Radiative Neutron Capture Into the Giant Resonance Region of CALCIUM-41.
Neutron radiative capture is a useful tool in the investigation of the contribution of non-E1 effects in the capture reaction, since the recoil effective charge of the captured neutron in small for these higher multipolarities. Therefore, the direct contributions of these higher multipolarities to the cross section does not obscure the more interesting resonance effects in the giant resonance region. The ('40)Ca(n,(gamma))('41)Ca reaction is useful in studying these effects in that the ground state of ('41)Ca has a large spectroscopic factor, and neutron capture in this reaction can only excite the T = 1/2 component of the giant resonance region, reducing the complexity of the analysis. The work reported here is a study of the ('40)Ca(n,(gamma))('41)Ca reaction for excitation energies in the giant resonance region of ('41)Ca. A detailed comparison will be made between the measured yield curve and angular distributions of cross section and analyzing power and calculations based on the direct-semidirect model. Particular attention will be given to the strength of non-E1 radiation in the reaction. In general, the data are very well described by calculations based on the direct-semidirect model. The cross section measurements are reproduced quite well by including only E1 terms in the calculations. But the presence of non-zero odd a(,i) and b(,i) coefficients extracted from the angular distributions of cross section and analyzing power indicate the presence of non-E1 radiation in the reaction. The addition of a semidirect E2 term using either a surface-peaked or a volume form factor improves the agreement between the data and the calculated coefficients. Additional analysis was done including a direct M1 term in the calculations, the effect of which was to further improve the agreement with the b(,1) coefficients. The agreement with the 90(DEGREES) analyzing power was also improved. Finally, an analysis was done to determine what amplitudes contributed to the capture process. It was found that if the g(,7/2) "spin-flip" amplitude was neglected, the g(,9/2) amplitude accounts for about 80% of the E1 cross section. When E2 amplitudes were also included, no unique solution could be determined because of the large number of amplitudes involved.
- Pub Date:
- Physics: Nuclear