A neutron detector for pulsed mixed fields: preliminary measurements

It is well-known that neutron detectors generally suffer from dead-time effects and have strong limitations when measuring in pulsed radiation fields. An active neutron monitor based on a BF3 proportional counter and logarithmic electronics was developed to withstand pulsed fields with high intensity, very short duration and high repetition rate. This paper discusses results of preliminary measurements carried out at the Italian National Hadrontherapy Center (CNAO) in Pavia and at the San Raffaele Hospital in Milan. In the first case neutrons were produced by 7 MeV protons accelerated by a LINAC and impinging on a copper Faraday cup. In the second case an electron radiotherapy LINAC produced energy-tunable bremsstrahlung x-rays beams up to 18 MV with an associated neutron component. The neutron monitor was capable to withstand neutron reaction rates up to 2·106 s-1 without showing saturation effects. A promising technique is also shown to reject very intense, pulsed gamma fields, due to the innovative operating principle of the detector.