Electron-volt spectroscopy at a pulsed neutron source using a resonance detector technique

We present measurements on the energy resolution of a neutron Resonance Detector Spectrometer (RDS) using Pb and 4He/H2 mixture scattering samples. The final neutron energy is selectively measured by means of an absorbing 238U foil which emits a prompt gamma ray cascade generated by (n,?) reactions, revealed employing a conventional NaI(Tl) scintillator, properly shielded. Despite a low signal to background ratio, it is possible to identify four recoil peaks corresponding, in energy, to the four resonances of the 238U in the epithermal region and compare their position with the prediction. Moreover, the double difference technique, which imply the use of two foils of different thickness, shows to enhance the energy resolution, as indicated by the reduction of the intrinsic width of the recoil peak at 6.6 eV.