Neutron beam parameters on LVR-15 reactor for neutron capture therapy

Some years ago, a research group was formed in Prague, Czechoslovakia, to study Boron Neutron Capture Therapy (BNCT). The important task for physicists was to design a suitable neutron source. First the authors concentrated on the design of a thermal beam and experimental verification of the beam parameters. Then the modeling and measurements for an epithermal beam were performed. Some difficulties arose when the reactor VVR-S was being reconstructed as the multi-purpose experimental reactor LVR-15. For this reason, physical tests had to be repeated under the new conditions. The configuration of moderating and shielding materials was designed by using multigroup transport codes. It was composed of layers of graphite, heavy water, lead and a bismuth block of high purity (99.999%). Activation and gamma sources in lead were lowered by using a thin boron carbide layer. The detailed design is shown