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Position-Dependent Neutron Spectra in a Multiplying Medium

R. J. Cerbone, R. E. Slovacek, E. R. Gaerttner

Nuclear Science and Engineering

Volume 30 / Number 1 / October 1967 / Pages 75-84


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Position-dependent thermal spectra have been measured in a paraffin-moderated  235U multiplying assembly using two independent methods. Steady-state spectra were obtained with the time-of-flight technique employing a 24.40-m flight in conjunction with the Rensselaer Polytechnic Institute linear accelerator; asymptotic (in time) spectra were obtained with the pulsed-LINAC chopper technique.  A new technique was developed to monitor the source intensity with a tracking reliability of ± 1.5%. The measured spectra are compared to a series of DTF-IV transport calculations using a P1 kernel and P1 source; the spatial source was obtained from a transport calculation. The spectrum calculations were performed with a polyethylene  kernel utilizing either the Goldman model or the Koppel-Young four-oscillator model. The experimental spectra are generally in closer (better than 5%) agreement with calculations using the Goldman kernel than with those using the Koppel-Young kernel. This result is consistent with the total cross section of polyethylene measured by Armstrong.

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