Determination of the gamma-ray dose in an epithermal neutron beam.

: Neutron beams used for Boron Neutron Capture Therapy (BNCT) are always accompanied by photons. These two irradiation components have different relative biological effectiveness. Therefore it is necessary to determine the neutron and photon absorbed dose in the mixed field separately. All gamma-ray detectors however are also sensitive for neutrons. In this work preliminary results are presented using TLD-700 chips, a Mg(Ar) ionisation chamber and a GM-counter to determine the gamma-ray component in a mixed beam of gamma-rays and neutrons. The results show a good agreement between the GM-counter and the ionisation chamber, indicating a small relative neutron sensitivity (ku) for these detectors. The sensitivity of TLD-700 for thermal neutrons however gives rise to a detector response for which a correction is necessary. The uncertainty however in the relative gamma-ray sensitivity (hu) of the detectors is at this moment too large to determine accurate values of the relative neutron sensitivities.