.d.S.A. ; Supervision, J.L. and Z.L. ; Funding acquisition, Z.Q. All authors have read and agreed to the published version of the manuscript. This research was funded by the National Natural Science Foundation of China, grant number 11975115; Special Projects of the Central Government in Guidance of Local Science and Technology Development, grant number YDZX20216200001297; the Research and Development of Medical Isotopes based on High-current Superconducting Linear Accelerator Project; the Science and Technology Planning Project of Gansu, grant number 20 JR10 RA645; Lanzhou University Talent Cooperation Research Funds sponsored by both Lanzhou City, grant number 561121203 and Gansu provincial science and technology plan projects for talents, grant number 054000029. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** The data presented in this study are available on reasonable request from the corresponding author. **Conflicts of Interest:** The authors declare no conflict of interest. * _[PERSON] et al. (2011)_ [PERSON]; [PERSON]; [PERSON]; [PERSON] Theoretical modeling of yields for proton-induced reactions on natural and enriched molybdenum targets. _Phys. Med. Biol._**2011**, _56_, 5469. [CrossRef] [PubMed]
* _[PERSON] et al. (2017)_ [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] Physicsdesign of the CIADS 25 MeV demo facility. _Nucl. Instrum. Methods. Phys. Res. A_**2017**, _843_, 11-17. [CrossRef]
* _[PERSON] et al. (1986)_ [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] A high-power target system for radioisotope production. In Proceedings of the Eleventh International Conference on Cyclotrons and their Applications, Tokyo, Japan, 13-17 October 1986. * _[PERSON] (2022)_ [PERSON] Development of Target System for Medical Isotope Tc-99m Production Based on the Superconducting Linac. Master's Thesis, Lanzhou University, Lanzhou, China, 16 May 2022. * _ICRP (1977)_ ICRP. _Recommendations of the ICRP. ICRP Publication 26. Annals of the ICRP_; Pergamon Press: Osaka, Japan, 1977; pp. 1-53.