Photoneutron production from C, Al, S by bremsstrahlung up to 200 MeV

Summary

By means of a special type of moderated neutron counter for which the energy response is nearly constant up to at least 50 MeV, a study of the total photoneutron cross-section below 200 MeV was undertaken at the Orsay electron linear accelerator. The investigated nuclides were C, Al and S. It was found that the cross-sections well above the giant resonance are relatively important, and that their integrated values up to meson threshold are 5▽6 times the giant resonance contribution. Besides it was possible, by taking into account the energy response of two different parts of the neutron counter, to separate the photoneutron cross-sections for neutrons below and above 15 MeV energy respectively. The fast neutron contribution is particularly important in C and S, and less so in Al. Moreover above 140 MeV there is a gradual increase of the cross-sections, probably related to an effect of neutron multiplicity.

Riassunto

Presso il Laboratorio dell’Acceleratore Lineare di Orsay è stata misurata la sezione d’urto di fotoproduzione totale di neutroni fino a 200 MeV in C, Al e S impiegando un contatore a efficienza costante fino a circa 50 MeV di energia di fotoneutroni. Le sezioni d’urto, opportunamente corrette per gli effetti di molteplicità, sembrano essenzialmente acoordarsi con un meccanismo di fotodisintegrazione a quasi-deutone proposto da Levingerσ _qd (E _γ) =K(NZ/A)σ _d (E _γ) purcliè si assuma perK un valore compreso tra 10 e 12. Le sezioni d’urto integrate hanno un valore parecchio elevato e soddisfano le, regole di somma solo tenendo conto di termini dovuti a un potenziale dipendente dalla velocita.