Standardization of fast pulse reactor dosimetry

A dosimetry method, developed at the National Bureau of Standards and known as the Flux Transfer Technique, is proposed for accurately determining the total fast flux in the vicinity of a fast-pulse reactor of bare-critical assembly. The method is to determine the fast flux from the comparison of free-field 239Pu fission-rate measurements made at the reactor facility to calibration measurements made in a standard 252Cf neutron flux. Use of the technique at the Army Pulse Radiation Facility shows that total fluxes can be measured in and near the reactor to a determinable accuracy of +-5 percent. For comparison, but with less accuracy of +-8 percent, the same total fluxes were verified using 237Np, 234U, 236U and 238U. The technique has several important advantages. It uses a recognized standard neutron source for calibration. Accurate fission rates ae measured and compared with dual-isotope fission chambers that are easily calibrated. The method is independent of errors in foil masses. The method does not require the use of an unfolding code and the effects of cross section errors are lessened because of the need to evaluate only cross section ratios. The method is simple and is readily amenable to absolute error analysis and interlaboratory calibration;