Properties of a Cold-Neutron Irradiation Facility for In Vitro Research on Boron Neutron Capture Therapy at the Geesthacht Neutron Facility

A new irradiation facility, GBET (basic research on boron neutron capture therapy), especially designed for in vitro experiments on boron neutron capture therapy was put into operation at the Geesthacht Neutron Facility of the GKSS Research Center. Its location at a cold-neutron guide without direct view of the reactor core has two advantages: First, contamination of the primary beam with fast neutrons or photons is negligible. Second, GBET yields a high cold-neutron flux of 1.4 × 10⁸/(cm²s) over an area of 3 × 4 cm. As a result of the energy dependence of the neutron absorption cross section of boron, this corresponds to a higher effective thermal flux of 4.7 × 10⁸/(cm²s). This effect is used to reduce the irradiation times by a factor of 3.32.

The effective flux is sufficient for irradiation of thin samples like cell monolayers in conventional culture flasks. For such in vitro irradiations, a survival fraction of 1% is achieved at a homogeneous boron concentration of 100 ppm ¹⁰B within ~20 min. Furthermore, the beam can be used for boron radiography. The respective experimental conditions are discussed, especially the neutron flux distribution, available for these different types of samples.