Total cross-sections of various homogeneous substances for ultracold neutrons

By transmission measurements at the time-of-flight spectrometer for ultracold neutrons at the FRM Munich, the total cross-sections of gold, aluminium and copper were determined as a function of neutron energy in the range 10^?7<E<5× 10^?4eV and the temperature range 33–303 °K. No significant deviations from the expected 1/v dependence of the cross-sections were found if the neutron velocityv is corrected for the index of refraction. From the measured total cross-sections at low temperature the following values for the thermal capture cross-sections could be calculated: $$Au:99.3 pm 0.5b;Al:227 pm 6mb;Cu:3.77 pm 0.12b.$$ For aluminium in addition a value of 389±50 °K for the Debye temperature at 298 °K could be obtained from the temperature dependence of the total cross-sections. Additional measurements on glass, mica and air also showed proportionality of the total cross-sections to 1/v.