Long Wavelength Crystal Spectrometer and the Neutron Absorption Cross Sections of Gold and Boron

Abstract

The absorption cross sections of gold and boron have been measured at long neutron wavelengths with a single crystal spectrometer. Mica along with microcrystalline filters of Be and BeO was used as a monochromator for the wavelength range from 4 to 8.75 Å, and for longer wavelengths a mechanical monochromator was used to remove second and higher order neutrons. Neutron beams with negligible higher order contamination were obtained with a wavelength resolution Δλ/λ of 0.018.The total cross section of gold for wavelengths from 5 to 11.5 Å is σt = (54.56 ± 0.09) λ (0.46 ± 0.67) barns. Evaluation of the thermal neutron (2200 m/sec) absorption cross sections gave (98.8 ± 0.3) barns for gold and (7.56 ± 6) barns for boron in glass plates for use as secondary standards.