Fig. 1. Flowchart of the simulation process.

Fig. 2. Incident energy spectrum of the space radiation environment in the orbit of eXTP.

Fig. 3. Mass model of the focal plane detector SDD.

Fig. 4. Mass model of simplified aluminum spherical shell and SDD.

Fig. 5. Structure of single SFA module.

Fig. 6. Mass model of the eXTP satellite.

Fig. 7. Planar density distribution at the position of SDD (left: frontview; right: backview).

Fig. 8. Particle background evolution as a function of the size and the thickness of the aluminum spherical shell.

Fig. 9. Fitting curves of different particle backgrounds as a function of the thickness of the aluminum spherical shell.

Fig. 10. Total particle background evolution as a function of the thickness of the aluminum spherical shell .

Fig. 11. Equivalent aluminum thickness distribution of the whole eXTP at the SDD position.

Fig. 12. Comparison of particle background level obtained with interpolation of planar density distribution and with simulation.

Fig. 13. Structure of the mass model before and after structure modifications (left: before modifications; right: after modifications).

Fig. 14. Equivalent aluminum thickness distribution after the structure modifications.

Fig. 15. Comparison of the particle background levels after the structure modifications, from the interpolation of planar density distribution and the simulation, respectively.

Fig. 16. Variation of the secondary positron composition as a function of the shielding thickness.