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Measurements on proton energy spectra from n, p reactions on Mg, Al, Si and S show the existence of well defined peaks even at excitation energy values where the excitation levels of the residual nucleus are very dense. Comparing our results with some proton spectra from d, p reactions a similarity is found in the position of these peaks on the residual excitation energy scale. By means of this comparison it is possible to establish that the n, p reactions go through a mechanism of the type of surface effect, where the residual nucleus is left preferably in some excited states probably corresponding to single particle excitation. Le misure di spettri di energia di protoni dalla reazione n, p su Mg, Al, Si e S qui presentate mostrano l’esistenza di picchi ben definiti in questi spettri, anche in corrispondenza a valori dell’energia di eccitazione del nucleo residuo dove i livelli eccitati di questo nucleo sono molto fitti. Confrontando i nostri risultati con alcuni spettri di protoni emessi da reazioni d, p, si trova che i picchi esistenti in ambedue queste reazioni si trovano agli stessi valori dell’energia di eccitazione. Questo confronto permette di concludere che le reazioni n, p qui studiate procedono attraverso un meccanismo del tipo ad interazione di superficie, dove il nucleo residuo rimane preferibilmente in stati eccitati che corrispondono a livelli di eccitazione di particella singola.

This work describes a spectrometer for protons of energy between 2 and 14 MeV. This spectrometer is particularly suitable for the study of protons emitted by nuclei bombarded with 14 MeV neutrons. The background of this instrument is particularly low. The resolution of the instrument is discussed.

Accuracy limits of the time of occurrence of an event detected by a scintillation counter are investigated. Two methods « non linear » and « linear » for extracting time information from the output current pulse of the photomultiplier are compared taking into account statistics of photoelectron emission, transit time and multiplication spread in the phototube and finite width of the response of the phototube to one photoelectron. Resolution obtained by the « non linear » method is better, but linear method dispenses from an amplitude selection of pulses.