Radiative capture of fast neutrons by 40Ca

Abstract

The radiative capture cross section for the reaction 40Ca(n, γ) 41Ca has been measured for the neutron energy range of 6.8–18.2 MeV. A NaI(Tl) anti-Compton spectrometer, a pulsed neutron beam, and time-of-flight techniques were utilized. The γ-ray spectra show strong transitions to the 1 f 7 2 ground state and a relatively high intensity of unresolved γ-rays to a group of levels at about 2 MeV, where two 3 2 − states are known to carry the 2 p 3 2 strength, and to levels around 4 MeV, which is the centroid energy of the 2 p 1 2 strength. Absolute cross sections were determined for these γ-ray transitions as well as the integrated cross section for transitions to bound states of 41Ca. Only the cross section for the transition to the f 7 2 ground state of 41Ca shows the resonance behavior predicted by the semidirect (collective) capture theory, but the agreement between the theoretical and measured f 7 2 cross sections is not satisfactory. The measured cross sections for the other γ-ray peaks are almost constant with neutron energy below about 15 MeV, in sharp contrast to the cross sections predicted by the semidirect theory for p 3 2 and p 1 2 transitions.