US Patent 8139705 Screened chamber for ion therapy

In a shielded chamber for neutron therapy including a therapy room which has a central beam axis along which a high-energy therapy beam is introduced into the Chamber through one end wall thereof and which includes at the opposite end a labyrinth entrance with at least two shielding wall sections displaced longitudinally along the central beam axis and extending into the room from opposite side walls, the wall sections include structures for causing spallation to thereby generate from the high energy neutrons in the high energy neutron beam a plurality of low energy neutrons which are then moderated by the wall sections.