Resonance-Region Neutron Spectrometer Measurements on Silver and Tungsten

A high speed rotating-shutter spectrometer has been built for making slow neutron measurements in the resonance region, using a neutron "pile" as a source. One of the principal advantages of the new apparatus is that comparatively small samples are required---typically less than one gram. Thus measurements can be made on many comparatively rare materials, such as certain separated isotopes.Measurements are reported here on silver and tungsten. These measurements were made with an effective resolution in reciprocal velocity somewhat better than 1.0 microsecond/meter at high energies. In silver, the measurements show clearly resolved resonances at 5, 16, 30, 41, and 53 ev, and numerous unresolved resonances at higher energies. The constants of the 5-ev resonance are Eᵣ=5.17±0.08 ev, σ₀=12,000±1500 barns (10,000 barns for metallic silver at room temperature), Γ=0.17±0.02 ev, Γₙ≈0.011 ev. The tungsten work includes measurements on separated-isotope samples of the four major isotopes. The resonance-level spacings observed in these isotopes are: 10 to 30 ev in 182, about 20 ev in 183, perhaps 100 ev in 184, and several hundred ev in 186.