A high-sensitivity neutron dosimeter using the coherent demodulation technique

We have developed a high-sensitivity neutron dosimeter which incorporates an algorithm of the coherent demodulation technique. This dosimeter is constructed with five CsI(Tl)-p-i-n photodiode scintillation detectors four of which are coupled to neutron-gamma converting foils (Cd or Sm) of varying sizes. The sizes of the foil converters are varied to fit the sine function. When the five-channel dosimeter is exposed to neutrons, capture gammas are emitted in proportion to the size of the corresponding foil and the scintillation detectors´ electrical responses vary accordingly. Through modulation-demodulation processing of the detector signals, the neutron fluence can be determined while rejecting the uniform influence of the gamma-ray background. The effectiveness of the dosimeter was confirmed in a mixed neutron/gamma field. A neutron fluence of 1.31×10⁴ nvt was detected with an efficiency of 4.4% in a gamma background of 6.4 mR=1.6×10^-2 mC/kg