Risonanze (n,n) ed (n,p) nel P31 e S32

Riassunto Vengono misurate e confrontate la sezione d'urto totale e quella per il processo (n, p) nel P31 e S32 per neutroni da 1,9 a 3,66 MeV. Le tecniche di misura sono estesamente discusse. I massimi dei due processi coincidono per lo Zolfo fino a 3 MeV; per il Fosforo coincidono solo fino a 2,5 MeV. Se ne conclude che, ad energie elevate, l'idea del nucleo intermedio non è più accettabile, senza qualche modifica. Summary Total cross sections for P31 and S32 have been measured for neutrons with energy ranging from 1,90 to 3,66 MeV. For the same neutron energies, the cross sections for the (n, p) reaction have been remeasured for P31 with the β-activation method. Resonances for σt and σ(n, p) in S32 occur at the same energies up to 3 MeV. In P31 the position of the resonance coincide very closely up to 2,5 MeV, at higher energies, however, the coincidence ceases. The energy of the neutron in both experiments (σt and σ(n, p)) is rigorously determined in the same way so that no systematic error may occur. One must then conclude that at relatively low energies the experimental data are consistent with the conception of an intermediate nucleus, for nuclear reactions. At higher energies a more complicated picture appears to be necessary. Transmission experiments for σt-determination are discussed in view of the unusual accuracy of the present measurements (1%). The computations ofRose andShapiro for the optimum absorber thickness were repeated and extended to cover the case in which the statistical errors are negligible and only constant relative errors are present. Neutrons were detected with scintillation counters utilizing anthracene crystals and 1P21 photomultipliers. The source of monochromatic neutrons was the D,D reaction in heavy ice target, 80 keV thick.