Optimum design and criticality safety of a beam-shaping assembly with an accelerator-driven subcritical neutron multiplier for boron neutron capture therapies

The beam-shaping assembly for boron neutron capture therapies with a compact accelerator-driven subcritical neutron multiplier was designed so that an epithermal neutron flux of 1.9×109 cm−2 s−1 at the treatment position was generated by 5 MeV protons in a beam current of 2 mA. Changes in the atomic density of 135Xe in the nuclear fuel due to the operation of the beam-shaping assembly were estimated. The criticality safety of the beam-shaping assembly in terms of Xe poisoning is discussed.