Parameters for the Neutron Resonance in Gold

A highly detailed study of the 4.906-ev neutron resonance in ${\mathrm{Au}}^{197}$ has been made for the purpose of establishing preliminary values for a "standard" resonance. Such a standard can serve as a basis for comparing results from various neutron spectrometers and should assist in reducing large discrepancies in resonance parameters which now exist. The new measurements were made on a crystal spectrometer with unusually good resolution. Methods of "shape analysis" were used to fit the data to the one-level formula and the following parameters were obtained: $E_0=4.906\mathrm{}\pm 0.010$ ev; ${\sigma }_{t0\mathrm{}}{\Gamma }^2=(725\mathrm{}\pm 15)\times {10}^{-24\mathrm{}}$ ${\mathrm{cm}}^2$ ${\mathrm{ev}}^2$; ${\sigma }_{t0\mathrm{}}=(37\mathrm{}000\pm 500)\times {10}^{-24\mathrm{}}$ ${\mathrm{cm}}^2$; $\Gamma =0.140\mathrm{}\pm 0.003$ ev; and ${\sigma }_p=(11.1\mathrm{}\pm 0.8)\times {10}^{-24\mathrm{}}$ ${\mathrm{cm}}^2$. The one-level formula with these parameters gives an accurate fit to the data over the entire energy range from 0.35 to 15 ev. The nuclear radii corresponding to the two possible spin orientations of the incident neutron were found to be the same to within experimental error.