A thermal neutron facility for radiobiological studies

Within the Petten BNCT project a thermal neutron facility for radiobiological studies is needed for further test and development of boron compounds. The Argonaut reactor of ECN, the Low Flux Reactor operating at a power of 30 kW, offers opportunities for the development of thermal neutron beams. Optimising calculations have been performed with the Monte Carlo code MCNP, resulting in a design of an extended graphite moderator followed by a lead shield with a bismuth window. This assembly has been built as a modular construction for easy positioning on and removal from an irradiation trolley of the reactor. The facility yields a thermal fluence rate of φtherm = 1.2 · 109 cm−2s−1, and a resulting dose rate from the unwanted beam components (γ-rays, fast and epithermal neutrons) lower than 1 Gy/h (physical dose). Experimental validation of the calculations has been performed by neutron activation detectors. Finally, the fluence rates in the vials used for the radiobiological experiments are determined with a set of neutron activation detectors.