Activation Measurements of the Doppler Effect in Thin Uranium-238 Metal at up to 1000 K

Activation measurements of the Doppler effect in a 1/E slowing-down spectrum for thin ²³⁸U-metal foils, of surface area to mass ratio between 8 and 25 cm²/g, have been made at temperatures up to 1000 K. The activation technique was modified to remove the dependence on flux monitor foils by rotating both a heated and a reference foil. The results show consistently higher Doppler ratios than those predicted by flat-flux models using either exact numerical solutions or the assumption of equivalence.