Triple chamber technique for thermal neutron dose measurements in fast neutron beams

Collimated fast neutron beams used in radiotherapy are always contaminated with photons and thermal neutrons. From foil activation measurements the relative dose contribution of thermal neutrons to the absorbed neutron dose in different depths in a tissue equivalent phantom was determined. The sensitivities of a TE-Chamber, a GM-counter with a 6Li-shield and an unshielded GM-counter to fast neutrons, thermal neutrons and photons are presented. The triple chamber technique using these three devices is compared to foil activation technique with respect to the determination of relative thermal neutron depth dose curves. Finally the triple chamber technique is applied for the determination of depth dose curves of fast neutrons, thermal neutrons and photons in a solid TE-phantom.