FACTORS IN THE PRECISION OF SLOW NEUTRON CAPTURE CROSS SECTION MEASUREMENTS USING A SIMPLE MOXON--RAE DETECTOR.

The practicality of using relatively simple apparatus for precise measurements of slow neutron capture cross sections has been explored. The capture gamma-ray production rate was measured by means of a very simple detector of the type invented by Moxon and Rae which consisted of a thick graphite converter placed next to a thin plastic scintillator mounted on a two-inch photomultiplier tube. All cross sections were measured relative to Au. It was found that cross sections can be obtained to a precision in the range of 1–2% provided that proper attention is given to sample purity, geometry, and corrections for multiple scattering and self-absorption. A variety of elements were tested covering a cross section range from 150 barn. Results are given for the elements Ni, Cu, Zr, Nd, Tb and Er at neutron energies of 0.033, 0.075, 0.115 and 0.270 eV and for Al, Ag and Ta at 0.070, 0.115, 0.364 and 0.835 eV. The measured values are consistent with 1v dependence of the capture cross section for those elements having no nearly resonances.