The transfer function for a subcritical system measured by prompt gamma radiation

The source transfer function has been measured in a natural uranium-light water moderated sub-critical assembly as a function of source frequency and position. Using a square wave input of fast neutrons from the D-T reaction prompt gamma radiation from fission was detected and the time variation of the detector output recorded on a multichannel analyser. By Fourier analysing the recorded waveform the source transfer function was found. Two group diffusion theory was used to determine the spatially dependent source transfer function for a system similar to the experimental one. The computer programs ATEST and GAMMARESFU, were written to calculate the neutron flux in the core and also prompt fission gamma rays response function outside the subcritical assembly at chosen frequency and detector position. The method gave good agreement with the experiment. (U.K.)