Frontgrade also advertises a rad-hard RISC-V, as does Microchip (a PIC64 variant), that I know nothing about, but seems like an inevitable next step. Seems like you could grab some Xilinx rad-hard FPGA and bobs your uncle.
A whole body exposure of 5Gy would kill you, although it would happen over two weeks.
10kGy? Spectacularly fatal.
In comparison radtherapy patients get 20 gray in 1-2 weeks so it's the 20/10000 = 0.02% of what these designs target